PLASTICITY AND FRACTURE INITIATION IN RUBBER-TOUGHENED POLY(METHYL METHACRYLATE)

The deformation behavior of rubber toughened poly(methylmethacrylate), RT-PMMA, has been investigated in terms of the ability of the material to nucleate plasticity. Work-hardening rate parameter K measurements in the early stages of the nonelastic response in a constant strain-rate test are used to probe the development of micro shear zones as a function of rubber volume fraction. The results reveal the existence of a sharp transition from difficult to easy shear band nucleation for a critical rubber volume fraction V(c). This abrupt change in mechanical behavior also shows in the evolution of the critical stress intensity factor K(I)c measured at the onset of crack initiation. These findings are discussed in terms of the morphological parameters of the blends.