大形転がり軸受用浸炭鋼の三方向残留応力を考慮した疲労き裂発生・進展に関する評価法の基礎検討

抄録

To correctly evaluate the safety of mechanical components, considering manufacturing induced residual stresses is essential. In this study, the risk analysis of fatigue crack initiation and propagation in cylindrical rollers for large size carburized bearings subjected to the rolling contact stress in services was conducted with consideration of the heat treatment stresses. Firstly, the residual stresses were reproduced by inherent strains measured using extended contour method, which combined the conventional contour method and surface stress measurement methods such as the X-ray diffraction method. The total stress in bearings during services is the summation of residual stress and contact stress. The location of fatigue crack initiation was examined using the Dang Van criterion. As a source of stress concentration, cavities were assumed as a harmful type of defects like inclusions with poor adhesion to the base microstructure. The direction of crack initiation around the defect was also examined using the Dang van criterion. The stress intensity factor (SIF) around the vacancy was calculated considering both residual stress and contact stress with a hypothetical initial crack. The SIF for a three-dimensional crack was modified by applying the shape factor. The effect of residual stress, the vacancy diameter and the shape of the defect on the crack propagation were discussed and compared with the threshold effective stress intensity factor of the standard bearing steel. A step-by-step approach was proposed to evaluate the risk of crack initiation and propagation by considering the residual stress distribution.