The resolution dependence of measured fractal characteristics for a real un-dismantled electrical contact interface

Abstract

An electrical contact interface is visualized by rendering “contact maps” from X-ray Computer Tomography (CT) images without the need for dismantling the specimens. The contact maps consist of approximately 1500 pixels × 1500 pixels with each pixel relating to an 8.0 μm × 8.0 μm × 8.0 μm volume at the interface. The specimens consist of bolting a cable lug to a printed circuit board. The resolution dependence of measured fractal characteristics is studied for a contact interface with a normal force of 1.6 kN. The total mechanical area of contact, A m, is found to be invariant with resolution whereas the largest contact spot size, A L, is found to decrease with higher resolution. The number of spots on the apparent area of contact is found to increase with resolution but a spot increasingly has areas of non-contact within itself at higher resolution. The fractal dimension, D, of the spot area is found to converge to 1 at lower resolution consistent with self-affinity behaviour. At higher resolution D converges to a value <2.