2022
|
Sadeghpour, E.; Nonn, A. Data-driven models for structure-property prediction in additively manufactured steels Werkstoffsimulation Artikel In: Computational Materials Science, 215 , S. 111782, 2022, ISSN: 0927-0256. @article{SADEGHPOUR2022111782,
title = {Data-driven models for structure-property prediction in additively manufactured steels},
author = {E. Sadeghpour and A. Nonn},
url = {https://www.sciencedirect.com/science/article/pii/S0927025622004931},
doi = {https://doi.org/10.1016/j.commatsci.2022.111782},
issn = {0927-0256},
year = {2022},
date = {2022-09-15},
urldate = {2022-01-01},
journal = {Computational Materials Science},
volume = {215},
pages = {111782},
abstract = {Data-driven models are developed to predict the mechanical properties of polycrystalline materials. The case study is the prediction of the yield strength of a 3D-printed 316L steel from morphological and crystallographic features. Three different artificial intelligence models including feed-forward (FNN), convolution (CNN), and graph (GNN) neural networks are employed to train the data-driven models and are compared in terms of performance and computational requirements. The dataset required for training is generated by performing crystal plasticity finite element simulations. The FNN model has the smallest input size and takes in some statistical parameters describing the material microstructure, but its accuracy is relatively low. The CNN approach inputs voxel-based realizations of the microstructure and is able to give accurate estimations; however, its training process is time-consuming and computationally expensive. In the GNN approach, the polycrystalline material is represented by a graph whose nodes and lines represent the grains and adjacency between grains. It is observed that GNN yields a better performance compared to the other two approaches and has the capability of handling complex tasks.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Data-driven models are developed to predict the mechanical properties of polycrystalline materials. The case study is the prediction of the yield strength of a 3D-printed 316L steel from morphological and crystallographic features. Three different artificial intelligence models including feed-forward (FNN), convolution (CNN), and graph (GNN) neural networks are employed to train the data-driven models and are compared in terms of performance and computational requirements. The dataset required for training is generated by performing crystal plasticity finite element simulations. The FNN model has the smallest input size and takes in some statistical parameters describing the material microstructure, but its accuracy is relatively low. The CNN approach inputs voxel-based realizations of the microstructure and is able to give accurate estimations; however, its training process is time-consuming and computationally expensive. In the GNN approach, the polycrystalline material is represented by a graph whose nodes and lines represent the grains and adjacency between grains. It is observed that GNN yields a better performance compared to the other two approaches and has the capability of handling complex tasks. |
Wiesent, L.; Spear, A.; Nonn, A. Computational analysis of the effects of geometric irregularities on the interaction of an additively manufactured 316L stainless steel stent and a coronary artery Werkstoffsimulation Artikel In: Journal of the Mechanical Behavior of Biomedical Materials, Volume 125 , 2022. @article{Wiesent2022,
title = {Computational analysis of the effects of geometric irregularities on the interaction of an additively manufactured 316L stainless steel stent and a coronary artery},
author = {L. Wiesent and A. Spear and A. Nonn },
url = {https://www.sciencedirect.com/science/article/pii/S1751616121005117?dgcid=author
},
doi = {https://doi.org/10.1016/j.jmbbm.2021.104878},
year = {2022},
date = {2022-01-01},
journal = {Journal of the Mechanical Behavior of Biomedical Materials},
volume = {Volume 125},
abstract = {Customized additively manufactured (laser powder bed fused (L-PBF)) stents could improve the treatment of complex lesions by enhancing stent-artery conformity. However, geometric irregularities inherent for L-PBF stents are expected to influence not only their mechanical behavior but also their interaction with the artery. In this study, the influence of geometrical irregularities on stent-artery interaction is evaluated within a numerical framework. Thus, computed arterial stresses induced by a reconstructed L-PBF stent model are compared to those induced by the intended stent model (also representing a stent geometry obtained from conventional manufacturing processes) and a modified CAD stent model that accounts for the increased strut thickness inherent for L-PBF stents. It was found that, similar to conventionally manufactured stents, arterial stresses are initially related to the basic stent design/topology, with the highest stresses occurring at the indentations of the stent struts. Compared to the stent CAD model, the L-PBF stent induces distinctly higher and more maximum volume stresses within the plaque and the arterial wall. In return, the modified CAD model overestimates the arterial stresses induced by the L-PBF stent due to its homogeneously increased strut thickness and thus its homogeneously increased geometric stiffness compared with the L-PBF stent. Therefore, the L-PBF-induced geometric irregularities must be explicitly considered when evaluating the L-PBF stent-induced stresses because the intended stent CAD model underestimates the arterial stresses, whereas the modified CAD model overestimates them. The arterial stresses induced by the L-PBF stent were still within the range of values reported for conventional stents in literature, suggesting that the use of L-PBF stents is conceivable in principle. However, because geometric irregularities, such as protruding features from the stent surface, could potentially damage the artery or lead to premature stent failure, further improvement of L-PBF stents is essential.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Customized additively manufactured (laser powder bed fused (L-PBF)) stents could improve the treatment of complex lesions by enhancing stent-artery conformity. However, geometric irregularities inherent for L-PBF stents are expected to influence not only their mechanical behavior but also their interaction with the artery. In this study, the influence of geometrical irregularities on stent-artery interaction is evaluated within a numerical framework. Thus, computed arterial stresses induced by a reconstructed L-PBF stent model are compared to those induced by the intended stent model (also representing a stent geometry obtained from conventional manufacturing processes) and a modified CAD stent model that accounts for the increased strut thickness inherent for L-PBF stents. It was found that, similar to conventionally manufactured stents, arterial stresses are initially related to the basic stent design/topology, with the highest stresses occurring at the indentations of the stent struts. Compared to the stent CAD model, the L-PBF stent induces distinctly higher and more maximum volume stresses within the plaque and the arterial wall. In return, the modified CAD model overestimates the arterial stresses induced by the L-PBF stent due to its homogeneously increased strut thickness and thus its homogeneously increased geometric stiffness compared with the L-PBF stent. Therefore, the L-PBF-induced geometric irregularities must be explicitly considered when evaluating the L-PBF stent-induced stresses because the intended stent CAD model underestimates the arterial stresses, whereas the modified CAD model overestimates them. The arterial stresses induced by the L-PBF stent were still within the range of values reported for conventional stents in literature, suggesting that the use of L-PBF stents is conceivable in principle. However, because geometric irregularities, such as protruding features from the stent surface, could potentially damage the artery or lead to premature stent failure, further improvement of L-PBF stents is essential. |
2021
|
Schimmer, F.; Gebhardt, J.; Motsch-Eichmann, N.; Hausmann, J.; Ehrlich, I. The effect of curvature on the low-velocity impact resistance of CF/PEEK laminates Leichtbau Konferenzbeitrag In: 30 Years IVW Anniversary Colloquium, Leibnitz-Institut für Verbundwerkstoffe Kaiserslautern, 2021. @inproceedings{Schimmer2021,
title = {The effect of curvature on the low-velocity impact resistance of CF/PEEK laminates},
author = {F. Schimmer and J. Gebhardt and N. Motsch-Eichmann and J. Hausmann and I. Ehrlich},
year = {2021},
date = {2021-09-09},
booktitle = {30 Years IVW Anniversary Colloquium},
address = {Kaiserslautern},
organization = {Leibnitz-Institut für Verbundwerkstoffe},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|
Keim, V. Numerical ductile fracture propagation control for pipelines transporting natural gases and CO2-mixtures Werkstoffsimulation Promotionsarbeit Rheinisch-Westfälische Technische Hochschule Aachen, 2021. @phdthesis{nokey,
title = { Numerical ductile fracture propagation control for pipelines transporting natural gases and CO2-mixtures},
author = {V. Keim},
editor = {Rheinisch-Westfälische Technische Hochschule Aachen},
url = {https://publications.rwth-aachen.de/record/824366},
doi = {RWTH-2021-07542},
year = {2021},
date = {2021-08-06},
urldate = {2021-08-06},
edition = {RWTH-2021-07542},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
howpublished = {Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
|
Rajaraman, D.; Keim, V.; Pondicherry, K.; Nonn, A.; Hertelé, S.; Fauconnier, D. Stress state characterization of ductile materials during scratch abrasion Werkstoffsimulation Artikel In: Wear, S. 203712, 2021, ISSN: 0043-1648. @article{RAJARAMAN2021203712,
title = {Stress state characterization of ductile materials during scratch abrasion},
author = {D. Rajaraman and V. Keim and K. Pondicherry and A. Nonn and S. Hertelé and D. Fauconnier},
url = {https://www.sciencedirect.com/science/article/pii/S0043164821001010},
doi = {https://doi.org/10.1016/j.wear.2021.203712},
issn = {0043-1648},
year = {2021},
date = {2021-01-01},
journal = {Wear},
pages = {203712},
abstract = {Abrasive wear limits the lifetime of many machine components. Most empirical models relate the abrasive wear resistance to material hardness. In reality, however, other material properties are also influencing as scratch abrasion damage follows from a highly complex stress trajectory upon scratching. Numerical (finite element) simulation of scratch abrasion requires the use of a material damage model, which translates this stress trajectory into material degradation and removal. Most damage models include the first two stress invariants. However, fully incorporating the complex stress trajectories that occur during scratch abrasion may require damage models with dependence of the third deviatoric parameter (Lode angle). This paper serves as an a-priori study to evaluate the stress states that may occur during scratch abrasion. Three mechanisms (ploughing, wedging, cutting) are considered. Hereto, the results of an extensive parametric study using elastic-plastic finite element simulations of a scratch indentation process are discussed. Complex, non-proportional variations in stress state values are observed to occur during scratch abrasion. Distinct stress state trajectories are identified for the three abovementioned mechanisms. These variations are critically discussed to motivate a selection of suitable damage models for rigorous finite element analysis of the wear processes associated with scratch abrasion.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abrasive wear limits the lifetime of many machine components. Most empirical models relate the abrasive wear resistance to material hardness. In reality, however, other material properties are also influencing as scratch abrasion damage follows from a highly complex stress trajectory upon scratching. Numerical (finite element) simulation of scratch abrasion requires the use of a material damage model, which translates this stress trajectory into material degradation and removal. Most damage models include the first two stress invariants. However, fully incorporating the complex stress trajectories that occur during scratch abrasion may require damage models with dependence of the third deviatoric parameter (Lode angle). This paper serves as an a-priori study to evaluate the stress states that may occur during scratch abrasion. Three mechanisms (ploughing, wedging, cutting) are considered. Hereto, the results of an extensive parametric study using elastic-plastic finite element simulations of a scratch indentation process are discussed. Complex, non-proportional variations in stress state values are observed to occur during scratch abrasion. Distinct stress state trajectories are identified for the three abovementioned mechanisms. These variations are critically discussed to motivate a selection of suitable damage models for rigorous finite element analysis of the wear processes associated with scratch abrasion. |
Xue, L.; Keim, V.; Paredes, M.; Nonn, A.; Wierzbicki, T. Anisotropic effects on crack propagation in pressurized line pipes under running ductile fracture scenarios Werkstoffsimulation Artikel In: Engineering Fracture Mechanics, 249 , S. 107748, 2021, ISSN: 0013-7944. @article{XUE2021107748,
title = {Anisotropic effects on crack propagation in pressurized line pipes under running ductile fracture scenarios},
author = {L. Xue and V. Keim and M. Paredes and A. Nonn and T. Wierzbicki},
url = {https://www.sciencedirect.com/science/article/pii/S001379442100196X},
doi = {https://doi.org/10.1016/j.engfracmech.2021.107748},
issn = {0013-7944},
year = {2021},
date = {2021-01-01},
journal = {Engineering Fracture Mechanics},
volume = {249},
pages = {107748},
abstract = {The current analyses present results of running ductile fracture propagation in high strength X100 line pipe steels under the influence of anisotropy. Mechanical anisotropy is commonly available in pipe products as a result of the manufacturing process, especially, those subjected to hot/cold-worked deformation. The outcomes of the present analyses show that its effect on the behavior of running ductile fracture in cracked pipes undergoing depressurization is meaningful. For instance, the Crack-Tip Opening Angle (CTOA) not only exhibits a strong dependence to the pipe’s diameter size, but also to the material’s anisotropy nature when compared to a hypothetical isotropic material. Moreover, laboratory scale tests such as those performed on Battelle Drop Weight Tear (BDWT) samples provide useful information about initiation of ductile crack propagation when the anisotropy features are taken into account in the material description.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The current analyses present results of running ductile fracture propagation in high strength X100 line pipe steels under the influence of anisotropy. Mechanical anisotropy is commonly available in pipe products as a result of the manufacturing process, especially, those subjected to hot/cold-worked deformation. The outcomes of the present analyses show that its effect on the behavior of running ductile fracture in cracked pipes undergoing depressurization is meaningful. For instance, the Crack-Tip Opening Angle (CTOA) not only exhibits a strong dependence to the pipe’s diameter size, but also to the material’s anisotropy nature when compared to a hypothetical isotropic material. Moreover, laboratory scale tests such as those performed on Battelle Drop Weight Tear (BDWT) samples provide useful information about initiation of ductile crack propagation when the anisotropy features are taken into account in the material description. |
2020
|
Wiesent, L.; Schultheiß, U.; Lulla, P.; Noster, U.; Schratzenstaller, T.; Schmid, C.; Nonn, A.; Spear, A. Computational analysis of the effects of geometric irregularities and post-processing steps on the mechanical behavior of additively manufactured 316L stainless steel stents Werkstoffsimulation Artikel In: PLOS ONE, 15 (12), S. e0244463, 2020, ISSN: 1932-6203. @article{Wiesent2020a,
title = {Computational analysis of the effects of geometric irregularities and post-processing steps on the mechanical behavior of additively manufactured 316L stainless steel stents},
author = {L. Wiesent and U. Schultheiß and P. Lulla and U. Noster and T. Schratzenstaller and C. Schmid and A. Nonn and A. Spear},
editor = {A. Riveiro Rodr{'{i}}guez}},
url = {https://dx.plos.org/10.1371/journal.pone.0244463},
doi = {10.1371/journal.pone.0244463},
issn = {1932-6203},
year = {2020},
date = {2020-12-29},
journal = {PLOS ONE},
volume = {15},
number = {12},
pages = {e0244463},
abstract = {Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed fusion and provides a methodological approach for their numerical evaluation. A combined experimental and computational framework is used, based on both actual and computationally reconstructed laser powder bed fused stents. Process-related morphological deviations between the as-designed and actual laser powder bed fused stents were observed, resulting in a diameter increase by a factor of 2-2.6 for the stents without surface treatment and 1.3-2 for the electropolished stent compared to the as-designed stent. Thus, due to the increased geometrically induced stiffness, the laser powder bed fused stents in the as-built (7.11 ± 0.63 N) or the heat treated condition (5.87 ± 0.49 N) showed increased radial forces when compressed between two plates. After electropolishing, the heat treated stents exhibited radial forces (2.38 ± 0.23 N) comparable to conventional metallic stents. The laser powder bed fused stents were further affected by the size effect, resulting in a reduced yield strength by 41{%} in the as-built and by 59{%} in the heat treated condition compared to the bulk material obtained from tensile tests. The presented numerical approach was successful in predicting the macroscopic mechanical response of the stents under compression. During deformation, increased stiffness and local stress concentration were observed within the laser powder bed fused stents. Subsequent numerical expansion analysis of the derived stent models within a previously verified numerical model of stent expansion showed that electropolished and heat treated laser powder bed fused stents can exhibit comparable expansion behavior to conventional stents. The findings from this work motivate future experimental/numerical studies to quantify threshold values of critical geometric irregularities, which could be used to establish design guidelines for laser powder bed fused stents/lattice structures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed fusion and provides a methodological approach for their numerical evaluation. A combined experimental and computational framework is used, based on both actual and computationally reconstructed laser powder bed fused stents. Process-related morphological deviations between the as-designed and actual laser powder bed fused stents were observed, resulting in a diameter increase by a factor of 2-2.6 for the stents without surface treatment and 1.3-2 for the electropolished stent compared to the as-designed stent. Thus, due to the increased geometrically induced stiffness, the laser powder bed fused stents in the as-built (7.11 ± 0.63 N) or the heat treated condition (5.87 ± 0.49 N) showed increased radial forces when compressed between two plates. After electropolishing, the heat treated stents exhibited radial forces (2.38 ± 0.23 N) comparable to conventional metallic stents. The laser powder bed fused stents were further affected by the size effect, resulting in a reduced yield strength by 41{%} in the as-built and by 59{%} in the heat treated condition compared to the bulk material obtained from tensile tests. The presented numerical approach was successful in predicting the macroscopic mechanical response of the stents under compression. During deformation, increased stiffness and local stress concentration were observed within the laser powder bed fused stents. Subsequent numerical expansion analysis of the derived stent models within a previously verified numerical model of stent expansion showed that electropolished and heat treated laser powder bed fused stents can exhibit comparable expansion behavior to conventional stents. The findings from this work motivate future experimental/numerical studies to quantify threshold values of critical geometric irregularities, which could be used to establish design guidelines for laser powder bed fused stents/lattice structures. |
Wiesent, L.; Schultheiß, U.; Lulla, P.; Nonn, A.; Noster, U. Mechanical properties of small structures built by selective laser melting 316 L stainless steel – a phenomenological approach to improve component design Werkstoffsimulation Artikel In: Materialwissenschaft und Werkstofftechnik, 51 (12), S. 1615–1629, 2020. @article{Wiesent2020,
title = {Mechanical properties of small structures built by selective laser melting 316 L stainless steel – a phenomenological approach to improve component design},
author = {L. Wiesent and U. Schultheiß and P. Lulla and A. Nonn and U. Noster},
doi = {10.1002/mawe.202000038},
year = {2020},
date = {2020-12-17},
journal = {Materialwissenschaft und Werkstofftechnik},
volume = {51},
number = {12},
pages = {1615--1629},
abstract = {Experimental investigations are conducted to quantify the influence of specimen thickness and orientation on the mechanical properties of selective laser melted stainless steel 316 L. The results indicate that the mechanical strength and ductility increase with increasing specimen thickness until a saturation value is reached from a specimen thickness of about 2 mm. Specimen orientation dependency is pronounced for thin specimens (< 1.5 mm), whereas only small deviations in strength are observed for thicker specimens with orientations of 30°, 45° and 90° to build direction. The mechanical properties of the specimen orientation of 0° to build direction shows great deviation to the other orientations and the smallest overall strength. A reliable design of selective laser melted components should account for specimen thickness and orientation, e. g. by a correction factor. Furthermore, it is recommended to avoid loads vertical (90°) and parallel (0°) to build direction to guarantee higher ductility and strength.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Experimental investigations are conducted to quantify the influence of specimen thickness and orientation on the mechanical properties of selective laser melted stainless steel 316 L. The results indicate that the mechanical strength and ductility increase with increasing specimen thickness until a saturation value is reached from a specimen thickness of about 2 mm. Specimen orientation dependency is pronounced for thin specimens (< 1.5 mm), whereas only small deviations in strength are observed for thicker specimens with orientations of 30°, 45° and 90° to build direction. The mechanical properties of the specimen orientation of 0° to build direction shows great deviation to the other orientations and the smallest overall strength. A reliable design of selective laser melted components should account for specimen thickness and orientation, e. g. by a correction factor. Furthermore, it is recommended to avoid loads vertical (90°) and parallel (0°) to build direction to guarantee higher ductility and strength. |
Kastenmeier, A. Biegeverhalten faserverstärkter Kunststoffrohre unter Berücksichtigung einer mehrreihigen Bolzenverbindung Leichtbau Promotionsarbeit Universität der Bundeswehr München, Ostbayerische Technische Hochschule Regensburg, urn:nbn:de:bvb:706-7105, 2020. @phdthesis{Kastenmeier2020,
title = {Biegeverhalten faserverstärkter Kunststoffrohre unter Berücksichtigung einer mehrreihigen Bolzenverbindung},
author = {A. Kastenmeier},
editor = {Ehrlich, Ingo, Prof. Dr.-Ing.; Brünig, Michael, Univ.-Prof. Dr.-Ing. habil.; Gebbeken, Norbert, Univ.-Prof. Dr.-Ing. habil. },
url = {https://athene-forschung.unibw.de/135000
},
year = {2020},
date = {2020-12-10},
address = {Werner-Heisenberg-Weg 39, 85577 Neubiberg},
school = {Universität der Bundeswehr München, Ostbayerische Technische Hochschule Regensburg, urn:nbn:de:bvb:706-7105},
abstract = {In der vorliegenden Arbeit wird die Charakterisierung des mechanischen Verhaltens von auskragenden Rohren aus kohlenstofffaserverstärktem Kunststoff (CFK) mit Querkraftbelastung an einem Ende und einer mehrreihigen Bolzenverbindung am anderen Ende behandelt. Bolzenverbindungen mit Fügepartner aus CFK werden im Stand der Technik nur an ebenen, zug- oder druckbelasteten, Verbindungen untersucht, weshalb der Einfluss der Biegebelastung, der gekrümmten Auflageflächen und des geschlossenen Rohrprofils untersucht und qualifiziert wird. Zudem zeigt sich ein Effekt der Abstützung bzw. resultierenden Verformungsbehinderung. Die Grundlage der Untersuchungen bilden 2-Punkt-Biegeversuche mit Verzerrungs- und Verschiebungsmessungen, die über FE-Modelle numerisch abgebildet und in einer Verzerrungs- und Spannungsanalyse detaillierter ausgewertet werden. Zur Darstellung des Einflusses der Biegebelastung werden zudem reine Zug- und Drucklasten aufgebracht, ausgewertet und abgeglichen. In drei Variationen des Biegeversuchs werden zudem, sowohl experimentell als auch numerisch, Effekte zu einer möglichen Steigerung der Verbindungsfestigkeit untersucht. Dazu zählt die Verwendung von zusätzlichen Schichten aus Titanlegierung im Kraftüberleitungsbereich, ein Versetzen der Bolzen im Umfang und eine Änderung der Abstützung in Lastrichtung. Für das Biegeverhalten der CFK-Rohre im frei auskragenden Bereich werden kontinuumsmechanische Modelle der anisotropen Elastizität für Rohre unter reiner Biegebelastung beschrieben, adaptiert und bezüglich der Ergebnisse bewertet. Um die Vergleichbarkeit der Berechnungsmodelle und Versuche zu gewährleisten, wird einerseits der Einfluss der speziellen Schichtstruktur in gewickelten CFK-Rohren diskutiert und andererseits werden die transversal-isotropen Materialeigenschaften der Einzelschicht an Probekörpern aus den Rohren bestimmt. },
type = {Dissertation},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
In der vorliegenden Arbeit wird die Charakterisierung des mechanischen Verhaltens von auskragenden Rohren aus kohlenstofffaserverstärktem Kunststoff (CFK) mit Querkraftbelastung an einem Ende und einer mehrreihigen Bolzenverbindung am anderen Ende behandelt. Bolzenverbindungen mit Fügepartner aus CFK werden im Stand der Technik nur an ebenen, zug- oder druckbelasteten, Verbindungen untersucht, weshalb der Einfluss der Biegebelastung, der gekrümmten Auflageflächen und des geschlossenen Rohrprofils untersucht und qualifiziert wird. Zudem zeigt sich ein Effekt der Abstützung bzw. resultierenden Verformungsbehinderung. Die Grundlage der Untersuchungen bilden 2-Punkt-Biegeversuche mit Verzerrungs- und Verschiebungsmessungen, die über FE-Modelle numerisch abgebildet und in einer Verzerrungs- und Spannungsanalyse detaillierter ausgewertet werden. Zur Darstellung des Einflusses der Biegebelastung werden zudem reine Zug- und Drucklasten aufgebracht, ausgewertet und abgeglichen. In drei Variationen des Biegeversuchs werden zudem, sowohl experimentell als auch numerisch, Effekte zu einer möglichen Steigerung der Verbindungsfestigkeit untersucht. Dazu zählt die Verwendung von zusätzlichen Schichten aus Titanlegierung im Kraftüberleitungsbereich, ein Versetzen der Bolzen im Umfang und eine Änderung der Abstützung in Lastrichtung. Für das Biegeverhalten der CFK-Rohre im frei auskragenden Bereich werden kontinuumsmechanische Modelle der anisotropen Elastizität für Rohre unter reiner Biegebelastung beschrieben, adaptiert und bezüglich der Ergebnisse bewertet. Um die Vergleichbarkeit der Berechnungsmodelle und Versuche zu gewährleisten, wird einerseits der Einfluss der speziellen Schichtstruktur in gewickelten CFK-Rohren diskutiert und andererseits werden die transversal-isotropen Materialeigenschaften der Einzelschicht an Probekörpern aus den Rohren bestimmt. |
Lindner, M.; Berndt, D.; Tschurtschenthal, K.; Ehrlich, I.; Jungbauer, B.; Schreiner, R.; Pipa, A. V.; Hink, R.; Brandenburg, R.; Neuwirth, D.; Karpen, N.; Bonaccurso, E.; Weichwald, R.; Max, A.; Caspari, R. Aircraft Icing Mitigation by DBD-based Micro Plasma Actuators Leichtbau Konferenzbeitrag In: AIAA AVIATION 2020 FORUM, 2020. @inproceedings{Lindner2020,
title = {Aircraft Icing Mitigation by DBD-based Micro Plasma Actuators},
author = {M. Lindner and D. Berndt and K. Tschurtschenthal and I. Ehrlich and B. Jungbauer and R. Schreiner and A. V. Pipa and R. Hink and R. Brandenburg and D. Neuwirth and N. Karpen and E. Bonaccurso and R. Weichwald and A. Max and R. Caspari},
url = {https://arc.aiaa.org/doi/10.2514/6.2020-3243},
doi = {10.2514/6.2020-3243},
year = {2020},
date = {2020-06-08},
publisher = {AIAA AVIATION 2020 FORUM},
abstract = {We present the application of plasma actuators as a technology for ice prevention at airfoils. The miniaturized dielectric barrier discharge (DBD) plasma actuators (PA) were fabricated by means of microelectromechanical systems (MEMS). We elucidate how to make the actuator samples scalable and applicable to any desired shape by the use of flexible inorganic zirconia substrates. For this purpose, we applied our developed embedding method to integrate the micro actuators in modern carbon/glass fiber reinforced polymer (CFRP/GFRP) materials. Next, the embedded actuator samples were mounted on a mechanical air profile-like fixture and placed in the icing wind tunnel iCORE. The samples were tested in rime ice conditions at temperatures of -15 to -20° C and air speeds up to 30 m/s. Unlike other groups we used a thin film zirconia substrate as dielectric for the plasma actuator. Due to the low substrate thickness of just 150 µm, an operating voltage of 2 kVRMS is already sufficient enough for a stable plasma formation. The experiments show that the operated actuator was able to prevent the ice formation and first indications of a De-icing function were also found. Hence, we show that it is feasible to realize an anti-icing system with zirconia-based plasma actuators operated at lower voltages compared to conventional ones.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We present the application of plasma actuators as a technology for ice prevention at airfoils. The miniaturized dielectric barrier discharge (DBD) plasma actuators (PA) were fabricated by means of microelectromechanical systems (MEMS). We elucidate how to make the actuator samples scalable and applicable to any desired shape by the use of flexible inorganic zirconia substrates. For this purpose, we applied our developed embedding method to integrate the micro actuators in modern carbon/glass fiber reinforced polymer (CFRP/GFRP) materials. Next, the embedded actuator samples were mounted on a mechanical air profile-like fixture and placed in the icing wind tunnel iCORE. The samples were tested in rime ice conditions at temperatures of -15 to -20° C and air speeds up to 30 m/s. Unlike other groups we used a thin film zirconia substrate as dielectric for the plasma actuator. Due to the low substrate thickness of just 150 µm, an operating voltage of 2 kVRMS is already sufficient enough for a stable plasma formation. The experiments show that the operated actuator was able to prevent the ice formation and first indications of a De-icing function were also found. Hence, we show that it is feasible to realize an anti-icing system with zirconia-based plasma actuators operated at lower voltages compared to conventional ones. |
Keim, V.; Paredes, M.; Nonn, A.; Münstermann, S. FSI-simulation of ductile fracture propagation and arrest in pipelines: Comparison with existing data of full-scale burst tests Werkstoffsimulation Artikel In: International Journal of Pressure Vessels and Piping, 182 , S. 104067, 2020, ISSN: 0308-0161. @article{Keim2020b,
title = {FSI-simulation of ductile fracture propagation and arrest in pipelines: Comparison with existing data of full-scale burst tests},
author = {V. Keim and M. Paredes and A. Nonn and S. Münstermann},
doi = {10.1016/j.ijpvp.2020.104067},
issn = {0308-0161},
year = {2020},
date = {2020-01-01},
journal = {International Journal of Pressure Vessels and Piping},
volume = {182},
pages = {104067},
abstract = {The fracture propagation and arrest control for pipelines transporting rich natural gases and high vapor pressure liquids is based on the Battelle Two-Curve Model (BTCM). Distinct limitations of this model were demonstrated for past and modern steels and gas mixtures. These can be related to the insufficient description of individual physical processes and interactions between the pipe material and transported mixture during the running ductile fracture. In the past, fluid-structure interaction (FSI) models enabled a more sophisticated, coupled analysis of the failure scenario. To quantify their capability of describing the multi-physical processes, the FSI models need to be verified by experimental data from full-scale burst tests (FSBT). Therefore, this paper deals with the simulation of five FSBTs from the literature on API grade X65 pipes with different pipe geometries, mixtures and initial conditions. The FSI is modeled by the coupled Euler-Lagrange (CEL) method. The modified Mohr-Coulomb (MMC) model is implemented in the CEL framework to describe the deformation and ductile fracture in the X65/L450 pipes. 3D Euler equations are used to calculate the mixture decompression with the GERG-2008 equation of state defining the volumetric behavior of a CO2-rich mixture, CH4 and H2. The extended model considers the effect of soil backfill on the pipe deformation and inertia. The numerical predictions agree well with the experimental findings in terms of the crack propagation speed and arrest length underlining the capability of the developed numerical tool.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The fracture propagation and arrest control for pipelines transporting rich natural gases and high vapor pressure liquids is based on the Battelle Two-Curve Model (BTCM). Distinct limitations of this model were demonstrated for past and modern steels and gas mixtures. These can be related to the insufficient description of individual physical processes and interactions between the pipe material and transported mixture during the running ductile fracture. In the past, fluid-structure interaction (FSI) models enabled a more sophisticated, coupled analysis of the failure scenario. To quantify their capability of describing the multi-physical processes, the FSI models need to be verified by experimental data from full-scale burst tests (FSBT). Therefore, this paper deals with the simulation of five FSBTs from the literature on API grade X65 pipes with different pipe geometries, mixtures and initial conditions. The FSI is modeled by the coupled Euler-Lagrange (CEL) method. The modified Mohr-Coulomb (MMC) model is implemented in the CEL framework to describe the deformation and ductile fracture in the X65/L450 pipes. 3D Euler equations are used to calculate the mixture decompression with the GERG-2008 equation of state defining the volumetric behavior of a CO2-rich mixture, CH4 and H2. The extended model considers the effect of soil backfill on the pipe deformation and inertia. The numerical predictions agree well with the experimental findings in terms of the crack propagation speed and arrest length underlining the capability of the developed numerical tool. |
2019
|
Lindner, M.; Berndt, D.; Jungbauer, B.; Ehrlich, I.; Schreiner, R.; Pipa, A. V.; Hink, R.; Foest, R.; Brandenburg, R.; Max, A.; Caspari, R. Fabrication, surface integration and testing of miniaturized dielectric barrier discharge plasma actuators for active flow control applications. Leichtbau Konferenzbeitrag In: AIAA Aviation 2019 Forum Dallas, Texas, 2019. @inproceedings{Lindner2019,
title = {Fabrication, surface integration and testing of miniaturized dielectric barrier discharge plasma actuators for active flow control applications.},
author = {M. Lindner and D. Berndt and B. Jungbauer and I. Ehrlich and R. Schreiner and A. V. Pipa and R. Hink and R. Foest and R. Brandenburg and A. Max and R. Caspari},
url = {https://arc.aiaa.org/doi/abs/10.2514/6.2019-2998},
doi = {10.2514/6.2019-2998},
year = {2019},
date = {2019-07-15},
address = {Dallas, Texas},
organization = {AIAA Aviation 2019 Forum},
abstract = {We present the realization and characterization of miniaturized dielectric barrier discharge (DBD) based plasma actuators (PA) by means of microelectromechanical systems (MEMS). Different organic and inorganic dielectric materials and electrode metals have been tested with respect to their resistance against low-temperature plasma. To make the actuator samples scalable and applicable to any desired shape we developed an embedding method to integrate the micro actuator in modern carbon/glass fiber reinforced polymer (CFRP/GFRP) materials to meet the requirements of modern aviation and automotive bodywork. In this context, we further show that the realization of PA can even be carried out on flexible inorganic foils. Additionally, microfabrication mehtods give the possibility of introducing a serrated high voltage electrode with which the plasma formation can be facilitated at the peaks due to a local field enhancement. Measurements of the unduced air flow obtained by a Pitot tube show similar velocities as known from macroscopic actuators. We observed that the ionic wind flow its limited in the case when the actuators are placed too close together. This is attributed to a mututal influence of the electric field configuration resulting in lower total electric field strength.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
We present the realization and characterization of miniaturized dielectric barrier discharge (DBD) based plasma actuators (PA) by means of microelectromechanical systems (MEMS). Different organic and inorganic dielectric materials and electrode metals have been tested with respect to their resistance against low-temperature plasma. To make the actuator samples scalable and applicable to any desired shape we developed an embedding method to integrate the micro actuator in modern carbon/glass fiber reinforced polymer (CFRP/GFRP) materials to meet the requirements of modern aviation and automotive bodywork. In this context, we further show that the realization of PA can even be carried out on flexible inorganic foils. Additionally, microfabrication mehtods give the possibility of introducing a serrated high voltage electrode with which the plasma formation can be facilitated at the peaks due to a local field enhancement. Measurements of the unduced air flow obtained by a Pitot tube show similar velocities as known from macroscopic actuators. We observed that the ionic wind flow its limited in the case when the actuators are placed too close together. This is attributed to a mututal influence of the electric field configuration resulting in lower total electric field strength. |
Afanasev, A. Force-oriented 3D printing of continuous fiber-reinforced plastic structures. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M. (Hrsg.): Applied Research Conference 2019 – ARC 2019 , S. 213–218, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2019, ISBN: 978-3-96409-182-6. @inproceedings{Afanasev2019,
title = {Force-oriented 3D printing of continuous fiber-reinforced plastic structures.},
author = {A. Afanasev},
editor = {J. Mottok and M. Reichenberger},
isbn = {978-3-96409-182-6},
year = {2019},
date = {2019-07-08},
booktitle = {Applied Research Conference 2019 – ARC 2019 },
pages = {213--218},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {Due to the low mechanical properties, i. e. strength and stiffness of additively manufactured plastic components their use as load-bearing structures is rarely feasible. The solution for this problem may be the use of reinforced plastic filaments with continous fiber reinforcement. By prior identification of highly stressed areas in the component, the reinforcing fibers can be implemented optimally, thus improving the mechanical properties substantially. For this purpose, it is necessary to analyze the load conditions of the component and use the obtained information for the force-oriented implementation of the reinforcement fiber tracts in the 3D printed component. This paper examines the possibilities of obtaining information from a FE analysis by using the FE software ANSYS WORKBENCH for the force-oriented implementation of reinforcing fibers in a 3D printed component and the possibility of subsequent toolpath generation from the obtained information. For this purpose a FE model with a preferably accurate description of bearing and contact conditions for subsequent usage is created and a topology optimization is performed. The vector principles plot analysis option in ANSYS MECHANICAL provides information of particular importance for force-oriented 3D printing. It provides the relative sizes of the principal quantities as well as their direction. Vector principals provide the directions of the highest normal stresses or elastic strains in reaction to a load condition for previously defined body points. By processing the data with the software MATLAB, the information can be used as a basis for the generation of machine code for the implementation of individual reinforcing fiber tracts in a component.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Due to the low mechanical properties, i. e. strength and stiffness of additively manufactured plastic components their use as load-bearing structures is rarely feasible. The solution for this problem may be the use of reinforced plastic filaments with continous fiber reinforcement. By prior identification of highly stressed areas in the component, the reinforcing fibers can be implemented optimally, thus improving the mechanical properties substantially. For this purpose, it is necessary to analyze the load conditions of the component and use the obtained information for the force-oriented implementation of the reinforcement fiber tracts in the 3D printed component. This paper examines the possibilities of obtaining information from a FE analysis by using the FE software ANSYS WORKBENCH for the force-oriented implementation of reinforcing fibers in a 3D printed component and the possibility of subsequent toolpath generation from the obtained information. For this purpose a FE model with a preferably accurate description of bearing and contact conditions for subsequent usage is created and a topology optimization is performed. The vector principles plot analysis option in ANSYS MECHANICAL provides information of particular importance for force-oriented 3D printing. It provides the relative sizes of the principal quantities as well as their direction. Vector principals provide the directions of the highest normal stresses or elastic strains in reaction to a load condition for previously defined body points. By processing the data with the software MATLAB, the information can be used as a basis for the generation of machine code for the implementation of individual reinforcing fiber tracts in a component. |
Seppenhauser, P. Examinations of the Printer Head Prototype for UV Resins with Continous Fiber-Reinforcement Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M. (Hrsg.): Applied Research Conference 2019 – ARC 2019, S. 241–248, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2019, ISBN: 978-3-96409-182-6. @inproceedings{Seppenhauser2019,
title = {Examinations of the Printer Head Prototype for UV Resins with Continous Fiber-Reinforcement},
author = {P. Seppenhauser},
editor = {J. Mottok and M. Reichenberger},
isbn = {978-3-96409-182-6},
year = {2019},
date = {2019-07-08},
booktitle = {Applied Research Conference 2019 – ARC 2019},
pages = {241--248},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {Additive manufacturing (AM) technologies with thermoplastic materials have been successfully used for several years in automotive, aerospace and medical industries. The use of UV resins provides high surface strength as well as high chemical resistance. In addition, very fast curing times in the range of a few seconds to fractions of a second are possible. The embedding of inorganic or organic fiber materials such as glass or carbon fibers in plastics leads to an improvement of the specific strength and specific rigidity of the components comparable to high-alloy steels. The aim is the creation of layered, continously fiber-reinforced structures by an AM process. A first printer head prototype was developed for this purpose, consisting of an impregnation, a feed and two curing modules. This paper deals with the design of the modules and their functionality. In summary, it can be said that the modules fulfill their function, but there is still a need for improvement. In particular, the transport of the impregnated fiber roving needs to be improved so that the roving is transportable as well as not too cured before being placed on the printing bed.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Additive manufacturing (AM) technologies with thermoplastic materials have been successfully used for several years in automotive, aerospace and medical industries. The use of UV resins provides high surface strength as well as high chemical resistance. In addition, very fast curing times in the range of a few seconds to fractions of a second are possible. The embedding of inorganic or organic fiber materials such as glass or carbon fibers in plastics leads to an improvement of the specific strength and specific rigidity of the components comparable to high-alloy steels. The aim is the creation of layered, continously fiber-reinforced structures by an AM process. A first printer head prototype was developed for this purpose, consisting of an impregnation, a feed and two curing modules. This paper deals with the design of the modules and their functionality. In summary, it can be said that the modules fulfill their function, but there is still a need for improvement. In particular, the transport of the impregnated fiber roving needs to be improved so that the roving is transportable as well as not too cured before being placed on the printing bed. |
Schimmer, F.; Ladewig, S.; Motsch, N.; Hausmann, J. M.; Ehrlich, I. Comparison of Low-Velocity Impact Damage Behavior of Unidirectional Carbon Fiber-Reinforced Thermoset and Thermoplastic Composites. Leichtbau Artikel In: Key Engineering Materials, 809 (22), S. 9-14, 2019. @article{Schimmer2019,
title = {Comparison of Low-Velocity Impact Damage Behavior of Unidirectional Carbon Fiber-Reinforced Thermoset and Thermoplastic Composites.},
author = {F. Schimmer and S. Ladewig and N. Motsch and J. M. Hausmann and I. Ehrlich},
url = {https://www.scientific.net/KEM.809.9},
doi = {https://doi.org/10.4028/www.scientific.net/KEM.809.9},
year = {2019},
date = {2019-06-01},
journal = {Key Engineering Materials},
volume = {809},
number = {22},
pages = {9-14},
abstract = {This paper investigates the damage behavior of thermoset and thermoplastic fiber-reinforced composites. The specimens were subjected to low-velocity impacts (LVI) to produce barely visible impact damages (BVID). To compare the dependency of the matrix system and the laminate lay-up on the impact damage, four test series were set up. Therefore, laminates with an epoxy (EP) and a polyether ether ketone (PEEK) matrix in a quasi-isotropic (QI) [+45/0/-45/90]2s and an orthotropic (OT) fiber lay-up [0/90]4s were manufactured. To eliminate the influence of variant fiber systems, the thermoplastic tape and the thermoset prepreg contain similar carbon fibers (CF). After impact testing with three different impact energies, inner damages were investigated by using ultrasonic analyses. To get a deeper understanding of the interior damage mechanisms, cross sections of the damaged areas were examined via reflected light microscopy. By using these destructive and non-destructive test methods, significant differences in the damage behavior of composites with thermoplastic and thermoset matrix systems were identified for both laminate lay-ups.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper investigates the damage behavior of thermoset and thermoplastic fiber-reinforced composites. The specimens were subjected to low-velocity impacts (LVI) to produce barely visible impact damages (BVID). To compare the dependency of the matrix system and the laminate lay-up on the impact damage, four test series were set up. Therefore, laminates with an epoxy (EP) and a polyether ether ketone (PEEK) matrix in a quasi-isotropic (QI) [+45/0/-45/90]2s and an orthotropic (OT) fiber lay-up [0/90]4s were manufactured. To eliminate the influence of variant fiber systems, the thermoplastic tape and the thermoset prepreg contain similar carbon fibers (CF). After impact testing with three different impact energies, inner damages were investigated by using ultrasonic analyses. To get a deeper understanding of the interior damage mechanisms, cross sections of the damaged areas were examined via reflected light microscopy. By using these destructive and non-destructive test methods, significant differences in the damage behavior of composites with thermoplastic and thermoset matrix systems were identified for both laminate lay-ups. |
Siegl, M.; Ehrlich, I. Internationale Forschung zum Biege- und Deformationsverhalten von faserverstärkten Kunststoffrohren. Leichtbau Forschungsbericht Ostbayerische Hochschule Regensburg VMK Verlag für Marketing & Kommunikation GmbH & Co. KG, Forschungsbericht 2019, 2019, ISBN: 978-3-9818209-6-6. @techreport{Siegl2019,
title = {Internationale Forschung zum Biege- und Deformationsverhalten von faserverstärkten Kunststoffrohren.},
author = {M. Siegl and I. Ehrlich},
editor = {Ostbayerische Technische Hochschule },
isbn = {978-3-9818209-6-6},
year = {2019},
date = {2019-06-01},
address = {VMK Verlag für Marketing & Kommunikation GmbH & Co. KG},
institution = {Ostbayerische Hochschule Regensburg},
abstract = {Rohre aus faserverstärktem Kunststoff werden unter anderem in der Elektroindustrie und demRohrleitungsbau eingesetzt. Die Gründe dafür sind vielfältig. Speziell Glasfasern bieten nebendem Leichtbaupotential auch sehr gute Isolationseigenschaften. Dabei sind diese Rohre häufigeiner Biegebelastung ausgesetzt, dessen Auswirkungen auf die Struktur sich wegen der komplexenMaterialbeschaffenheit mit gängigen Berechnungsmodellen nicht vollständig beschreiben lassen.Deshalb wird im Rahmen des deutsch-französischen Forschungsprojekts 4-Point-Bending Testsdas Biege- und Deformationsverhalten von faserverstärkten Kunststoffrohren unter Biege -belastung umfassend untersucht.},
type = {Forschungsbericht 2019},
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Rohre aus faserverstärktem Kunststoff werden unter anderem in der Elektroindustrie und demRohrleitungsbau eingesetzt. Die Gründe dafür sind vielfältig. Speziell Glasfasern bieten nebendem Leichtbaupotential auch sehr gute Isolationseigenschaften. Dabei sind diese Rohre häufigeiner Biegebelastung ausgesetzt, dessen Auswirkungen auf die Struktur sich wegen der komplexenMaterialbeschaffenheit mit gängigen Berechnungsmodellen nicht vollständig beschreiben lassen.Deshalb wird im Rahmen des deutsch-französischen Forschungsprojekts 4-Point-Bending Testsdas Biege- und Deformationsverhalten von faserverstärkten Kunststoffrohren unter Biege -belastung umfassend untersucht. |
Schlamp, M.; Ehrlich, I. Analyse des Impact-Verhaltens gekrümmter Strukturbauteile von Luftfahrzeugen zur Entwicklung eines Strukturüberwachungssystems für faserverstärkte Kunststoffe - BIRD Leichtbau Forschungsbericht Ostbayerische Hochschule Regensburg VMK Verlag für Marketing & Kommunikation GmbH & Co. KG, Forschungsbericht 2019, 2019, ISBN: 978-3-9818209-6-6 . @techreport{Schlamp2019,
title = {Analyse des Impact-Verhaltens gekrümmter Strukturbauteile von Luftfahrzeugen zur Entwicklung eines Strukturüberwachungssystems für faserverstärkte Kunststoffe - BIRD},
author = {M. Schlamp and I. Ehrlich},
editor = {Ostbayerische Technische Hochschule},
url = {https://www.oth-regensburg.de/fileadmin/media/forschung/Magazin_Forschung/190703_Magazin_Forschung_2019.pdf},
isbn = {978-3-9818209-6-6 },
year = {2019},
date = {2019-06-01},
address = {VMK Verlag für Marketing & Kommunikation GmbH & Co. KG},
institution = {Ostbayerische Hochschule Regensburg},
abstract = {Die in Flugvorausrichtung weisenden Bauteile von Luftfahrzeugen sind oftmals durch Einschlägeaufgrund von Vogelschlag, Hagel oder aufgewirbelten Kleinteilen gefährdet. Diese Einschläge,sogenannte Impacts, weisen bei faserverstärkten Kunststoffen ein stark krümmungs- undmaterialabhängiges Verhalten und Schadensausmaß auf. Impact-Schädigungen führen oftmalszu hohen Reparaturkosten, welche durch eine genauere Kenntnis des Schadens verringert werdenkönnen. Zur Klassifizierung dieser Schädigungen steht dabei vor allem das auftretende Frequenz-signal des Impacts im Fokus der Untersuchungen.},
type = {Forschungsbericht 2019},
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Die in Flugvorausrichtung weisenden Bauteile von Luftfahrzeugen sind oftmals durch Einschlägeaufgrund von Vogelschlag, Hagel oder aufgewirbelten Kleinteilen gefährdet. Diese Einschläge,sogenannte Impacts, weisen bei faserverstärkten Kunststoffen ein stark krümmungs- undmaterialabhängiges Verhalten und Schadensausmaß auf. Impact-Schädigungen führen oftmalszu hohen Reparaturkosten, welche durch eine genauere Kenntnis des Schadens verringert werdenkönnen. Zur Klassifizierung dieser Schädigungen steht dabei vor allem das auftretende Frequenz-signal des Impacts im Fokus der Untersuchungen. |
Romano, M.; Ehrlich, I.; Gebbeken, N. Parametric characterization of a mesomechanic kinematic in plain and twill weave 2/2 reinforced composites by FE-calculations. Leichtbau Artikel In: Archives of Materials Science and Engineering (ArchivesMSE), 1-2 (97), S. 20-38, 2019, ISSN: 1897-2764. @article{Romano2019,
title = {Parametric characterization of a mesomechanic kinematic in plain and twill weave 2/2 reinforced composites by FE-calculations.},
author = {M. Romano and I. Ehrlich and N. Gebbeken},
url = {HTTPS://ARCHIVESMSE.ORG/RESOURCES/HTML/CMS/MAINPAGE
HTTPS://ARCHIVESMSE.ORG/RESOURCES/HTML/ARTICLESLIST?ISSUEID=12181
HTTPS://ARCHIVESMSE.ORG/RESOURCES/HTML/ARTICLE/DETAILS?ID=190365},
doi = {10.5604/01.3001.0013.2869},
issn = {1897-2764},
year = {2019},
date = {2019-05-01},
journal = {Archives of Materials Science and Engineering (ArchivesMSE)},
volume = {1-2},
number = {97},
pages = {20-38},
abstract = {Purpose: A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by numerical investigations. Design/methodology/approach: Due to the definition of plain representative sequences of balanced plain-weave and twill-weave 2/2 fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. Findings: The mesomechanic kinematic can be observed in the FE analyses for both kinds of fabric constructions. Research limitations/implications: The FE analyses consider elasticity and contraction due to Poisson effects, respectively, of the model under selected longitudinal strains. Practical implications: The results are evaluated at relevant positions on the centre-line of the ondulated warp-yarn of the plain representative model. A direct and linear coupling in case of the transversal kinematic behaviour, and thereby a corresponding definite reduction of the evaluated longitudinal strains in terms of the difference of the applied and determined longitudinal strains is identified. Originality/value: Both characteristic purely kinematic reactions due to geometric constraints directly depend on the introduced degree of ondulation. This non-dimensional parameter relates amplitude and length of one complete ondulation, and thus represents the intensity of the ondulation of the respective fabric construction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Purpose: A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by numerical investigations. Design/methodology/approach: Due to the definition of plain representative sequences of balanced plain-weave and twill-weave 2/2 fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. Findings: The mesomechanic kinematic can be observed in the FE analyses for both kinds of fabric constructions. Research limitations/implications: The FE analyses consider elasticity and contraction due to Poisson effects, respectively, of the model under selected longitudinal strains. Practical implications: The results are evaluated at relevant positions on the centre-line of the ondulated warp-yarn of the plain representative model. A direct and linear coupling in case of the transversal kinematic behaviour, and thereby a corresponding definite reduction of the evaluated longitudinal strains in terms of the difference of the applied and determined longitudinal strains is identified. Originality/value: Both characteristic purely kinematic reactions due to geometric constraints directly depend on the introduced degree of ondulation. This non-dimensional parameter relates amplitude and length of one complete ondulation, and thus represents the intensity of the ondulation of the respective fabric construction. |
Putzer, M. Development of subject-specific musculoskeletal models for studies of lumbar loading Leichtbau Promotionsarbeit Universität der Bundeswehr München, 2019. @phdthesis{Putzer2019,
title = {Development of subject-specific musculoskeletal models for studies of lumbar loading },
author = {M. Putzer},
url = {https://athene-forschung.unibw.de/116114?show_id=126811
https://pdb-org.com/cgi-bin/pdbfm/Manager.pl?file=Dissertation.pdf&link=ba0b806f842cf0e93cce79122908bd4e&a=117
URN:NBN:DE:BVB:706-5924},
year = {2019},
date = {2019-01-21},
school = {Universität der Bundeswehr München},
abstract = {Anatomical differences between individuals are often neglected in musculoskeletal models, but they are necessary in case of subject-specific questions regarding the lumbar spine. A modification of models to each subject is complex and the effects on lumbar loading are difficult to assess. The objective of this thesis is to create a validated musculoskeletal model of the human body, which facilitates a subject-specific modification of the geometry of the lumbar spine. Furthermore, important parameters are identified in sensitivity studies and a case study regarding multifidus muscle atrophy after a disc herniation is conducted. Therefore, a generic model is heavily modified and a semi-automatic process is implemented. This procedure remodels the geometry of the lumbar spine to a subject-specific one on basis of segmented medical images. The resulting five models are validated with regard to the lumbar loading at the L4/L5 level. The influence of lumbar ligament stiffness is determined by changing the stiffness values of all lumbar ligaments in eleven steps during a flexion motion. Sensitivities of lumbar loading to an altered geometry of the lumbar spine are identified by varying ten lumbar parameters in simulations with each model in four postures. The case study includes an analysis of the loading of the multifidus muscle and of the lumbar discs throughout various stages of disc herniation. This time each model performs four motions with two different motion rhythms. The results indicate that lumbar motion and loading is dependent on lumbar ligament stiffness. Furthermore, subject-specific modelling of the lumbar spine should include at least the vertebral height, disc height and lumbar lordosis. The results of the case study suggest that an overloading of the multifidus muscle could follow disc herniation. Additionally, a subsequent atrophy of the muscles could expose adjacent levels to an increased loading, but these findings are highly dependent on the individual. },
type = { Dissertation},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
Anatomical differences between individuals are often neglected in musculoskeletal models, but they are necessary in case of subject-specific questions regarding the lumbar spine. A modification of models to each subject is complex and the effects on lumbar loading are difficult to assess. The objective of this thesis is to create a validated musculoskeletal model of the human body, which facilitates a subject-specific modification of the geometry of the lumbar spine. Furthermore, important parameters are identified in sensitivity studies and a case study regarding multifidus muscle atrophy after a disc herniation is conducted. Therefore, a generic model is heavily modified and a semi-automatic process is implemented. This procedure remodels the geometry of the lumbar spine to a subject-specific one on basis of segmented medical images. The resulting five models are validated with regard to the lumbar loading at the L4/L5 level. The influence of lumbar ligament stiffness is determined by changing the stiffness values of all lumbar ligaments in eleven steps during a flexion motion. Sensitivities of lumbar loading to an altered geometry of the lumbar spine are identified by varying ten lumbar parameters in simulations with each model in four postures. The case study includes an analysis of the loading of the multifidus muscle and of the lumbar discs throughout various stages of disc herniation. This time each model performs four motions with two different motion rhythms. The results indicate that lumbar motion and loading is dependent on lumbar ligament stiffness. Furthermore, subject-specific modelling of the lumbar spine should include at least the vertebral height, disc height and lumbar lordosis. The results of the case study suggest that an overloading of the multifidus muscle could follow disc herniation. Additionally, a subsequent atrophy of the muscles could expose adjacent levels to an increased loading, but these findings are highly dependent on the individual. |
Wiesent, L.; Schultheiß, U.; Schmid, C.; Schratzenstaller, T.; Nonn, A. Experimentally validated simulation of coronary stents considering different dogboning ratios and asymmetric stent positioning Werkstoffsimulation Artikel In: PLOS ONE, 14 (10), S. 1-25, 2019. @article{Wiesent2019,
title = {Experimentally validated simulation of coronary stents considering different dogboning ratios and asymmetric stent positioning},
author = {L. Wiesent and U. Schultheiß and C. Schmid and T. Schratzenstaller and A. Nonn},
doi = {10.1371/journal.pone.0224026},
year = {2019},
date = {2019-01-01},
journal = {PLOS ONE},
volume = {14},
number = {10},
pages = {1-25},
publisher = {Public Library of Science},
abstract = {In-stent restenosis remains a major problem of arteriosclerosis treatment by stenting. Expansion-optimized stents could reduce this problem. With numerical simulations, stent designs/ expansion behaviours can be effectively analyzed. For reasons of efficiency, simplified models of balloon-expandable stents are often used, but their accuracy must be challenged due to insufficient experimental validation. In this work, a realistic stent life-cycle simulation has been performed including balloon folding, stent crimping and free expansion of the balloon-stent-system. The successful simulation and validation of two stent designs with homogenous and heterogeneous stent stiffness and an asymmetrically positioned stent on the balloon catheter confirm the universal applicability of the simulation approach. Dogboning ratio, as well as the final dimensions of the folded balloon, the crimped and expanded stent, correspond well to the experimental dimensions with only slight deviations. In contrast to the detailed stent life-cycle simulation, a displacement-controlled simulation can not predict the transient stent expansion, but is suitable to reproduce the final expanded stent shape and the associated stress states. The detailed stent life-cycle simulation is thus essential for stent expansion analysis/optimization, whereas for reasons of computational efficiency, the displacement-controlled approach can be considered in the context of pure stress analysis.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In-stent restenosis remains a major problem of arteriosclerosis treatment by stenting. Expansion-optimized stents could reduce this problem. With numerical simulations, stent designs/ expansion behaviours can be effectively analyzed. For reasons of efficiency, simplified models of balloon-expandable stents are often used, but their accuracy must be challenged due to insufficient experimental validation. In this work, a realistic stent life-cycle simulation has been performed including balloon folding, stent crimping and free expansion of the balloon-stent-system. The successful simulation and validation of two stent designs with homogenous and heterogeneous stent stiffness and an asymmetrically positioned stent on the balloon catheter confirm the universal applicability of the simulation approach. Dogboning ratio, as well as the final dimensions of the folded balloon, the crimped and expanded stent, correspond well to the experimental dimensions with only slight deviations. In contrast to the detailed stent life-cycle simulation, a displacement-controlled simulation can not predict the transient stent expansion, but is suitable to reproduce the final expanded stent shape and the associated stress states. The detailed stent life-cycle simulation is thus essential for stent expansion analysis/optimization, whereas for reasons of computational efficiency, the displacement-controlled approach can be considered in the context of pure stress analysis. |
Kramer, S. L. B.; Jones, A.; Mostafa, A.; Ravaji, B.; Tancogne-Dejean, T.; Roth, C. C.; Gorji, M.; Pack, K.; Foster, J. T.; Behzadinasab, M.; Sobotka, J. C.; McFarland, J. M.; Stein, J.; Spear, A. D.; Newell, P.; Czabaj, M. W.; Williams, B.; Simha, H.; Gesing, M.; Gilkey, L. N.; Jones, C. A.; Dingreville, R.; Sanborn, S. E.; Bignell, J. L.; Cerrone, A. R.; Keim, V.; Nonn, A.; Cooreman, S.; Thibaux, P.; Ames, N.; Connor, D. O.; Parno, M.; Davis, B.; Tucker, J.; Coudrillier, B.; Karlson, K. N.; Ostien, J. T.; Foulk, J. W.; Hammetter, C. I.; Grange, S.; Emery, J. M.; Brown, J. A.; Bishop, J. E.; Johnson, K. L.; Ford, K. R.; Brinckmann, S.; Neilsen, M. K.; Jackiewicz, J.; Ravi-Chandar, K.; Ivanoff, T.; Salzbrenner, B. C.; Boyce, B. L. The third Sandia fracture challenge: predictions of ductile fracture in additively manufactured metal Werkstoffsimulation Artikel In: International Journal of Fracture, 218 (1), S. 5-61, 2019, ISSN: 1573-2673. @article{Kramer2019,
title = {The third Sandia fracture challenge: predictions of ductile fracture in additively manufactured metal},
author = {S. L. B. Kramer and A. Jones and A. Mostafa and B. Ravaji and T. Tancogne-Dejean and C. C. Roth and M. Gorji and K. Pack and J. T. Foster and M. Behzadinasab and J. C. Sobotka and J. M. McFarland and J. Stein and A. D. Spear and P. Newell and M. W. Czabaj and B. Williams and H. Simha and M. Gesing and L. N. Gilkey and C. A. Jones and R. Dingreville and S. E. Sanborn and J. L. Bignell and A. R. Cerrone and V. Keim and A. Nonn and S. Cooreman and P. Thibaux and N. Ames and D. O. Connor and M. Parno and B. Davis and J. Tucker and B. Coudrillier and K. N. Karlson and J. T. Ostien and J. W. Foulk and C. I. Hammetter and S. Grange and J. M. Emery and J. A. Brown and J. E. Bishop and K. L. Johnson and K. R. Ford and S. Brinckmann and M. K. Neilsen and J. Jackiewicz and K. Ravi-Chandar and T. Ivanoff and B. C. Salzbrenner and B. L. Boyce},
doi = {10.1007/s10704-019-00361-1},
issn = {1573-2673},
year = {2019},
date = {2019-01-01},
journal = {International Journal of Fracture},
volume = {218},
number = {1},
pages = {5-61},
abstract = {The Sandia Fracture Challenges provide a forum for the mechanics community to assess its ability to predict ductile fracture through a blind, round-robin format where mechanicians are challenged to predict the deformation and failure of an arbitrary geometry given experimental calibration data. The Third Challenge (SFC3) required participants to predict fracture in an additively manufactured (AM) 316L stainless steel bar containing through holes and internal cavities that could not have been conventionally machined. The volunteer participants were provided extensive data including tension and notched tensions tests of 316L specimens built on the same build-plate as the Challenge geometry, micro-CT scans of the Challenge specimens and geometric measurements of the feature based on the scans, electron backscatter diffraction (EBSD) information on grain texture, and post-test fractography of the calibration specimens. Surprisingly, the global behavior of the SFC3 geometry specimens had modest variability despite being made of AM metal, with all of the SFC3 geometry specimens failing under the same failure mode. This is attributed to the large stress concentrations from the holes overwhelming the stochastic local influence of the AM voids and surface roughness. The teams were asked to predict a number of quantities of interest in the response based on global and local measures that were compared to experimental data, based partly on Digital Image Correlation (DIC) measurements of surface displacements and strains, including predictions of variability in the resulting fracture response, as the basis for assessment of the predictive capabilities of the modeling and simulation strategies. Twenty-one teams submitted predictions obtained from a variety of methods: the finite element method (FEM) or the mesh-free, peridynamic method; solvers with explicit time integration, implicit time integration, or quasi-statics; fracture methods including element deletion, peridynamics with bond damage, XFEM, damage (stiffness degradation), and adaptive remeshing. These predictions utilized many different material models: plasticity models including J2 plasticity or Hill yield with isotropic hardening, mixed Swift-Voce hardening, kinematic hardening, or custom hardening curves; fracture criteria including GTN model, Hosford-Coulomb, triaxiality-dependent strain, critical fracture energy, damage-based model, critical void volume fraction, and Johnson-Cook model; and damage evolution models including damage accumulation and evolution, crack band model, fracture energy, displacement value threshold, incremental stress triaxiality, Cocks-Ashby void growth, and void nucleation, growth, and coalescence. Teams used various combinations of calibration data from tensile specimens, the notched tensile specimens, and literature data. A detailed comparison of results based of these different methods is presented in this paper to suggest a set of best practices for modeling ductile fracture in situations like the SFC3 AM-material problem. All blind predictions identified the nominal crack path and initiation location correctly. The SFC3 participants generally fared better in their global predictions of deformation and failure than the participants in the previous Challenges, suggesting the relative maturity of the models used and adoption of best practices from previous Challenges. This paper provides detailed analyses of the results, including discussion of the utility of the provided data, challenges of the experimental-numerical comparison, defects in the AM material, and human factors.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Sandia Fracture Challenges provide a forum for the mechanics community to assess its ability to predict ductile fracture through a blind, round-robin format where mechanicians are challenged to predict the deformation and failure of an arbitrary geometry given experimental calibration data. The Third Challenge (SFC3) required participants to predict fracture in an additively manufactured (AM) 316L stainless steel bar containing through holes and internal cavities that could not have been conventionally machined. The volunteer participants were provided extensive data including tension and notched tensions tests of 316L specimens built on the same build-plate as the Challenge geometry, micro-CT scans of the Challenge specimens and geometric measurements of the feature based on the scans, electron backscatter diffraction (EBSD) information on grain texture, and post-test fractography of the calibration specimens. Surprisingly, the global behavior of the SFC3 geometry specimens had modest variability despite being made of AM metal, with all of the SFC3 geometry specimens failing under the same failure mode. This is attributed to the large stress concentrations from the holes overwhelming the stochastic local influence of the AM voids and surface roughness. The teams were asked to predict a number of quantities of interest in the response based on global and local measures that were compared to experimental data, based partly on Digital Image Correlation (DIC) measurements of surface displacements and strains, including predictions of variability in the resulting fracture response, as the basis for assessment of the predictive capabilities of the modeling and simulation strategies. Twenty-one teams submitted predictions obtained from a variety of methods: the finite element method (FEM) or the mesh-free, peridynamic method; solvers with explicit time integration, implicit time integration, or quasi-statics; fracture methods including element deletion, peridynamics with bond damage, XFEM, damage (stiffness degradation), and adaptive remeshing. These predictions utilized many different material models: plasticity models including J2 plasticity or Hill yield with isotropic hardening, mixed Swift-Voce hardening, kinematic hardening, or custom hardening curves; fracture criteria including GTN model, Hosford-Coulomb, triaxiality-dependent strain, critical fracture energy, damage-based model, critical void volume fraction, and Johnson-Cook model; and damage evolution models including damage accumulation and evolution, crack band model, fracture energy, displacement value threshold, incremental stress triaxiality, Cocks-Ashby void growth, and void nucleation, growth, and coalescence. Teams used various combinations of calibration data from tensile specimens, the notched tensile specimens, and literature data. A detailed comparison of results based of these different methods is presented in this paper to suggest a set of best practices for modeling ductile fracture in situations like the SFC3 AM-material problem. All blind predictions identified the nominal crack path and initiation location correctly. The SFC3 participants generally fared better in their global predictions of deformation and failure than the participants in the previous Challenges, suggesting the relative maturity of the models used and adoption of best practices from previous Challenges. This paper provides detailed analyses of the results, including discussion of the utility of the provided data, challenges of the experimental-numerical comparison, defects in the AM material, and human factors. |
Keim, V.; Marx, P.; Nonn, A.; Münstermann, S. Fluid-structure-interaction modeling of dynamic fracture propagation in pipelines transporting natural gases and CO2-mixtures Werkstoffsimulation Artikel In: International Journal of Pressure Vessels and Piping, 175 , S. 103934, 2019, ISSN: 0308-0161. @article{KEIM2019103934,
title = {Fluid-structure-interaction modeling of dynamic fracture propagation in pipelines transporting natural gases and CO2-mixtures},
author = {V. Keim and P. Marx and A. Nonn and S. Münstermann},
doi = {10.1016/j.ijpvp.2019.103934},
issn = {0308-0161},
year = {2019},
date = {2019-01-01},
journal = {International Journal of Pressure Vessels and Piping},
volume = {175},
pages = {103934},
abstract = {As part of current design standards, the Battelle Two-Curve Model (BTCM) is still widely used to predict and secure ductile crack arrest in gas transmission pipelines. For modern linepipe steels and rich natural gases or CO2 mixtures, the BTCM might lead to incorrect predictions. On the one hand, it suffers from the insufficient description of the individual physical processes in the pipe material and fluid itself. Furthermore, the model does not account for fluid-structure-interaction (FSI) effects during simultaneous running-ductile fracture (RDF) and mixture decompression. Numerical FSI models allow for a more sophisticated, coupled analysis of the driving forces for the failure of pipelines. This paper deals with the development of an FSI model for the coupled prediction of 3D pressure profiles acting on the inner pipe wall during crack propagation. The coupled Euler-Lagrange (CEL) method is used to link the fluid and structure models. In a Lagrange formulation, the modified Bai-Wierzbicki (MBW) model describes the plastic deformation and ductile fracture as a function of the underlying stress/strain conditions. The fluid behavior is calculated in a 3D model space by Euler equations and the GERG-2008 reference equation of state (EOS). The coupled CEL model is used to predict the RDF in small-diameter pipe sections for different fluid mixtures. The calculated 3D pressure distributions ahead and behind the running crack tip (CT) significantly differ in axial and circumferential directions depending on the mixture composition. The predicted FSI between the pipe wall and fluid decompression in 3D CEL/FSI model provides reliable knowledge about the pressure loading of the pipeline during RDF.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
As part of current design standards, the Battelle Two-Curve Model (BTCM) is still widely used to predict and secure ductile crack arrest in gas transmission pipelines. For modern linepipe steels and rich natural gases or CO2 mixtures, the BTCM might lead to incorrect predictions. On the one hand, it suffers from the insufficient description of the individual physical processes in the pipe material and fluid itself. Furthermore, the model does not account for fluid-structure-interaction (FSI) effects during simultaneous running-ductile fracture (RDF) and mixture decompression. Numerical FSI models allow for a more sophisticated, coupled analysis of the driving forces for the failure of pipelines. This paper deals with the development of an FSI model for the coupled prediction of 3D pressure profiles acting on the inner pipe wall during crack propagation. The coupled Euler-Lagrange (CEL) method is used to link the fluid and structure models. In a Lagrange formulation, the modified Bai-Wierzbicki (MBW) model describes the plastic deformation and ductile fracture as a function of the underlying stress/strain conditions. The fluid behavior is calculated in a 3D model space by Euler equations and the GERG-2008 reference equation of state (EOS). The coupled CEL model is used to predict the RDF in small-diameter pipe sections for different fluid mixtures. The calculated 3D pressure distributions ahead and behind the running crack tip (CT) significantly differ in axial and circumferential directions depending on the mixture composition. The predicted FSI between the pipe wall and fluid decompression in 3D CEL/FSI model provides reliable knowledge about the pressure loading of the pipeline during RDF. |
Keim, V.; Cerrone, A.; Nonn, A. Using local damage models to predict fracture in additively manufactured specimens Werkstoffsimulation Artikel In: International Journal of Fracture, 218 (1), S. 135-147, 2019, ISSN: 1573-2673. @article{Keim2019b,
title = {Using local damage models to predict fracture in additively manufactured specimens},
author = {V. Keim and A. Cerrone and A. Nonn},
doi = {10.1007/s10704-019-00371-z},
issn = {1573-2673},
year = {2019},
date = {2019-01-01},
journal = {International Journal of Fracture},
volume = {218},
number = {1},
pages = {135-147},
abstract = {This paper explores the efficacy of employing local damage models, normally applied to ductile material systems manufactured by subtractive techniques, to additively manufactured laboratory specimens. While these specimens were ductile and metallic, their additive character (i.e. porosity and surface roughness) could have had potential to activate multiple life-limiting failure paths, thus obfuscating failure prediction. Herein, two damage models are considered and compared: the micromechanical Gurson-Tvergaard-Needleman model and a Crack Band model of the strain-based, phenomenological genre. Simulations used to calibrate elastic and plastic material properties and predict damage in a novel, non-standard specimen were quasi-static, explicit. Both damage models proved capable in resolving the experimentally-observed failure path and associated loading conditions. The analyses described herein were made as part of the Third Sandia Fracture Challenge.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This paper explores the efficacy of employing local damage models, normally applied to ductile material systems manufactured by subtractive techniques, to additively manufactured laboratory specimens. While these specimens were ductile and metallic, their additive character (i.e. porosity and surface roughness) could have had potential to activate multiple life-limiting failure paths, thus obfuscating failure prediction. Herein, two damage models are considered and compared: the micromechanical Gurson-Tvergaard-Needleman model and a Crack Band model of the strain-based, phenomenological genre. Simulations used to calibrate elastic and plastic material properties and predict damage in a novel, non-standard specimen were quasi-static, explicit. Both damage models proved capable in resolving the experimentally-observed failure path and associated loading conditions. The analyses described herein were made as part of the Third Sandia Fracture Challenge. |
Keim, V.; Nonn, A.; Münstermann, S. Application of the modified Bai-Wierzbicki model for the prediction of ductile fracture in pipelines Werkstoffsimulation Artikel In: International Journal of Pressure Vessels and Piping, 171 , S. 104 - 116, 2019, ISSN: 0308-0161. @article{Keim2019d,
title = {Application of the modified Bai-Wierzbicki model for the prediction of ductile fracture in pipelines},
author = {V. Keim and A. Nonn and S. Münstermann},
doi = {10.1016/j.ijpvp.2019.02.010},
issn = {0308-0161},
year = {2019},
date = {2019-01-01},
journal = {International Journal of Pressure Vessels and Piping},
volume = {171},
pages = {104 - 116},
abstract = {The complex mechanical and corrosive loads of modern pipeline systems transporting oil, natural gas and CO2 impose steadily increasing requirements on material properties. The majority of current design standards still limit the application of modern high toughness linepipe steels due to the simple specification of material requirements in terms of energy levels from Charpy impact or Battelle Drop-Weight-Tear (BDWT) tests. In consequence, research activities have been conducted recently aiming at developing modified or novel experimental methods for the characterization of the ductile fracture behavior. To quantify the effects of various parameters on fracture behavior and derive suitable correlations, it is necessary to accompany these activities by numerical simulations with appropriate ductile damage models. In this paper, the MBW model is applied to study the structural behavior of pipelines in ductile fracture regime. Due to its precise incorporation of the underlying load conditions, the damage model is successfully used to simulate the slant fracture behavior in Battelle Drop weight tear test specimens and pipe sections. In comparison to ductile damage models applied in former studies, namely the Gurson-Tvergaard-Needleman and Cohesive Zone model, the presented numerical methodology allows for a more detailed investigation of loading, material and geometry effects on fracture and crack arrest behavior of pipelines.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The complex mechanical and corrosive loads of modern pipeline systems transporting oil, natural gas and CO2 impose steadily increasing requirements on material properties. The majority of current design standards still limit the application of modern high toughness linepipe steels due to the simple specification of material requirements in terms of energy levels from Charpy impact or Battelle Drop-Weight-Tear (BDWT) tests. In consequence, research activities have been conducted recently aiming at developing modified or novel experimental methods for the characterization of the ductile fracture behavior. To quantify the effects of various parameters on fracture behavior and derive suitable correlations, it is necessary to accompany these activities by numerical simulations with appropriate ductile damage models. In this paper, the MBW model is applied to study the structural behavior of pipelines in ductile fracture regime. Due to its precise incorporation of the underlying load conditions, the damage model is successfully used to simulate the slant fracture behavior in Battelle Drop weight tear test specimens and pipe sections. In comparison to ductile damage models applied in former studies, namely the Gurson-Tvergaard-Needleman and Cohesive Zone model, the presented numerical methodology allows for a more detailed investigation of loading, material and geometry effects on fracture and crack arrest behavior of pipelines. |
2018
|
Nonn, A.; Paredes, M.; Keim, V.; Wierzbicki, T. Comparison of Fracture Models to Quantify the Effects of Material Plasticity on the Ductile Fracture Propagation in Pipelines Werkstoffsimulation Konferenzbeitrag In: Proceedings of the 2018 12th International Pipeline Conference, Volume 3: Operations, Monitoring, and Maintenance, Materials and Joining, Calgary, Alberta, Canada, 2018, ISBN: 978-0-7918-5188-3. @inproceedings{Nonn2018,
title = {Comparison of Fracture Models to Quantify the Effects of Material Plasticity on the Ductile Fracture Propagation in Pipelines},
author = {A. Nonn and M. Paredes and V. Keim and T. Wierzbicki},
doi = {10.1115/IPC2018-78366},
isbn = {978-0-7918-5188-3},
year = {2018},
date = {2018-09-24},
booktitle = {Proceedings of the 2018 12th International Pipeline Conference, Volume 3: Operations, Monitoring, and Maintenance, Materials and Joining},
address = {Calgary, Alberta, Canada},
series = {International Pipeline Conference},
abstract = {Various numerical approaches have been developed in the last years aimed to simulate the ductile fracture propagation in pipelines transporting CO2 or natural gas. However, a reliable quantification of the influence of material plasticity on the fracture resistance is still missing. Therefore, more accurate description of the material plasticity on the ductile fracture propagation is required based on a suitable numerical methodology.In this study, different plasticity and fracture models are compared regarding the ductile fracture propagation in X100 pipeline steel with the objective to quantify the influence of plasticity parameters on the fracture resistance. The plastic behavior of the investigated material is considered by the quadratic yield surface in conjunction with a non-associated quadratic plastic flow potential. The strain hardening can be appropriately described by the mixed Swift-Voce law. The simulations of ductile fracture are conducted by an uncoupled, modified Mohr-Coulomb (MMC) and the micromechanically based Gurson-Tvergaard-Needleman (GTN) models. In contract to the original GTN model, the MMC model is capable of describing ductile failure over wide range of stress states. Thus, ductile fracture resistance can be estimated for various load and fracture scenarios. Both models are used for the simulation of fracture propagation in DWTT and 3D pressurized pipe sections. The results from the present work can serve as a basis for establishing the correlation between plasticity parameters and ductile fracture propagation.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Various numerical approaches have been developed in the last years aimed to simulate the ductile fracture propagation in pipelines transporting CO2 or natural gas. However, a reliable quantification of the influence of material plasticity on the fracture resistance is still missing. Therefore, more accurate description of the material plasticity on the ductile fracture propagation is required based on a suitable numerical methodology.In this study, different plasticity and fracture models are compared regarding the ductile fracture propagation in X100 pipeline steel with the objective to quantify the influence of plasticity parameters on the fracture resistance. The plastic behavior of the investigated material is considered by the quadratic yield surface in conjunction with a non-associated quadratic plastic flow potential. The strain hardening can be appropriately described by the mixed Swift-Voce law. The simulations of ductile fracture are conducted by an uncoupled, modified Mohr-Coulomb (MMC) and the micromechanically based Gurson-Tvergaard-Needleman (GTN) models. In contract to the original GTN model, the MMC model is capable of describing ductile failure over wide range of stress states. Thus, ductile fracture resistance can be estimated for various load and fracture scenarios. Both models are used for the simulation of fracture propagation in DWTT and 3D pressurized pipe sections. The results from the present work can serve as a basis for establishing the correlation between plasticity parameters and ductile fracture propagation. |
Ladewig, S. Discussion about Viscosity Theories for Fibre-Reinforced Thermoplastics Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Bogner, W. (Hrsg.): Applied Research Conference 2018 -- ARC 2018, S. 144–149, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2018, ISBN: 978-3-96409-018-8. @inproceedings{Ladewig2018,
title = {Discussion about Viscosity Theories for Fibre-Reinforced Thermoplastics},
author = {S. Ladewig},
editor = {J. Mottok and M. Reichenberger and W. Bogner},
isbn = {978-3-96409-018-8},
year = {2018},
date = {2018-07-10},
booktitle = {Applied Research Conference 2018 -- ARC 2018},
pages = {144--149},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {The effect of process variables such as shear rate and temperature on the viscosity of polypropylene during the processing of thermoplastic based composites was investigated in this study. The melt impregnation is used in the process of continuous glass fibre reinforced thermoplastic composites. To develop a mathematical model for roving impregnation, it's essential to know about the viscous behaviour of the matrix system. Therefore, this paper will discuss rheological models to describe these phenomena, based on the gathered viscosity data from the partner laboratory at the University of West Bohemia in Pilsen.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The effect of process variables such as shear rate and temperature on the viscosity of polypropylene during the processing of thermoplastic based composites was investigated in this study. The melt impregnation is used in the process of continuous glass fibre reinforced thermoplastic composites. To develop a mathematical model for roving impregnation, it's essential to know about the viscous behaviour of the matrix system. Therefore, this paper will discuss rheological models to describe these phenomena, based on the gathered viscosity data from the partner laboratory at the University of West Bohemia in Pilsen. |
Wenzl, C. Comparison of Analytical and Numerical Results for the Deformation of Circular Curved Structures under Pressure Load. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Bogner, W. (Hrsg.): Applied Research Conference 2018 – ARC 2018 , S. 150–155, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2018, ISBN: 978-3-96409-018-8. @inproceedings{Wenzl2018,
title = {Comparison of Analytical and Numerical Results for the Deformation of Circular Curved Structures under Pressure Load. },
author = {C. Wenzl},
editor = {J. Mottok and M. Reichenberger and W. Bogner},
isbn = {978-3-96409-018-8},
year = {2018},
date = {2018-07-10},
booktitle = {Applied Research Conference 2018 – ARC 2018 },
pages = {150--155},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {The Ostbayerische Technische Hochschule (OTH Regensburg) conducts studies about the damage process of physical impacts on curved geometries made of fiber reinforced plastics (FRP). These studies are executed to deepen the research in the field of the influence of a structures curvature on the process of a physical impact. Therefore, the damage behaviour and the deformation during an impact are explored. This paper presents an investigation of the deformation-behaviour of circular curved structures under a static pressure load. This simplification from a dynamic to a static problem leads to several analytic solutions. At first, analytic solutions for circular curved structures with isotropic material properties, for example the theorem of Ecsedi and Dluhi for composite arches is going to be considered. Furthermore, the results are verified by a FEM (Finite Element Method) simulation. The simulation is performed with the help of the program ANSYS. This paper provides an overview over several calculation methods for isotropic materials. This information can be used to develop further calculation methods for pressure loaded structures. Especially methods for the calculation of unconstant curved structures have to be improved. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Ostbayerische Technische Hochschule (OTH Regensburg) conducts studies about the damage process of physical impacts on curved geometries made of fiber reinforced plastics (FRP). These studies are executed to deepen the research in the field of the influence of a structures curvature on the process of a physical impact. Therefore, the damage behaviour and the deformation during an impact are explored. This paper presents an investigation of the deformation-behaviour of circular curved structures under a static pressure load. This simplification from a dynamic to a static problem leads to several analytic solutions. At first, analytic solutions for circular curved structures with isotropic material properties, for example the theorem of Ecsedi and Dluhi for composite arches is going to be considered. Furthermore, the results are verified by a FEM (Finite Element Method) simulation. The simulation is performed with the help of the program ANSYS. This paper provides an overview over several calculation methods for isotropic materials. This information can be used to develop further calculation methods for pressure loaded structures. Especially methods for the calculation of unconstant curved structures have to be improved. |
Gebhardt, J. Low Velocity Impact of GFRP Laminate – Experimental Observations and Numerical Modelling. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Bogner, W. (Hrsg.): Applied Research Conference 2018 – ARC 2018, S. 211–215, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2018, ISBN: 978-3-96409-018-8. @inproceedings{Gebhardt2018,
title = {Low Velocity Impact of GFRP Laminate – Experimental Observations and Numerical Modelling.},
author = {J. Gebhardt},
editor = {J. Mottok and M. Reichenberger and W. Bogner},
isbn = {978-3-96409-018-8},
year = {2018},
date = {2018-07-10},
booktitle = {Applied Research Conference 2018 – ARC 2018},
pages = {211--215},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {Within the framework of the development of a Structural Health Monitoring System (SHM) for composite aircraft structures subjected to impact hazards like bird strikes and swirled up small parts during take-off and landing, lab scaled tests are conducted to achieve a fundamental understanding of composite damage mechanisms. An experimental and numerical investigation of low-velocity impacts of composite plates is conducted. By comparing the quasi-continous measuring signal and post-impact damage areas to numerical analysis results, the simulation can be adapted to the experiment by a numerical calibration. A drop tower test device for low-velocity impact testing, according to DIN EN 6038 was instrumented with a force transducer to determine the time-dependent contact force between the impactor and and specimen following ASTM D3763. In each test case, two plates are tested with 9, 12 and 16 joules impact energy, and the transient force characteristics as well as the damage surfaces are evaluated. The investigated impact scenarios last typically 6 ms with multiple load drops and superposed oscillations. Through the high-resolution measurement of the contact force it seems to be possible to use a spectograph to identify the delamination threshold load. The formation of the damage area was simulated in a numerical model utilizing LS-DYNA which shows good agreement with the experiment. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Within the framework of the development of a Structural Health Monitoring System (SHM) for composite aircraft structures subjected to impact hazards like bird strikes and swirled up small parts during take-off and landing, lab scaled tests are conducted to achieve a fundamental understanding of composite damage mechanisms. An experimental and numerical investigation of low-velocity impacts of composite plates is conducted. By comparing the quasi-continous measuring signal and post-impact damage areas to numerical analysis results, the simulation can be adapted to the experiment by a numerical calibration. A drop tower test device for low-velocity impact testing, according to DIN EN 6038 was instrumented with a force transducer to determine the time-dependent contact force between the impactor and and specimen following ASTM D3763. In each test case, two plates are tested with 9, 12 and 16 joules impact energy, and the transient force characteristics as well as the damage surfaces are evaluated. The investigated impact scenarios last typically 6 ms with multiple load drops and superposed oscillations. Through the high-resolution measurement of the contact force it seems to be possible to use a spectograph to identify the delamination threshold load. The formation of the damage area was simulated in a numerical model utilizing LS-DYNA which shows good agreement with the experiment. |
Siegl, M.; Ehrlich, I. Einfluss von Prozessparametern auf die Schmelzimprägnierung zur Herstellung von faserverstärkten Thermoplasten. Leichtbau Forschungsbericht Ostbayerische Technische Hochschule Regensburg VMK Verlag für Marketing & Kommunikation GmbH & Co. KG, 2018, ISBN: 978-3-9818209-4-2. @techreport{Siegl2018b,
title = {Einfluss von Prozessparametern auf die Schmelzimprägnierung zur Herstellung von faserverstärkten Thermoplasten.},
author = {M. Siegl and I. Ehrlich},
editor = {Ostbayerische Technische Hochschule},
isbn = {978-3-9818209-4-2},
year = {2018},
date = {2018-06-01},
address = {VMK Verlag für Marketing & Kommunikation GmbH & Co. KG},
institution = {Ostbayerische Technische Hochschule Regensburg},
abstract = {Die Erforschung von faserverstärkten Kunststoffen (FVK) mit thermoplastischer Matrix ist aufgrund der Schweißeignung als Verbindungstechnologie, der thermischen Umformbarkeit, der Recyclebarkeit sowie der verkürzten Prozesszeiten im Vergleich zu den vorwiegend eingesetzten faserverstärkten Duroplasten erstrebenswert. Die Wechselwirkung zwischen den physikalischen, mechanischen und geometrischen Parametern erhöht den Komplexitätsgrad des Herstellungsprozesses. Ziel ist daher die Entwicklung einer Imprägniertechnik, die eine Fasertränkung mittels eines Thermoplastschmelzbades ermöglicht.},
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Die Erforschung von faserverstärkten Kunststoffen (FVK) mit thermoplastischer Matrix ist aufgrund der Schweißeignung als Verbindungstechnologie, der thermischen Umformbarkeit, der Recyclebarkeit sowie der verkürzten Prozesszeiten im Vergleich zu den vorwiegend eingesetzten faserverstärkten Duroplasten erstrebenswert. Die Wechselwirkung zwischen den physikalischen, mechanischen und geometrischen Parametern erhöht den Komplexitätsgrad des Herstellungsprozesses. Ziel ist daher die Entwicklung einer Imprägniertechnik, die eine Fasertränkung mittels eines Thermoplastschmelzbades ermöglicht. |
Pongratz, C.; Ehrlich, I. High-End-Strukturen für den Leichtbau – mit faserverstärktem 3D-Druck Leichtbau Forschungsbericht Ostbayerische Hochschule Regensburg VMK Verlag für Marketing & Kommunikation GmbH & Co. KG, Forschungsbericht 2018, 2018, ISBN: 978-3-9818209-4-2. @techreport{Pongratz2018,
title = {High-End-Strukturen für den Leichtbau – mit faserverstärktem 3D-Druck},
author = {C. Pongratz and I. Ehrlich},
editor = {Ostbayerische Technische Hochschule},
isbn = {978-3-9818209-4-2},
year = {2018},
date = {2018-06-01},
address = {VMK Verlag für Marketing & Kommunikation GmbH & Co. KG},
institution = {Ostbayerische Hochschule Regensburg},
abstract = {Additive Fertigung, oder auch 3D-Druck, erlaubt die Herstellung von komplexen Bauteilen mitnahezu beliebiger Geometrie. Werden dabei Kunststoffe genutzt, sind die mechanischen Eigen-schaften des erzeugten Bauteils jedoch begrenzt und oft nur für Prototyping-Anwendungengeeignet. Ziel des Projekts FIBER-PRINT ist die Entwicklung bzw. Weiterentwicklung eines additi-ven Fertigungsprozesses mit Faserverstärkung. Durch die Einbringung und kraftflussgerechteAnordnung von Endlosfasern kann die mechanische Belastbarkeit signifikant gesteigert werdenund dadurch können auch lasttragende Strukturen additiv gefertigt werden.},
type = {Forschungsbericht 2018},
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Additive Fertigung, oder auch 3D-Druck, erlaubt die Herstellung von komplexen Bauteilen mitnahezu beliebiger Geometrie. Werden dabei Kunststoffe genutzt, sind die mechanischen Eigen-schaften des erzeugten Bauteils jedoch begrenzt und oft nur für Prototyping-Anwendungengeeignet. Ziel des Projekts FIBER-PRINT ist die Entwicklung bzw. Weiterentwicklung eines additi-ven Fertigungsprozesses mit Faserverstärkung. Durch die Einbringung und kraftflussgerechteAnordnung von Endlosfasern kann die mechanische Belastbarkeit signifikant gesteigert werdenund dadurch können auch lasttragende Strukturen additiv gefertigt werden. |
Paredes, M.; Keim, V.; Nonn, A.; Wierzbicki, T. Effect of plasticity parameter on the crack propagation in steel pipelines Werkstoffsimulation Konferenzbeitrag In: Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium, 2018. @inproceedings{Paredes2018,
title = {Effect of plasticity parameter on the crack propagation in steel pipelines},
author = {M. Paredes and V. Keim and A. Nonn and T. Wierzbicki},
year = {2018},
date = {2018-04-01},
booktitle = {Proceedings of the conference on Technology for future and ageing piplines},
address = {Ghent, Belgium},
abstract = {A reliable characterization of material fracture resistance and derivation of ductile-fracture-arrest criteria for modern linepipe steels belong to major challenges within the current pipeline research. Although many efforts have been undertaken to meet these challenges, there are still open issues related to the understanding and quantification of the material properties on unstable ductile fracture propagation. There is a general consensus that the fracture velocity is controlled by the speed of travelling plastic hinge (propagating neck or plastic instability/collapse) due to axial through-wall thinning in front of the fracture. To account for the effect of material ductility on fracture propagation resistance, a plasticity parameter, the yield-to-tensile ratio, has been recently implemented in the Battelle fracture velocity model. The improved results from this modification indicate that an accurate prediction of crack propagation and arrest require a comprehensive characterization and consideration of material plasticity and fracture.
Therefore, this paper aims to study and quantify the influence of plasticity (characteristic stress/strain values, strain hardening, plastic anisotropy) parameters on dynamic crack propagation in the X100 steel pipelines. Plastic anisotropy is described by Hill’48 quadratic yield function along with a non-associated flow rule which allows to incorporate the effect of a different directionality of the r-values from the yield stress ratios without losing advantages of quadratic functions. The strain hardening is captured by a linear combination of Swift power law and Voce exponential law. The ductile fracture propagation is simulated by Modified-Mohr-Coulomb (MMC) fracture model which includes a joint effect of stress triaxiality, Lode angle and is applicable to problems with changing loading history. The model parameters are verified based on results from single-edge-notched (SENT) and drop-weight-tear-test (DWTT) tests. The influence of plasticity parameters on the fracture propagation is examined and quantified using 3D pressurized pipe models. The results will provide valuable insights on key plasticity parameters affecting fracture resistance and thus serve as a basis for more accurate assessment of deformation/fracture process of the modern pipeline steels.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
A reliable characterization of material fracture resistance and derivation of ductile-fracture-arrest criteria for modern linepipe steels belong to major challenges within the current pipeline research. Although many efforts have been undertaken to meet these challenges, there are still open issues related to the understanding and quantification of the material properties on unstable ductile fracture propagation. There is a general consensus that the fracture velocity is controlled by the speed of travelling plastic hinge (propagating neck or plastic instability/collapse) due to axial through-wall thinning in front of the fracture. To account for the effect of material ductility on fracture propagation resistance, a plasticity parameter, the yield-to-tensile ratio, has been recently implemented in the Battelle fracture velocity model. The improved results from this modification indicate that an accurate prediction of crack propagation and arrest require a comprehensive characterization and consideration of material plasticity and fracture.
Therefore, this paper aims to study and quantify the influence of plasticity (characteristic stress/strain values, strain hardening, plastic anisotropy) parameters on dynamic crack propagation in the X100 steel pipelines. Plastic anisotropy is described by Hill’48 quadratic yield function along with a non-associated flow rule which allows to incorporate the effect of a different directionality of the r-values from the yield stress ratios without losing advantages of quadratic functions. The strain hardening is captured by a linear combination of Swift power law and Voce exponential law. The ductile fracture propagation is simulated by Modified-Mohr-Coulomb (MMC) fracture model which includes a joint effect of stress triaxiality, Lode angle and is applicable to problems with changing loading history. The model parameters are verified based on results from single-edge-notched (SENT) and drop-weight-tear-test (DWTT) tests. The influence of plasticity parameters on the fracture propagation is examined and quantified using 3D pressurized pipe models. The results will provide valuable insights on key plasticity parameters affecting fracture resistance and thus serve as a basis for more accurate assessment of deformation/fracture process of the modern pipeline steels. |
Siegl, M.; Rieger, D.; Kovárík, T.; Ehrlich, I. Long-Term Behavior of Thermoplastics under UV Light tested by a self-build Device Leichtbau Konferenzbeitrag In: OTH Regensburg, OTH Amberg-Weiden (Hrsg.): Proceedings of the 3rd OTH-Clusterkonferenz, S. 118–122, Regensburg, Germany, 2018, ISBN: 978-3-9818209-4-2. @inproceedings{Siegl2018,
title = {Long-Term Behavior of Thermoplastics under UV Light tested by a self-build Device},
author = {M. Siegl and D. Rieger and T. Kovárík and I. Ehrlich},
editor = {OTH Regensburg, OTH Amberg-Weiden},
url = {https://www.oth-regensburg.de/fileadmin/media/forschung/Dateien_2018/Clusterkonferenz-Tagungsband-2018.pdf},
isbn = {978-3-9818209-4-2},
year = {2018},
date = {2018-03-01},
booktitle = {Proceedings of the 3rd OTH-Clusterkonferenz},
pages = {118--122},
address = {Regensburg, Germany},
series = {Schriftenreihe der OTH Regensburg und der OTH Amberg-Weiden},
abstract = {This article presents first results of artificial aging experiments by ultraviolet (UV) irradiation on thermoplastic materials conducted as an intent of the research project Thermoplastic Composite Structures (TheCoS) in collaboration of the Ostbayerische Technische Hochschule (OTH) Regensburg and the University of West Bohemia (UWB) in Pilsen as part of a cross-border cooperation. In technical applications, thermoplastic materials are often affected by aging and a related deterioration of the mechanical properties. Therefore, it is necessary to identify the aging behavior of thermoplastic materials. For this, experiments were performed for three thermoplastic materials, namely polypropylene (PP), ultra high molecular weight polyethylene (UHMWPE) and high impact strength polystyrene (HIPS). For these experiments, a UV chamber was constructed according to the international standard EN ISO 4892-3 for simulation of exposure behind window glass. The results are evaluated by testing the flexural strength and the dynamic mechanical response after a selected period of time under UV light and then compared to untreated test specimens.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
This article presents first results of artificial aging experiments by ultraviolet (UV) irradiation on thermoplastic materials conducted as an intent of the research project Thermoplastic Composite Structures (TheCoS) in collaboration of the Ostbayerische Technische Hochschule (OTH) Regensburg and the University of West Bohemia (UWB) in Pilsen as part of a cross-border cooperation. In technical applications, thermoplastic materials are often affected by aging and a related deterioration of the mechanical properties. Therefore, it is necessary to identify the aging behavior of thermoplastic materials. For this, experiments were performed for three thermoplastic materials, namely polypropylene (PP), ultra high molecular weight polyethylene (UHMWPE) and high impact strength polystyrene (HIPS). For these experiments, a UV chamber was constructed according to the international standard EN ISO 4892-3 for simulation of exposure behind window glass. The results are evaluated by testing the flexural strength and the dynamic mechanical response after a selected period of time under UV light and then compared to untreated test specimens. |
Keim, V.; Nonn, A.; Lenz, D.; Brinnel, V.; Münstermann, S. Simulation of the ductile fracture behaviour of high toughness pipeline steels using combined damage models Werkstoffsimulation Konferenzbeitrag In: Proceedings of the conference on Technology for future and ageing piplines, Ghent, Belgium, 2018. @inproceedings{Keim2018,
title = {Simulation of the ductile fracture behaviour of high toughness pipeline steels using combined damage models},
author = {V. Keim and A. Nonn and D. Lenz and V. Brinnel and S. Münstermann},
year = {2018},
date = {2018-01-01},
booktitle = {Proceedings of the conference on Technology for future and ageing piplines},
address = {Ghent, Belgium},
abstract = {The complex mechanical and corrosive loads of modern pipeline systems transporting oil, natural gas and CO2 impose steadily increasing requirements on material properties. The majority of current design standards still limit the application of modern high toughness linepipe steels due to the specification of material requirements in terms of energy levels from Charpy impact or Drop-Weight-Tear tests (DWTT). Furthermore, abnormal fracture appearance (AFA), abnormal fracture behavior (AFB) and separations question the correlation between laboratory tests and components’ fracture behavior. In consequence, research activities have been conducted recently aiming at developing modified or novel experimental methods for the characterization of ductile-to-brittle fracture behavior. To quantify the effects of various parameters on fracture behavior and derive suitable correlations, it is necessary to accompany these activities by numerical simulations with appropriate damage models for ductile and cleavage fracture. In this paper, a coupled, phenomenological damage model for ductile fracture is applied to study the structural behavior of pipelines due to its pronounced computational efficiency, which is combined with a cleavage fracture model in later phases of the project. The parameters for the model are determined by small scale tests with various multi-axial loading conditions. The validated damage model was successfully used to simulate the fracture behavior DWTT specimens. Finally, these models allow for the investigation of material, geometry and loading effects on fracture and crack arrest behavior of pipes in transition region.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The complex mechanical and corrosive loads of modern pipeline systems transporting oil, natural gas and CO2 impose steadily increasing requirements on material properties. The majority of current design standards still limit the application of modern high toughness linepipe steels due to the specification of material requirements in terms of energy levels from Charpy impact or Drop-Weight-Tear tests (DWTT). Furthermore, abnormal fracture appearance (AFA), abnormal fracture behavior (AFB) and separations question the correlation between laboratory tests and components’ fracture behavior. In consequence, research activities have been conducted recently aiming at developing modified or novel experimental methods for the characterization of ductile-to-brittle fracture behavior. To quantify the effects of various parameters on fracture behavior and derive suitable correlations, it is necessary to accompany these activities by numerical simulations with appropriate damage models for ductile and cleavage fracture. In this paper, a coupled, phenomenological damage model for ductile fracture is applied to study the structural behavior of pipelines due to its pronounced computational efficiency, which is combined with a cleavage fracture model in later phases of the project. The parameters for the model are determined by small scale tests with various multi-axial loading conditions. The validated damage model was successfully used to simulate the fracture behavior DWTT specimens. Finally, these models allow for the investigation of material, geometry and loading effects on fracture and crack arrest behavior of pipes in transition region. |
Bohmann, T.; Schlamp, M.; Ehrlich, I. Acoustic emission of material damages in glass fibre-reinforced plastics Leichtbau Artikel In: Composites Part B: Engineering, 155 , S. 444 - 451, 2018, ISSN: 1359-8368. @article{Bohmann2018,
title = {Acoustic emission of material damages in glass fibre-reinforced plastics},
author = {T. Bohmann and M. Schlamp and I. Ehrlich},
doi = {10.1016/j.compositesb.2018.09.018},
issn = {1359-8368},
year = {2018},
date = {2018-01-01},
journal = {Composites Part B: Engineering},
volume = {155},
pages = {444 - 451},
abstract = {The aim of this study is to compare two different standardized testing procedures, tensile testing and Mode-I double cantilever beam (DCB) testing, to evaluate a possible correlation between the dominant failure in glass fibre-reinforced plastics and their according acoustic emissions (AE). AE is processed by using a burst collection of all recorded transient signals and is further analysed with the k-means clustering algorithm. To generate damage related AE, a series of experiments for tensile testing and Mode-I DCB testing is performed on 16-layer glass fibre/epoxy specimens with a cross-ply lay-up for tensile and an unidirectional lay-up for Mode-I DCB testing. Three sensors at tensile testing and one sensor at Mode-I DCB testing gather AE data. The results of clustered burst signals show a good accordance between both testing procedures, with a similar weighted peak frequency (WPF) range in each classified cluster. In total, three different clusters are determined. An assignment of these three clusters to the three dominant damage mechanisms, visually observed by microscopy, is suggested.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The aim of this study is to compare two different standardized testing procedures, tensile testing and Mode-I double cantilever beam (DCB) testing, to evaluate a possible correlation between the dominant failure in glass fibre-reinforced plastics and their according acoustic emissions (AE). AE is processed by using a burst collection of all recorded transient signals and is further analysed with the k-means clustering algorithm. To generate damage related AE, a series of experiments for tensile testing and Mode-I DCB testing is performed on 16-layer glass fibre/epoxy specimens with a cross-ply lay-up for tensile and an unidirectional lay-up for Mode-I DCB testing. Three sensors at tensile testing and one sensor at Mode-I DCB testing gather AE data. The results of clustered burst signals show a good accordance between both testing procedures, with a similar weighted peak frequency (WPF) range in each classified cluster. In total, three different clusters are determined. An assignment of these three clusters to the three dominant damage mechanisms, visually observed by microscopy, is suggested. |
2017
|
Romano, M.; Ehrlich, I.; Gebbeken, N. Structural mechanic material damping in fabric reinforced composites: A review. Leichtbau Artikel In: Archives of Materials Science and Engineering (ArchivesMSE), 88 (1), S. 12–41, 2017, ISSN: 1897-2764. @article{Romano2017bb,
title = {Structural mechanic material damping in fabric reinforced composites: A review. },
author = {M. Romano and I. Ehrlich and N. Gebbeken},
url = {https://athene-forschung.unibw.de/?id=131530},
doi = {10.5604/01.3001.0010.7747},
issn = {1897-2764},
year = {2017},
date = {2017-11-01},
journal = {Archives of Materials Science and Engineering (ArchivesMSE)},
volume = {88},
number = {1},
pages = {12--41},
abstract = {Purpose: A review regarding the acting mechanisms of structural dynamic material damping in fabric reinforced composites is presented. Design/methodology/approach: Mechanical acting principles identified by different investigations are considered. Aspects of the determination and calculation of structural mechanical material properties of fabric reinforced composites are described. Approaches intending the description and classification of ondulations in fabrics reinforced single layers are demonstrated. Findings: The mesomechanic geometry of fabrics is not considered sufficiently by relatively simple homogenization approaches. Yet, it significantly affects its structural dynamic material properties, especially the dynamic ones. Research limitations/implications: In each case the different damping mechanisms act coupled and occur at the same time. Therefore a separation procedure is required in any case. Practical implications: Against the background of the comparison and remarks of the presented papers a reasonable further procedure is recommended. Thereby, FE-calculations with a parametrical variation of the mesomechanic geometry in order to identify kinematic correlations due to geometric constraints are suggested. Originality/value: The idea of the representation of the geometric conditions in terms of a degree of ondulation is described. Such a non-dimensional specific value representing the intensity of the ondulation would enable the comparability of the results of different kinds of investigations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Purpose: A review regarding the acting mechanisms of structural dynamic material damping in fabric reinforced composites is presented. Design/methodology/approach: Mechanical acting principles identified by different investigations are considered. Aspects of the determination and calculation of structural mechanical material properties of fabric reinforced composites are described. Approaches intending the description and classification of ondulations in fabrics reinforced single layers are demonstrated. Findings: The mesomechanic geometry of fabrics is not considered sufficiently by relatively simple homogenization approaches. Yet, it significantly affects its structural dynamic material properties, especially the dynamic ones. Research limitations/implications: In each case the different damping mechanisms act coupled and occur at the same time. Therefore a separation procedure is required in any case. Practical implications: Against the background of the comparison and remarks of the presented papers a reasonable further procedure is recommended. Thereby, FE-calculations with a parametrical variation of the mesomechanic geometry in order to identify kinematic correlations due to geometric constraints are suggested. Originality/value: The idea of the representation of the geometric conditions in terms of a degree of ondulation is described. Such a non-dimensional specific value representing the intensity of the ondulation would enable the comparability of the results of different kinds of investigations. |
Kastenmeier, A.; Schmid, V.; Ehrlich, I. Specimen Preparation and Material Characterization of Filament Wound GFRP Composite Tubes. Leichtbau Artikel In: Athens Journal of Technology & Engineering, 4 (3), S. 191-205, 2017, ISSN: 2241-8237. @article{Kastenmeier2017,
title = {Specimen Preparation and Material Characterization of Filament Wound GFRP Composite Tubes.},
author = {A. Kastenmeier and V. Schmid and I. Ehrlich},
editor = {P. Petratos and N. Mourtos and T. Trafalis and T. Attard and V. Sisiopiku},
url = {https://www.athensjournals.gr/technology/2017-4-3-2-Kastenmeier.pdf},
doi = {10.30958/AJTE.3-4-1},
issn = {2241-8237},
year = {2017},
date = {2017-09-04},
journal = {Athens Journal of Technology & Engineering},
volume = {4},
number = {3},
pages = {191-205},
abstract = {Filament wound composite structures are widely used in the field of pressure vessels, tubes, pipelines or rocket cases. The mechanical behavior of these structures is typically different from those of flat laminated structures due to an alternating lay-up sequence, winding tension and manufacturing induced imperfections. However, design and analysis issues require the same engineering data as used for laminated structures in general. It has therefore become necessary to establish an accompanying quality assurance procedure following the production process to identify the material properties of the manufactured tubes especially for the single layer. Consequently, there are three different approaches of determining the elastic moduli and tensile strengths of a filament wound laminate. Either specimens are resected from a curved tube, from a tube with plane areas or standardized flat specimens are manufactured under deviating production conditions. All approaches entail disadvantages, whether in terms of manufacturing or testing parameters including geometry, lay-up sequence, porosity, fiber tension and load direction. This study presents the discrepancies in the determination of mechanical properties of a filament wound glass-fiber-reinforced polymer tube on curved or cylindrical specimens and flat specimens produced to meet the specifications of international standards. In order to obtain material properties not only in longitudinal but also in transverse direction of the tubes, the so-called split-disk tensile test modeled after ASTM Standard D 2290, is used with tube segments.The procedures of specimen production and preparation are described in detail. Material properties such as the fiber volume and void content of the composite specimens are conducted in order to consider quality and production differences. Finally tensile tests are performed and the results are compared and discussed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Filament wound composite structures are widely used in the field of pressure vessels, tubes, pipelines or rocket cases. The mechanical behavior of these structures is typically different from those of flat laminated structures due to an alternating lay-up sequence, winding tension and manufacturing induced imperfections. However, design and analysis issues require the same engineering data as used for laminated structures in general. It has therefore become necessary to establish an accompanying quality assurance procedure following the production process to identify the material properties of the manufactured tubes especially for the single layer. Consequently, there are three different approaches of determining the elastic moduli and tensile strengths of a filament wound laminate. Either specimens are resected from a curved tube, from a tube with plane areas or standardized flat specimens are manufactured under deviating production conditions. All approaches entail disadvantages, whether in terms of manufacturing or testing parameters including geometry, lay-up sequence, porosity, fiber tension and load direction. This study presents the discrepancies in the determination of mechanical properties of a filament wound glass-fiber-reinforced polymer tube on curved or cylindrical specimens and flat specimens produced to meet the specifications of international standards. In order to obtain material properties not only in longitudinal but also in transverse direction of the tubes, the so-called split-disk tensile test modeled after ASTM Standard D 2290, is used with tube segments.The procedures of specimen production and preparation are described in detail. Material properties such as the fiber volume and void content of the composite specimens are conducted in order to consider quality and production differences. Finally tensile tests are performed and the results are compared and discussed. |
Bohmann, T.; Schlamp, M.; Ehrlich, I. Analysis of the Acoustic Emission Failure Frequencies of Glass Fiber Reinforced Composite Components. Leichtbau Konferenzbeitrag In: Kippel, C.; Mottok, J.; Reichenberger, M. (Hrsg.): Applied Research Conference 2017 – ARC 2017, S. 369-373, Ostbayerische Technische Hochschule Regensburg Book-on-demand Verlag, Norderstedt, 2017. @inproceedings{Bohmann2017,
title = {Analysis of the Acoustic Emission Failure Frequencies of Glass Fiber Reinforced Composite Components. },
author = {T. Bohmann and M. Schlamp and I. Ehrlich},
editor = {C. Kippel and J. Mottok and M. Reichenberger},
year = {2017},
date = {2017-07-07},
booktitle = {Applied Research Conference 2017 – ARC 2017},
pages = {369-373},
publisher = {Book-on-demand Verlag},
address = {Norderstedt},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {Acoustic Emission (AE) of composite materials during a damage process can be very informative regarding the resulting damage in the structure of a composite. The thereby generated frequencies of the AE-signal depend on the type of damage that occurred. Whenever a solid body is damaged, a soundwave is generated by the released energy of breaking the solid structure in certain high stress areas. Especially with fiber-reinforced plastics, the direction of the load can cause different types of damage in a composite. In context of the investigation, a method is to be created, which detects the kind of damage that occurs due to load cases by the classification of failure frequencies of damage mechanisms in fibre-reinforced plastics. The frequency specific AE-signal for fiber breaking. matrix cracking and delamination is described in literature, thereby an AE-sensor measures the main frequencies of propagating soundwaves on the surface of a solid body. Three different types of specimen have been tested in a tensile test, to generate an AE-signal for each of the possible damage mechanisms. In addition to that, the specimens for simulating the matrix cracking have been tested in three different thickness measurements. Therefore, the influence of different energy levels of the propagating AE-signal is investigated. To measure the acoustic emission, a preliminary equipment showed a oversteering AE-signal, due to the sensitivity of the AE-sensor. To avoid the oversteering while testing, the sensor is mounted on the clamping claw of a tensile testing machine, whose frequency distribution has been investigated by exciting the component. The energy level difference of the AE-signal has only an influence on the amplitude of the measured frequencies. At certain frequencies a rise of the amplitudes can be identified, which can have an interrelation with the eigenfrequencies of the clamping claws, where the AE-sensor is mounted. Consequently, to measure acoustic emission due to failure in solid bodies, the influence of eigenfrequencies of the clamping claws has to be taken into account. It has been shown that frequency distributions of the different damage mechanisms with the used AE-sensor system deviate from the results given by literature. The possible reasons and effects for that are discussed. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Acoustic Emission (AE) of composite materials during a damage process can be very informative regarding the resulting damage in the structure of a composite. The thereby generated frequencies of the AE-signal depend on the type of damage that occurred. Whenever a solid body is damaged, a soundwave is generated by the released energy of breaking the solid structure in certain high stress areas. Especially with fiber-reinforced plastics, the direction of the load can cause different types of damage in a composite. In context of the investigation, a method is to be created, which detects the kind of damage that occurs due to load cases by the classification of failure frequencies of damage mechanisms in fibre-reinforced plastics. The frequency specific AE-signal for fiber breaking. matrix cracking and delamination is described in literature, thereby an AE-sensor measures the main frequencies of propagating soundwaves on the surface of a solid body. Three different types of specimen have been tested in a tensile test, to generate an AE-signal for each of the possible damage mechanisms. In addition to that, the specimens for simulating the matrix cracking have been tested in three different thickness measurements. Therefore, the influence of different energy levels of the propagating AE-signal is investigated. To measure the acoustic emission, a preliminary equipment showed a oversteering AE-signal, due to the sensitivity of the AE-sensor. To avoid the oversteering while testing, the sensor is mounted on the clamping claw of a tensile testing machine, whose frequency distribution has been investigated by exciting the component. The energy level difference of the AE-signal has only an influence on the amplitude of the measured frequencies. At certain frequencies a rise of the amplitudes can be identified, which can have an interrelation with the eigenfrequencies of the clamping claws, where the AE-sensor is mounted. Consequently, to measure acoustic emission due to failure in solid bodies, the influence of eigenfrequencies of the clamping claws has to be taken into account. It has been shown that frequency distributions of the different damage mechanisms with the used AE-sensor system deviate from the results given by literature. The possible reasons and effects for that are discussed. |
Nonn, A.; Paredes, M.; Nordhagen, H. O.; Munkejord, S. T.; Wierzbicki, T. Challenges in fluid-structure modeling of crack propagation and arrest in modern steel pipelines Werkstoffsimulation Konferenzbeitrag In: 14th International Congress on Fracture (ICF14), Rhodes, Greece, 2017. @inproceedings{Nonn2017,
title = {Challenges in fluid-structure modeling of crack propagation and arrest in modern steel pipelines},
author = {A. Nonn and M. Paredes and H. O. Nordhagen and S. T. Munkejord and T. Wierzbicki},
year = {2017},
date = {2017-06-18},
booktitle = {14th International Congress on Fracture (ICF14)},
address = {Rhodes, Greece},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|
Pongratz, C.; Ehrlich, I. DampSIM: Lebensdauerüberwachung von faserverstärkten Kunststoffen auf Basis der strukurdynamischen Werkstoffdämpfung. Leichtbau Forschungsbericht Ostbayerische Hochschule Regensburg VMK Verlag für Marketing & Kommunikation GmbH & Co. KG, Forschungsbericht 2017, 2017, ISBN: 978-3-9818209-3-5. @techreport{Pongratz2017,
title = {DampSIM: Lebensdauerüberwachung von faserverstärkten Kunststoffen auf Basis der strukurdynamischen Werkstoffdämpfung.},
author = {C. Pongratz and I. Ehrlich},
editor = {Ostbayerische Technische Hochschule},
isbn = {978-3-9818209-3-5},
year = {2017},
date = {2017-06-01},
address = {VMK Verlag für Marketing & Kommunikation GmbH & Co. KG},
institution = {Ostbayerische Hochschule Regensburg},
abstract = {Im Fokus der Untersuchungen steht die Strukturintegrität von Bauteilen aus faserverstärktenKunststoffen. Im realen Anwendungsfall können diese Strukturen Schlag- oder Impactbelastungenunterliegen, die häufig kaum sichtbare oder unsichtbare Schäden im Inneren des Bauteils ver -ursachen. Diese Schäden stellen deshalb ein besonderes Sicherheitsrisiko dar. Ziel des Forschungs-projekts ist die effiziente Detektion solcher Schäden. Als Indikator des Materialzustands wird einvibrationsbasierter Ansatz angewendet, der zusätzlich zu den Eigenfrequenzen die struktur -dynamische Werkstoffdämpfung einbindet.},
type = {Forschungsbericht 2017},
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Im Fokus der Untersuchungen steht die Strukturintegrität von Bauteilen aus faserverstärktenKunststoffen. Im realen Anwendungsfall können diese Strukturen Schlag- oder Impactbelastungenunterliegen, die häufig kaum sichtbare oder unsichtbare Schäden im Inneren des Bauteils ver -ursachen. Diese Schäden stellen deshalb ein besonderes Sicherheitsrisiko dar. Ziel des Forschungs-projekts ist die effiziente Detektion solcher Schäden. Als Indikator des Materialzustands wird einvibrationsbasierter Ansatz angewendet, der zusätzlich zu den Eigenfrequenzen die struktur -dynamische Werkstoffdämpfung einbindet. |
Romano, M. Charakterisierung von gewebeverstärkten Einzellagen aus kohlenstofffaserverstärktem Kunststoff (CFK) mit Hilfe einer mesomechanischen Kinematik sowie strukturdynamischen Versuchen Leichtbau Promotionsarbeit Universität der Bundeswehr München, 2017, ISBN: 978-3-8440-5177-3. @phdthesis{Romano2017b,
title = {Charakterisierung von gewebeverstärkten Einzellagen aus kohlenstofffaserverstärktem Kunststoff (CFK) mit Hilfe einer mesomechanischen Kinematik sowie strukturdynamischen Versuchen},
author = {M. Romano},
editor = {OTH Regensburg},
url = {https://www.shaker.de/de/content/catalogue/index.asp?lang=de&ID=8&ISBN=978-3-8440-5177-3&search=yes},
doi = {10.2370/9783844051773},
isbn = {978-3-8440-5177-3},
year = {2017},
date = {2017-04-01},
school = {Universität der Bundeswehr München},
abstract = {Die vorliegende Arbeit behandelt die analytische und numerische Identifikation einer mesomechanischen Kinematik in gewebeverstärkten Einzellagen sowie deren Validierung über die Strukturdynamik von flachen stabförmigen Probekörpern aus kohlenstofffaserverstärktem Kunststoff (CFK). Unter der Voraussetzung, dass das wiederholte Wirken der Kinematik Energie dissipiert, trägt sie bei zyklischer viskoelastischer Deformation zusätzlich zur reinen viskoelastischen Werkstoffdämpfung in gewebeverstärkten Einzellagen bei.
Die analytischen und numerischen Untersuchungen beschränken sich auf die Betrachtung des ebenen, zweidimensionalen Zusammenhangs einer vollständigen Ondulation bzw. einer repräsentativen Sequenz in Dickenrichtung. Zur Parameteridentifikation werden die geometrischen Abmessungen in definierten Schritten variiert. Dafür wird der Grad der Ondulation in gewebeverstärkten Einzellagen Õ=A/L als dimensionslose Kennzahl eingeführt. Zur Validierung der dämpfungserhöhenden Wirkung der in den analytischen und numerischen Untersuchung identifizierten mesomechanischen Kinematik in gewebeverstärkten Einzellagen werden in experimentellen strukturdynamischen Untersuchungen frei abklingende Transversalschwingungen von einseitig fest eingespannten Probekörpern untersucht. Im Detail werden flache stabförmige Probekörper aus kohlenstofffaserverstärktem Epoxidharz mit Lagenaufbauten aus 0°-unidirektionalen und gewebeverstärkten Einzellagen untersucht. Die Ergebnisse der experimentellen strukturdynamischen Untersuchungen dienen schließlich der Validierung des analytischen Modells und der numerischen Berechnungen. Die dämpfungserhöhende Wirkung der identifizierten mesomechanischen Kinematik wird schließlich in Abhängigkeit des eingeführten Grades der Ondulation Õ quantifiziert. },
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
Die vorliegende Arbeit behandelt die analytische und numerische Identifikation einer mesomechanischen Kinematik in gewebeverstärkten Einzellagen sowie deren Validierung über die Strukturdynamik von flachen stabförmigen Probekörpern aus kohlenstofffaserverstärktem Kunststoff (CFK). Unter der Voraussetzung, dass das wiederholte Wirken der Kinematik Energie dissipiert, trägt sie bei zyklischer viskoelastischer Deformation zusätzlich zur reinen viskoelastischen Werkstoffdämpfung in gewebeverstärkten Einzellagen bei.
Die analytischen und numerischen Untersuchungen beschränken sich auf die Betrachtung des ebenen, zweidimensionalen Zusammenhangs einer vollständigen Ondulation bzw. einer repräsentativen Sequenz in Dickenrichtung. Zur Parameteridentifikation werden die geometrischen Abmessungen in definierten Schritten variiert. Dafür wird der Grad der Ondulation in gewebeverstärkten Einzellagen Õ=A/L als dimensionslose Kennzahl eingeführt. Zur Validierung der dämpfungserhöhenden Wirkung der in den analytischen und numerischen Untersuchung identifizierten mesomechanischen Kinematik in gewebeverstärkten Einzellagen werden in experimentellen strukturdynamischen Untersuchungen frei abklingende Transversalschwingungen von einseitig fest eingespannten Probekörpern untersucht. Im Detail werden flache stabförmige Probekörper aus kohlenstofffaserverstärktem Epoxidharz mit Lagenaufbauten aus 0°-unidirektionalen und gewebeverstärkten Einzellagen untersucht. Die Ergebnisse der experimentellen strukturdynamischen Untersuchungen dienen schließlich der Validierung des analytischen Modells und der numerischen Berechnungen. Die dämpfungserhöhende Wirkung der identifizierten mesomechanischen Kinematik wird schließlich in Abhängigkeit des eingeführten Grades der Ondulation Õ quantifiziert. |
Siegl, M.; Ehrlich, I. Transformation of the Mechanical Properties of Fiber-Reinforced Plastic Tubes from the Cartesian Coordinate System into the Cylindrical Coordinate System for the Application of Bending Models. Leichtbau Artikel In: Athens Journal of Τechnology & Engineering, 4 (1), S. 47-62, 2017, ISSN: 2241-8237. @article{Siegl2017,
title = {Transformation of the Mechanical Properties of Fiber-Reinforced Plastic Tubes from the Cartesian Coordinate System into the Cylindrical Coordinate System for the Application of Bending Models.},
author = {M. Siegl and I. Ehrlich},
editor = {P. Petratos and N. Mourtos and T. Trafalis and T. Attard and V. Sisiopiku},
url = {https://www.athensjournals.gr/technology/2017-4-1-4-Siegl.pdf},
doi = {10.30958/AJTE.3-4-1},
issn = {2241-8237},
year = {2017},
date = {2017-03-01},
journal = {Athens Journal of Τechnology & Engineering},
volume = {4},
number = {1},
pages = {47-62},
abstract = {Fiber-reinforced plastic (FRP) tubes are used in many different industries, such as electrical engineering and pipeline construction. The tubes are frequently subjected to bending loads, depending on the application. In order that the dimensioning of the tubes can be ensured, analytical bending models are used to calculate the resulting stresses, strains and displacements in the individual layers of the laminate. This enables the making of a statement about the failure of the fiber-reinforced tube by choosing an appropriate failure criterion. For the use of these bending models, it is necessary to understand the respective underlying theory. The theory provides the basis for the mathematical description of the mechanical properties for a single-layered tube and using the relationships between the stresses and strains that occur in the Cylindrical coordinate system for this calculation step. For this reason, a redefinition of the compliance matrix from the transformation about the winding angle to the Cylindrical coordinate system and a modification of the stress and strain vectors is necessary, because the defined Cartesian coordinate system of the model cannot be used for wounded FRP tubes. The transformation causes an exchange of entries in the compliance matrix, which remain in the correct relationship between the particular stress and strains. This step is not specified and may lead to incorrect results due to the incorrect entry of compliances. The present publication refers to sketch on this issue and represent a simplification of the changeover to the level required by the bending models notation of vectors in the form of a permutation. In addition, a new name for the pre-acquisition of the redefined compliances is given to prevent confusion when entering the material law of a bending model. Finally, the permuted and redefined compliances are proved in an example to determine their accuracy.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fiber-reinforced plastic (FRP) tubes are used in many different industries, such as electrical engineering and pipeline construction. The tubes are frequently subjected to bending loads, depending on the application. In order that the dimensioning of the tubes can be ensured, analytical bending models are used to calculate the resulting stresses, strains and displacements in the individual layers of the laminate. This enables the making of a statement about the failure of the fiber-reinforced tube by choosing an appropriate failure criterion. For the use of these bending models, it is necessary to understand the respective underlying theory. The theory provides the basis for the mathematical description of the mechanical properties for a single-layered tube and using the relationships between the stresses and strains that occur in the Cylindrical coordinate system for this calculation step. For this reason, a redefinition of the compliance matrix from the transformation about the winding angle to the Cylindrical coordinate system and a modification of the stress and strain vectors is necessary, because the defined Cartesian coordinate system of the model cannot be used for wounded FRP tubes. The transformation causes an exchange of entries in the compliance matrix, which remain in the correct relationship between the particular stress and strains. This step is not specified and may lead to incorrect results due to the incorrect entry of compliances. The present publication refers to sketch on this issue and represent a simplification of the changeover to the level required by the bending models notation of vectors in the form of a permutation. In addition, a new name for the pre-acquisition of the redefined compliances is given to prevent confusion when entering the material law of a bending model. Finally, the permuted and redefined compliances are proved in an example to determine their accuracy. |
Romano, M.; Ehrlich, I.; Gebbeken, N. Parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites: analytical and numerical investigations. Leichtbau Artikel In: Frattura ed Integrità Strutturale (Fracture and Structural Integrity), 11 (39), S. 226-247, 2017, ISSN: 1971-8993. @article{Romano2017,
title = {Parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites: analytical and numerical investigations.},
author = {M. Romano and I. Ehrlich and N. Gebbeken},
url = {http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.39.22
http://www.fracturae.com/index.php/fis/article/view/IGF-ESIS.39.22/1860
http://www.fracturae.com/index.php/fis/article/download/IGF-ESIS.39.22/1860
http://www.gruppofrattura.it/pdf/fig/numero39/#234},
doi = {10.3221/IGF-ESIS.39.22 },
issn = {1971-8993},
year = {2017},
date = {2017-01-01},
journal = {Frattura ed Integrità Strutturale (Fracture and Structural Integrity)},
volume = {11},
number = {39},
pages = {226-247},
abstract = {A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by analytical and numerical investigations. Due to the definition of plain representative sequences of balanced plain-weave fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. The mesomechanic kinematic can be observed in both the analytic model and the FE-analyses. The analytic model yields hyperbolic correlations due to the strongly simplifying presumptions that neglect elasticity. In contrast the FE-analyses yield linear correlations in much smaller amounts due to the consideration of elastic parts, yet distinctly.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by analytical and numerical investigations. Due to the definition of plain representative sequences of balanced plain-weave fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. The mesomechanic kinematic can be observed in both the analytic model and the FE-analyses. The analytic model yields hyperbolic correlations due to the strongly simplifying presumptions that neglect elasticity. In contrast the FE-analyses yield linear correlations in much smaller amounts due to the consideration of elastic parts, yet distinctly. |
2016
|
Wätzig, A.; Schmid, V.; Ehrlich, I. Damage Modelling of Adhesive Joints Using the Cohesive Zone Model. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Stolle, R. (Hrsg.): Applied Research Conference 2016 – ARC 2016, Pro Business Verlag, Berlin, 2016, ISBN: 9783864604942. @inproceedings{Wätzig2016,
title = {Damage Modelling of Adhesive Joints Using the Cohesive Zone Model. },
author = {A. Wätzig and V. Schmid and I. Ehrlich},
editor = {J. Mottok and M. Reichenberger and R. Stolle},
isbn = {9783864604942},
year = {2016},
date = {2016-06-24},
booktitle = {Applied Research Conference 2016 – ARC 2016},
publisher = {Pro Business Verlag},
address = {Berlin},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|
Nübler, S.; Schmid, V.; Ehrlich, I. FEM-Simulation of a Tube to Flange Joint under Bending Load. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Stolle, R. (Hrsg.): Applied Research Conference 2016 – ARC 2016, Pro Business Verlag, Berlin, 2016, ISBN: 9783864604942. @inproceedings{Nübler2016,
title = {FEM-Simulation of a Tube to Flange Joint under Bending Load.},
author = {S. Nübler and V. Schmid and I. Ehrlich},
editor = {J. Mottok and M. Reichenberger and R. Stolle},
isbn = {9783864604942},
year = {2016},
date = {2016-06-24},
booktitle = {Applied Research Conference 2016 – ARC 2016},
publisher = {Pro Business Verlag},
address = {Berlin},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|
Steinmann, S.; Ehrlich, I. Investigation of transverse impact stress in fiber reinforced plastics under high-velocity impact and determination of the experimental procedure. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Stolle, R. (Hrsg.): Applied Research Conference 2016 – ARC 2016, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2016, ISBN: 9783864604942. @inproceedings{Steinmann2016,
title = {Investigation of transverse impact stress in fiber reinforced plastics under high-velocity impact and determination of the experimental procedure.},
author = {S. Steinmann and I. Ehrlich},
editor = {J. Mottok and M. Reichenberger and R. Stolle},
isbn = {9783864604942},
year = {2016},
date = {2016-06-24},
booktitle = {Applied Research Conference 2016 – ARC 2016},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {The examination of material properties under a transverse impact stress is interpreted as an important regular feature for components of fiber-reinforced plastics. In many applications the knowledge of this material stress is not sufficiently available. The transverse impact is defined as a critical material stress, which can lead to failure of the material with a variety of failure modes. In the research project Hybrid Impact Safety, supported by the Bavarian Research Foundation (Bayerische Forschungsstiftung), different materials of fiber reinforced plastics and their layered structures are examined regarding their impact resistance and the incoming failure modes. The materials basalt fiber-, carbon fiber-, and glass fiber-reinforced plastic, are loaded transversely in different speed ranges and the absorbed energy is determined. ABRATE describe the speed ranges for velocity investigations on fiber-reinforced plastics. The load operation in ballistic speed range with low masses is defined as a dynamic process, and the lower speed range with high masses as a quasi-static process. The relation of the applied energy to the projected area of damage caused by the transverse impact is detected. The dissipated energies, depending on the materials, are compared and evaluated. The layered structure is crucial for the spread of the damaged area and residual energy restrained in the material. The findings of the monolithic materials give conclusions about the damage propagation under impact loads and help to identify the damage in the material. The highvelocity-impact is performed by a ballistic gun system. The speed range is between 350 m/s and 450 m/s. This work defines an experimental procedure for high velocity impact, the conditions of the experiment and carrying out the material tests in a highvelocity speed range. The aim is to increase the impact resistance and minimize the damage spread by a target array of different materials in a single layered structure. },
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The examination of material properties under a transverse impact stress is interpreted as an important regular feature for components of fiber-reinforced plastics. In many applications the knowledge of this material stress is not sufficiently available. The transverse impact is defined as a critical material stress, which can lead to failure of the material with a variety of failure modes. In the research project Hybrid Impact Safety, supported by the Bavarian Research Foundation (Bayerische Forschungsstiftung), different materials of fiber reinforced plastics and their layered structures are examined regarding their impact resistance and the incoming failure modes. The materials basalt fiber-, carbon fiber-, and glass fiber-reinforced plastic, are loaded transversely in different speed ranges and the absorbed energy is determined. ABRATE describe the speed ranges for velocity investigations on fiber-reinforced plastics. The load operation in ballistic speed range with low masses is defined as a dynamic process, and the lower speed range with high masses as a quasi-static process. The relation of the applied energy to the projected area of damage caused by the transverse impact is detected. The dissipated energies, depending on the materials, are compared and evaluated. The layered structure is crucial for the spread of the damaged area and residual energy restrained in the material. The findings of the monolithic materials give conclusions about the damage propagation under impact loads and help to identify the damage in the material. The highvelocity-impact is performed by a ballistic gun system. The speed range is between 350 m/s and 450 m/s. This work defines an experimental procedure for high velocity impact, the conditions of the experiment and carrying out the material tests in a highvelocity speed range. The aim is to increase the impact resistance and minimize the damage spread by a target array of different materials in a single layered structure. |
Faber, M.; Kastenmeier, A.; Ehrlich, I. Three-dimensional finite element analysis of a composite tube with multi-row bolted joints. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, M.; Stolle, R. (Hrsg.): Applied Research Conference 2016 – ARC 2016, Technische Hochschule Augsburg Pro Business Verlag 2016 , Augsburg, 2016, ISBN: 9783864604942. @inproceedings{Faber2016,
title = {Three-dimensional finite element analysis of a composite tube with multi-row bolted joints.},
author = {M. Faber and A. Kastenmeier and I. Ehrlich},
editor = {J. Mottok and M. Reichenberger and R. Stolle},
isbn = {9783864604942},
year = {2016},
date = {2016-06-22},
booktitle = {Applied Research Conference 2016 – ARC 2016},
publisher = {Pro Business Verlag 2016 },
address = {Augsburg},
organization = {Technische Hochschule Augsburg},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
|
Pongratz, C.; Ehrlich, I. Structural Dynamic Analysis of Thin Composite Plates Using Noncontact Measurement and Excitation. Leichtbau Konferenzbeitrag In: Mottok, J.; Reichenberger, J.; Scharfenberg, G.; Ziemann, O. (Hrsg.): Applied Research Conference 2016 – ARC 2016, S. 351-358, Ostbayerische Technische Hochschule Regensburg Pro Business Verlag, Berlin, 2016, ISBN: 978-3-86460-494-2. @inproceedings{Pongratz2016b,
title = {Structural Dynamic Analysis of Thin Composite Plates Using Noncontact Measurement and Excitation.},
author = {C. Pongratz and I. Ehrlich},
editor = {J. Mottok and J. Reichenberger and G. Scharfenberg and O. Ziemann},
isbn = {978-3-86460-494-2},
year = {2016},
date = {2016-06-22},
booktitle = {Applied Research Conference 2016 – ARC 2016},
pages = {351-358},
publisher = {Pro Business Verlag},
address = {Berlin},
organization = {Ostbayerische Technische Hochschule Regensburg},
abstract = {A wide field of applications for fiber-reinforced plastics exists in the aeronautics as well as in the automotive industry due to the superior specific stiffness and strength these materials offer. A drawback of fiber-reinforced plastics is their vulnerability to so called delamination damages. Those damages are a particular safety issue as they are virtually invisible from the outside. A structural health monitoring principle is researched and tested, which aims to allow structure integrity statements without permanent monitoring or during operation, based on the vibrational behavior. The first step to achieve this is to determine the properties describing the vibrational behavior of intact composite plates. The modal properties were determined using a Laser Scanning Vibrometer. The specimen plates were measured on a free-free bearing. Excitation is provided by sound waves emitted from a speaker placed underneath the plate. By combining the excitation via speaker with the Laser Scanning Vibrometer, a non-contact excitation and measurement setup is gained. Utilizing this setup, different carbon fiber-reinforced plastic plates were measured and analyzed. The obtained results are discussed and the structural dynamic properties of different plates compared.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
A wide field of applications for fiber-reinforced plastics exists in the aeronautics as well as in the automotive industry due to the superior specific stiffness and strength these materials offer. A drawback of fiber-reinforced plastics is their vulnerability to so called delamination damages. Those damages are a particular safety issue as they are virtually invisible from the outside. A structural health monitoring principle is researched and tested, which aims to allow structure integrity statements without permanent monitoring or during operation, based on the vibrational behavior. The first step to achieve this is to determine the properties describing the vibrational behavior of intact composite plates. The modal properties were determined using a Laser Scanning Vibrometer. The specimen plates were measured on a free-free bearing. Excitation is provided by sound waves emitted from a speaker placed underneath the plate. By combining the excitation via speaker with the Laser Scanning Vibrometer, a non-contact excitation and measurement setup is gained. Utilizing this setup, different carbon fiber-reinforced plastic plates were measured and analyzed. The obtained results are discussed and the structural dynamic properties of different plates compared. |
Pongratz, C.; Schlamp, M.; Jungbauer, B.; Ehrlich, I. Detection of Delamination Damages in Thin Composite Plates using Noncontact Measurement of Structural Dynamic Behavior Leichtbau Artikel In: Athens Journal of Τechnology & Engineering, 3 (4), S. 315-331, 2016, ISSN: 2241-8237. @article{Pongratz2016,
title = {Detection of Delamination Damages in Thin Composite Plates using Noncontact Measurement of Structural Dynamic Behavior},
author = {C. Pongratz and M. Schlamp and B. Jungbauer and I. Ehrlich},
editor = {P. Petratos and N. Mourtos and T. Trafalis and T. Attard and V. Sisiopiku},
url = {https://www.athensjournals.gr/technology/2016-3-4-3-Pongratz.pdf},
doi = {10.30958/AJTE.3-4-3},
issn = {2241-8237},
year = {2016},
date = {2016-06-20},
booktitle = {Proceedings of the 4th Annual International Conference on Industrial, Systems and Design Engineering},
journal = {Athens Journal of Τechnology & Engineering},
volume = {3},
number = {4},
pages = {315-331},
address = {Athens, Greece},
abstract = {Plate-shaped composite structures are typically implemented in a variety of applications related to the aeronautics or automotive industry. Subjected to real environmental conditions, those structures may be burdened by impact loads. Low-velocity impacts in particular are a high safety issue since they can cause barely visible or invisible damages inside the structure. The caused defects vary from notches and cracks to delaminations underneath the surface. Their common consequence is a significant reduction of compression and fatigue strength. To determine the integrity of composite structures, different principles, mainly ultrasonic testing, can be used. Because these methods are typically time consuming, a faster and more easily applied integral test method might offer advantages. Such a test method can be gained byanalyzing the vibrational behavior of composite structures. Using the vibrational analysis approach, not only the response frequencies are considered, but also other modal properties, especially the modal damping. The single measurement of the response frequencies might prove an insufficient damage indication because their frequency shift is subtle and is strongly dependent on its present bearing. For the experimental tests, plate-shaped specimens were chosen due to the simple geometry and relevance to applications. By using structural dynamic measurements and analysis, intact as well as impact damaged plates were measured. For the contact-less measurements of the vibrating specimens, a Laser Scanning Vibrometer is used. The plate-shaped specimens are oscillated by acoustic excitation. The necessary bearing is realized in the form of a thread suspension or, more generalized, a free boundary condition. This minimizes any hampering of the evolving modes of vibration. The obtained results of the conducted measurements are compared and discussed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Plate-shaped composite structures are typically implemented in a variety of applications related to the aeronautics or automotive industry. Subjected to real environmental conditions, those structures may be burdened by impact loads. Low-velocity impacts in particular are a high safety issue since they can cause barely visible or invisible damages inside the structure. The caused defects vary from notches and cracks to delaminations underneath the surface. Their common consequence is a significant reduction of compression and fatigue strength. To determine the integrity of composite structures, different principles, mainly ultrasonic testing, can be used. Because these methods are typically time consuming, a faster and more easily applied integral test method might offer advantages. Such a test method can be gained byanalyzing the vibrational behavior of composite structures. Using the vibrational analysis approach, not only the response frequencies are considered, but also other modal properties, especially the modal damping. The single measurement of the response frequencies might prove an insufficient damage indication because their frequency shift is subtle and is strongly dependent on its present bearing. For the experimental tests, plate-shaped specimens were chosen due to the simple geometry and relevance to applications. By using structural dynamic measurements and analysis, intact as well as impact damaged plates were measured. For the contact-less measurements of the vibrating specimens, a Laser Scanning Vibrometer is used. The plate-shaped specimens are oscillated by acoustic excitation. The necessary bearing is realized in the form of a thread suspension or, more generalized, a free boundary condition. This minimizes any hampering of the evolving modes of vibration. The obtained results of the conducted measurements are compared and discussed. |
Niedernhuber, M.; Holtmannspötter, J.; Ehrlich, I. Fiber-oriented repair geometries for composite materials. Leichtbau Artikel In: Composites Part B, 94 , S. 327-337, 2016. @article{Niedernhuber2016,
title = {Fiber-oriented repair geometries for composite materials. },
author = {M. Niedernhuber and J. Holtmannspötter and I. Ehrlich},
url = {https://doi.org/10.1016/j.compositesb.2016.03.027
http://www.sciencedirect.com/science/article/pii/S1359836816300518
},
doi = {10.1016/j.compositesb.2016.03.027},
year = {2016},
date = {2016-04-01},
journal = {Composites Part B},
volume = {94},
pages = {327-337},
abstract = {In this paper, the idea of fiber-oriented repair geometries for carbon fiber reinforced plastics (CFRP) is investigated. It considers the differing mechanical properties of unidirectional fiber reinforced material by excluding overlapping regions perpendicular to the fiber direction of the particular layer.
A mechanical and numerical comparison of tensile strength of stepped joints with continuous step lengths per ply and stepped joints with reduced step lengths in plies with fiber orientation differing from load direction is performed.
Finite element simulations show similar shear stresses. Mechanical tests of CFRP laminates with stepped joints show no significant deviation in tensile strength, in spite of a joint length reduction of nearly 40%. This leads to the possibility of a significant reduction of repair area.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this paper, the idea of fiber-oriented repair geometries for carbon fiber reinforced plastics (CFRP) is investigated. It considers the differing mechanical properties of unidirectional fiber reinforced material by excluding overlapping regions perpendicular to the fiber direction of the particular layer.
A mechanical and numerical comparison of tensile strength of stepped joints with continuous step lengths per ply and stepped joints with reduced step lengths in plies with fiber orientation differing from load direction is performed.
Finite element simulations show similar shear stresses. Mechanical tests of CFRP laminates with stepped joints show no significant deviation in tensile strength, in spite of a joint length reduction of nearly 40%. This leads to the possibility of a significant reduction of repair area. |
Cerrone, A. R.; Nonn, A.; Hochhalter, J. D.; Bomarito, G. F.; Warner, J. E.; Carter, B. J.; Warner, D. H.; Ingraffea, A. R. Predicting failure of the Second Sandia Fracture Challenge geometry with a real-world, time constrained, over-the-counter methodology Werkstoffsimulation Artikel In: International Journal of Fracture, 198 (1), S. 117-126, 2016, ISSN: 1573-2673. @article{Cerrone2016,
title = {Predicting failure of the Second Sandia Fracture Challenge geometry with a real-world, time constrained, over-the-counter methodology},
author = {A. R. Cerrone and A. Nonn and J. D. Hochhalter and G. F. Bomarito and J. E. Warner and B. J. Carter and D. H. Warner and A. R. Ingraffea},
url = {https://doi.org/10.1007/s10704-016-0086-x},
doi = {10.1007/s10704-016-0086-x},
issn = {1573-2673},
year = {2016},
date = {2016-03-01},
journal = {International Journal of Fracture},
volume = {198},
number = {1},
pages = {117-126},
abstract = {An over-the-counter methodology to predict fracture initiation and propagation in the challenge specimen of the Second Sandia Fracture Challenge is detailed herein. This pragmatic approach mimics that of an engineer subjected to real-world time constraints and unquantified uncertainty. First, during the blind prediction phase of the challenge, flow and failure locus curves were calibrated for Ti--6Al--4V with provided tensile and shear test data for slow (0.0254 mm/s) and fast (25.4 mm/s) loading rates. Thereafter, these models were applied to a 3D finite-element mesh of the non-standardized challenge geometry with nominal dimensions to predict, among other items, crack path and specimen response. After the blind predictions were submitted to Sandia National Labs, they were improved upon by addressing anisotropic yielding, damage initiation under shear dominance, and boundary condition selection.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
An over-the-counter methodology to predict fracture initiation and propagation in the challenge specimen of the Second Sandia Fracture Challenge is detailed herein. This pragmatic approach mimics that of an engineer subjected to real-world time constraints and unquantified uncertainty. First, during the blind prediction phase of the challenge, flow and failure locus curves were calibrated for Ti--6Al--4V with provided tensile and shear test data for slow (0.0254 mm/s) and fast (25.4 mm/s) loading rates. Thereafter, these models were applied to a 3D finite-element mesh of the non-standardized challenge geometry with nominal dimensions to predict, among other items, crack path and specimen response. After the blind predictions were submitted to Sandia National Labs, they were improved upon by addressing anisotropic yielding, damage initiation under shear dominance, and boundary condition selection. |
