First pseudo-grain failure model for inelastic composites with misaligned short fibers

This paper presents a new model and an experimental investigation of the elastic–plastic flow until failure in short-fiber reinforced thermoplastics typically produced by injection molding. The distribution of fiber orientations and lengths is reproduced statistically within a representative volume element (RVE) of the composite microstructure. Then, the RVE is decomposed fictitiously into pseudo-grains (PGs) inside of which the fiber orientation and aspect ratio are unique. An incremental Mori–Tanaka model is used to predict the phase averages of the stresses and strains inside each PG. Damage intervenes in a second homogenization step: the macroscopic stress accounts for the fact that PGs fail one after the other in function of the fiber orientation and the applied strain mode. Hence, the model is called “first pseudo-grain failure model” by analogy with the “first ply failure model” in laminated composites. An evaluation of the proposed model against experimental data is conducted for short-glass-fiber reinforced polyamide 6,6 (PA6,6). It is shown that the model yields satisfactory predictions of the response under uniaxial tension of composite samples with different fiber contents cut under various directions relative to the main injection flow direction.