Crack propagation analysis of mode-I fracture in pultruded composites using micromechanical constitutive models

An experimental and analytical study is carried out to characterize the fracture behavior of fiber reinforced plastic pultruded composites. The composite material system used in this study consists of roving and continuous filament mat (CFM) layers with E-glass fiber and polyester matrix. Eccentrically loaded single-edge-notch-tension ESE(T) fracture toughness specimen were cut from a thick pultruded plate, with the roving orientation transverse to the loading direction. Three-dimensional micromechanical constitutive models for the CFM and roving layers are developed. The micromodels can generate the effective nonlinear behavior while recognizing the in situ response at the fiber and matrix levels. The ability of the proposed micromodels to predict the effective elastic properties as well as the nonlinear response under multi-axial stress states is verified and compared to the stress-strain response from a series of off-axis tests. The micromodels are implemented in a finite element code with a cohesive layer to model the nonlinear fracture behavior of a pultruded composite material with different crack configurations. The properties for the cohesive layer were calibrated from one ESE(T) specimen with a crack to width ratio, a/W of 0.5. Good prediction is demonstrated for a range of notch sizes and geometries. The use of cohesive elements with nonlinear micromodels is effective in modeling the transverse mode-I crack growth behavior in pultruded composites. (C) 2002 Elsevier Science Ltd. All rights reserved.