A Importância de Atingir Níveis Elevados de Disponibilidade e Segurança em Sistemas Complexos

Abstract

Grease lubrication is applied to almost every situation, especially for rolling bearing lubrication. Usually, a rolling bearing fails by fatigue, when a spall is formed and it comes out of the contact surface. As it is well known, spalling is prone to appear in heavily loaded EHL contacts. Its presence depends essentially on the Hertzian pressure, thus the maximum shear stress. The depth of the cracks is similar to the depth of maximum shear stress. Crack initiation is also dependent on the lubrication conditions, namely on the specific film thickness A. Values of A greater than 3 virtually eliminate spalling, whereas values closer to 1 (or even smaller) tend to promote it. The concept of specific film thickness or lubricant parameter A, however, has a limited application if one is dealing with grease lubrication. Prediction of fatigue, in general, and spalling in particular, should be handled with caution. The main objective of this work is the experimental evaluation of fatigue failures in a pure rolling hertzian contact lubricated by grease. A comparative study with the base oils is done. The experimental work is performed with a two disk machine, adapted for grease lubrication. The procedures are described and the results obtained with a base oil and a grease are shown. Also, a critical analysis is performed.