Anisotropy in Thin, Canning Sheet Metals
The in-plane anisotropy of ductile sheet metal may be characterised by r-values given that tensile straining is uniform. In low ductility material, tensile failure occurs by the formation of an inclined groove within which the plasticity is localised. Under these conditions, where lateral and axial displacements cannot determine an r-value reliably, the inclination of the local groove is used. Anisotropy is characterised with a quadratic orthotropic yield criterion within three r-values, found from tension tests at 0°, 45° and 90° to the roll. Application to biuaxial stress states are made from elliptical bulge forming. The theory is shown to reproduce the pressure-height curves and pole strain paths having assumed an equivalence between flow curves from tension and bulge tests. However, the circular bulge test is a better choice for providing the hardening parameters and fracture strains for use in biaxial stress applications. There appears to be no advantage in using nonquadratic yield criteria for canning materials.
David W.A. REES
Sheet metal, anisotropy, yield criteria, flow curves, equivalence, necking, tension, bulge forming.