Finite element simulation of ring expansion and fragmentation: The capturing of length and time scales through cohesive models of fracture

The expanding ring test of Grady and Benson (1983) is taken as a convenient yet challenging validation problem for assessing the fidelity of cohesive models in situations involving ductile dynamical fracture. Attention has be en restricted to 1100-0 aluminum samples. Fracture has been modelled by rec ourse to an irreversible cohesive law embedded into cohesive elements. The finite element model is three-dimensional and fully Lagrangian. In order to limit the extent of deformation-induced distortion, we resort to continuou s adaptive remeshing. The cohesive behavior of the material is assumed to b e rate independent and, consequently, all rate effects predicted by the cal culations are due to inertia and the rate dependency in plastic deformation . The numerical simulations are revealed to be highly predictive of a numbe r of observed features, including: the number of dominant and arrested neck s; the fragmentation patterns; the dependence of the number of fragments an d the fracture strain on the expansion speed; and the distribution of fragm ent sizes at fixed expansion speed.