Material modelling for rate-dependent adhesives

Development of rate-dependent constitutive models for polymeric adhesives is essential for carrying out meaningful stress analyses of bonded structures subject to sustained and fluctuating loads. This paper presents a complete range of experimental data for a typical adhesive system including constant strain rate, creep and recovery in tension and, in a number of cases, compression as well. Fundamental relationships have been defined that are valid across the entire experimental domain. We then investigate how such data can be modelled using the advanced materials models that are currently available in most commercial FE codes. The rate-dependent yielding elasto-plastic models appear to be more universal than the power law creep models but even these are shown to be deficient. State of the art, unified theory, visco-plastic models are then reviewed and it is shown that these offer much potential. A method for determining appropriate model parameters has been outlined and the parameters for this particular adhesive are given. Good fits have been found for much of the experimental data and areas for improvement have been identified.