Continuum damage modelling of environmental degradation in joints bonded with EA9321 epoxy adhesive

A mesh independent continuum damage model has been proposed to predict the residual strength of adhesively bonded joints by introducing a displacement-based damage parameter into the constitutive equation of damaged materials. Joints bonded with a ductile adhesive EA9321 were studied for a range of environmental degradation. The moisture dependent damage parameter for EA9321 was calibrated using an aged, mixed-mode flexure (MMF) test. The parameter was then used without further modification to model failure in aluminum and composite single lap joints (SLJ) bonded with the same adhesive. The FEA package ABAQUS was used to implement the coupled mechanical-diffusion analyses required. The elastic-plastic response of the adhesive and the substrates, both obtained from the bulk tensile tests, were incorporated. A von Mises yield model was considered and both 2D and 3D modelling were undertaken and the results compared. The predicted joint residual strengths agreed well with the corresponding experimental data and the damage propagation pattern in the adhesive was also predicted correctly. The mesh independence of the model was demonstrated. This continuum damage model provides a means of predicting environmental degradation in ductile adhesive bonded joints, where failure is predominantly within the adhesive layer.