多孔金属材料应力/力增强现象的研究

多孔材料由于具有高比刚度、高比强度、强的吸收能量的能力等优点使其作为包装材料、防撞材料以及汽车工业等领域大量使用。本文经过数值模拟和实验研究发现在冲击荷载作用下多孔金属材料中会出现以下几种应力增强现象:1） 在较小冲击载荷作用下出现的应力增强，其原因是多孔材料胞孔形状的不规则性引起的。2）多孔材料完全密实化以后出现的应力增强，其原因是多孔材料变成致密的固体后，材料性质发生根本变化引起的。3）多孔材料未完全密实化时出现的应力增强，其原因是多孔材料产生塑性变形以后，塑性波速随应变增大而增大，即在加载过程中高幅值扰动的传播速度大于其前方的低幅值扰动的传播速度，从而出现应力增强。4）冲击端出现的应力增强。这与众所周知的冲击理论相一致，冲击端的应力随着冲击速度的增加而增加。在以上几种应力/力增强现象中，第三种应力增强现象在使用多孔材料作为防撞性目的时需特别注意，此时会对被保护物体造成更严重的伤害。本文可以为多孔材料防撞性设计与运用提供一定的参考。

Investigation on the Stress/Force Enhancement in Cellular Metallic Materials

Cellular metallic materials possess high specific stiffness, high specific strength and strong energy-absorbing capability, and have been used significantly as packaging material and crash material. In this paper, through numerical simulation and experimental study, four kinds of stress/force enhancement of cellular metallic materials under impact loads were researched as follows: 1) under small impact load, stress enhancement appears in cellular material and the reason is related to the irregularity of cell shape; 2) when cellular material is fully consolidated, stress enhancement happens because the material has been a dense solid and its property has changed completely; 3) stress enhancement happens before the cellular material is fully consolidated, and the reason lies in that when cellular material is undergoing plastic deformation, the plastic wave propagates increasingly fast with increasing strain and when the propagation velocity of high amplitude perturbation is greater than that of low amplitude perturbation in the front, stress enhancement forms over a period of time; 4) stress enhancement appears at impact end, because according to the well known shock-wave propagation theory, stresses at impact end continuously increase with increasing impact velocities. In these situations, the third one is of great significant to be noted because this kind of stress enhancement may severely damage the substance under protection. This paper will provide a valuable reference for the crashworthiness design of cellular materials.