Werkstoffsimulation

@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}

}

@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}

}

@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}

}

@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}

}