Analytical Study on Reliability Improvement and Rationalization of Maintenance of High-Strength Steel by Surface Crack Nondamaging Technology (in Case of Stress Ratio R =-1.0)

The threshold stress intensity factor (?K-th) has dependent on the crack size during the propagation of microfatigue cracks. Ando et al. proposed a new surface crack nondamaging technology to evaluate this dependence. This technology has been validated in situations where the stress ratio is positive (R > 0). However, to expand the application range of this technology, it is necessary to verify its applicability in the case of stress ratio R < 0. Therefore, this applicability was examined based on the results of the previous experiments. This study aims to investigate the effect of the residual stress distribution (RS]) of cavitation peening (CP) in the case of R < 0 on the harmless crack size (a(hml)) of steel with crack-like surface defects. To compare with the residual stress distribution (RS]) of CP, two types (RS2 and RS3) with different residual stress distributions were used. The surface residual stresses of RS], RS2, and RS3 were the same, but the distribution of depth from the surface was different. Compressive residual stress is the dominant factor that renders surface defects harmless. The depth of the residual stress significantly influenced a(hml). Moreover, the trend of the defect size that can be rendered harmless, estimated based on fracture mechanics, was slightly larger than that of the experimental results. However, surface crack nondamaging technology can be applied even when the stress ratio is negative (R < 0).