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

开孔金属泡沫已经有几十年的历史了。它们被设计成受骨小梁启发的仿生材料。通常它们用于轻质结构或吸收动能，例如在碰撞应用中。由于普通泡沫铝的强度和吸能性能不是很好，而且其性能的重复性也很差，到目前为止，泡沫金属在实际应用中还没有得到很好的应用。这一点可以通过一种新的涂层技术来改变，这种技术通过电沉积来沉积纳米晶镍。这种涂层允许平台应力(强度)和能量吸收的显著增加。如果这些创新材料在应用中被接受，就有必要了解混合泡沫(泡沫铝+镍涂层)的材料性能。描述材料行为的理论模型和数值工具仍然缺乏。用不同厚度、不同微观结构的纳米晶镍以及与其他金属和金属合金的电化学涂层为开孔泡沫铝的力学实验提供了丰富的样品基础。这种大的样品变化对于将要开发的力学模型的可靠验证是必不可少的。该项目的目的是在拉伸、压缩、剪切和扭转载荷条件下对这种混合泡沫进行实验表征。基于这些结果，将在微观和宏观尺度上模拟材料的行为。申请人希望从对这种混合泡沫变形过程中复杂的微观机械行为的模拟中得到更深层次的理解。该模拟提供了有关泡沫塑料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，应通过改变支柱的几何形状和涂层厚度来优化泡沫的结构。需要对泡沫的单支柱进行细观力学试验，以将局部过程如弯曲、断裂和接触与宏观试验所确定的泡沫的整体变形联系起来。微观-宏观转移将在微观尺度上进行均质化。作为均化的结果，可以通过对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.