Nonlinear constitutive models for pultruded FRP composites

Abstract

Three nonlinear multi-axial constitutive models for pultruded fiber reinforced plastic composites are proposed and examined in this study. The first two are macromechanical models that idealize the entire composite material as homogeneous orthotropic under plane stress conditions. The third is a new three-dimensional (3D) micromechanical model where the fiber and matrix responses are explicitly recognized and the nonlinear behavior is expressed at the matrix level. The pultruded composite material system considered in this study consists of two alternating layers of roving and continuous filament mat. The two layers have E-glass/vinylester fiber/matrix constituents. Coupon tests were performed for calibration and verification of the proposed models. Nonlinear response is calibrated using V-notch tests, to generate the axial-shear stress–strain, and uniaxial transverse tests. 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 three 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. The nonlinear curves predicted by the two nonlinear orthotropic models are also in good agreement with the experimental results but not for all off-axis orientations. All three models can be easily integrated within a finite element code for the general nonlinear analysis of pultruded composite structures using layered shell or 3D type elements.