The Effect of Strain Rate on the Strain to Fracture of a Sheet Steel Under Biaxial Tensile Stress Conditions

Abstract

The present investigation was undertaken as a preliminary study into the influence of strain rate on the forming limit diagram for low carbon steel. For a variation in strain rate from 10−3 s−1 to 70 s−1 experiments have shown that, in the positive quadrant of the forming limit diagram, the position of the forming limit curve is lowered with increasing strain rate. Further, it is suggested that a degree of correlation exists between strain rate and the work hardening exponent “n,” and as such the influence of strain rate on the forming limit diagram manifests itself through the change in n value. Slow speed forming was carried out under oil pressure using a bulge test with elliptical dies. To attain higher strain rate a water-hammer forming technique was employed together with the same die sets as those used for bulge forming.