Prediction of the elasticĝ€"plastic stress/strain response for injection-molded long-fiber thermoplastics

This article proposes a model to predict the elasticĝ€" plastic response of injection-molded long-fiber thermoplastics (LFTs). The model accounts for elastic fibers embedded in a thermoplastic resin that exhibits the elasticĝ€"plastic behavior obeying the Rambergĝ€ "Osgood relation and J-2 deformation theory of plasticity. It also accounts for fiber length and orientation distributions in the composite formed by the injection-molding process. Fiber orientation was predicted using an anisotropic rotary diffusion model recently developed for LFTs. An incremental procedure using Eshelby's equivalent inclusion method and the Moriĝ€" Tanaka assumption is applied to compute the overall stress increment resulting from an overall strain increment for an aligned-fiber composite that contains the same fiber volume fraction and length distribution as the actual composite. The incremental response of the latter is then obtained from the solution for the aligned-fiber composite by averaging over all fiber orientations. Failure during incremental loading is predicted using the Van Hattumĝ€" Bernado model that is adapted to the composite elasticĝ€"plastic behavior. The model is validated against the experimental stressĝ€ "strain results obtained for long-glass-fiber/polypropylene specimens.