Behaviour and fracture of polyethylene at high temperature under high pressure of methane.

To study the damage mechanisms and the fracture in a low density polyethylene used for the sheathing of flexible pipelines, several specimen geometries were tested. The experiments consist of a saturation with methane up to a pressure of 10MPa at high temperature (e.g.70 and 100 degrees C) followed by a rapid decompression of samples. The experimental damage was located and quantified from both optical and scanning electronic microscopy (SEM) observations using image analysis possibilities. An attempt is proposed to modelling the different phases of the rapid decompression. The crack initiation criterion is based on the local maximum shear stress. The numerical calculations are in good agreement with the experimental results.