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

大多数金属微构件，例如冠状动脉支架，都是由少晶微结构组成的。因此，这种成分只有很少的晶体，在横截面上只有一个晶体。这种结构的变形行为与多晶体结构的变形行为有很大的不同，因为必须考虑单晶和邻近颗粒的各向异性。商业上可用的材料通常都很好地研究了它们的循环性能。但各自的数据都是基于尺寸远大于微观成分的标准试件的实验数据。在先前的一个项目中，已经从低聚晶体的静态单轴变形行为方面研究了其变形机制。使用了不同取向的扁平试件以及有缺口的钢丝。基于这些结果，建立了连续介质力学模型和晶体塑性分析来预测微构件的单轴静态变形行为。本项目的目标是基础实验研究，并以支架材料为例模拟寡晶在循环变形过程中的变形机制。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，如果颗粒尺寸达到部件壁厚的量级，则在机械载荷过程中会发生静态和循环的尺寸效应。基于实验知识和先前开发的模拟模型，实验和模拟将扩展到单轴循环变形和多轴静态以及循环(分别为弯曲或弯曲疲劳)载荷，并考虑不同晶粒取向的统计。

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.