A Time Dependent Fracture Toughness Measure for PE Pipe Resins [PE]

Medium density polyethylene (MDPE) pipe resins exhibit extraordinarily long time-to-failure, due to their superior brittle cracking resistance. Attempts to quantify this phenomenon using the J integral approach have been hampered by the large specimen thickness required to effect plane strain conditions and because monotonic loading does not readily initiate brittle cracks in MDPE pipe resins. A procedure to determine fracture toughness (J,,) using fatigue crack propagation has been developed. In addition to simplifying J,, measurements, the new method produces useful information about the time dependence of crack initiation and propagation. J,, of four MDPEs was determined, but J,,, by itself, was not able to quantify differences in brittle cracking resistance between the resins. However, by incorporating both time and energy, a measure of the power to fracture has been obtained which can differentiate between these pipe resins on the basis of their brittle cracking resistance.