Anisotropic meanfield modeling of debonding and matrix damage in SMC composites

This paper presents an anisotropic, micromechanical damage model for sheet molding compound (SMC) composites, that is a thermoset matrix reinforced with long ( ≈ 25 mm ) glass fibers. The model captures the dominant damage mechanisms – matrix damage and fiber-matrix interface debonding – in a Mori-Tanaka homogenization framework. Matrix damage is modeled as a phase-averaged isotropic stiffness degradation. The interface damage is governed by an equivalent interface stress on the lateral fiber surface. Hereby, the inhomogeneous stress distribution in the fiber-matrix interface is taken into account in the definition of the equivalent stress. A Weibull distribution for the interface strength is assumed. The model can account for an anisotropic distribution and evolution of load-carrying fibers with intact interfaces. The model is validated by means of tensile tests on unsaturated polyester polyurethane hybrid and epoxy resin systems with different glass fiber contents (23-50vol.%). The model yields satisfyingly accurate predictions under uniaxial and biaxial stress states.