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

Abstract

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.