On the tension-tension fatigue behaviour of a carbon reinforced thermoplastic part I: limitations of the ASTM D3039/D3479 standard

Investigating the fatigue behaviour of a material often requires a lot of experiments in order to have statistically valid results. However, the number of successful fatigue experiments, where tab failure did not occur, can be significantly smaller than the total number of experiments. This manuscript studies the fatigue behaviour of a carbon fabric reinforced PPS using the specimen geometry proposed by ASTM D3479/D3479M. All specimens failed in the tabbed section, meaning that fatigue life may be significantly underestimated and the proposed geometry needs improvement. Therefore, the main emphasis of this manuscript is on stiffness reduction and permanent deformation of the material, rather than on the number of cycles to failure. It may be concluded that for the [(0,90)]4s stacking sequence the material does not show significant stiffness reduction and that only limited permanent deformation is present. Furthermore, the material shows very brittle failure behaviour and the stress-span between infinite fatigue life and failure in a few dozen cycles is very narrow.