Lifetime Prediction of a Crankpin using a Ball on Disk Type Rolling Contact Fatigue Life Testing

This paper describes an experimental method to predict the rolling contact fatigue life of a crankpin in a market vehicle engine. The fatigue life up to pitting was evaluated by two laboratory tests including a fatigue life measurement using a ball-on-disk test machine and a crankpin durability measurement by an engine bench test. The surface observation after the tests revealed that the surface dent triggers pitting in both tests. The Weibull plot of the percent failure vs. cycle to failure as a function of the contact stress was presented. In order to directly evaluate the effect of the contact stress on the lifetime, the lifetime values measured at L50 are plotted in the diagram showing the contact stress vs. cycle to failure. The obtained relation can predict the lifetime under the controlled condition in which the number of maximum torque points is countable. A method to place the lifetime of the market vehicle engine on the Weibull plot of percent failure vs. cycle to failure is developed. The established relation between the contact stress and travel distance can include the laboratory test data as well as the market vehicle engine data. The proposed method is able to predict the lifetime of the crankpin of the market vehicle engine using the laboratory ball-on-disk test data.