Characterizing Cohesive Zone Parameters to Model Crack Growth in Composite Materials

Abstract

CFRP is gaining interest in several industries such as aerospace, sports, and oil field. When this material is assembled, the adhesive is considered a preference over screws and fasteners as screws holes can lead to matrix delamination. Prior applying an adhesive, surface pre-treatment is done to enhance bonding. Due to the complexity of the composite material namely in complex geometry, one can consider finite element analysis as an optimum method to model the material behavior. Failure of crack growth under cyclic loading is typically modeled using the CZM. However, finding the constitutive behavior parameters is considered challenging. In this work, the maximum stress, which is difficult to calculate experimentally, is estimated using the virtual closure technique (VCCT) as it is considered less complicated and costy than the conventional methods. The VCCT is a finite element method that is employed to simulate monotonic crack growth. From this model, the maximum stress is recorded and used as the maximum traction stress in the cohesive zone model (CZM) to simulate fatigue crack growth. The bilinear traction separation law was employed to simulate the cohesive process zone. To calibrate the model results, an experiment is conducted on two samples those were treated by two different methods. One sample has a sandblasting surface pre-treatment and the other is pre-treated by peelply. Each pre-treatment enhances different material toughness and hence validity of the results if supported. Both samples were tested under both static and cyclic loadings. The maximum energy release rate and the crack length were selected as comparison parameters between the models results and the experimental observations. Overall, it was noticed that the results are considered having reasonable fit.