RESIDUAL STRESS EVALUATION IN MACHINED SURFACES OF COPPER BY MOLECULAR DYNAMIC SIMULATION

摘要

Residual stresses in machined surfaces are often regarded as a determining factor of component service life. However, little work has been conducted to investigate the distribution of residual stresses in machined surfaces at nano-scale. In this paper, an MD simulation study is performed to study the residual stresses in machined surfaces of single crystal copper by diamond tools. We adopt a fixed cutting speed of 400m/s, vary depth of cut from 0.5nm to 1.5 nm, and change the tool rake angle from -30° to +30°. The results are then compared and discussed in the following aspects. First, it is found that both tool rake angle and depth of cut affect the morphologies of the formed chips, and as well as the cutting force evolution during machining process. Second, the normal residual stress in the tangential direction is more significant and has a clearer pattern than those in other directions for all the simulation cases. As such, the focus of the study is on this particular stress component. Third, with the increase of depth of cut, the maximum tensile residual stress decreases, and the residual stress becomes compressive at a shorter distance into the machined surface. Also, the use of negative rake angle makes the residual stress overall more tensile when closer to surface, and more compressive as the depth into surface further increases. It is actually consistent with traditional metal machining theory. The use of negative tool rake angle requires a larger thrust force, and this in turn overall makes the residual stress more compressive.