Study of nanocontact and incipient nanoscratch process using the quasicontinuum method

As a developed multiscale method, the quasicontinuum(QC) method is introduced to investigate the process of nanocontact and incipient nanoscratch between a large tip and a single crystal aluminum substrate with low computation cost. Through an analysis of the simulation result, microscopic mechanisms of deformation are studied and revealed. In the nanocontact process, it is found that the normal force of the tip shows stair-like increase with increase of indentation depth in the elastic deformation stage. The asymmetrical strain energy accumulation under both sides of the tip beneath substrate surface produces small fluctuations in friction force at the stage of plastic deformation. In the nanoscratch process, the elastic recovery of the scratched surface starts to appear obviously when the scratching distance is of 3.8 nm with the glide band expanding and localized strain sharply increasing. As a result, part of the dislocations underlying surface extend to the surface and form twinning deformation. Meanwhile, the crystal lattice deep beneath the surface undergoes severe distortion and rotation. A comparison of friction coefficient for the scratch process is also made between theoretical values and our numerical results. The effect of elastic strain energy feedback on friction coefficient in elastic recovery of the scratched surface is quantitatively analyzed.