Relation between Fatigue Strength of Notched Specimen and Plastic Deformation Value by Roller-Working

In this study, the fatigue test has been carried out to investigate the effect of plastic deformation value by roller-working on the fatigue strength of notched specimen. Herein, the authors have tested four types of specimens whose deformation values have been changed by roller-working and final shape and dimensions are the same. The reason why fatigue strengh changes with different plastic deformation value, has been examined by analyzing the residual stress, hardness distribution and crack tip opening displacement etc. The main results obtained in this test are as follows : (1) The resistance of the fatigue crack initiation increases with the increase of plastic deformation value. (2) When deformation value becomes too large by roller working, the residual stress may be released by cycle stress and the critical stress of non-propagating crack tip opening becomes decrease. (3) The fatigue limit of notched specimen by roller-working tends to deteriorate gradually when the plastic deformation value becomes too large, the optimum deformation value would exist for improvement of fatigue limit of notched specimen by roller-working.