A MULTISCALE MODEL OF RATE DEPENDENCE OF NANOCRYSTALLINE THIN FILMS

The rate dependence of nanocrystalline thin films is modeled as the competition between two microstructural deformation mechanisms: intra-granular crystal plasticity and inter-granular diffusion-based grain-boundary sliding. The analysis is conducted within the framework of a multiscale finite-element scheme based on the mathematical theory of homogenization. The key parameters entering the description of the grain interior and grain boundary models are calibrated through comparison with high strain rate tensile tests and creep experiments, respectively. The prediction of the viscoplastic response of gold thin films is validated against tensile test measurements obtained over seven decades of strain rate. The relative contribution of the microstructural damage mechanisms is analyzed.