Slow Crack Growth
Plastic Pipes Conference Association # 2004 Milan
Whittle, Teo
PVC-U and PVC-M pipes may be used in applications where they are subjected to cyclic pressures generated by the operation of pumps and valves. It is therefore important that the pipe material’s response to cyclic loading is quantified and that pipelines are designed and operated within the material’s established capability. Using rotational bending specimens, PVC-U and PVC-M were shown to exhibit very similar resistance to crack growth under cyclic loading. That is, the increased static toughness of PVC-M did not manifest itself in an increased resistance to fatigue crack growth rate. It was further shown that PVC-U and PVCM exhibit similar increase in fatigue crack growth rate as the test temperature increased. The rotational bending method was also used to investigate the fatigue threshold of PVC-M and PVC-U. Both materials were found to exhibit a threshold stress intensity factor, ∆Kth, of approximately 0.3 MPa.m0.5 at 20°C. It is concluded that the same cyclic fatigue design principles should be applied to both PVC-U and PVC-M pipes. Moreover, the existence of a threshold value should be taken into account so that derating for fatigue is not required if the amplitude of the stress intensity factor is below the threshold.
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