NiTi self-expanding stents can be exploited in medical applications such as thoracic aortic aneurysm owing to its effects on minimizing problems such as low twistability, unsuitable dynamic performance, and inadequate radial mechanical strength. The present simulation models NiTi superelasticity based on the thermodynamics of the Helmholtz free energy (Auricchio theory) and the thermodynamics of the Gibbs free energy (Lagoudas theory). The three-dimensional nonlinear finite element method is used to evaluate the influences of bend number on the superelastic manners of new geometries designed for Z-shaped thoracic aortic aneurysm NiTi stents by the use of a radial strain (crimping) test. NiTi stents with the lowest number of bends and highest segment length showed the best mechanical performance owing to their lower chronic outward force, higher radial resistive force, and whole superelastic behavior. This numerical study can provide a suitable way of assessing the biomechanical properties of thoracic aortic aneurysm stents given the effects of geometrical parameters.

中文翻译：

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弯曲次数对医用镍钛超弹性行为影响的计算研究

NiTi 自膨式支架可用于医疗应用，例如胸主动脉瘤，因为它可以最大限度地减少诸如低扭曲性、不合适的动态性能和径向机械强度不足等问题。本模拟基于亥姆霍兹自由能的热力学（Auricchio 理论）和吉布斯自由能的热力学（拉古达斯理论）对 NiTi 超弹性建模。三维非线性有限元方法用于通过径向应变（压接）试验评估弯曲次数对 Z 形胸主动脉瘤 NiTi 支架设计的新几何形状的超弹性方式的影响。具有最低弯曲次数和最高段长度的 NiTi 支架由于其较低的慢性向外力而显示出最佳的机械性能，更高的径向阻力和整体超弹性行为。鉴于几何参数的影响，该数值研究可以提供一种合适的方法来评估胸主动脉瘤支架的生物力学特性。