Cyclic-dynamic properties of particle foams

颗粒泡沫塑料具有密度低、压力下机械能吸收高、零件设计自由度大、制造成本低等特点。因此，它们注定要用于各种应用，目前包括运动鞋和车辆内饰的安全相关部件。通过在发泡过程中选择工艺参数，可以根据应用具体调整泡孔结构的特性，从而调整注塑部件的行为。然而，根据目前的研究状况，关于颗粒泡沫的结构-性能关系存在很大的不确定性。因此，虽然现有的计算方法适用于预测材料在任何多轴应力状态下的宏观行为，但它们都是基于实质性的简化，例如忽略泡沫细观水平上的局部应力和应变极大值。因此，在整体压力加载的情况下，蜂窝结构内部会发生局部弯曲、屈曲或拉伸破坏。封闭单胞气体及其压缩对材料的力学行为也有很大影响。如果最终部分承受较长时间的循环载荷，经验研究确定为循环蠕变。泡孔气体与泡孔结构之间的相互作用和循环蠕变现象还没有得到充分的研究，本项目主要对泡沫颗粒在准静态和循环压缩加卸载下的力学行为进行了实验和数值研究。利用研制的常压压缩试验台和X射线层析分析技术，研究了泡沫塑料泡沫塑料的气泡、气泡结构和基质聚合物之间的相互作用以及泡沫塑料颗粒的力学性能随时间的变化规律。重点研究了泡沫颗粒的粘弹性和蠕变行为，以及反复加载和卸载时的整体和局部应力-应变曲线。泡孔形态的分析是颗粒泡沫数值模拟的基础。在该项目中，将考虑单元结构、单元气体和粘弹性来模拟第一个单一加载和卸载步骤。特别是，要检测地方一级的非弹性效应和不稳定性，并确定它们对全球行为的影响。因此，这项工作将为改进对材料的理解创造重要的基础，这是更节省资源和更可靠地设计机械长期加载颗粒泡沫部件所必需的。

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.