Interlaminar Crack Propagation Analysis of ENF Specimens Based on the Cohesive Zone Model

Abstract

Based on classical laminated plate theory and cohesive zone model, a theoretical model of general delamination cracked laminates is established for crack propagation of pure mode Ⅱ ENF specimen. Compared with the conventional beam theory, the proposed model fully consideres the softening process of the cohesive zone and introduced the nonlinear behavior of ENF specimens before failure. The predicted failure load is smaller than the beam theory and closer to the experimental data in literature. Compared with the beam theory with only fracture toughness considered, the proposed model can simultaneously analyze the influence of interface strength, fracture toughness and initial interface stiffness on the load-displacement curves in ENF tests. The results show that the interface strength mainly affects the mechanical behavior of specimens before failure, but has no influence on crack propagation. The fracture toughness is the main parameter affecting crack propagation, and the initial interface stiffness only affects the linear elastic loading section. The length of cohesive zone increases with the increase of fracture toughness and decreases with the increase of interface strength. The effect of interface strength on the length of cohesive zone is more obvious than fracture toughness. When the tip of the adhesive zone reaches the half-strength of the specimen, the length of the adhesive zone decreases to a certain extent.