The mechanism of rolling contact fatigue is complex and many factors have to be considered. Surface roughness and the presence of surface defects are known to be important factors. The aim of this project is to investigate the effect of surface defects on rolling contact fatigue of wheel/rail steels by finite element analysis and using a twin-disc rolling-sliding test machine.
A two dimensional plane strain, line contact elastic plastic finite element model is developed to simulate rolling contact in the presence of a surface indentation. Calculations also have been performed for different slopes of the indents to study the effect of indent geometry. It is shown that the introduction of the indentation on a smooth surface provokes more severe local stress concentration.
The damage effect is caused mainly by the results of high surface pressure and high equivalent plastic strain around the shoulders of indentation. Experimental study into effects of surface defects on rolling contact fatigue of wheel/rail steels has been undertaken on a twin-disc rolling-sliding test machine.
Furrows and dents were artificially introduced into the disc surfaces, and surface micro cracks and pits were monitored by means of surface replication. The results showed that artificial dents only reduce the fatigue life of the contact with oil, but not water lubrication. With oil lubrication the fatigue failure initiates close to the surface defect. However with water as the lubricant the whole of the surface undergoes cracking with the defect having no preferential effect. The possible mechanisms behind this behaviour have been discussed. In addition, studies have been carried out to investigate the entrainment of solid particles into the disk contact. This kind of damage can accelerate surface fatigue and also lead to excessive wear. An attempt has been made to quantify the wear process and develop a simple empirical model.
