ELASTOPLASTIC CONVERGENT AND DIVERGENT CRACK PATHS IN TEAR TESTING OFSHEET MATERIALS

When an initially-parallel-sided tab of material, cut into an isotropi c finite-width sheet, is torn by pulling the outer tabs in one directi on, and the centre in the opposite, the cracks may follow a parallel p ath, diverge outwards, or converge inwards depending on the widths of the inner and outer ''legs''. At the same time, the untorn portion of the material may rotate relative to the pulling axis. The phenomenon i s observed in globally elastic tearing, elastoplastic tearing, and in rigid-plastic tearing. A fracture mechanics model using minimum energy explains the tear paths and rotations. Experiments on NS4 aluminium a lloy confirm the analysis. The relationship of leg widths and bend rad ii with standard trousers tear testing of ductile materials is explain ed.