Nanoscratching of Polycrystalline Copper Examined Through Strain Gradient Crystal Plasticity E. Günay∗, M. Özdemir, T. Yalçinkaya Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Türkiye ∗ enes.gunay@metu.edu.tr Keywords: Crystal plasticity, scratching, size effect Nanoscratch tests, where a specimen is scratched with a nano-scale indenter, have been recognized as a significant tool for assessing the mechanical and tribological attributes of materials. This study investigates the deformation mechanisms and material response during nanoscratch test of polycrystalline Cu through finite element method utilizing a lower-order strain gradient crystal plasticity framework. Test results such as the reaction forces on the indenter, apparent friction coefficient, and pile-up topography change with different grain diameters and different crystal textures. This behavior is examined with the aforementioned strain gradient theory where the density of geometrically necessary dislocations is calculated to get size-dependent material response. The crystal plasticity framework is implemented into ABAQUS as a user material subroutine (UMAT) and validated through comparisons with single crystal Cu experiments in the literature. A 3D mesh is generated to model the scratch specimen at grain level. A Berkovich indenter causes deformation on the specimen using displacement-controlled boundary conditions, as opposed to force-controlled experimental conditions. Scratch simulations are carried out on copper specimens with average grain diameters between 4 µm - 8 µm and crystal orientations distributed randomly or aligned with the scratch direction. 35
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