Application of the incubation time criterion for dynamic brittle fracture

The complex issue of penetration and perforation of brittle plates subjected to normal impact is addressed. Fracture and fragmentation are simulated numerically by using simultaneously two failure criteria: ductile and brittle failure. A new brittle failure criterion, which is based on incubation time, is proposed. The criterion, inspired from the Tuler-Butcher criterion, is implemented in a commercial finite element code by means of a user subroutine. It is validated by comparing numerical predictions to experimental ballistic results of normal impact on polymethylmethacrylate plates. It is shown that the projectile's exit velocity and the timing of the penetration are faithfully reproduced. It is also verified visually that the experimental damage/fracture pattern, namely radial cracking and dishing, are both well captured by the proposed criterion.