Effect of Strain Gradient on Elastic and Plastic Size Dependency in Polycrystalline Copper

This study unveils the presence of size effect not only in the plastic regime but also in the elastic regime under strain gradient. This discovery emerges from a comprehensive set of experiments encompassing micro-cantilever bending and micro-pillar compression tests. Subsequent finite element analysis serves to not only expose the limitation of classical continuum theory but also to effectively demonstrate the enhanced predictive capabilities of couple stress theory in both elastic and plastic size effects. To incorporate couple stress theory, a systematic and rigorous finite element analysis-based optimization was devised to determine length scale parameters, which are additional material properties in couple stress theory. The resulting length scale parameters for polycrystalline copper were found to be 0.536 and 0.669µm in the elastic and plastic regimes, respectively. The study also explores the physical interpretation of these length scale parameters in both regimes.