Adjusting for Running-in: Extension of the Archard Wear Equation

The Archard equation is widely employed to predict wear in engineering practice, but its use is usually restricted to the cases of sufficiently long wear duration, so the transient running-in behavior can be neglected with respect to the steady-state wear. To address this problem, here the steady state wear equation is extended into the running-in regime based on the bearing ratio curve representing the initial surface topography. This approach is verified using a unidirectional dry sliding of steel against PTFE and the extended equation is shown to be able to predict service life or to obtain wear coefficients regardless of the test duration if the initial surface topography is defined. It is also found that the bearing ratio curve can be efficiently approximated using the logistic function calibrated by four standard surface roughness parameters. This approximation proves to be more accurate than the widely used Gaussian normal distribution function.