成形极限预测韧性断裂准则及屈服准则的影响

将韧性断裂准则用于预测板材成形极限,通过数值模拟HS钢、IF钢和6111-T4铝合金3种板材在单向拉伸、平面应变和双向等拉等不同应变路径下的变形过程,获得试件中心区域主应变最大单元的应变历史,结合成形极限实验数据计算韧性断裂准则的材料常数;通过对接近平面应变变形路径下的模拟结果与实验获得的网格应变相比较分析了Hill48,Hill90和Barlat89 3种各向异性屈服准则对模拟获得的应变路径的影响.结果表明,Barlat89屈服准则可以较好地描述单元的应变路径;在此基础上比较了几种韧性断裂准则用于预测板材断裂成形极限的计算结果, Cockcroft-Latham准则和总塑性功准则的计算结果比较理想,材料常数的确定也较为简单.

Suitability of some ductile fracture criteria and yield criteria in forming limit prediction

Some ductile fracture criteria was applied to predict the forming limit of sheet matels.The numerical simulation for deformation processes with uniaxil tensile,plane strain,equi-biaxial strain and some other strain paths were carried out for HS steel,IF steel and 6111-T4 aluminum alloy sheets.Ductile fracture criteria was combined with the finite element simulation.The constants in the criteria were determined by using the calculated strain path and stress at the element with maximal major strain combined with the critical values of strain obtained in the tests.The effect of yield criteria Hill48,Hill90 and Barlat89 on strain path in numerical simulation was compared and evaluated with the measured strain path near the plane strain.Barlat89 can reasonably well predict the strain paths of three kinds of sheet matels.Further calculations were carried out for the forming limit with several ductile fracture criteria combined with Barlat89.It is shown that Cockcroft-Latham and the total plastic work criteria give more reasonable prediction and the material constants in the criteria can be calculated easily.