EFFECT OF NOTCH SEVERITY ON FATIGUE FRACTURE IN A RUBBER-MODIFIED GLASSY POLYMER

The research concerned the effect of notch severity on the fatigue beh aviour of series of rubber-modified glassy polymers, consisting of a s tyrene-acrylonitrile copolymer with different amounts of an olefin rub ber. Tests were conducted under displacement control and two different loading conditions. Both stages of fatigue lifetimes, that is, fractu re initiation and crack propagation, were examined. It was observed th at the initial notch severity determines the duration of the crack-ini tiation stage, while crack propagation does not depend on it. The crac k velocity appears to be controlled by the maximum applied stress inte nsity factor, and the correlation does not depend on the rubber conten t, The results obtained have been interpreted by considering three dif ferent zones in the specimen during the fracture process: a far-field viscoelastic continuum, a process zone and a failure zone.