A modified mathematical model for simulating gear crack from root with linear growth path in a pinion is developed, in which an improved potential energy method is used to calculate the time-varying meshing stiffnesses of the meshing gear pair while we also take the deformation of gear-body into consideration. The formulas for the meshing stiffness are deduced when the crack grows as the linear growth path in the pinion. A 16DOF dynamic model of a one-stage spur gear system is used to study the response from the system considering time-varying meshing stiffnesses and different levels of crack growing in the pinion. As vibration signals induced by the tooth crack are buried in normal vibration signals which are induced by the normal gear pair in meshing at the early stage of crack growth, the algorithm combined autoregressive modeling method and demodulation method is proposed to process the signals to investigate the response characteristics as the crack grows, and the comparison of the relationship between indicators and the crack levels from different simulation methods are given.

Vibration characteristics of a deep groove ball bearing caused by a localized surface defect are greatly affected by defect sizes, such as the length, width, and depth. However, effects of the defect depth, the time-varying contact stiffness between the ball and defect, and the relationship between the time-varying contact stiffness and defect sizes have not been considered in previous defect models. In this work, a new defect model considering a new force–deflection relationship is presented to replace the Hertzian force–deflection relationship to describe the ball-line contact between the ball and defect edge. Both the time-varying displacement impulse and time-varying contact stiffness are considered. The relationship between the time-varying contact stiffness and defect sizes is obtained. Effects of defect sizes on the vibrations of the deep groove ball bearing, especially the defect depth that cannot be described by previous defect models, are investigated. The simulation results are compared with those from the previous defect models. The results show that the model developed can predict a more realistic impulse caused by a localized surface defect for dynamic simulation of the deep groove ball bearing. An experimental investigation is also presented to validate the proposed model.