Studies of environmental stress-crack propagation in low-density polyethylene

Correlations of the stress-intensity factor K with crack speed a have been obtained for environmental stress cracking (ESC) of a series of low-density polyethylenes in detergent. In the majority of the materials, the crack speed increases initially with increasing K, then becomes constant, and finally starts decreasing. The ESC resistance increases with increasing molecular weight and, in general, the quenched materials show greater ESC resistance than slowly cooled ones. The crack propagation results agree well with the ESC model of Williams. Attempts have also been made to understand the micromechanics of ESC failure from a combined approach of K, the crack tip characteristics, and the fracture surface appearance. The roughness of the fracture surface increases with increasing K.