Sub critical crack advance vs. impact fracture on high impact polystyrene with different second phase volume contents and structures

Also for polymers, many fractures in service occurs after a period in which an existing crack has propagated in a sub-critical manner, while the labor atory tests are mainly concentrated on impact fractures. Aim of this paper is then to investigate the sub critical fracture in some high impact polyst yrene (HIPS) materials with different second phase volume fraction and part icle size and to compare it with the outcomes of impact Fracture Mechanics experiments. Large differences in the results of the two mechanical test pr ocedures are evidenced: the materials behaviour is then examined from the s tructural point of view and an interesting case of interfacial failure, whi ch disappears at high strain rate, is attested on some HIPSs by means of di fferent techniques, i.e. electron microscopy, nuclear magnetic resonance sp ectroscopy and dynamic mechanical spectroscopy, indicating that the slow cr ack fracture behaviour can be influenced by parameters that do not affect o rdinary mechanical tests. (C) 1999 Kluwer Academic Publishers.