Determining subsurface stress distributions in tribological samples from dislocation cell sizes in low energy dislocation structures

Abstract

The stress distribution that caused any observable low energy dislocation structure can be inferred from the scale thereof. For dislocation cells, the empirical formula τ ≈ 10 Gb/ L, with τ the resolved shear stress, L the average dislocation cell diameter, G the shear modulus and b the Burgers vector, is especially useful in this regard. As an example, it was applied to the subsurface dislocation cell size distribution underneath the wear scar on a copper foil 0.1 mm thick that had been glued onto a steel rod and then tested in a crossed-rods apparatus. The result confirms the theoretical expectation that the minimum required thickness, when foils are used to simulate the tribological behavior of bulk material, is at least twice, and more safely three times, the average contact spot diameter.