The widespread development and use of implants made from NiTi is accompanied by the publication of many NiTi material characterization studies. These publications have increased significantly the knowledge about the mechanical properties of NiTi. However, this knowledge also increased the complexity of the numerical simulation of NiTi implants or devices. This study is focused on the uniaxial behavior of NiTi tubing due to cyclic loading and had the goal to deliver both precise and application-oriented results. Single aspects of this study have already been published (Wagner in Ein Beitrag zur strukturellen und funktionalen Ermüdung von Drähten und Federn aus NiTi-Formgedaechtnislegierungen, Ph.D. Thesis, 2005; Eucken and Duerig in Acta Metall 37:2245-2252, 1989; Yawny et al. in Z Metallkd 96:608-618, 2005); however, there is no publication known that shows all the single effects combined in a “duty cycle case.” It was of particular importance to summarize the main effects of pre-strain and subsequent small or large strain amplitudes on the material properties. The phenomena observed were captured in an extended Abaqus® Nitinol material model, presented by Rebelo et al. (A Material Model for the Cyclic Behavior of Nitinol, SMST Extended Abstracts 2010). The cyclic tensile tests were performed using a video extensometer to obtain accurate strain measurement on small electro-polished dog-bone specimen that were incorporated into a stent framework so that standard manufacturing methods could be used for the fabrication. This study indicates that a prestrain beyond 6% strain alters the transformation plateaus and if the cyclic displacement amplitude is large enough, additional permanent deformations are observed, the lower plateau and most notably the upper plateau change. The changes to the upper plateau are very interesting in the sense that an additional stress plateau develops: its “start stress” is lowered thereby creating a new plateau up to the highest level of cyclic strain, followed by resuming the original plateau until full transformation. This study was conducted in the course of the work of a consortium of several stent manufacturers, SAFE Technology Limited and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices.
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机译：由NiTi制成的植入物的广泛开发和使用伴随着许多NiTi材料表征研究的发表。这些出版物大大增加了有关NiTi力学性能的知识。但是，这些知识也增加了NiTi植入物或设备数值模拟的复杂性。这项研究的重点是循环载荷引起的NiTi管的单轴行为，目标是提供精确的和面向应用的结果。这项研究的单一方面已经发表过（瓦格纳（Wagner）在《物理学报》，2005年；博士论文《 Eut Beitrag zur strukturellen and funktionalen》，Eucken and Duerig in Acta Metall 37：2245-2252，1989； Yawny等人，Z Metallkd 96：608-618，2005）；但是，没有出版物可以显示“占空比情况”中所有单个效应的组合。总结预应变以及随后的大小应变幅度对材料性能的主要影响尤为重要。 Rebelo等人提出的扩展的Abaqus ®镍钛诺材料模型中捕获了观察到的现象。 （镍钛诺循环行为的材料模型，SMST Extended Abstracts 2010）。使用视频引伸计进行循环拉伸测试，以对合并到支架框架中的小型电抛光狗骨头样品进行准确的应变测量，从而可以使用标准的制造方法进行制造。这项研究表明，超过6％应变的预应变会改变变换平台，如果循环位移幅度足够大，则会观察到其他永久变形，下部平台尤其是上部平台会发生变化。上部高原的变化非常有趣，因为它会形成一个额外的应力高原：降低其“起始应力”，从而创建一个新的高原，直至最高循环应变水平，然后恢复原始高原直至完全转变。这项研究是在SAFE Technology Limited和DassaultSystèmesSimulia Corp.等多家支架制造商组成的联盟的工作过程中进行的，致力于发展适用于镍钛诺设备寿命预测的疲劳定律。
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