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

大多数金属微组件，例如冠状动脉支架，由低聚晶体微结构组成。因此，这样的部件仅具有很少的晶体，达到在横截面中仅一个晶体的程度。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，因为必须考虑单个晶粒以及相邻晶粒的各向异性。但是，这些数据都是基于尺寸比微型元件大得多的标准试样的实验数据。在以前的一个项目中，已经研究了低晶体的静态单轴变形行为。已经使用了平行取向的扁平试样以及缺口丝。在此基础上，建立了一个连续介质力学模型和晶体塑性分析方法，预测了微构件的单轴静态变形行为，并以支架材料为例，对低聚晶体在循环变形过程中的变形机制进行了基础性的实验研究和模拟。结果将可转移到各种小型化材料系统，因为对于所有类型的变形，静态和循环，基于实验知识和先前开发的模拟模型，将实验和模拟扩展到单轴循环变形和多轴静态以及循环变形（分别为弯曲或弯曲疲劳）载荷，考虑由于不同晶粒取向引起的统计。

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.