Test MethodOn the tension-tension fatigue behaviour of a carbon reinforced thermoplastic part II: Evaluation of a dumbbell-shaped specimen

For performing uni-axial fatigue tests on composite materials, ASTM D3479/D3479M Standard Test Method for Tension-Tension Fatigue of Polymer Matrix Composite Materials is often considered. This standard prescribes a rectangular shaped specimen with end tabs. However, in part I of this study it became clear that for some materials, such as the carbon PPS under study, the proposed geometry is not ideal for fatigue tests. In this manuscript, a dumbbell (dogbone) shape is assessed to see whether it performs better under fatigue loading conditions, primarily meaning that failure does not occur in the tabbed section. The shape is first optimised using finite element modelling, after which fatigue experiments are performed. It may be concluded, for the material under study, that the dumbbell shape is preferable to rectangular since failure never occurred under or near the tabbed section, and fatigue life is highly underestimated when using the rectangular specimen.