A semi-analytical model for the mode II fracture toughness of multidirectional composite laminates

Mode II delamination is one of the most common failure types in laminated composite structures. Accurate determination of mode II fracture toughness is important for structural design and analysis. This study attempts to establish a semi-analytical model for determining the mode II fracture toughness of multidirectional (MD) laminates. Six kinds of CFRP laminates with different interfaces (0 degrees/0 degrees, +22.5 degrees/-22.5 degrees, +45 degrees/-45 degrees, 90 degrees/90 degrees, 0 degrees/45 degrees, and 0 degrees/90 degrees) are designed and tested using end-notched flexure set-up, to provide experimental data for model validation. The effects of interfacial angles on fracture toughness are investigated. The fracture toughness is divided into two parts, including the fracture work for pure delamination along the interface, and that for matrix damages related to the interfacial angles and their interactions. Combining with mechanical analysis and numerical results of the intra-ply damage area in the front of crack tip, the detailed form of the semi-analytical model is derived. This model has a clear correlation with the interfacial angles. Test results are in good agreements with those from the semi-analytical model, which proves the applicability of the model. In addition, morphologies of delamination paths showing migration and fiber bridging are discussed, which provides extra justification for the proposed model.

Automated summary

This study establishes a semi-analytical model for determining the mode II fracture toughness of multidirectional laminates. The effects of interfacial angles on fracture toughness are investigated and the model has a clear correlation with the interfacial angles, showing good agreement with test results.