微小ドリル穴付き試験片を用いた転がり疲労き裂進展試験法の提案

概要

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In order to improve the reliability of rolling bearings, it is necessary to clarify effects of hydrogen on rolling contact fatigue properties of bearing steels. This study shows a new method for the rolling contact fatigue crack growth testing. A small artificial hole makes quantitative evaluation of crack growth possible under rolling contact fatigue, although the rolling contact fatigue generally induces invisible inner crack initiation and growth from defects such as nonmetallic inclusions in the bearing steels. Firstly, shape of a small hole for rolling contact fatigue crack growth test was optimized on the basis of shear stress distribution around a small hole analyzed by FEM. New rolling contact fatigue tests were performed using uncharged specimens (hydrogen content CH = 0.4 mass ppm) and hydrogen-charged specimens (CH = 0.8 ~ 1.2 mass ppm) with a small artificial hole (diameter d = 50 or 100 μm, depth h = 100 μm) for bearing steel SUJ2. The Mode II fatigue growth rate of the hydrogen-charged specimens was about twice higher than that of the uncharged specimens. These results demonstrated that the new rolling contact fatigue testing was useful to investigate Mode II fatigue crack growth.