A critical plane approach for multiaxial fatigue life prediction of short fiber reinforced thermoplastic composites

•A critical plane damage model for multiaxial fatigue of fiber thermoplastics.•Different R ratios, fiber orientation, temperatures, and notch effect are included.•Incorporation of the multiaxial fatigue damage model into a general fatigue model to include temp and frequency effects. The usage of short fiber reinforced thermoplastics has been increasing in many industries recently. These composites have many advantages such as high specific strength, lightweight, wear and rust resistance, high stiffness, fast processing rate, and relatively low manufacturing cost. Multiaxial cyclic loading and non-proportionality between different loading sources are inevitable in many applications with such materials. In this study, the multiaxial fatigue behavior of short glass fiber reinforced thermoplastics under different environmental and loading conditions is modeled using a critical plane-based damage approach. This model was recently used for uniaxial fatigue life prediction of Short Fiber Reinforced Thermoplastic Composites. In this paper the model is applied to a large amount of experimental multiaxial fatigue data, demonstrating significantly better correlations than other models used in the literature. The effects of fiber orientation, stress state, mean stress, and stress concentration on multiaxial fatigue behavior are considered in the model. Temperature and frequency effects on multiaxial fatigue behavior were also included by applying the proposed damage model into a general fatigue model. Model predictions are presented and discussed by comparing them with experimental data from the literature.