Volume 33, Issue 1 (January 2005)
An Investigation of Hydraulic Bulging as a Biaxial Straining Test for Sheet Metal
The hydraulic bulging test was studied as a means to furnish accurate stress-strain relationships for constant straining rate through the large plastic strain range sustainable in biaxial tension. Careful attention to detail proved to be necessary.
Precise instrumentation was designed to monitor the progress of bulging with minimal interference in the process. Plastic behavior at the pole of the bulge was assessed by refined analysis taking into account curvature and thickness gradation near the pole. Effects of the initial dominance of bending and the later tendency to ‘secondary bulging’ on the derived stress-strain relationship were identified.
Tests of near-isotropic sheet iron showed good agreement with the flow stress level observed in uniaxial tension but revealed significant variation in the progress of strain hardening. The appearance of two-stage strain-hardening was found to be emphasized in biaxial tension.