High strain rate material models for epoxide and silicone adhesives

This work calibrates an empirical material model for a silicone adhesive by finding the best fit to experimental data over a range of high strain rates. Following the literature precedent of using the empirical nature of the Johnson-Cook model for epoxide modelling, the Modified Johnson-Cook material model is repurposed to enable this for silicone adhesive without the need for a new user-defined material or further development within commercial finite-element method (FEM) software, which significantly reduces the complexity of the implementation. To the authors’ knowledge, such a model is not available anywhere in the open literature. The developed material model is verified against experimental split-Hopkinson pressure bar (SHPB) data of ceramic/steel material couples bonded with a silicone adhesive. This work also tests, by numerical simulation, whether several material models, previously used in the literature for high strain rate modelling of epoxides, can replicate SHPB test data of ceramic/steel material couples bonded with such an adhesive. For silicones, the Modified Johnson-Cook material model, with the calibrated parameters determined in this work, is shown to give good agreement with the results of SHPB testing where the simulation predicted 76.2% transmitted strain, closely matched the experimental value of 70.4%. For epoxides, both the Plastic-Kinematic material model with Cowper-Symonds strain rate scaling, and the Johnson-Cook material model with the Grüneisen equation of state, give good agreement with the results of SHPB testing, with 95.5% and 97.6% transmitted strain respectively, versus the experimental value of 91.2%.