Study of polyethylene pipe resins by a fatigue test that simulates crack propagation in a real pipe

A fatigue test that simulates the step-wise crack propagation found in pipes in the field, and uses a standard compact-tension specimen, was employed to study and rank crack resistance of various pipe resins. The thermal history during compression moulding of the test specimens strongly affected fracture kinetics. It was found that crack-resistant properties of in-service pipe were best reproduced if compression-moulded plaques were fast cooled under load. This procedure was used to prepare specimens from candidate pipe resins for fatigue testing. The resins were compared in terms of discontinuous crack growth kinetics. The ranking based on resistance to fatigue crack propagation correlated with results of a standard PENT creep test. However, fatigue failure times were an order of magnitude less than the standard creep times. After comparing the initiation and failure times of the resins with detailed kinetics of step-wisse crack propagation, a simplified and rapid procedure is proposed which calls for evaluating only the first jump after initiation.