2019
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Keim, V.; Cerrone, A.; Nonn, A. Using local damage models to predict fracture in additively manufactured specimens Werkstoffsimulation Artikel In: International Journal of Fracture, Bd. 218, Nr. 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. |
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, Bd. 14, Nr. 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. |
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 Proceedings Article 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. |
Paredes, M.; Keim, V.; Nonn, A.; Wierzbicki, T. Effect of plasticity parameter on the crack propagation in steel pipelines Werkstoffsimulation Proceedings Article 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. |
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 Proceedings Article 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. |