Study on Viscoelastic Behavior During Slow Crack Growth of Medium Density Polyethylene Pipes

The viscoelastic behavior of a medium density polyethylene (MDPE) pipe is investigated by using samples cut out from thick-walled MDPE pipe. Preliminary experimental work has been performed to characterize the nonlinear time-dependent response of such semi-crystalline thermoplastic material. Tests have been carried out at 80 °C, on smooth tensile, full notched creep tensile (FNCT) and pennsylvania notched tensile (PENT) specimens. Research on the resistance to slow crack growth (SCG) of MDPE pipes and prediction of pipe lifetime is also presented. The primary aim of this investigation is focused on the simulation and analysis of the stress and strain distribution of the crack tip using finite element method, which is helpful to understand the mechanism of crack propagation. The results demonstrate that the resistance to SCG of welding joint is worse than the pipe, and it can be concluded that FNCT not only describes the SCG behavior, but also it has less fracture time than PENT.