Analysis of the crack resistance of adhesive joints using the finite element method and the cohesive zone model

The method of cohesive zones allows us to evaluate the stability of the material, both to the beginning of the growth of an existing crack, and to the occurrence and development of defects in places of stress concentration. The ability to reliably determine the destruction parameters of adhesive joints (AJ) and predict the behavior of structural elements with their use under loading is an important task for the aircraft industry. It is proposed to use in the finite-element 3D model of stratification according to mode I of the AJ sample in the form of a two-console beam, the length of the cohesive zone (lcz) calculated from the experimentally determined parameters — the local interlayer cohesive strength of the material (σIC) and the intensity of release of elastic energy (GIC). The calculated length of the cohesive zone is applied in the model to calculate the minimum number of finite elements at their optimal size, which ensures higher accuracy of calculations of the main parameters of crack resistance of samples of laminated carbon fiber while minimizing the amount of calculations. The objects of study were AJ sheets of aluminum alloy D-16, which were glued together with dispersion-filled adhesives of industrial grades EPK-1, VK-9, and K-300-61, which are widely used as structural adhesives in the production of aerospace structures. As a result of the research, the main parameters of crack resistance were determined and the optimal length of the final cohesive element was selected, and the resulting model accurately describes the process of crack growth. The results obtained correlate well with the results of experiments.