DEFORMATION OF RUBBER-TOUGHENED POLYCARBONATE - MACROSCALE ANALYSIS OF THE DAMAGE ZONE

Two commercial core-shell rubbers were used as impact modifiers for po lycarbonate (PC). Specimens with a single semicircular edge notch were stretched uniaxially in order to study the prefracture damage evoluti on of blends under a triaxial tensile stress state. The irreversible d eformation of modified PC included a cavitation mechanism in addition to the three shear modes of unmodified PC. At the macroscopic level, t he cavitation condition could be described by a mean stress concept. T he corresponding critical volume strain for cavitation in PC blends wa s determined to be independent of rubber content but differed for the two impact modifiers. The critical volume strain for cavitation was us ed as an index of cavitation resistance for the impact modifiers. The effect of rubber content and temperature on Izod impact strength of th e PC blends was also reported. From the relationship between the cavit ation resistance and the Izod impact strength, it was proposed that im pact modifiers with a higher cavitation resistance impart better tough ness to blends with PC. (C) 1994 John Wiley & Sons, Inc.