Crazing limit of polymers in creep and stress relaxation

The appearance of the first visible damage in polymers in the form of crazes or microcracks may be assumed to be a sign of failure. Experimental investigations have shown that in uniaxial creep and stress relaxation experiments, under isothermal conditions, a certain time between the quasi-spontaneous loading and visible crazing is needed. This ‘incubation time’ is very strongly dependent on the magnitude of the quasi-spontaneously applied stress or induced strain. Based on the Reiner-Weissenberg theory of strength, simple relations allowing the prediction of crazing are developed. The agreement between theoretical computation and experiment is very good.