This research is a further research to clarify the surface failure mechanism and the failure prediction and diagnosis of the surface modified gears. In this research, electroless Ni-P alloy plating, sulphurizing, Sn plating with thermal diffusion and ion-nitriding were employed as surface modification. Wear characteristics, rolling contact fatigue behavior and gear performance of these surface modified specimens were examined under oil lubrication and in vacuum. These experimental results were discussed using the analytical results by BEM, wavelet transform and so on.
The rolling contact fatigue strength of the surface modified roller was higher than that of the roller without surface modification. The contact stress of the roller coated with modified layer having lower elastic modulus was lower than that of the roller without surface modification. It could be considered that the higher rolling contact strength by the surface modification was mainly due to the lower contact stress by the surface modification. The friction coefficient of electroless Ni-P plated, Sn plated and surphurized gear sets was lower than that of non-coated gear set in vacuum. The change in the tooth profile of these gears was well corresponding to the change in the tooth root strain wave.
By the roller test for the failure prediction and diagnosis of pitting and spalling, it could be said that the pitting failure and the spalling failure can be separately predicted by considering both the magnitude of the forced displacement between the contact rollers and the pattern of the wavelet map. Concerning the prediction and diagnosis of gear surface failure by the wavelet transform of the dynamic characteristics of the gear, it could be clarified that the failed tooth can be determined by the vibration data of the gear box and the failure position on tooth flank may be determined by the data of dynamic tooth root strain. The wavelet transform analysis was more usefull than the FFT analysis for the diagnosis of the gear failure.