Measurement and simulation of cyclic deformation of oligocrystalline structures using the example of coronary stents

大多数金属微部件，例如冠状动脉支架，由低晶微结构组成。因此，这种成分只有很少的晶体，在横截面上只有一个晶体。由于要考虑到单晶和邻近晶粒的各向异性，这种结构的变形行为与多晶结构的变形行为有很大的不同。市售材料的循环性能通常得到了很好的研究。但各自的数据都是基于标准试件的实验数据，尺寸远大于微构件的实验数据。在以前的项目中，已经研究了寡晶的变形机制，涉及它们的静态单轴变形行为。不同取向的平面试样以及缺口导线已被使用。基于这些结果，建立了连续力学模型和晶体塑性分析来预测微部件的单轴静态变形行为。本课题以支架材料为例，对低晶在循环变形过程中的变形机制进行基础实验研究和模拟。研究结果将适用于各种小型化材料系统，因为对于所有类型的变形，无论是静态变形还是循环变形，如果晶粒尺寸达到部件壁厚的大小，则在机械载荷期间会发生尺寸效应。在已有的实验知识和已建立的仿真模型的基础上，将实验和仿真扩展到考虑不同晶粒取向统计的单轴循环变形和多轴静载荷以及循环（分别为弯曲或弯曲疲劳）载荷。

Most metallic micro components, for example coronary stents, consist of oligocrystalline microstructures. Therefore such components have only few crystals, to the point of only one crystal in cross section. The deformation behavior of such structures is remarkably different with respect to the one of polycrystals because anisotropy of single crystallites as well as neighboring grains have to be taken into account.Commercially available materials are generally well investigated regarding their cyclic properties. But the respective data are based on experimental data of standard test specimens with much larger dimensions than the ones of micro components.In a previous project the deformation mechanisms of oligocrystals have been investigated with respect to their static uniaxial deformation behavior. Differently oriented flat specimens as well as notched wires have been used. Based on these results a continuum mechanical model as well as a crystal plasticity analysis have been developed to predict the uniaxial static deformation behavior of micro components.The goal of the proposed project is fundamental experimental research accompanied with simulation on the deformation mechanisms of oligocrystals during cyclic deformation using the example of stent materials. The results will be transferable to various miniaturized material systems, because for all types of deformation, static as well as cyclic, size effects occur during mechanical load if the grain size reaches the magnitude of the component wall thickness.Based on the experimental know how and the previously developed simulation models experiment as well as simulation will be extended to uniaxial cyclic deformation and multiaxial static as well as cyclic (bending or bending fatigue respectively) load taking statistics due to different grain orientations into account.