Residual Stress Measurement of Full-Scale Jet-Engine Bearing Elements Using the Contour Method

摘要

Compressive residual stresses provide a well-known advantage to the fatigue life of bearing materials under rolling contact fatigue (RCF), but the stresses change under fatigue loading and may later contribute to failures. Previous measurements of the depth-wise distribution of residual stresses in post-fatigue bearings with X-rays involved the time consuming process of etching to determine subsurface stresses and only in limited locations. By contrast, the contour method determines the 2D residual stress map over a full cross section. The method involves the sectioning of the part using Electrical Discharge Machining, measuring the out of plane displacements of the exposed cross section, and using the afforded field as boundary conditions on a finite element model of the component to back calculate the causative residual stress. For this investigation, the residual hoop stresses in the split inner rings of the main shaft bearing assembly of an aircraft jet engine was mapped using the contour method. Prior to measurement, the full-scale bearing made of hardened AISI M50 was subjected to RCF during engine operation. In this talk, the unique challenges of the particular measurements are discussed. The tested bearings showed effectively no residual stresses induced by the RCF, probably because they were conservatively removed from service prior to sufficient cyclic loading. A more highly loaded bearing will be measured in future work.