||An original experimental set-up, made of two coaxial rings in relative motion, a sapphire and steel, enabled temperature measurements on both sides of the third body at the friction interface. Hot spots have been identified and temperature gradient across the third body accurately measured. Infrared camera and thermocouples have shown to be an effective tool for this research.
Investigations conducted using SEM enabled detailed analysis of friction interfaces of both components, the sapphire and steel rings. Two types of third body (layers) have been identified, the compact, smooth micro-plates—where the actual contact occurs, and granular—which seem to accumulate in depressions or against material obstacles. There are also clear indications that the hot spots and depressions on steel friction surface are directly related. These areas of contact seem to be ‘shrinking’ in height after the application and complete component cooling.
The investigation of the third body phenomenon and its influence on interface temperatures has direct relation to the observations made in automotive disc brakes.
A thermal numerical model, which was also developed, introduced the third body as a uniform layer with energy storage and conduction. The obtained thermal gradients seem to be accurate, when compared with measurements conducted. The results are also similar to those found in literature. In addition, when only a fraction (1/1000th and 1/2000th) of the total nominal friction surface was considered to be in the actual contact, experimental temperature results were exactly within the predicted range. This indicates that the actual contact area varies during application.