SLOW CRACK-PROPAGATION IN POLYETHYLENE - DETERMINATION AND PREDICTION

A model is developed connecting the stress intensity factor K(I) with the propagation rate dh/dt of slow cracks. The model is based on the concept of the chain relaxation capability. Experimental K(I) versus dh/dt data are reported for polyethylenes of varying molecular mass M, density-rho, initial notch length h0 and at different stress levels-sigma. Predictions of the theory concerning the effect of each of these parameters on crack propagation are confirmed by the experimental results. In particular, the equation for K(I) as a function of dh/dt does not contain h0 nor sigma. Experimental plots of K(I) versus dh/dt for common M but different h0 values coincide into a single curve. Also plots for specimens of the same class but subjected to different stress levels form a single curve.