Modification of statistical characteristics of friction surfaces in the process of running-in

A method of proposed how to calculate changes of statistical characteristic of friction surface in the process of running-in. Fatigue failure of the tallest microprojections is assumed to occur when surfaces run-in. A relationship has been established between the typical time when microprojections destroy and statistical characteristics of friction surfaces and parameters describing multicycle fatigue of coupled materials. An expression has been derived how the probability density of the heights of projections on contacting surfaces change in time. Calculations have revealed that running-in smoothes friction surfaces and strongly decelerates the rate of changes of the dispersity of the heights of projections. Pressure stabilizes, dispersion of pressure over actual contact spots reduces. It is proposed to assume the time of running in as the time after which the dispersion of projection heights practically ceases to change.