Influence of cracks on dynamic characteristics and stress intensity factor of gears

Abstract

Dynamic and three-dimensional finite element analytical models of cracked gears are established, and the dynamic characteristics (natural frequency and vibration shape) of the gear body are investigated when tooth cracks in the gear appear. Further, the influence of crack position and length on the dynamic characteristics of the gear structure are simulated and discussed. From this it was possible to determine that the crack position and crack length had an influence on the gear’s natural frequency and vibration shape. When the crack appears, the natural frequencies of the gear drop, and the vibration shapes also change. The influence of crack position on natural frequency and vibration shape are bigger than that of crack length. The natural frequencies’ decreases are bigger when the crack in the gear occurs at the tooth root rather than at the top of the tooth. Moreover, when the crack appears, the vibration shapes of the gear body are obviously different from without the crack, and the dynamic stresses of the gear body also change. On this basis, using the theory of fracture mechanics and the finite element method by ANSYS, the stress intensity factors were analyzed when the gear crack appeared. The variations in stress intensity factors are discussed related to changes in crack length, gear module, number of teeth, and load, when gear cracks occur at the pitch circle and tooth root. The pragmatic expressions of stress intensity factors are given by combining with the results obtained from the finite element method and the influence laws of multiple parameters on stress intensity factors are gained. These establish a good foundation for the fracture analysis and fault diagnosis of gears.