A new technique for visual examination of the progressive development of fretting is evolved and found to be especially useful in following the progress of fretting from the initial stage to the later stages. The qualitative investigation, co-ordinated with a quantitative study in three different atmospheres, dry air, carbon dioxide, and helium, yielded results supporting the mechanism of fretting suggested by the authors in a previous publication. Visual observation also leads to the conclusion that chemical reaction, for example, oxidation, of metal with the environment takes place when the metal is being removed, or after it has been removed, from the surface.

The phenomenon of stick-slip, which manifests itself in the squeaking of rubbing surfaces and is of considerable practical importance, can be advantageously studied at very low sliding speeds. An apparatus has been developed in which a flat surface is driven at speeds on the order of 10−7 to 10−4 cm/sec, the driving force being a weight. The speed is controlled by the viscous drag of a paddle in a bath of pitch. There is no appreciable elastic restraint in this drive, so that stick-slip vibration of the moving surface does not occur. A stationary rider is pressed against the moving surface by a dead weight. The friction is measured by the elastic deflection of a ring, the stiffness of which controls the tendency of the rider toward stick-slip vibration. Results are briefly described.

Experimental work was carried out on the boundary lubrication of a copper-copper couple with pure cetane, palmitic acid solution of cetane, and some other organic materials. The purpose was to get information about α and μlube, which appear in the friction equation: μ=αμsolid+(1−α)μlube, by using two different kinds of copper surface, a clean surface, and an oxidized surface. α was found to be small with palmitic acid solution, and the estimated shear strength of palmitic acid was high under the examined condition. α and μlube seemed to be properties which are independent of each other. α is closely related to the attraction force between the lubricant and the substrate, whereas μlube is related to the complexity of molecular structure of the lubricant. A comparison was made of bulk-liquid and thin-film lubrication. μlube was smaller in thin-film lubrication than it was in bulk-liquid lubrication. This suggests that the frictional resistance may be partly contributed by liquid in the edge space around the real contact.

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