多孔材料冲击动力学行为及梯度优化实验研究

Cellular materials with their high stiffness and specific strength, as well as the excellent energy absorption capacities, have attracted great attention in the designs of lightweight and crashworthy structures. However, to the mass-sensitive components, the designers concern a lot the mass reduction guaranteeing the total amount of energy absorption. The present project focuses on the optimization of graded density cellular material in dynamic energy absorption. The primitive purpose is to solve the scientific problems, such as testing the dynamic behaviors of cellular materials in the range of large strain, the propagation of plastic/shock waves as well as the critical impact speeds to ignite in uniform/graded density foams. The mechanism of the rate-sensitivity and the dynamic behavior in large strain regime will be highlighted in order to establish the dynamic constitutive relation. In parallel, the shock relation will also be studied for the purpose of establishing the equation of state. Furthermore, the constitutive relation and the equation of state will be embedded into the finite element codes, Abaqus, in order to realize numerically the optimization of graded density cellular material. The works in this project will provide an intrinsic understanding of cellular materials in energy absorption and offer a reference for the reasonable use and optimizing the preparation of cellular materials.

多孔材料以其密度低、比强度和比刚度高以及吸能特性优异，在轻质耐撞性结构设计中获得了重要应用。在质量敏感的吸能构件上，吸能量一定的情况下如何进一步减少吸能构件的质量是设计者非常关心的问题。本项目着眼于梯度多孔材料以动态吸能为目标函数的优化设计；从解决多孔材料动态大变形测量的实验技术设计开发、塑性波/冲击波在（梯度）多孔材料中的传播规律及其临界条件等科学问题出发，研究多孔材料率相关性、动态大变形特征及机理并建立动态本构，同时研究冲击波传播规律，建立适用于多孔材料冲击压溃的物态方程；最后将动态本构和物态方程在有限元软件中的实现并通过设计实验和CT扫描建立的细观有限元模型进行验证，进而用于梯度多孔材料的优化设计。研究成果将提高对多孔材料的动态吸能特性及机理的理解，为工程实际中的合理选用和材料制造的优化设计等提供依据。

多孔材料因其密度低、比强度和比刚度高，以及吸能特性优异，在轻质耐撞性结构设计中得到了重要应用。在质量敏感的吸能构件上，设计者非常关心在吸能量一定的情况下如何进一步减少吸能构件的质量。本项目主要通过试验、结合仿真计算和理论分析，旨在研究梯度多孔材料的吸能特性、冲击波/塑性波传播规律。通过本项目的研究，完善了多孔材料大变形恒应变率测量的实验技术，并获得了可信度高的多孔材料动态应力应变曲线。通过试验和数值模拟研究了等质量正梯度、均匀和负梯度泡沫铝在100到300m/s下的冲击响应，研究发现：正梯度样品的冲击应力恒定，塑性变形量最大；负梯度样品的峰值应力最高，塑性变形量最小。这些结论表明：通过合理设计泡沫杆的密度分布，能够使样品产生恒定的冲击应力和高能量吸收效率。另外，还研究了3D打印的藕孔结构，发现多孔结构的率敏感性主要是基体材料率敏感性和横向微惯性效应竞争的结果。最后，对两种3D打印点阵结构进行了高速撞击试验，获得了不同密度点阵结构的冲击Hugoniot关系。