Fatigue life prediction of short fiber-reinforced thermoplastics

In order to predict the fatigue behavior of Short Fiber-Reinforced Thermoplastic (SFRT) parts, a large amount of experimental tests on specimens is generally required. It is known that the damage occurring in such materials, while cyclically loaded is a hierarchical process. Indeed, the composite degradation mainly develops at the matrix-level, driving the macro-properties decay up to the final failure of the component. The present work proposes a multiscale model that enables the prediction of lifetime duration of SFRTs, this implying a significant reduction of experiments for the material characterization. With the proposed criterion, a failure parameter derived from the stress distribution within the thermoplastic matrix is formulated. Nevertheless, the computation of the complete stress field within the composite requires the generation of equivalent microstructures, which frequently make use of complex algorithms. In this interest, an innovative approach based on the Pseudo-Grain methodology is hereby developed and validated in order to compute the cumulative stress distribution functions without relying on the generation of complex geometries. Eventually, the proposed micro-mechanical model has been validated with a bulk of experimental data, showing that the effect of fiber volume fraction and local fiber orientation onto the fatigue strength of SFRTs is well captured.