RAPID CRACK-PROPAGATION IN POLYETHYLENE PIPE - COMBINED EFFECT OF STRAIN-RATE AND TEMPERATURE ON FRACTURE-TOUGHNESS

The need to predict the mechanical behaviour of polymers is motivated by the increasing use of these materials in structural applications. I n order to consider safety in the design of engineering components, th e question of a criterion for rapid crack propagation has been investi gated in a medium density polyethylene (MDPE) used to extrude pipes fo r gas distribution. Work on the strain rate-temperature equivalence (( epsilon) over dot<-->T) was performed to study the yield stress, sigma (s), as a function of (epsilon) over dot and T. A shifting procedure e nabled a behavioural master curve, sigma(s) versus 1/(a(T)(epsilon) ov er dot to be drawn, where a(T) is the shift factor. Both cracked-ring and Charpy specimens were tested to characterize the fracture toughnes s K-IC (T) of the MDPE. The values of the K-IC (T) based on linear ela stic fracture mechanics are superposed to form a fracture toughness ma ster curve: K-IC versus 1/(a(T)(epsilon) over dot).