Residual Stresses of Bearing Rings

Abstract

Residual stresses due to quenching of steel bars and tubes having circular cross section have been investigated theoretically and experimentally by several authors, but we can scarcely find any report on the residual stresses of rings. In this paper we propose an experimental method for measuring the residual stresses of a ring and report on some properties of them. The residual stresses of a ring σ_r and σ_θ are a sum of σ_r′, σ_θ′ of dislocation type, and σ_r″ , σ_θ″ of incompatibility type. For the formr
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\ oindentwhere a and b are the inner outer and radius of the ring and \fboxω is the Volterra’s dislocation angle which is made by a cut through a width of the ring. For the latter
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\ oindentwhere Δa means the increment of a when the outer surface of the ring has been ground by r. Using the above formulas the quenching stresses of bearing rings have been obtained from the experimental data \fboxω and Δa. The effects of shot blasting on the residual stresses have been investigated. We have obtained the follwing results. (1) The incompatibility type residual stress much exceeds the other. (2) The tangential stress σ_θ′, σ_θ″ is prominent compared with the radial stress σ_r′, σ_r″. The tangential stress σ_θ is a tension on the outer surface of the ring and has a tendency to change the sign by the shot blasting on the surface. And the stress distribution is unsymmetrical with respect to the median line of the width. (3) The measurement of micro hardness shows an increase of hardness of the surface by the shot blasting. It means the increase of micro stresses.