Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models
Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models
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DOI：
10.1007/s40830-018-0150-7
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发表时间：
2018-03-01
影响因子：
2.2
通讯作者：
Petrini, Lorenza
中科院分区：
文献类型：
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作者：
Allegretti, Dario;Berti, Francesca;Petrini, Lorenza
外周镍钛(NiTi)支架利用超弹性治疗股动脉粥样硬化。支架承受循环载荷，可能导致疲劳断裂和治疗失败。加载条件和器件几何形状的复杂性，再加上材料的非线性行为，可能会导致多轴和非比例变形。有限元分析可以通过比较器件的应力状态和材料的疲劳极限来评估疲劳风险。对于NiTi器件来说，由于其复杂的热力行为，最合适的疲劳模型还没有完全被理解。本文通过计算模型和实验验证对镍钛支架的疲劳性能进行了评估。考虑了四种不同的基于应变的模型：冯·米塞斯准则和三种临界面模型(法特米-社会、布朗-米勒和史密斯-沃森-托珀模型)。制作了两种不同细胞几何形状的同种材料支架，并对其疲劳性能进行了实验表征。实验结果与数值结果的比较凸显了冯·米塞斯准则对失效风险的高估。相反，所选择的临界平面模型，即使基于不同的损伤机制，也能给出更好的疲劳寿命估计。为了合理选择最可靠的疲劳模型，需要对NiTi支架的裂纹扩展机理进行进一步的研究。
Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.