Simulation of asperity plowing in an atomic force microscope Part 1: Experimental and theoretical methods

The plowing of a soft workpiece by a hard tool asperity is recognized as a fundamental tribological problem and key contributor to friction and wear in bulk metal forming processes such as rolling and extrusion. However, experiments on an asperity scale have been difficult to perform to date since measurements of plow track geometry, the forces required to create the plow track, and the plowing speed must be made over a very small length scale. It is therefore the purpose of this paper to describe a new experimental method that stimulates single asperity plowing of a soft workpiece material in an atomic force microscope. Using a sharp diamond indentor as a tool asperity, plow tracks were formed in 99.99% pure aluminu which was chosen to demonstrate that the method gave repeatable results over a range of forces and speeeds. A mathematical model of plowing was modified to take the plow track geometry, the measured normal and plowing forces, and the plowing speed as input variables and provide a measure of the friction factor (and hence shear stress) along the indentor-workpiece interface, as well as the workpiece flow strength. The companion paper presents the results of asperity plowing experiments (based upon the methods presented in the present article) on specific aluminum alloys of differing hardnesses.