Compressive Response and Crushing of Cellular Solids

摘要蜂窝固体是一类具有高刚度、高强度、高重量比、高吸能等特性的轻质材料。现代泡沫由聚合物、金属、陶瓷和其他材料制成。它们被用作夹层结构的核心结构部件，并用于大气和空间飞行器、汽车部件、船舶结构、土木工程结构、公共交通车辆、体育用品等领域的冲击缓解、缓冲和其他能量吸收应用。发泡工艺的进步使它们的制造达到规定的细胞尺寸和密度。为了使该技术充分发挥其潜力，基底材料的细胞大小、密度和性能必须与感兴趣的泡沫特性相关。该项目的主要目的是通过实验和分析来了解微观结构如何影响开孔泡沫的所有相关力学性能。不同密度和细胞大小的聚氨酯和泡沫铝将被用作代表性的材料系统。典型的泡沫压缩响应包括一个接近线性的弹性状态，结束于一个极限载荷，随后是一个广泛的载荷平台。极限荷载表示失稳的开始和局部化。聚氨酯泡沫塑料的失稳主要表现为微观结构的弹性屈曲，而泡沫铝的失稳主要表现为塑性坍塌。高原表示能量吸收能力，与破碎在物料中的逐步扩散有关。该项目旨在了解控制这些行为的微观机制，并开发能够复制这些行为的模型。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)测量泡沫的弹性和“非弹性”机械性能；(b)泡沫微观结构表征；(c)泡沫支撑的原位力学性能测量。建模将包括：(a)弹性特性的梁型模型；(b)弹性特性和失稳起始的数值特征胞型模型；(c)大尺度模型，可以再现压缩响应的各个方面，包括大变形破碎。首先，微观结构将被表示为规则的开尔文细胞，但具有真实的支撑几何特征。其他更有代表性的微观结构将视需要加以考虑。

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.