COOPERATIVE CAVITATION IN RUBBER-TOUGHENED POLYCARBONATE

Particle cavitation in the stress-whitened zone ahead of a semicircula r notch in polycarbonate blended with a core-shell rubber was characte rized by transmission electron microscopy. Cavitation of rubber partic les at five locations in the stress-whitened zone was correlated with the local stress and strain history. It was found that cavitation init iated some distance ahead of the notch when a mean stress condition wa s met. Initially, only a fraction of the particles cavitated and these were randomly distributed. Single cavitated particles grew into cavit ated domains by cooperative cavitation of nearby particles until cavit ation was arrested when shear yielding of the matrix provided an alter native mechanism for relief of strain energy. Far from the notch, wher e the stress state approached uniaxial tension, cavitated domains grew into linear arrays of cavitated particles. A mechanism of cooperative crazing in microlayer composites of polycarbonate and styrene/acrylon itrile copolymer was adapted to cooperative cavitation of core-shell r ubber particles. It was proposed that cooperative cavitation of nearby particles occurred by impingement of a small plastic zone that formed at the equator of a cavitated particle.