Experimental analysis of viscoelastic criteria for crack initiation and growth in polymers

Different viscoelastic theories have been applied to characterize the resistance to crack initiation and propagation in the fracture of two poly-diethyleneglicol-bis-allyl-carbonate grades that have different crosslinking densities. Tensile creep compliance curves have been obtained on unnotched specimens, and fracture tests have been conducted on single edge notched specimens loaded in tension at different temperatures and displacement rates. A theory developed by Schapery for linearly viscoelastic materials has been found to be fairly adequate to describe the experimental results obtained, provided that the hypothesis of the yield stress being constant with time is removed. The time-temperature equivalence has also been found to satisfactorily account for the temperature dependence of the fracture resistance at initiation; however, the same did not hold as good for propagation. A simple scheme to analyse fracture data obtained from viscoelastic materials is also proposed.