Accurate determination of plastic yield curves and an approximation point for the plastic yield locus with the bulge test

Plastic flow curves and plastic yield loci are essential for the numerical description of plastic material behavior with isotropic hardening. The Bulge test is a suitable experiment to prevent the necessity for an extrapolation beyond the tensile strain and it gives additionally an approximation point for the yield locus under biaxial stress condition. Nevertheless an accurate evaluation strategy is necessary. It can be shown that the response surface algorithm with a full quadratic approach leads to accurate and reliable results for the plastic yield curves by using a pure membrane theory. It will be demonstrated, that bending effects can be neglected for a typical geometry of the Bulge test (200 mm diameter) and the relevant sheet thickness range of automotive industry (0.5 mm up to 3 mm). It is recommended to take the strain rate sensitivity into account for the determination of the approximation point for the plastic yield locus. The reached strain rates for a pressure controlled Bulge test of 200 mm diameter reaches typically more than 0.1 s-1 and therefore the difference between the static stress and the Bulge stress cannot be neglected anymore.     «

Plastic flow curves and plastic yield loci are essential for the numerical description of plastic material behavior with isotropic hardening. The Bulge test is a suitable experiment to prevent the necessity for an extrapolation beyond the tensile strain and it gives additionally an approximation point for the yield locus under biaxial stress condition. Nevertheless an accurate evaluation strategy is necessary. It can be shown that the response surface algorithm with a full quadratic approach lea...     »