Fatigue crack initiation from small defects under low stress ratios inSAE52100 bearing steel

摘要

Axial-loading fatigue tests were carried out under low stress ratios, R = -∞ ～ —5.33, by use of a cylindrical specimen of SAE52100 bearing steel having drill holes of 50～ 200 μm in diameter. The maximum stresses, σ_(max)= 0 ～300 MPa were combined with the minimum stresses, σ_(min) of —1600 or —1800 MPa. Even at σ_(max) = 0, fatigue cracks were initiated at hole edges by cyclic compressive stress of σ_(min) = —1800 MPa, and the cracks finally became non-propagating. When σ_(max) was positive, fatigue cracks were initiated even at σ_(min) = —1600 MPa and they also became non-propagating. The length of non-propagating cracks increased with an increase in σ_(max)· Those phenomena were considered to be related to the tensile residual stress that was induced by the plastic deformation in the vicinity of hole edges. The relationship between the length of non-propagating crack and the residual stress field was investigated in terms of elastic-plastic finite element analysis.