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Smooth specimens were tested under reversed push-pull conditions (stress ratio R= minimum/maximum stress = -1) to examine the effect of shot peening on their fatigue behaviour. In order to give a broad range of application of the forged steels used for connecting rods, one was formed by the powder metallurgical process. The steels were tested in the original normalized as well as shot peened conditions.
Shot peening had little effect on the fatigue limit stress of these steels. It was apparent that shot peening produced a gradient of residual compressive stresses that was greater than that of the loading stresses. As a consequence, the anticipated beneficial effect on fatigue life was suppressed. It is suggested that the work hardening caused by shot peening was more beneficial in improving the fatigue strength than the accompanying induced residual compressive stresses.