负梯度泡沫金属中的局部密实化现象

Phenomenon of Local Densification in Negative Graded Metal Foam

基于一维非线性的刚性-塑性硬化模型,研究了在恒速冲击作用下负梯度泡沫的冲击波控制方程和传播特性。采用LS-DYNA有限元软件对三维随机Voronoi技术生成的梯度泡沫金属模型进行数值模拟,验证了理论预测,并定义了冲击波模型下梯度泡沫材料的局部密实化应变与第二临界速度。通过对冲击速度、密度梯度、相对密度参数的影响研究发现:冲击波模型的理论解与有限元模型的数值解吻合较好,基于R-PH模型的冲击波理论能较好地预测负梯度泡沫金属的力学性能;局部密实化应变在不同冲击速度下存在3个增长阶段;密度梯度绝对值和相对密度越大,局部密实化应变越小,第二临界速度越大。最后讨论了负梯度泡沫中局部密实化现象对支撑端应力的影响。

Based on the one-dimensional nonlinear rigid-plastic hardening(R-PH)model,the control equations and mechanical response characteristics of the shock wave propagation of the negative graded foam under constant velocity impact are studied.The LS-DYNA finite element software is used to numerically simulate the graded metal foam model generated by the three-dimensional stochastic Voronoi technology to verify the theoretical prediction.The local densification strain and the second critical velocity of the graded foam material under the shock wave model are defined.By studying the effects of impact velocity,density gradient and relative density parameters,it is found that the theoretical solution of the shock wave model is in good agreement with the numerical solution of the finite element model.The shock wave theory based on the R-PH model can better predict the negative graded foam metal.The mechanical properties of the local densification strain have three growth stages at different impact velocities;the larger the absolute value of the density gradient and the relative density,the smaller the local densification strain and the larger the second critical velocity.Finally,the effect of local densification on the stress at the support end in the negative graded foam is explained.