Nonlinear elastic-degrading models for the analysis of pultruded composites

Two nonlinear multi-axial constitutive models for pultruded fiber reinforced plastic (FRP) composites are proposed and examined in this study. In the first model, the overall effective response of the pultruded composite material is predicted using 3D micromechanical models for the layers that span the thickness. These micromodels account for the nonlinear response in their matrix while the fiber constituent is assumed to be linear elastic and transversely isotropic. The nonlinear material response of the matrix is achieved using an isotropic elastic-degrading (ED) model. The second is an orthotropic material model where the degraded nonlinear mechanical properties are functions of the strain energy density. The pultruded composite material system considered in this study consists of two alternating layers of roving and continuous filament mat (CFM). The two layers have E-glass/vinylester fiber/matrix constituents. Coupon tests were performed for calibration and verification of the proposed models. Off-axis coupons were cut with different roving orientations in order to generate in-plane multi-axial stress states. The nonlinear axial stress-strain curves of the off-axis tests are compared with the predicted curves from the two proposed models. Good agreement is shown for all off-axis angles when comparing the experimental stress-strain curves with those predicted by the 3D micromodel and the nonlinear orthotropic model.