Residual stress and half-value breadth of the fatigue-fractured surfaces of various steels-such as WT-80c, SUS 403, SPV 50, SCMV 4 and S35C-were measured by X-ray diffraction. Fatigue tests were performed under the stress ratio R of 0 to 0.4. The half-value breadth b was found to increase with increasing the maximum stress intensity factor Kmax but the residual stress σr usually decreased with increasing Kmax.
The residual stress on the fatigue-fractured surface is said to be decomposed into four parts: that is (1) tensile residual stress due to monotonic deformation, (2) the release of stress due to fractured surface roughness, (3) compressive stress due to crack closure, and (4) compressive stress due to reversible plastic deformation. The present results were discussed in relation to the latter three causes.
From the measurement of the roughness of fractured surface, it was shown that the main reason why σr decreased with increasing Kmax was the effect of roughness.
Under the constant Kmax condition, the larger the R value was, the larger the σr was. This may be related to the reversible plastic deformation and/or to crack closure.
Other factors which influence the relative position of σr-Kmax curve, such as yield stress, fracture mechanism, were also discussed.
