In situ measurement of contact area in coated surfaces

Abstract

Few attempts to directly measure the contact area of solid bodies have been made. In fact, it shapes up as a complex problem, because there usually is no direct access to the relevant surface of the experimental setup. Promising work in electrical measurement of the contact area by relating it to the contact resistance has been made by Bowden, Tabor and Holm from the 1930s on. This method has some restrictions due to the mutability of contamination layers involved in the most sensitive part of the setup. It is suggested to reintroduce observation of the contact area by electrical measurement, taking advantage of recent progress made in thin film coatings. By use of low conductive coating materials like oxides or carbon based films the contact resistance is increased by several orders of magnitude. The measured value of contact resistance in low conductive coated samples is within a range to be measured nearly independent of parasitic inductions like usual contaminations. Current work is on quasi-statical experiments and calibration. The first results joining earlier efforts are reported and the experimental setup, preparation method, advantages and known limitations are put up for discussion.