含缺陷铝合金厚板预拉伸断裂研究

由于材料中存在空洞等缺陷,铝合金厚板在预拉伸过程中易发生断裂,对拉伸设备造成损伤。基于GTN损伤本构方程,建立铝合金板预拉伸断裂模型。基于小试件拉伸断裂试验测试结合数值模拟,确定GTN损伤本构参数,对五种典型厚度铝合金板预拉伸断裂进行研究。计算铝合金板断裂过程中的应力应变及损伤变量的变化规律,并将表面位置和断裂截面位置处的各变量进行对比。结果表明,随着拉伸率的增大,铝合金板由平面应力状态变为应变集中,其部位由正中心位置向边缘偏移,空洞体积分数最大值也由正中心位置转移到应变集中处;随厚度增加断裂应变略有降低,且受初始空洞体积分数的影响较大。通过对不同厚度、不同拉伸率的铝合金板预拉伸分析,得到初始空洞体积分数和初始缺陷尺寸随厚度变化规律。

Study of Pre-stretching Fracture for Aluminum Alloy Thick Plates with Defects

Due to the existence of defects, such as voids, in the material, the fracture of aluminum alloy thick plate will probably occur during the pre-stretching process, which is extremely harmful for the pre-stretching machine. The GTN damage constitutive is adopted to establish a model for pre-stretching fracture of aluminum alloy plate. The damage constitutive coefficients of GTN model are optimized by tensile fracture experiments and numerical simulations, five typical thicknesses of aluminum alloy plates are selected to investigate the pre-stretching fracture. The stress, strain and damage parameter of aluminum alloy plate during the fracture are calculated, the difference of variations on the surface and the fracture section are compared and discussed. The results show that, as the tension processing, the plane stress state in the aluminum alloy plate changes to strain concentration, and the location of concentration change from the center of the plate to edge position, meanwhile, the variations of the void volume fractions are the same as strain concentration; as the thickness of plate increasing, the fracture strain decreases slowly, and is affected by the void volume fraction significantly. Through the analysis of different thickness and tension ratio of pre-stretching aluminum alloy plates, the varying pattern of initial void volume fraction and the radii of initial voids with the thickness are obtained.