Evaluation of bending fatigue strength in automotive gear steel subjected to shot peening techniques.

Abstract

The effect of residual stress is known to have a large influence on the integrity of engineered components including gears. Shot peening is a popular process used to introduce compressive residual stresses into a material which are beneficial to their fatigue life. Bending fatigue failure of gears is one of a number of failure modes a gear designer must account for and which can cause catastrophic failure of a gearbox.This paper presents results from the Innovate UK funded ULTRAN project to demonstrate the effects of a number of different shot peening processes upon the bending fatigue strength of an automotive gear steel. Results to be presented include residual stress measurements, bending fatigue results from pulsator tested gears and a study of the fatigue crack growth in the material.Four different shot peening techniques are presented along with baseline data. Whilst there was a large change in bending fatigue strength between the as-carburised and shot peened samples, the changes in residual stress caused by the optimised and the duplex shot peening methods did not correspond to a similarly dramatic increase in fatigue strength