Systematic molecular dynamics study of load, speed, and temperature effects on atomic stick-slip friction

Zhenjia Gao, Purdue University

Abstract

Nanotechnology is leading to rapid development of mechanical components whose structure and function are controlled at the atomic scale. Friction plays a critical role in such devices, and one of the primary challenges for their design is that the moving interfaces often exhibit atomic stick-slip friction. It can be difficult to directly compare stick-slip friction results reported by different groups because the models used vary greatly and reported friction parameters are often not the same. There has been little consistency between trends reported in such studies. We have neither a complete nor a consistent picture of how operating conditions affect atomic stick-slip friction. Therefore, in this paper, we have performed a systematic study on the effects of load, speed, and temperature. We predict their effects both individually and in combination to clearly explain the role they play in atomic stick-slip and provide a fundamental understanding of why those dependencies exist. We performed molecular dynamics simulation of an Ag tip sliding on a Cu substrate. The interactions between all atoms in the simulation were modeled using EAM potentials which were recently developed based on first-principles data and fitting to experiment. All simulations were performed using the IMD molecular dynamics simulation package. The simulations were run in the NVT ensemble with the temperature control being performed using a Nos´e-Hoover thermostat. We performed simulations at sliding velocities of 1, 5, and 10 m/s, average normal stresses of 0, 100, 200, 300, 400, and 500 MPa, and temperatures of 10, 100, 200, 300 and 400 K. Simulations were run for all possible combinations of the loads, speeds and temperatures specified above. We then determined the average, minimum and maximum values of the shear stress as functions of velocity, load, and temperature. The atom diffusion was also investigated to show what happened during stick-slip under different operational conditions. Finally, the dislocation theory was used to explain the stick-slip. The common neighbor method (CNA) was used to show the crystal structure alternating between face center cubic (FCC) hexagonal close packed (hpc). The displacement and shear stress were measured in the contact area to show why and how the stick-slip happened.

Degree

M.S.E.

Advisors

Martini, Purdue University.

Subject Area

Mechanical engineering

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