Dynamic Behavior Of Void Growth And Coalescence For Purity Aluminum Under Dynamic Loading

1) By means of an explicit nonlinear dynamic finite element computer code Ls-dyna, the growth of void in aluminum with a preexisting flaw under plate impact loading was investigated. Results show as follows: Firstly, it is observed that void nucleation occur from the boundary of preexisting flow and ductile matrix; Once voids have been nucleation, they grow linearly through localized plastic deformation; Secondly, the growth rate of void radius increases linearly with the shock loading amplitude; Thirdly, the yield strength and size of preexisting flaw have an obvious influence on the relative growth rate.2) The dynamic behavior of the growth of void in aluminum under different strain rate loading are studied through axisymmetric unit cell model. Numerical results show that the mean tensile stress initially increases with time as expected but, after reaching a maximum, starts to decrease; The maximum mean tensile stress can be used to identify the point at which unstable void growth occurs, and increases with loading strain rate, which bear an analogy to spall strength; The loading strain rate has an obvious influence on the growth rate of voids, and inertia is found to have a strong stabilizing effect on void growth process; Stress triaxiality has an obvious influence on the maximum mean tensile stress and void growth rate..3) By using of clindrical cell model with two voids, we investigated the influence of initial"intervoid ligament distance", the loading strain rate, the constitutive behavior and the stress state on coalescence of voids. Results show as follow: Firstly, initial"intervoid ligament distance"has very weakly effect on the critical intervoid ligament distance; Secondly, the critical intervoid ligament distance would be bigger with the increase of the strain rate loading; Thirdly, the critical intervoid ligament distance would be smaller with higher level strain hardening. Fourthly, the onset of coalescence for plane stress loading condition is more easy than that of plane strain and the axisymmetric loadings.4) Based on numerical and theoretical analyses about void growth, a simple dynamic damage evolution model is proposed for elastic- rigid-perfectly plastic materials, which is used to simulate the spall test on copper in order to verify the model applicability.