Fatigue and fracture behaviour of PVC at elevated temperatures
Master Thesis
2008
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University of Cape Town
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Abstract
A series of failures in underground water-carrying uPVC piping in a luxury resort in Dubai gave rise to a research opportunity to determine the effect of temperature on fatigue life performance of uPVC piping. Two different modes of testing were used to determine this temperature effect, namely SN and Fracture Mechanics Paris testing. The temperatures tested were 20%C and 45%C. In addition to temperature tests, a potential ageing effect was also investigated by comparing pipes which had been in service in the resort, and previously unused piping. The SN tests consisted of externally and symmetrically stressing, across the diameter, sections of pipe from the luxury Madinat Jumeirah resort in Dubai where the failures had occurred. The Paris equation generating FM tests used Compact Tension specimens and produced an equation relating the crack growth rate to the cyclic stress intensity amplitude. In addition, material properties were measured which could then be used for fatigue lifetime predictions. In addition to the lifetime tests, fracture toughness tests were also completed. These were done with a view to determining the fracture toughness of the material, and also to ascertain if there was an orientation effect for crack growth. The potential ageing effect was also investigated. This was achieved by means of using differently orientated specimens. SENB specimens were used to determine circumferential fracture toughness and C-Shaped specimens for longitudinal cracks (the direction of on-site crack growth). Fracture surfaces were inspected and calculations performed to indicate critical flaw sizes were broadly consistent with linear elastic fracture mechanics (LEFM). Using the material properties garnered from the Paris fatigue and fracture toughness tests, lifetime predictions were made and compared to the SN data for cycles to failure The research studies revealed that there was a distinct difference in fatigue performance as a result of a temperature increase from 20%C to 45%C, as characterised by both SN and Paris fatigue tests. There was also, but to a lesser degree, an ageing effect. The temperature performance factor for the SN curves was between 1.6 and 4.6, while for the Paris characterisation the temperature performance factor was between 3 and 3.5.
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Includes bibliographical references.
Reference:
Von Zwiklitz, L. 2008. Fatigue and fracture behaviour of PVC at elevated temperatures. University of Cape Town.