On the Residual Stresses Due to Repeated Stressing of Annealed Steels

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During repeated stressing of annealed steels in reversed bending, the residual compressive stress is introduced near the surface of specimen and its magnitude changes with the number of stress cycles. The residual stress appears from very early period of stress repetition and the maximum value occurs at about 105 stress cycles, thereafter the residual stress fades gradually. At or near the fracture, the residual stress was found to vanish approximately. The higher the carbon content or the yield point of the steel, the larger the residual stress produced. The change of hardness due to the repeated stressing is quite similar to that of residual stress. In the case of ascending stressing, both the residual stress and the hardness were found to increase than in the case of stressing at a primary stress amplitude. By numerical calculations, the contribution of residual stress to the fatigue strength at a fixed stress amplitude was studied. On the basis of a new S-N curve, the role of residual stress in the coaxing phenomenon was also made clear.