Improvement of the Fatigue Strength of Notched Specimens by artificially induced Residual Stresses

THE question of whether or not residual stresses have any significant effect on fatigue strength has been the subject of much research for some time. However, in 1956 Puchner 1 showed that a large increase in the fatigue strength of specimens containing discontinuous longitudinal welds could be obtained by heating the specimen locally with an oxyacetylene torch, in such a way as to introduce residual compressive stresses at the site of the most dangerous notch from the point of view of fatigue failure (namely, at the ends of the welds). His results have been confirmed by recent work of the British Welding Research Association. In view of the potential practical importance of these results, it was decided to carry out an exploratory programme of tests to determine the effect of inducing residual stresses by mechanical means.