A semi-analytical method for the determination of fracture toughness and bridging law in ELS test

Fracture toughness and bridging law are necessary for characterizing the delamination behavior with the effect of fiber bridging. Accurate determination of them in a simple way is particularly important for the design of composite structures. The end-loaded split (ELS) method, which can obtain stable delamination growth, has been applied in the ISO 15,114 standard to measure the mode II fracture toughness. However, geometric nonlinearity and difficulty on the crack observation are unavoidable. To deal with those problems, a semi-analytical method is proposed in this study for determining the fracture toughness and the bridging law. Predictions from the semianalytical method are consistent with experimental results of CFRP and GFRP laminates. Furthermore, numerical modelling is performed based on a tri-linear cohesive zone model which integrates the determined bridging law. Numerical load-displacement responses have good agreements with the experimental ones, which illustrates the applicability and accuracy of the proposed method. The proposed method overcomes the problem of real-time monitoring of the crack growth length and the relative sliding displacement at the pre-crack tip, and considers the correction factors to solve the nonlinear problem caused by the large displacement, which is simple and efficient for practical application.