Modelling of the mechanical properties of strengthened metal foams on different scales

开孔金属泡沫已有几十年的历史。它们被设计为仿生材料，灵感来自骨小梁。通常它们用于轻型结构或用于吸收动能，例如在碰撞应用中。由于泡沫铝的强度和能量吸收性能不突出，而且性能的可重复性差，泡沫金属至今在应用中还没有很好的确立。这可以通过一种新的涂层技术来改变，其中通过电沉积来沉积纳米晶镍。这种涂层允许显著增加平台应力（强度）和能量吸收。如果这些创新材料在应用中被接受，则有必要了解混合泡沫（泡沫铝+镍涂层）的材料行为。用于描述材料行为的理论模型和数值工具仍然缺失。在开孔泡沫铝表面电化学涂覆不同厚度、不同微观结构的纳米晶镍，以及其它金属和合金，为力学实验提供了丰富的样品基础。样品的这种大的变化是必要的可靠验证的力学模型开发。该项目的目的是在拉伸，压缩，剪切和扭转载荷条件下的这种混合泡沫的实验表征。基于这些结果，将在微观和宏观尺度上模拟材料行为。申请人期望从这种混合泡沫体的变形期间的复杂微观力学行为的模拟中得到更深入的理解。模拟给出了泡沫结构和性能之间关系的信息，并可用于具体检查涂层对性能的影响。根据这些结果，应通过修改支柱的几何形状和涂层厚度来优化泡沫结构。需要对泡沫的单个支柱进行微观力学测试，以将局部过程（如弯曲、断裂和接触）与从宏观测试确定的泡沫的全局变形相关联。微观-宏观转移将通过微观尺度上的均质化进行。作为均匀化的结果，可以通过微观结构的数值模拟来确定宏观模型参数。

Open-cell metal foams are available for several decades. They are designed as bionic materials inspired by trabecular bones. Usually they are used in lightweight construction or for absorption of kinetic energy, e.g. in crash applications. Up to now metal foams are not well established in the applications because the strength and energy absorption of the usual aluminum foams are not outstanding and their properties are badly reproducible. This can be changed by a new coating technique where a nanocrystalline Nickel is deposited by electrodeposition. Such coatings allow for a significant increase of the plateau stress (strength) and of the energy absorption. If these innovative materials are accepted in the applications it becomes necessary to understand the material behaviour of the hybrid foam (Aluminum foam + Nickel coating). Theoretical models and numerical tools for the description of the material behaviour are still missing. The electrochemical coating of open-pore aluminum foams with nanocrystalline Ni in different thicknesses and with different microstructures as well as with other metals and with metal alloys yields a rich basis of samples for the mechanical experiments. This large variation of samples is essential for the reliable validation of the mechanical models to be developed.The aim of the project is the experimental characterization of such hybrid foams under tensile, compressive, shear and torsional load conditions. Based on these results, the material behaviour will be simulated on the micro and macro scale. The applicants expect a deeper understanding from the simulations of the complex micromechanical behaviour during the deformation of such hybrid foams. The simulation gives information on the relations between structure and properties of the foams and can be used to specifically examine the influence of the coating on the properties. Based on these results the structure of the foam shall be optimized by modifying the geometry of the struts and the coating thickness. Micromechanical tests on single struts of the foam are needed to relate the local processes as bending, fracture and contact with the global deformation of the foams determined from the macroscopic tests. The micro-macro transfer will be performed by a homogenization on the micro scale. As a result of the homogenization it is possible to determine the macroscopic model parameters by a numerical simulation of the microstructure.