Crack Initiation and Propagation Behavior Around the Defect in Steel Under Rolling Contact Fatigue

摘要

The clarification of uncertain factors of rolling contact fatigue (RCF) life variation is expected to lead us to better understanding of the RCF mechanism and further improvement of the service life of bearings. The objective of this study is to clarify the effect of defect location on RCF life. Artificial cavities, pores, and drilled holes were introduced to the specimens as a flaking origin under RCF for simplification on the presumption that their physical properties and interfacial rubbing between cavity and matrix were ignorable. The RCF test resulted in flakings initiated from the pore located right below the center of the track, when a specimen included numerous pores. Their RCF lives were simply determined by fracture mechanical parameters, size of pore, and orthogonal shear stress range parallel to rolling direction. On the other hand, RCF life was prolonged when the drilled hole in a specimen was located near the contact edge, although the resultant flakings appear the same irrespective of defect location. Therefore, defect location is one of the important factors for RCF life variation. The following were found through a further verification experiment and finite-element analysis: (1) A crack initiates from a drilled hole surface because of principal tensile stress at early stages of RCF irrespective of location of the hole. (2) Both of the orthogonal shear stresses, parallel and perpendicular to rolling direction, lead to the three-dimensional propagation of crack. (3) The weakening/damaging effect from a hole near the contact edge is less than that from a hole near the center of the contact track.