Fiber bridging mechanism in moisture-induced mode I delamination in carbon/epoxy composites: Finite element analysis and experimental investigation

Prolonged exposure of fiber reinforced composite structures to high moisture and temperature in outdoor environment could lead to the degradation of mechanical properties of the materials. To provides reliable prediction of the delamination behavior as the moisture progressively ingresses into the composites, we proposed a Bilinear-Exponential Traction-Separation (BETS) law-which can account for the fiber bridging mechanism-for investigating the mode I delamination of unidirectional carbon fiber reinforced epoxy composite laminates in wet states. Finite element analysis (FEA) of the delamination model was conducted to evaluate the effects of moisture content on the global force-displacement curves. A cohesive zone model (CZM) was used to describe the delamination behavior at the interface. With regard to the force-displacement curves, the BETS law agrees well with results from experimental study (using the double cantilever beam testing on the wet specimens) at both the elastic and failure regions. The delamination model governed by the BETS law also showed good agreement with the crack length versus the crosshead displacement. The FE model that considered the inputs from the BETS law yielded prediction about the evolution of the damage parameter and crack growth profile. In particular, the predicted crack extension increases linearly with increasing crosshead displacement. The proposed BETS law has the advantage of not requiring crack growth monitoring during experiment, and only one fitting parameter was needed to describe the bridging law at different moisture content levels.