SIMULATION OF CRACK GROWTH IN ADHESIVELY BONDED JOINTS VIA COHESIVE ZONE MODELS

Adhesively bonded joints have shown great advantages in the aerospace industry when compared with traditional mechanical fastening methods. These types of joints allow to reduce the overall structural weight, improve the fatigue life characteristics due to reduction of stress concentrations (uniform stress distribution), smooth external finish, sealed surfaces, and many others. However, one of the main concerns with these joints is their characterization under fatigue loading, i.e., a comprehensive study of crack growth which will allow the development of standardized tests and certification in the aerospace sector. At the moment, their certification for primary structures requires that critical disbond be prevented by proper design. To this end, Disbond Arrest Features (DAFs) have been tested as a mean to improve the fatigue resistance of bonded joints. In this work, the authors developed a numerical model to assess fatigue disbonding under mixed-mode loading, a condition which is frequently encountered in adhesive joints. The model was based on a cohesive zone formulation, which was implemented via userdefined subroutines UMAT in the finite element software Abaqus. Mixed mode disbonding was modelled through the Bürger’s modification of Paris’ law. Two test cases were simulated: a double cantilever beam (DCB) specimen and a modified cracked-lap shear specimen with a bolted DAF. The results of the simulations were compared with experimental data from previous tests, showing that the model is able to reproduce the observed fatigue disbonding and capture the disbond arrest provided by the DAF.