基于应变速率变化准则构建管材液压胀形成形极限图

Detemination of forming limit diagram for tube hydro-bulging based on strain rate change criterion

基于应变速率变化准则（Strain Rate Change Criterion,SRCC）,研究了管材液压胀形过程中极限破裂点与其相邻节点应变速率之间的关系。通过对比胀形区中截面极限状态点与其相邻网格节点的应变速率值,可以判断管材胀形过程是否发生了破裂失效。通过管材液压胀形成形极限破裂实验发现,在管材胀形区极限状态点达到破裂时刻的应变速率值与胀形过程其它时刻的应变速率值相比有明显的突变,说明随着胀形区变形程度的增加,由于加工硬化等现象,胀形区可能发生了分散性失稳,从而使得胀形区变形不均匀。分析实验结果表明,管材液压胀形区中心单元体与其相邻节点之间的应变速率比值达到100左右时,认为管材达到破裂状态,通过提取胀形区极限状态点的极限主应变值来构建成形极限图,实验结果与数值仿真结果吻合较好。

The relationship of strain rates between limit node and adjacent nodes during tube bulging was investigated based on strain rate change criterion（ SRCC）. By comparing the strain rate of the point of the cross section in the bulging area with the strain rate of the adjacent nodes,it can be determined that the failure of the tube bulging may occur. The fracture tests of tube hydro-bulging show that there are significant mutations of the strain rates of the limit broken point in tube bulging area compared with the strain rates at other moments during the bulging. The bulging area should be destabilized which resulting in uneven deformation with the increase of deformation degree of bulging area due to the work hardening. The experimental results show that the fracture may occur when the strain rate ratio between the central element and its adjacent nodes in bulging area reaches about 100,and the forming limit diagram for tube hydro-bulging can be established by ultimate strain status values. The results show that the prediction agrees well with experimental data.