Effect of Plastic Deformation by Roller-Working on Fatigue Strength of Notched Specimen

In this study, the fatigue test is performed to investigate the effect of plastic deformation by roller-working on the fatigue limit of a notched specimen. Three types of specimens are tested, whose different deformation values are obtained by roller-working and whose final finishing shape and dimensions are the same. The reason why fatigue limit changes with a change in the plastic deformation value is examined by analyzing residual stress, micro-Vickers hardness distribution and crack-tip opening displacement. The main results are as follows : (1) The resistance against fatigue crack initiation increases with an increase in the plastic deformation value. ( 2 ) When the deformation value becomes too large by roller-working, residual stress is released by cycle stress amplitude and the critical stress amplitude of non-propagating crack tip opening decreases. (3) The fatigue limit of the roller-worked notched specimen does not necessarily increase when the plastic deformation value becomes too large. (4) The optimum deformation value exists and is about 0.5 mm, to improve the fatigue limit of the roller-worked notched specimen.