Cyclic-dynamic properties of particle foams

颗粒泡沫的特征在于低密度、在压力下的高机械能吸收、大的部件设计自由度和低制造成本的独特组合。因此，它们注定用于各种应用，目前包括运动鞋和车辆内部的安全相关部件。通过选择发泡过程中的工艺参数，可以根据应用具体调整泡孔结构的性能，从而调整模塑件的性能。然而，根据目前的研究状况，颗粒泡沫的结构-性能关系存在很大的不确定性。因此，虽然计算方法是适用于预测宏观材料在任何多轴应力状态下的行为，他们是基于大量的简化，如忽略局部应力和应变最大值在泡沫的中间层。因此，在整体压力加载的情况下，在单元结构内发生局部弯曲、屈曲或拉伸失效。机械性能也受到封闭的电池气体及其压缩的显著影响。如果最后一部分在较长时间内承受循环载荷，则经验研究确定了循环蠕变。由于泡沫材料中胞气与胞结构之间的相互作用以及循环蠕变现象尚未得到充分的研究，本项目着重于对颗粒泡沫材料在准静态和循环压缩加载和卸载下的力学行为进行实验和数值研究。借助一个有待开发的测试台进行压缩试验在环境压力下和X射线断层分析的应用程序，细胞气体，细胞结构和基础聚合物之间的相互作用，以及随时间变化的颗粒泡沫的力学性能进行了研究。主要重点是颗粒泡沫的粘弹特性和蠕变行为，以及重复加载和卸载的整体和局部应力-应变曲线。泡孔形态分析是颗粒泡沫数值模拟的基础。在该项目中，考虑到细胞结构、细胞气体和粘弹性，将模拟第一个单一的加载和卸载步骤。特别是，非弹性效应和不稳定性的地方一级进行检测，并确定其对全球行为的影响。因此，这项工作将为改进材料理解奠定重要基础，这是机械长期负载颗粒泡沫部件的资源效率和可靠设计所必需的。

Particle foams are characterized by a unique combination of low density, high mechanical energy absorption under pressure, great part-design freedom and low manufacturing costs. They are thus predestined for a variety of applications, which currently include athletic shoes and safety-relevant parts of vehicle interiors. By selection of the processing parameters during foaming, the properties of the cell structure and thus the behavior of the molded parts can be specifically adjusted to the application. According to the current state of research, however, there are significant uncertainties regarding the structure-property relationships of particle foams. Thus, although calculation methods are available that are suitable for predicting macroscopic material behavior in any multiaxial stress states, they are based on substantial simplifications, such as neglecting local stress and strain maxima at the mesolevel of the foam. Hence, in the case of global pressure loading, local bending, buckling or tensile failure occur within the cell structure. The mechanical behavior is also significantly influenced by the enclosed cell gas and its compression. If the final part is subjected to cyclic load over a longer period of time, empirical studies determined a cyclical creep. Both, the interaction between cell gas and cell structure and the phenomenology of cyclic creep have not been adequately investigated yet.The project focuses on the experimental and numerical investigation of the mechanical behavior of particle foams under quasi-static as well as cyclic compressive loading and unloading. With the help of a to be developed test stand for performing compression tests under ambient pressure and the application of X-ray tomographic analyzes, the interactions between cell gas, cell structure and base polymer as well as the time-dependent mechanical properties of the particle foam are going to be investigated. The main focus is on the viscoelastic properties and the creep behavior of the particle foam as well as the global and local stress-strain curves with repetitive loading and unloading. The analysis of the cell morphology forms the basis for the numerical simulation of the particle foams. Within the project, first single loading and unloading steps are to be simulated taking into account cell structure, cell gas and viscoelasticity. In particular, inelastic effects and instabilities on the local level are to be detected and their effect on global behavior to be identified. Thus, the work is going to create important foundations for an improved material understanding, which is required for a more resource-efficient and reliable design of mechanical long-term-loaded particle foam parts.