Novel Bi-layer Beam Theories for Delamination Fracture Analysis

Abstract

Bi-layer beam-type fracture specimens are commonly used to evaluate delamination fracture of laminated composites. In this study, two newly developed bi-layer beam theories (i.e., shear deformable and interface deformable) are applied to the delamination fracture specimen analysis, and the improved solution for compliance and energy release rate (ERR) of the specimens are obtained 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 examined based on the 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 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. It is shown that the rigid joint model is the most approximate one 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 shear deformable and interface deformable bi-layer beam theories recently developed by the authors prompt semi-rigid and flexible joint deformation models, respectively, which greatly improve the solutions of fracture parameters, and they shed new light on the effect of crack tip deformation on delamination fracture analysis.