Investigation of Short Fiber Reinforced Polymers Fatigue Behaviour Using Specimens of Highly Coherent Fibres Orientation

The typical injection moulding induced, heterogeneous Fibres Orientation Distribution (FOD) of short fibres reinforced polymers, hinders the accurate evaluation of fatigue strengths of material volumes displaying homogeneous-like FOD. It is common practice to extrapolate these properties from fatigue dataset obtained by testing specimens of heterogeneous FOD at different angles from the loading direction. The present work investigates the potentials of encompassing specimens of highly coherent FOD, machined-out from those of heterogeneous FOD, in the standard experimental procedure to improve the fatigue strengths evaluation accuracy. To this end, static and fatigue tests on both specimen's configurations were carried out. The Alternating Energy Density (AED) fatigue parameter, incorporating strains measured by digital image correlation was applied to the dataset for clustering fatigue data from different microstructures. It separately clusters fatigue data of the integer and shell-only specimens, indicating its sensitivity to the material microstructure. Further, the master-SN curve approach was applied to the experimental dataset to predict the high cycle fatigue limits of microstructure with highly coherent FOD given as reference data associated to microstructure of heterogeneous FOD. However, it performed poorly in doing so, suggesting that shell-only specimens provide precious information which the existing models fail to accurately estimate.