ACCELERATED FATIGUE FRACTURE OF POLYETHYLENE PIPE MATERIAL - CRACK LAYER ANALYSIS

A fatigue accelerated pipe test method has been developed which is able to quickly differentiate pipes according to their crack propagation resistance. The differences in brittle crack propagation resistance between two pipe materials was quantified and related to the specific enthalpy of damage and the dissipation coefficient via the Crack Layer Theory. These values show that the ethylene/hexene copolymer was more resistant to brittle cracking than was the ethylene/butene copolymer, because in the latter a larger percentage of the irreversible work per cycle was expended on the fracture process. The ethylene/butene copolymer also had a smaller intrinsic toughness than did the ethylene/hexene copolymer, as manifested by its lower specific enthalpy of damage. These results agree with the kinetics of crack propagation, as well as the known field performance of these two materials.