Rubber-toughened adhesives are ductile materials that exhibit extensive non-linear deformation before failure. It is possible to model this deformation using elastic-plastic materials models and, in conjunction with a finite element analysis, to predict stress and strain distributions in the adhesive layer in a bonded joint. Limitations in the suitability of three elastic-plastic models for describing the deformation behaviour of a rubber-toughened adhesive have been revealed using results from tension, compression and shear tests. A new model has been developed that takes account of the influence of the cavitation of rubber particles on yield behaviour under stress states where there is a significant dilatational component. This model is able to accurately predict behaviour in tension and compression from shear hardening data.
The cavitation model and the exponent Drucker-Prager model have been used with finite element analyses to calculate force vs. extension curves and stress and strain distributions in joint test specimens of different geometry. The determination of adhesive properties and model parameters required for the analyses is explained. Comparisons of measured and predicted force vs. extension curves for each joint geometry have enabled the onset of failure in each joint to be identified. Stress and strain distributions in the adhesive, calculated at the loading conditions where failure has initiated, have been used to explore the validity of different criteria for failure based on establishing a critical level of some component of stress or strain in the adhesive necessary to initiate failure.