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Abstract
A molecular dynamic simulation study is presented to compare the machining of monocrystalline and polycrystalline copper structures with a rigid diamond tool at atomistic level. The equivalent grain size is 6 nm for the polycrystalline copper structure, which consists of 32 single crystals (i.e., grains) in total. Four cutting conditions of 3-D orthogonal machining are simulated for comparison. The results show that for both monocrystlline and polycrystalline machining, cutting forces increase with the increase of depth of cut, and the stress levels in primary and secondary shear zones increase with the increase of machining speed. More importantly, smaller cutting forces are required to machine the polycrystalline structure than the monocrystalline structure for all cutting conditions. This also leads to the lower stress levels in shear zones. In addition, in polycrystalline machining, the tangential forces are higher than the thrust forces, while the opposite is observed for monocrystalline machining. The results can be attributed to the grain boundary sliding mechanism in the nanostructured copper workpiece.