Plastic Pipes Conference Association # 1995 Edinburgh
Bon, Gueugnaut, Marty
This paper presents the fust pan of the methodology designed by Gaz de France to assess for the prediction of the slow crack growth in polyethylene gas pipes by means of the so-called uvirolen test which allows one to monitor the length-wise development of a longitudinal crack in the pipe wall thickness after a prenotching consecutive to the insertion of amandrel in the pipe. This test is incorporated in a French standard and has been submitted to the ad'hoc CEN and IS0 committees. The methodology developed is based upon both experimental measurement of the displacements field at the pipe outer surface by means of an image analysis procedure and a numerical simulation of the throughwall strain-stress distribution by means of an original model used by Gaz de France to assess for rhwlogical behaviour of PE. The fmt step of the work consisted in designing an original experimental setup in order to be able to make a mapping of the displacements disnibution in the pipe wall during and after the phase of cone insertion, without any prenotching. Then a modelization of the process was made using the model and the stressstrain distribution was calculated. This approach permits to evaluate the initial strain-stress distribution and the stress relaxation due to the cone insertion, taking account of the tempelahlre increase from 20°C to 80°C.
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