Determination of mixed-mode I/II fracture toughness and bridging law of composite laminates

Accurate determination of the fracture toughness and the bridging law in a simple way is meaningful for the composite structural design. This study proposes a semi-analytical approach to calculate the mixed-mode I/II fracture toughness, and the crack opening/sliding displacements. Based on the relation between them, the mixed-mode I/II bridging law is obtained by using the J-integral theory. The obtained fracture toughness and distribution of the bridging stress show good agreements with test results, which illustrates the applicability of the semi-analytical approach. The obtained bridging law is further integrated into a tri-linear cohesive zone model for simulating the delamination behavior. Numerical load–displacement responses are consistent with experimental ones, further verifying the semi-analytical approach. Only experimental load and displacement data are necessary in this semi-analytical approach while specific equipment and tedious measurements on the delamination length and the relative crack opening/sliding displacement during the delamination tests are avoided, which makes the proposed approach simple and applicable for engineering application.