Estudo da evolução da rugosidade de dentes de engrenagens durante ensaios de desgate tipo FZG

Abstract

Gears are elements used to transmit movement and power between machines denominated as drive and driven. Gear teeth are subject to the effects of bending stresses, which lead to fatigue fracture at the root of the teeth, and to contact stresses on the tooth flank, and these stresses (commonly called hertzian stresses) are the agents causing one of the main mechanisms of wear of gear teeth: pitting. However, other factors also influence this type of damage, such as: material of the part; type of tooth profile; surface finish, in addition to lubrication and operating conditions. The present work aims to monitor all these factors, submitting samples of spur gears, composed by two different types of alloy steel, in a bench test type FZG (back-to-back test rig), with emphasis on confronting the behavior of the roughness on the flanks of the teeth, over thousands of loading cycles, with the formation of pitting. On the tooth flank surface, at different stages of the test, roughness measurements were performed, making it possible to obtain the parameters Ra, Rq and Rsm. With the combination of images of the flanks obtained with a camera and with the aid of a computational tool of 3D modeling, a quantitative analysis of the area of the teeth damaged by the mechanism of pittings was obtained. Contact stress calculations using a routine programmed in Matlab, using a numerical model that allows the inclusion of the measured roughness to obtain a microscopic stress analysis. Therefore, it was possible to follow the progression of these characteristics and the experimental results showed that as the roughness increases, the formation of pittings intensifies, while this same behavior was not observed between the evolution of wear and the stress field of maximum subsurface shear (Tresca stress).