Rate-Dependent Large Strain Behavior of a Structural Adhesive

This paper describes the development of a nonlinear viscoelastic modelthat can account for rate dependence at large strains. The model wasbased on tensile and shear experiments on a urethane structuraladhesive. The most striking observation was that the stress-strainbehavior at large strains was rate dependent. As a result, a rate-dependent rubbery shear modulus was added to Popelar’s shear modifiedfree volume model. This was very effective in predicting ramp shearbehavior over a range of strain rates and temperatures. Thecorrespondence of model results and tensile data was reasonable below20% strain. At higher strains, the model over predicted the stresslevels for a given strain. This may have been due to the accumulation ofdamage, which has yet to be included in the model. The model was unableto capture the effect of salt water on the tensile behavior of theurethane.