Fracture analysis of plastically-deforming adhesive joints via the cohesive zone model

The cohesive zone model is used in the analysis of fracture of plastically-deforming adhesive joints. In this model the adhesive layer is replaced by a traction-separation law that captures the essential features of the fracture. For each mode, (I or II), the traction separation law is characterized by two parameters: the peak stress (normal or shear) supported by the adhesive layer, and the intrinsic toughness (Γ₀I or Γ₀ II).; The effects of the joint geometry on the fracture parameters are investigated. The variation of the peak opening stress with the energy-release rate in the adhesive layer of a double-cantilever beam joint is computed via continuum finite element calculations. The cohesive zone model is then implemented using these self-consistent pairs of fracture parameters. For the particular adhesive systems investigated it was found that increasing the levels of constraint resulted in elevated peak stresses in the layer, yet the intrinsic toughness remained essentially unchanged due to a corresponding reduction in critical displacements in the adhesive. Similarly, it was found that the peak stresses in the adhesive layer increased markedly with increasing strain rate yet the intrinsic toughness remained constant.; The asymmetric double-cantilever beam joint fractured via a wedge and the single lap-shear joint are investigated with the cohesive zone model. Using fracture parameters obtained independently for each mode, the numerical predictions for the peak loads, load-displacement curves and deformed shapes of the double-cantilever joints were in excellent agreement with experiments. For the elastic-plastic lap-shear joint a rigorous parametric analysis in terms of a number of non-dimensional groups is conducted. Elastic and plastic limits were seen at appropriate limits of the non-dimensional parameter range. Asymptotic limits for the strength in terms of joint overlap and overall length were seen, resolving the issue of specimen size-dependent strength. Finally, uneven thickness plastically-deforming lap-shear joints are investigated. It was seen that their failure is very similar to the plastic peel test. For several important cases the numerical predictions were compared to experimental results, all showing very good agreement.