Societies and Academies

Abstract

LONDON. Royal Society, March 19.—Sir William Hardy and Ida Bircumshaw: "Boundary lubrication: plane surfaces and the limitations of Amontons' law (Bakerian Lecture). When the slider has a plane face the coefficient of friction is a function of the load, decreasing as the load increases, until a point is reached beyond which the coefficient is independent of the load. When it has a spherical face, the coefficient is always independent of the load. The coefficient is a measure of the efficiency of the lubricating layer with respect to one variable-the load. Recollecting that the pressure between the bearing surfaces must be very great when the slider has a spherical face, the above results show that with low pressure the efficiency of the lubricant increases as the pressure increases until a limit is reached, beyond which Amontons' law holds. It is probable that, during the first period, when Amontons' law does not hold, the slider is floating on a layer of lubricant the thickness of which is a function of the pressure, whilst in the second period, where Amontons' law holds, all lubricant which can be squeezed out has been squeezed out, and a layer of constant molecular composition has been reached. In the first period friction is adjusted to the load by variations in the thickness of the layer of lubricant, and in the second period by the elastic forces between the atoms.