Quantitative evaluation of effect of surface roughness on fatigue strength

Abstract

In order to investigate the effect of surface roughness on the fatigue strength, fatigue tests for maraging steel which was subjected to aging treatment and was free of residual stress, were carried out. As an artificial surface roughness, extremely shallow periodical notches with notch radii p=O and 200 μm, and notch depths a = 12, 22, 40 and 65 μm were introduced. In addition to the effect of surface roughness, the effect of nonmetallic inclusions was also considered. The equivalent defect size (√areaR) which controls the fatigue limit of specimen containing the surface roughness is defined by the function of depth and pitch of the roughness. The lower bound of the fatigue limit for various levels of roughness can be predicted by substituting the equivalent maximum defect size (√areamax(t)) to the √area parameter model. The value of √areamax(t) can be evaluated by considering the interaction effect between the maximum inclusion size and roughness. The predicted values were examined by experiments and it is shown that the method of prediction is available for practical applications.