Size effect in microcompression of epoxy micropillars

Understanding the size effect on the mechanical properties of polymers is of great importance for a robust design of today's polymer-based micro-devices. In this article, we propose the microcompression approach based on the focused ion beam milling technique to probe the possible size effect on the mechanical behavior of epoxy micropillars. By systematically reducing their size from the micrometer to submicron scale, these micropillars display a constant elastic modulus in their inner cores while exhibit an increasing yield and fracture strengths with decreasing diameters. Such a size effect is attributed to the intrinsic material heterogeneity at the submicron scale and the presence of a nano-scale stiff surface layer wrapping around the micropillars. This study provides a theoretical framework for the microcompression analysis of polymerbased micropillars, paving the way for future study of a variety of polymer-based advanced material systems by microcompression.