Novel joint deformation models and their application to delamination fracture analysis

Abstract

Split beam type of fracture specimens is commonly used in the delamination evaluation of laminated composites. The compliance and energy release rate (ERR) of the specimens are examined in this study in the new light of the crack tip deformation. Three joint deformation models (i.e., the rigid, semi-rigid, and flexible joint models) describing the different degrees of crack tip deformation are obtained based on three corresponding bi-layer beam theories (i.e., the conventional composite beam, shear deformable bi-layer beam, and interface deformable bi-layer beam). Due to different considerations of the interface displacement compatibility in each bi-layer beam theory, these joint models, among which the semi-rigid and flexible joint ones are new, show three distinct levels of accuracy in predicting the crack tip deformation. By using these two novel joint models, the new terms, which are “missing” in the rigid joint model, are recovered for the compliances and ERRs of six common delamination specimens. As a validation, an asymmetric DCB specimen is examined by three joint models, as well as the numerical finite element analysis, and three distinct accuracy levels of the solutions are revealed again in comparison with finite element analysis. It is shown that the rigid joint model is the most approximate due to neglecting the crack tip deformation, the semi-rigid model provides better solutions due to partially inclusion of the joint deformation, and the flexible joint model is the most accurate because of the fully consideration of the crack tip deformation. The distinction on accuracy also indicates the significant effect of joint (crack tip) deformation on delamination specimen analysis. The novel semi-rigid and flexible joint deformation models presented in this study provide explicit closed-form solutions of fracture parameters which can be easily adopted in practice.