Modeling damage initiation and growth in discontinuous random fiber composites

Abstract

The motivation for the present work is to enable the designer to achieve optimum structural performance in discontinuous fiber reinforced composites by investigating the influence of fiber and resin properties. This is accomplished by exploring the damage initiation and growth in discontinuous structural reaction injection molded (SRIM) composite using a representative volume element (RVE). The RYE utilizes a moderate strain elasto-plastic-fracture constitutive formulation for the resin based on a multiplicative decomposition of the deformation gradient into elastic and plastic components. An elastic-fracture large strain constitutive response is utilized for the fiber. The resin properties (coefficient of linear thermal expansion, yield stress, fracture strain, modulus) are a function of temperature. The constitutive formulations for the resin and fiber are implemented into a commercial finite element program, ABAQUS®, as a user material subroutine to track damage initiation and growth. Processing stresses are accounted for using a finite element model with a transient heat transfer analysis to supply the temperature distribution at the nodes as a function of time to simulate the cool down of the composite from 93 to 21°C during manufacture. A tensile loading condition at 21°C was modeled with and without thermal processing stresses. The simulation is compared to experimental data. Further comparisons are made with tensile tests conducted at -40 and 77°C. Results indicate that thermal processing stresses must be accounted for to accurately predict damage initiation and growth in SRIM composites. Excellent agreement is displayed between the RVE model and test data. The methodology presented allows the designer to develop an understanding between resin properties, fiber properties and processing conditions on damage initiation and growth in composites.