Static friction coefficients for mechanical and structural joints

Abstract A review of available data on static friction of steel is presented. This is directed towards obtaining coefficients of friction applicable to structural connections, particularly those subject to vibratory loading. The data are found to be inadequate and widely scattered, showing some dependence on normal pressure. Using a new type of friction apparatus a programme was undertaken to clarify the relationship between static friction coefficient and contact pressure, and also to generate data relevant to mechanical connections. Results are presented both for machined surfaces and for those commonly encountered in structural work. Coefficients of static friction for dry mild steel surfaces under nominal contact pressures between 100 and 10,000 p.s.i. are numerically less than those usually quoted in the literature. Tests were also conducted to measure the coefficient of static friction under dynamic (sinusoidal) in-plane loading. Results indicate that this may be different from that obtained under purely static loads. This would significantly affect the break-away behaviour of friction connections under vibration.