Brittle matrix composites with heterogeneous reinforcement: Multi-scale model of a crack bridge with rigid matrix

Abstract A mechanical multi-scale model describing the relationship between the crack-opening and composite bridging stress in brittle matrix composites with heterogeneous reinforcement is introduced. Unlike currently utilized models, it is able to reflect the heterogeneity of fibrous reinforcement. Mechanical, geometrical and bond properties of individual fibers (e.g. fiber surface roughness, radius, strength) are defined as random variables. The functional dependency between these random variables and the fiber stress within the composite cross-section is introduced using local equilibrium equations. The response of the composite to an applied uniaxial tensile load is evaluated by averaging the fiber stress contributions in a crack bridge. In particular, the model describes the behavior of a single crack bridge in a composite assuming the matrix to be rigid. The fiber bridging action is represented using the shear-lag model. Upon fiber rupture the global load sharing for stress redistribution is considered. With these assumptions the rules for asymptotic Daniels’ fiber-bundle models can be applied for the evaluation of macroscopic crack bridge behavior. We use the model to illuminate the effect of selected sources of heterogeneity (fiber breaking strain, fiber radius and bond strength) on the crack bridge response and to approximately predict the ultimate state of a multiply cracked composite. The model constitutes a basis for the multi-scale simulation of the strain-hardening response of brittle-matrix composites.