Abstract
The application of a cyclic stress to a polymeric material causes its temperature to rise with the result that failure may occur by one of two completely different mechanisms. In the first the temperature rises for a time but then stabilizes and allows a conventional crack initiation and propagation process to take place. In the second type of failure the temperature continues to increase and results in a thermal softening failure in the material.
Uniaxial fatigue tests have been carried out on injection moulded acetal co-polymer specimens and the conditions under which each type of failure occurs have been analysed theoretically and empirically. Using relatively simple analysis, indication is given as to how quite acceptable predictions of the observed temperature rises may be made. The effects of mean stress, strain control, as opposed to load control, and cyclic waveform on polymer fatigue behaviour are also indicated.
In addition electron microscopy studies were carried out on the fatigue failures of the injection moulded specimens and these show that microscopic fatigue striations are present and that the size of the defect which has initiated crack growth is typically about 0.13 mm (0.005 in.).
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Crawford, R.J., Benham, P.P. Cyclic stress fatigue and thermal softening failure of a thermoplastic. J Mater Sci 9, 18–28 (1974). https://doi.org/10.1007/BF00554752
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DOI: https://doi.org/10.1007/BF00554752