Craze yielding and fracture mechanism in PE/PS/PE laminated films

The change in polystyrene (PS) layer thickness, which has been simultaneously determined during post-yield deformation, shows that crazing is the basic mechanism of toughening in all laminated films, and that shear deformation supplements the contribution of crazing especially for samples with high polyethylene (PE) volume fractions. Crazes formed in PS layers in the laminated films are slender and regular compared with the short and lenticular crazes formed in bulk PS film. When PE volume fraction increased, craze advance speed decreased because of the reduction of the stress concentration effect at craze tips. The life-time of the first mature craze to be formed at a given strain rate increased with PE volume fraction because the PE supporting the mature crazes could effectively inhibit craze rupture and blunt out the propagating crack by absorbing the stored elastic energy in the PS layer that would have been dissipated as fracture surface energy.