管材自由胀形时胀形区轮廓形状的影响因素

THE FACTORS AFFECTING THE PROFILE OF MIDDLE BULGE REGION DURING TUBE BULGE TEST

基于中间自由胀形区为椭圆形轮廓线的假设,对管材自由胀形过程进行了理论分析,研究了影响椭圆形状的主要因素及其对测试结果的影响.结果表明,影响椭圆形状的主要因素是管材胀形区长度和约束模具圆角半径.在其它条件一定时,椭圆的长短半轴比值随管材胀形区长度的减小或约束模具圆角半径的增大而减小,即管材胀形后的轮廓线形状从椭圆形逐渐变化为圆形然后又变为扁椭圆形.由胀形实验所得的应力-应变曲线随胀形区长度和约束模具圆角半径的不同而不同,但基本低于单向拉伸所得结果;而且在胀形区长度减小或约束模具圆角半径增大时,这种差别更大.

Tube bulge test is one novel method of determining the stress-strain relations of tubular materials,compared with the traditional tension test,which can give better description of the mechanical properties of tube.Based on the ellipstical surface assumption of the middle free bulge region during hydrobulging,the tube hydrobulge process is analyzed first.The main factors that affect the shape of the tube were determined and analyzed.Results show that the length of tube bulge region and the entrance radius of the die are two key factors that determine the profile of the middle free bulge region.When other conditions are fixed,the ratio of the two semi-radii will decrease as the decrease of the initial length of tube bulge region or the increase of the die radius.It means that the profile of the middle free bulge region after hydrobulging will change from long ellipsoid to sphere and then to flat ellipsoid.The stress-strain curves determined by tube bulge test differ for different length of tube bulge region and the entrance radius of the die,but are all lower than that of traditional tension test along axial direction.The smaller the length of tube or the bigger the entrance radii of the die,the bigger is the difference.