Development of corrugation as a result of varying normal load

Rail corrugation is initiated by a varying normal load with constant tangential load; by a varying tangential traction with constant normal load; or, occasionally, by a combination of the two. The types of corrugation proposed by Grassie and Kalousek [S.L. Grassie, J. Kalousek, Rail corrugation: characteristics, causes and treatments, J. Rail Rapid Transit, Proc. Inst. Mech. Eng. 207F (1993) 57–68] can usefully be categorized in this way. A simple expression is derived here for the growth rate of those types of corrugation that develop initially from varying normal load. It is shown that the initial growth rate is typically less than or the same order as the steady-state wear rate. This is similar to measured rates of corrugation development on an operating railway. The mechanism considered here corresponds essentially to a “free response” that reflects the dynamic behaviour of the system. While the mechanism could readily be included in a feedback loop that reflected also the “forced response” arising from development of the corrugation itself, this has not been done here.