Creep forces and strain of the material in wheel/rail contact from today's point of view

Slip occurs, whenever tractive and braking forces are transmitted between the wheels of railway vehicles and the rails. This produces high temperatures in the contact surfaces. They can be easily calculated in the case of smooth surfaces, because heat conduction is one-dimensional. In the realistic case of rough surfaces, there are much higher values of pressure in the asperities. While the influence of roughness on contact temperature can be neglected at first glance, the initial slope of creep force curves is significantly reduced. If we assume that the friction coefficient depends on temperature, there exists consequently an interaction between friction and temperature, which explains the reduction of creep forces at higher values of slip plausibly. Thermal stresses can have the same order of magnitude as contact stresses due to normal and tangential forces. This increases the strain of the material considerably, particularly in the rail.