Dezhi Zheng

Image Acquisition and Segmentation for Ceramic Bearing Ball Surface Inspection System

Surface and subsurface defects in ceramic bearing balls significantly affect ball strength and lifetime. A brief review of nondestructive evaluation technologies on hybrid bearing balls was presented. An automatic ceramic bearing ball surface inspection system based on computer image technology was developed. Various surface defects were imaged by microscope and image digitizer on a novel ball surface unfolding mechanism. Top-hat and logarithm transformations were applied to eliminate uneven lighting disturbance. An automatic seeded region growing algorithm based on histogram concavity analyses and Otsus method was developed for defects segmentation. The results show that the experimental system is effective for ceramic ball surface and subsurface defects detection

Transient dynamic analysis of high power density gear transmission

In this paper, the dynamic problem of high power density gear transmission in transient state is studied based on flexible multi-body model. First, the flexible gear transmission multi-body model is built with the detailed formula of contact force and component modes synthesis method. Second, the transient time as dynamic external excitation is undertaken for high power density gear transmission, which has larger flexibility than others. Numerical and theoretical results confirm a significant influence of transient state on the dynamic force and deformation. Furthermore, the reasonable time of gear transmission transient state can be avoided the great impact force, reduce vibration and noise in gear system. Consequently, the transient time of gear transmission is an innegligible excitation factor for gear transmission.

Analysis and Evaluation of Interface Mechanics for Thin Films using the Method of Image

The evaluation of interface mechanics was very useful for the design of thin solid film. According to the method of image, interface stresses and deformations of coating-substrate system were gained. Using this mathematical calculation model, the indentation test data was carried out and the results were analysed. Based on the mechanical model and test, the critical state of interface stresses from elastic deformation to plastic yield was evaluated. From experimental and calculating results, interface shear stress and normal stress had different affecting level for the coating failure under the same surface load. And a fitting relationship equation for the two stresses was also gained to determining the failure value in designing. The method of this paper could be used for thin film interface mechanics design and evaluation.

Performance and Failure Modes of Grease Lubricated Hybrid Ceramic Bearing in High Speed and High Temperature Condition

Ceramic rolling element bearings have promising applications in extreme operating conditions such as high speed, high temperature, and heavy load. In this study, a hybrid silicon nitride ceramic ball bearing lubricated with high temperature grease is presented. The structure and parameters of the bearing are specially designed to satisfy the requirement of grease lubrication, high temperature and high speed conditions. A test rig was developed for the experiments of ceramic bearing performance. The experimental results show that grease lubricated ceramic bearings with fine design have excellent high speed and high temperature performance. By analyzing the operation performance and failure bearing inspection, the failure modes of grease lubricated ceramic bearings is analyzed. Thermal instability caused by the grease insufficient supply is the main factor of failure.Copyright

High speed rolling bearing cage rotation speed monitoring using optical fiber sensor

For high speed rolling bearing applications, skidding between the rolling elements and raceways is abnormal operation condition, which can cause early failure of the bearings. The cage rotation speed is an indication of the bearing operation, especially the bearing skidding. Therefore, through monitoring the cage rotation speed, the effect of bearing skidding can be investigated. In this study, an optical fiber sensor monitoring approach is presented to measure the rotation speed of the cage. To measure the cage rotation speed, the transmitter of the sensor is placed on one side of the bearing, and the sensor receiver is placed on the other side. When the rolling elements run cross the light beam, the impulses are detected by the sensor. The cage rotation speed can be analyzed by counting the passing frequency of the rolling elements. A test rig was developed to evaluate the effectiveness of the sensor system in different oil lubrication environments. Experiments on the measurement system effectiveness in oil lubrication conditions were performed. The experimental results show that the approach is effective to evaluate the cage rotation speed and monitor rolling bearing skidding.

Surface Damage Under Extreme Conditions Existed in Aircraft Bearings

The extreme conditions of aircraft bearing steel M50 have been simulated by a two-disk test rig for investigating the surface damage of the ball/raceway contact surfaces. The slide/roll ratio are 0.12 and 0.15, correspondingly, the rolling speed are 43.2m/s and 49.5m/s. Aircraft engine oil 4050 as the supplied oil has been maintained at approximately 80°C in the tests. The ultimate Hertzian contact stresses of the surface damage obtained from the experiments are 3.8GPa in 0.12 slide/roll ratio and 3.5GPa in 0.15 slide/roll ratio. The damage mode is scuffing in 0.12 slide/roll ratio and it is oxidation, thermal fatigue and scuffing in 0.15 slide/roll ratio. Cracks in the contact areas originate from surface layer in the two slide/roll ratios.Copyright

Cage Instabilities in High-Speed Cylindrical Roller Bearings

A dynamic model of the cage in an oil-lubricated cylindrical roller bearing was developed and the cage whirl has been researched by this model. In model, the forces between elements, especially the effect of EHL (Elastic Hydrodynamic Lubrication) between cage pockets and rollers were fully considered according to the geometry relationship between elements. The effects of variation in clearance ratio, load and bearing operating velocity on cage whirl have been investigated. The results of the effect of cage clearance on cage instability basically accord with the Gupta’s results, but the starting time of the direct contact between cage and guiding race is delayed while the EHL was considered. The effect of normal load is more important than bearing angular velocity on cage whirl.Copyright

Analyses on the Splashing Parameters of High-Speed Oil Impacted a Wall in Jet Lubrications

A new model for the free jet breakup is derived from the TAB theory to determine the size of breakup in the energy conservation law. In addition, the splash behavior of droplets after impingement is determined by the newly proposed model, which incorporates both the size and the number models based on Wu Ziniu’s phenomenological theory. The numerical calculations for several experimental conditions are carried out for impinging sprays on a static flat wall. The results indicate that the splash ratio increases along with the jet velocity and the nozzle’s diameter probably as the exponential curve growth tendency. The new model generally predicts the splash behavior better than the previous models, and it performs for prediction of spattering ratio effectively. The model is useful in further calculation on the two-phase flow air volume fraction in the high-speed jet lubrications.