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. Finite element analysis (FEA) can be used with these models to predict stress and strain distributions in the adhesive layer in a bonded joint. At NPL, various elastic-plastic material models have been evaluated through FEA and experimental tests on different adhesive joint types.

In rubber-toughened adhesives cavitation occurs in the rubber particles when there is a significant component of hydrostatic stress. This cavitation gives rise to enhanced plastic deformation through shear yielding in the matrix adhesive between cavities. This cavitation process is not modelled by current elastic-plastic models. An elastic-plastic model that included cavitation was developed at NPL. This model has been code as a UMAT for use with the ABAQUS FE package. The model takes account of the replacement of rubber particles by an equal volume of effective cavities. This model is able to predict behaviour in tension and compression from shear hardening data (below left). Unlike other models, it also accurately predicts the change in Poisson's ratio with strain. Preliminary analyses showed that the cavitation model produced reasonable predictions of scarf-joint behaviour (below right). As well as improving the predictions of adhesive joint behaviour this model has been shown to accurately predict the deformation of plastic components under impact loading.

For more information, please contact Louise Crocker