Modeling of translayer fracture in thick-section FRP composites

This paper presents a combined method for modeling the mode-I and II crack growth behavior In thick section fiber reinforced polymeric (FRP) composites having a nonlinear material response. The material system used In this study was manufactured using the pultrusion process and consists of alternating layers of polymer resin reinforced with E-glass unidirectional rovings and continuous filament mats (CFM). Numerical finite element models are used to simulate the crack growth response In eccentrically loaded single-edge-notch, (tension), ESE(T) and notched butterfly specimens. Micro-mechanical constitutive models for the mat and the roving layers are used to generate the effective nonlinear material behavior from the in-situ fiber and matrix responses. Cohesive models are calibrated and used to predict the complete crack growth behavior for different crack configurations. The proposed framework of combined constitutive and cohesive models is shown to be an effective method for predicting the failure load and the crack growth behavior in thick-section fiber reinforced polymeric composites. The idea of combined constitute and cohesive-fracture analyses can be traced to Kanninen et al. [6,7] who considered the applicability of fracture mechanics in composite materials and advocated the Integration of micromechanical failure methods within a global structural analysis. Toll and Aronsson [8] investigated the use of the damage zone criterion and the damage zone models for determining the notched strength of injection-moulded plates having different fiber systems. In the damage zone criterion, the stress in the damaged zone was assumed equal to the material's unnotched strength, and failure occurred when the damage zone reached a critical length. They found better predictions when using the damage zone model, where the damaged zone was propagated when the stresses reached the unnotched strength ahead of an equivalent crack (damaged zone). A linear relationship between the cohesive stresses and the crack opening was used within this zone. In thick-composites, Haj-Ali and El-Hajjar [2, 3] analyzed mode-I transverse cracks in fiber reinforced polymeric (FRP) pultruded specimens having a characteristically small process zone. This study presents a summary on the use of combined micromechanical and cohesive fracture models to predict the failure loads and crack growth behavior of cracked thick-section composites under mode-I and II loading. The effect of the primary reinforcement system (i.e. rovings) on the fracture response is also assessed. In this approach, a 3-D micromechanical constitutive framework is used to generate the effective nonlinear material response based on the in situ matrix and fiber properties. The growth predictions are compared with experiments on mode-I and II specimens utilizing crack propagation gages and optical methods.