Experimental and numerical studies of coupling size effects on material behaviors of polycrystalline metallic foils in microscale plastic deformation

A more comprehensive investigation of size effects is essential for the design and optimization of micro-metal forming processes. In this work, the micro-tension of polycrystalline copper foils with different thicknesses and grain sizes is investigated using both experimental and numerical techniques. A nonlocal physically based crystal plasticity (CP) FEM using the densities of statistically stored dislocations and geometrically necessary dislocations as the internal state variables is applied to simulate the micro-tensile operations. The micro-tensile experiments show that the mechanical properties of copper foils are affected synthetically by the grain size, sample size, and crystallographic orientation. The simulation results show good agreement with the experimental results in terms of flow stress. In addition, the first order and second order size effects are well captured. The research finds that the number of grains across the thickness is a prominent factor to affect the intergranular and intragranular deformation heterogeneities, which play a key role in controlling the formation of shear bands, the strength, and failure modes of materials at microscale. The modeling gives access to more physically based details about the microscale plastic deformation, and shows the potential of using nonlocal physically based CPFEM in the investigation of micro-metal forming.