Evaluation of bendability of sheet metals using void coalescence models

Bendability of sheet metals often refers to the ratio of the minimum bend radius to the sheet thickness at which the bending process is accomplished successfully. Failure here denotes the occurrence of shear bands, localized necking, cracks or ultimately fracture. The conditions to prevent these types of failures are directly related to the exhaustion of tensile ductility of the outer material fiber at the convex side of the bent sheet. In the present work the bendability of sheet metals are predicted by considering two types of possible failure conditions; namely shear band formation or micro-necking within the material ligaments between neighboring voids. Such analysis is based on assuming a material with an initial void fraction together with a formulation for the laws governing void growth in volume and evolution in shape for porous solids. The results obtained display the effects of hardening as well as anisotropy. The predicted bendability plotted versus ductility is compared favorably with experimental evidence from the literature for various sheet metals.