Investigation on the in situ interfacial Mode II fracture toughness of the 3D woven composites

The interfacial mode II fracture toughness GIIC is an important parameter that significantly affects the damage evolution of the composite materials under shear load. Traditional interlaminar fracture toughness test methods are no longer suitable for the measurement of interfacial fracture toughness within the 3D woven composites (3DWCs) because these methods cause yarn breakage, which could overestimate the fracture toughness by more than ten times. To this end, this paper proposes a new method to obtain the in situ interfacial GIIC of the 3DWCs. The stable propagation of the mode II crack along the interface was achieved by the unique specimen design. A highly restored finite element (FE) model of the specimen was established, and the virtual crack closure technique (VCCT) was adopted to calculate the interfacial GIIC. The rationality of the experiments and the validation of the simulation have been carefully demonstrated. The values of GIIC obtained from three different off-axis angles are consistent, which proves the effectiveness of the proposed method.