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 c rosslinking densities. Tensile creep compliance curves have been obtai ned on unnotched specimens, and fracture tests have been conducted on single edge notched specimens loaded in tension at different temperatu res and displacement rates. A theory developed by Schapery for linearl y viscoelastic materials has been found to be fairly adequate to descr ibe the experimental results obtained, provided that the hypothesis of the yield stress being constant with time is removed. The time-temper ature equivalence has also been found to satisfactorily account for th e temperature dependence of the fracture resistance at initiation; how ever, the same did not hold as good for propagation. A simple scheme t o analyse fracture data obtained from viscoelastic materials is also p roposed.