多孔材料吸能行为对相对密度和冲击速度的依赖性

The Dependence of Energy Absorption Behavior of Cellular Materials on Relative Density and Impact Velocity

多孔材料是一种优异的吸能缓冲材料,但由于其变形模式的非单一性以及动态应力应变曲线的难获取性,其吸能行为对相对密度和冲击速度的依赖性关系还并不完全明朗.论文基于不需要提前作本构假定的波传播法,开展了多孔材料的吸能行为研究.采用多孔材料的细观有限元模型进行Taylor冲击虚拟实验,获取全场质点速度时程曲线,结合Lagrange分析法得到多孔材料的局部应力应变信息,进而探讨了动态吸能性能对材料相对密度和冲击速度的依赖性.研究结果表明多孔材料的吸能行为可依据变形模式分为三个阶段.在冲击模式下,多孔材料单位体积吸能与相对密度成线性增加关系,此时惯性起主导作用;在过渡模式下,惯性的主导作用减弱,单位体积吸能量的增加速率随相对密度的增加而减弱;在准静态模式下,多孔材料只能发生微小的变形,其吸能很少.论文进一步获得了区别于多孔材料准静态应力-应变曲线的动态应力-应变状态曲线,并考察了其与相对密度之间的关系.结果表明:随着相对密度的增加,多孔材料的动态压实应变将变小,而动态塑性平台应力将提高.

Cellular materials have been extensively used as the core materials of impact energy absorbers and anti-blast sacrificial cladding for their lightweight and superior energy absorption capability.However,the dependence of energy absorption behavior of cellular materials on relative density and impact velocity is still unclear due to the diversity of its deformation modes and the inaccessibility of its dynamic stress-strain curve.In this paper,the dynamic energy absorption behavior of cellular materials is investigated by using the wave propagation technique,of which the main advantage is that no pre-assumed constitutive relationship is required.In the virtual Taylor impact test,the particle velocity history curves of the whole field in cellular materials are obtained,and thus the local stress and strain history profiles of cellular materials are determined based on the Lagrangian analysis method.The dynamic energy absorption behavior can be investigated by integrating local stress-strain history curves.The results show that the energy absorption behavior of cellular materials can be divided into three stages according to the deformation modes.In the stage of shock mode,the specific energy absorption of cellular materials increases linearly with the relative density since the inertia effect is dominant at this stage;in the stage of transition mode, the inertia is relatively weak,and the rate increment of the specific energy absorption decreases gradually with the increase of relative density;in the stage of quasi-static mode,the energy absorption capacity is very weak,and it should be distinguished from the quasi-static energy absorption behavior under constant speed loading.Finally,the dynamic stress-strain state curve of cellular materials is obtained and its dependence on relative density is further investigated.The results show that,with the increase of relative density, the dynamic densification strain under the same stress level decreases and the dynamic plastic platform stress increases.