XFEM-based model for simulating zigzag delamination growth in laminated composites under mode I loading

Interfaces adjacent to a 90° ply in laminated composites show a typical zigzag path during the mode I delamination propagation process, which is considered to be closely related to high propagation values of fracture toughness. DCB (double cantilever beam) tests of specimens with a starter crack inserted into two 90° mid-layers were carried out, during which the zigzag delamination growth and pronounced R-curve behavior were obtained. To simulate the zigzag delamination propagation path, four XFEM-based delamination growth models were proposed which were comprised of a crack initiation model and a crack propagation model, respectively. In the framework of the delamination growth model, a new crack initiation model was developed, which took a quadratic criterion as the crack initiation criterion and the direction orthogonal to the maximum principal stress as the crack growth direction. Based on the mechanism of the delamination resistance, four crack propagation models considering whether the delamination follows a pure or mixed mode damage evolution law and whether a constant or varying critical fracture toughness dominates the damage evolution were introduced. By comparing the predictions from the four delamination growth models and the experimental results, the mode I delamination mechanism with a zigzag path was investigated. The delamination growth model that adopted a critical fracture toughness function and the mixed mode damage evolution law showed the best agreement with the experimental results and was recommended.