In situ scanning electron microscopic study of structural fatigue of struts, the characteristic elementary building units of medical stents
In situ scanning electron microscopic study of structural fatigue of struts, the characteristic elementary building units of medical stents
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DOI：
10.1016/j.msea.2007.04.129
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发表时间：
2008-05
期刊：
影响因子：
6.4
通讯作者：
M. Frotscher;K. Neuking;R. Böckmann;K. Wolff;G. Eggeler
中科院分区：
文献类型：
--
作者：
M. Frotscher;K. Neuking;R. Böckmann;K. Wolff;G. Eggeler
本研究讨论了医用支架的基本构建单元支柱组件的循环力学行为。支柱组件在室温空气中以5 Hz的频率进行约2500次循环。然后将它们集成到原位测试装置中，该测试装置允许在扫描电子显微镜中进行拉-拉循环。监测与循环载荷相关的应力-应变响应。记录了局部失效事件，这些事件不一定导致支柱组件完整性的完全丧失。早期裂纹总是形成在缺口的存在导致高局部应力的位置。这些早期失效可能导致整个支柱组件中的载荷重新分布。微型拉伸试验是一种有用的方法，可证明预疲劳暴露会削弱支柱组件的机械阻力。在大多数情况下，裂纹成核似乎控制着奥氏体状态下单个支柱元件和支柱组件的疲劳寿命。经常观察到，微裂纹成核直接跟随快速裂纹扩展和断裂。在拉伸试验过程中，表面缺陷被确定为裂纹开始的位置。但我们也发现了表面夹杂物周围的微裂纹，这些微裂纹在原位拉-拉循环或拉伸试验过程中不会扩展。
The present study addresses the cyclic mechanical behaviour of strut assemblies, the elementary building units of medical stents. Strut assemblies were subjected to approximately 2500 cycles at room temperature in air at a frequency of 5Hz. They were then integrated into an in situ test rig which allowed to perform pull–pull cycling in a scanning electron microscope. The stress–strain response associated with cyclic loading was monitored. And local failure events, which do not necessarily lead to a total loss of strut assembly integrity, were recorded. Early cracks always form at locations where the presence of notches results in high local stresses. These early failures can result in a redistribution of loads in the entire strut assembly. Miniature tensile testing is a useful method to show that pre-fatigue exposure weakens the mechanical resistance of a strut assembly. In most cases, crack nucleation seems to control the fatigue life of individual strut elements and strut assemblies in the austenitic state. It was often observed that micro-crack nucleation is directly followed by fast crack propagation and rupture. During tensile testing, surface flaws were identified as locations where cracks initiate. But we also found micro-cracks around surface inclusions which did not propagate during in situ pull–pull cycling or tensile testing.