The Bending Fatigue Response of Fatigue Strength of PVC Pipe and Pipe Joints

In a two-year program, seventy-eight specimens of PVC pipe with and without adhesive socket joints were tested in a four-point bending apparatus. Internal pressures were varied from atmospheric pressure (0 psig) to the rated internal pressure of 280 psig. Results of the plain pipe are compared to pipe with joints. All testing was done using a special apparatus developed to accommodate the large deformations required for fatigue testing of PVC pipes. This apparatus is described as well as the test results. Both strains and stresses are plotted against cycles-to-failure. Finite element elastic models of the socket joined specimens were analyzed to establish the areas of stress concentration and to explain the observed failure modes. Phase 1 testing indicated that the pipe internal pressure might have a significant effect on fatigue life. Joined pipe specimens with no internal pressure were weaker in bending fatigue than pressurized pipe. As a result, the internal pressure was systematically varied between 0 psig and the rated pressure 280 psig. Results of Phase 2 testing revealed a dependence on internal pressure. Also, the effects of an adhesive primer and roughening of the pipe surface on joint fatigue strength were also studied. Strain rate is known to exert a profound influence on the fatigue behavior of thermoplastic polymers. This effect has not been systematically studied and remains an unknown. This research was supported by two grants from the Pressure Vessel Research Council. Additional details of the research are compiled in the Welding Research Council (WRC) Bulletin 445.