RUBBER-ELASTIC BEHAVIOR OF POLY(VINYL CHLORIDE) CRAZE DURING DISCONTINUOUS FATIGUE-CRACK GROWTH

Deformation of crack-tip crazes was measured on poly(vinyl chloride) b y the optical interference method when the fatigue crack grew disconti nuously. The changes in the craze displacements and stresses during a crack growth retarded period were then analysed. With load repetition, crazes increase their size and deform rubber-elastically. Employing t he inverse Langevin approximation, a model was proposed that attribute s the increase of rubber-elastic extension to the increase of random l inks between tangled junctions of molecular chains in craze fibrils th rough disentanglement. The number of links was found to increase almos t linearly with repetition. The model explains the change of craze str ess-extension relation and also the difference of fracture-surface rou ghness.