Surface roughness evolution during early stages of mechanical cyclic loading

•A dislocation dynamics study of surface roughness evolution under cyclic loading.•Crystals of different sizes and initial dislocation densities were simulated.•Small crystals show surface slip localization in the form of thick surface steps.•Maximum surface step height increases with the square of the crystal size.•Surface cross-slip plays a significant role in surface roughness development.

The effect of crystal size and initial dislocation density on surface roughness evolution in FCC single crystals during the early number of cycles of mechanical cyclic loading is investigated using three dimensional discrete dislocation dynamics simulations. Crystals having size less than 2 μm show early development of surface slip localization, while larger ones show a more uniform distribution of surface steps. The surface roughness is found to increase with increasing number of loading cycles with larger crystals showing a high roughening rate compared to smaller crystals. Double cross-slip is observed to be the main mechanism that derives the development, growth and thickening of surface slip bands. The maximum surface height, which is an indicator of the surface stress concentration is observed to increase linearly with the number of loading cycles and quadratically with the crystal size for the simulated number of cycles. Finally, the results are shown to be in agreement with experimental results and provide further physics based understanding on the mechanisms controlling the evolution of the surface roughness.