Estudo sobre a curva S-N e o gráfico de Weibull para análise de resistência à fadiga de contato de engrenagens

Abstract

The study of the fatigue phenomenon has a relevant importance on mechanical components design, because it is estimated that it is responsible for approximately 90% of all metallic failures. On contact fatigue of gears, the Hertz stresses contribute to the tooth surface wear occurrence, what characterizes the phenomena known as pitting and spalling. As mainly existing tools for this study, the S-N curve and the Weibull statistical distribution can be applied. The S-N curve permits to estimate the fatigue resistance of the material. This curve relates the loading stress value with the expected fatigue life (number of cycles) until the failures occurrence. The Weibull curve relates the failure probability of a component with its expected fatigue life, therefore it can be used to estimate warranty periods. The purpose of this research work is to understand the existing concepts on determining the S-N curve and the Weibull curve for gears contact fatigue. Therefore, contact fatigue tests of gears were carried out with three types of materials: ABNT 4140 steel and two different austempered ductile irons (FFNA and FFNF). The tests were carried out using the FZG machine, which is based on the power recirculation principle. It was noticed that the FFNF showed the worst contact fatigue resistance and, consequently, the lowest scale parameter value. For a reliability of 90%, the ABNT 4140 steel showed the highest scale parameter value and also the most accentuated mortality rate among the studied materials, with best contact fatigue resistance for a failure probability of until 90%, approximately. Finally, this work intends to contribute to the graduation of the Mechanical Engineering students and postgraduate students of the Technological University of Parana.