A Theoretical Discussion of Pitting Failures in Gears

Abstract

This paper is primarily concerned with the theoretical consideration of the stresses that cause surface failure of gear teeth. Methods of calculating the permissible line load between contacting cylindrical surfaces for static or cyclic conditions are considered, and the probable effects of friction are discussed qualitatively. Maximum permissible case thicknesses are suggested for case-hardened steel components of varying core strength when subjected to contact stresses of the type encountered in gears, rollers, and cams. In the Appendix is given an account of the derivation (from Hertz's general solution) of expressions for the principal stresses at any point in the neighbourhood of the zone of contact between parallel cylinders. These expressions, which lend themselves to ready computation, reduce to the same form as those derived by Thomas and Hoersch for stresses in the plane of symmetry, but they are more widely applicable.