Fatigue criterion for short fiber reinforced thermoplastic (PA66 GF50) over a wide range of load ratios

International audienceComposites of polyamide matrix reinforced by short glass fibers are increasingly used as replacement for metal parts in the automotive industry, especially because they are light weighted and easy to manufacture. Automobile parts are usually subjected to fatigue loadings during their service life, which makes it necessary to have a reliable or predictable durability life. Short glass fiber reinforced (SGFR) thermoplastics are used in structural parts such as top strut and motor mounts wherein they are subjected to complex positive and negative loads. As they are injection-molded, they exhibit a complexfiber orientation distribution, which clearly has an effect on their mechanical properties. Moreover, the polyamide matrix in SGFR thermoplastics is sensitive to ambient humidity and temperature. Therefore, a fatigue criterion for this material should unify different load ratios, fiber orientation distributions for the given atmospheric conditions. In literature, a wide variety of fatigue criteria has been proposed ; nevertheless, single unified fatigue criterion yet has space for improvement. This article proposes anenergy-based fatigue criterion that tends to take into account a load ratio and fibers orientation effects