MODEL-BASED DIAGNOSTICS OF SIMULTANEOUS TOOTH CRACKS IN SPUR GEARS

Abstract

This study aims at developing a numerical model that could be used to simulate the effect of tooth cracks on the vibration behavior of spur gears. Gears are a key component that is widely used in various rotating equipment in order to transmit power and change speed. Any failure of this vital component may cause severe disturbance to production and incur heavy financial losses. The tooth fatigue crack is amongst the most common causes of gear failure. Early detection of tooth cracks is crucial for effective condition-based monitoring and decision making. The scope of this work was widened to include the influence of multiple simultaneous tooth cracks on the time and frequency domain responses at various locations and with different severity levels. As cracks significantly alter the gear mesh stiffness, a finite element analysis was performed to determine the stiffness variation with respect to the angular position for different combinations of crack lengths. A simplified six degrees of freedom nonlinear lumped parameter model of a one-stage gearbox was developed to simulate the vibration response of faulty spur gears with the consideration of inter-tooth friction. Four different multiple crack scenarios were proposed and studied. The performances of various statistical fault detection indicators were investigated. The vibration simulation results of the gearbox obtained using MATLAB were verified with those stated in the published research articles. It was observed that as the severity of a single crack increased, the values of the time-domain statistical indicators increased, with different rates. However, the number of cracks had an adverse effect on the values of all the performance indicators, except the RMS indicator. The number and amplitude of the sidebands in the frequency spectrum were also utilized to detect the severity of the faults in each scenario. It was observed that, in the case of consecutive tooth cracks, the number of spectrum peaks and the number of cracks were well consistent in the frequency range of 4 to 5 kHz. The main finding of this study was that the peak spectral amplitude is the most sensitive indicator to the number and severity of cracks.