EFFETTO DELLA VELOCITA' DI DEFORMAZIONE E DELLA TEMPERATURA SULLA RESISTENZA A FRATTURA DI POLISTIRENI A DIVERSO PESO MOLECOLARE

Double Torsion has been adopted to characterize fracture toughness of two polystyrenes having different average molecular mass. Stable crack propagation has been obtained for all temperatures and displacement rates considered. The time-temperature equivalence principle has been applied to derive "master" curves of fracture toughness, GIc, vs. crack speed. Results show that the toughness of the low-molecular mass material is substantially lower for lower crack speeds, but the difference is reduced with increasing crack speed. The observed behaviour has been interpreted in terms of fracture micromechanisms, using electron microscopy.