4056 SUJ2におけるせん断型疲労き裂進展(G03-12 き裂進展(1),G03 材料力学)

概要

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Growth behaviour of shear-type fatigue crack in a bearing steel, JIS SUJ2, was investigated by a biaxial fatigue testing machine using round specimens. Either following two kinds of defect with total length 400〜440μm and depth 200-300μm was introduced into specimen surface ; (1) a semi-elliptical pre-crack emanating from a 2-hole defect by a tension-compression loading, (2) a 3-hole defect oriented in the axial direction which has FIB slits at the edge of the defect. Fully reversed torsion corresponding to shearing stress amplitude at specimen surface, τ_a=600MPa, was applied to each specimen under static compressive stress σ_m=-1000〜-1200MPa. In case of defect (1), a shear-type crack propagated from the pre-crack in direction perpendicular to the specimen axis. At the specimen surface, the shear-type crack periodically branched from the crack tip and propagated 5〜10μm in Mode I directions. The shear-type crack growth was decelerated with the increase in the crack length and finally stopped at N≅7.5×10^6 cycles and 2a≅600μm. On the other hand, in case of defect (2), the shear-type crack propagated in axial direction, and the crack growth was accelerated with the increase in the crack length. These results revealed that friction between crack faces is a strong resistance in the shear-type crack growth.
一般社団法人日本機械学会の論文
2006-09-15