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

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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.