Revisiting creep test on polyethylene pipe—Data analysis and deformation mechanisms

Abstract Creep tests have long been used to determine long‐term hydrostatic strength (LTHS) for polyethylene (PE) pipe. In view that current standard requires some long‐term creep tests of over 9000 h to determine LTHS, this paper explores the possibility of using relatively short‐term creep tests for the same purpose. The study found that trend line for applied stress versus failure time changes at the failure time around 10 h, and the data trend in the low‐stress regime is consistent with that from the standard test. The trend line change is believed to be caused by the change of the involvement of amorphous and crystalline phases in PE in the deformation process, that is, sequential involvement of the amorphous phase first and then the crystalline phase in the low‐stress regime, and simultaneous involvement of both phases from the beginning in the high‐stress regime. Activation energies based on the Eyring's model and the Norton power law are determined to examine the proposed concept. Both models suggest that additional activation energy is needed for deformation in the high‐stress regime, which provides some support to the proposed concept and the possibility of using short‐term creep tests to determine LTHS.