Compressive Response and Crushing of Cellular Solids

摘要多孔固体是一类轻质材料，具有高刚度比、高强度比、优良的吸能特性等独特的性能。现代泡沫是由聚合物、金属、陶瓷和其他材料制成的。它们被用作夹层结构中的结构部件，以及大气和太空车辆、汽车部件、船舶结构、土木工程结构、公共交通车辆、体育用品等中的冲击缓解、缓冲和其他能量吸收应用。发泡工艺的进步使其能够按规定的泡孔尺寸和密度制造。为了充分发挥这项技术的潜力，基材的泡孔大小、密度和特性必须与感兴趣的泡沫特性相关。本项目的主要目标是通过实验和分析来了解微结构如何控制开孔泡沫的所有相关机械性能。不同密度和泡孔大小的聚氨酯和泡沫铝将作为代表性的材料体系。典型的泡沫压缩响应包括终止于极限载荷的近线弹性区域，然后是广泛的载荷平台。极限载荷代表失稳和局部化的开始。泡沫塑料的失稳主要是微观结构的弹性屈曲，而泡沫铝的失稳主要是由于塑性坍塌。代表能量吸收能力的平台与材料中破碎过程的逐步展开有关。该项目旨在了解管理这些行为的微观机制，并开发能够重现这些行为的模型。这个问题将通过实验和几个层次的建模来解决。实验将涉及：(A)测量泡沫塑料的弹性和非弹性机械性能；(B)表征泡沫塑料的微观结构；以及(C)现场测量泡沫支柱的机械性能。建模将涉及：(A)关于弹性性质的梁型模型；(B)关于弹性性质和失稳开始的数值特征单元型模型；以及(C)能够再现压缩响应的所有方面的大尺度模型，包括大变形压碎。首先，微结构将被表示为规则的开尔文单元，但具有真实的支撑几何特征。其他更具代表性的微观结构将被认为是必要的。

Abstract Cellular solids are a class of light-weight materials with unique properties such as high stiffness- and strength-to-weight ratios and excellent energy absorption characteristics. Modern foams are made from polymers, metals, ceramics and other materials. They are used as structural components as cores in sandwich structures and in impact mitigation, cushioning and other energy absorption applications in atmospheric and space vehicles, automotive components, ship structures, civil engineering structures, mass transit vehicles, sporting goods, etc. Advances in foaming processes enable their manufacture to prescribed cell sizes and densities. For this technology to reach its full potential, the cell size, density and properties of the base material must be related to the foam properties of interest. The main objective of this project is to use experiment and analysis to understand how the microstructure governs all relevant mechanical properties of open cell foams. Polyurethane and aluminum foams of various densities and cell sizes will be used as representative material systems. A typical foam compressive response consists of a nearly linear elastic regime terminating into a limit load which is followed by an extensive load plateau. The limit load represents the onset of instability and localization. For polyurethane foams the instability is elastic buckling of the microstructure while for aluminum foams it is due to plastic collapse. The plateau, which represents the energy absorbing capacity, is related to progressive spreading of the crushing through the material. The project aims to understand the micromechanisms governing these behaviors and to develop models which are able to reproduce them. The problem will be tackled through experiments coupled with several levels of modeling. The experiments will involve: (a) Measurement of the elastic and "inelastic" mechanical properties of the foams; (b) characterization of the foam microstructure; and (c) measurement of the mechanical properties of the foam struts in situ. The modeling will involve: (a) beam-type models for the elastic properties; (b) numerical characteristic cell-type models for the elastic properties and the onset of instability; and (c) large-scale models which can reproduce all aspects of the compressive response including the large deformation crushing. At first the microstructure will be represented as regular Kelvin cells but with realistic strut geometric characteristics. Other more representative microstructures will be considered as deemed required.