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This paper takes the ball diameter difference into consideration in the nonlinear dynamic model of the full ceramic bearing. The interactions between the elements of the bearing are derived based on the dynamic theory of the rolling bearing. The sound radiation is obtained using the sub-source decomposition method, and a verification experiment is carried out on the motorized spindle test rig to assess the precision of the model. The rotation speed, axial preload and radial loads are selected as influence factors, and parametric investigations are conducted to study the impact of the factors on the interactions between the elements. The circumferential distributions of the sound radiation are investigated, and parameters including sound pressure level and peak directivity angle are taken as evaluation indexes. Results show that the ball diameter difference has significant impact on the sound radiation of full ceramic bearings, and the impact grows with rotation speed. The sound directivity is closely related to the forces acting on the inner ring, and is affected by the axial and radial loads in different ways. This study provides information for the bearing acoustic characteristics, and is relevant for the design and operation of ceramic bearings.

As an extremely important component, flow field plays an important role in a proton exchange membrane (PEM) fuel cell. In this study, a two-dimensional model of interdigitated flow field was developed to simulate the effect of outlet channel width on PEM fuel cell performance using COMSOL Multiphysics, and the simulated results coincided accurately with the experimental results. From the results, the PEM fuel cell performance with narrower outlet channel width was better than that with conventional outlet channel width, since the molarity distribution of oxygen in the porous medium and the electrolyte current density distribution at the membrane cross section were more uniform, and the drainage capacity was stronger. The simulated results have certain reference significance for the design and optimization of interdigitated flow field.

Material properties are of great significance for structural safety. In this paper, the mechanical property tests are described and fatigue crack propagation (FCP) behavior for material that had experienced a certain number (10e7) of pre-cyclic stress (PCS) cycles are analyzed. The results illustrate that the material properties increase with the increase of PCS level for relatively lower PCS, and decrease with further increase of PCS. The FCP experiment shows that the FCP rates of the specimens subjected to PCS become lower than that of the specimen without PCS. ‘Turning’ points are clearly shown in the FCP rate curves, indicating that the FCP rate in the range of small ΔK is more sensitive to PCS. This paper presents a bi-linear approximation to describe the FCP behavior and predict the FCP life. It is found that the PCS has ‘coaxing’ effect on material FCP behavior. The fracture morphologies of the material with and without PCS are analyzed to discuss the ‘coaxing’ effect on microstructures. The PCS decreases the void number and void size in fatigue crack initiation zone, decreases the striation width in FCP zone, and increases the dimple size in final rupture zone.

In this paper, a method for recognizing the crack location on the outer ring of the full ceramic bearing is proposed, which considers the transmission of the vibration signal on the outer ring when a crack occurs. A two-degree-of-freedom nonlinear dynamic model of the full ceramic bearing with a crack is established, and the impact of the crack is evaluated through the change of the strain energy. Then, considering the attenuation of the vibration signal along the outer ring, the dynamic model is improved with a time-varying stiffness related with the crack position. By analyzing the ratio of the synchronous root mean square difference of the vibration signal, the position of the outer ring crack is recognized. The simulation results are compared with the experimental results to verify the accuracy and feasibility of the position recognition method. The research provides a new recognition method for bearing fault location, and helps with the fault diagnosis and status monitoring of bearing systems.

This paper mainly focuses on the calculation and analysis on the radiation noise of the angular contact ball bearing applied to the ceramic motorized spindle. The dynamic model containing the main working conditions and structural parameters is established based on dynamic theory of rolling bearing. The sub-source decomposition method is introduced in for the calculation of the radiation noise of the bearing, and a comparative experiment is adopted to check the precision of the method. Then the comparison between the contribution of different components is carried out in frequency domain based on the sub-source decomposition method. The spectrum of radiation noise of different components under various rotation speeds are used as the basis of assessing the contribution of different eigenfrequencies on the radiation noise of the components, and the proportion of friction noise and impact noise is evaluated as well. The results of the research provide the theoretical basis for the calculation of bearing noise, and offers reference to the impact of different components on the radiation noise of the bearing under different rotation speed.

Radiation noise (RN) is an important parameter for representing the characteristics of a bearing. By simplifying a ball bearing as a mass–spring–damping system, the differential equations for the vibration of an angular contact ceramic ball bearing (ACCBB) are established from the view of energy conservation considering nonlinear contact stiffness and damping. Then, the RN model of the bearing is constructed by Helmholtz's acoustic theory. The bearing noise is calculated using the proposed model, and the corresponding experiments are performed to confirm the model precision. The bearing noise consists of the noise at the characteristic frequency of each component; the rotational frequency is the primary contributor to the bearing noise. The radiation noise first increases with increasing rotational speed and the sound pressure level (SPL) has a high peak value at a critical speed of 28,000 r·min−1. Then, the noise decreases with increasing rotational speed. The directivity of sound field is discussed at different rotational speed. With increasing the rotational speed, the directivity level (DL) increases and the directivity angle (DA) skews towards the rotation direction. The research provides a theoretical basis to analyze the RN generated by ACCBBs at different rotational speeds.

The effect of ball diameter difference is quite obvious in full ceramic bearings due to the great stiffness, and leads to the problem of uneven loading in starved lubricated conditions. This paper takes the uneven loading condition into consideration in the dynamic model, and a verification experiment is carried out for the assessment of calculation accuracy. The factors of ball diameter tolerance, the arrangements of balls and the number of balls have impact on the interactions between the inner ring and the loaded balls, and the trends of sound radiation are studied in depth. The amplitude of sound radiation is used to show the interaction between the elements, and uneven loading conditions can be evaluated by the sound directivity. Results show that the tolerance is a key factor that has impact on the sound radiation, and the sound radiation and directivity have obvious change with the ball diameter tolerance. The arrangements of balls have impact on the sound radiation by changing the diameter difference between adjacent balls, and the loaded area of each loaded ball varies with the number of balls. The cases with different numbers of loaded balls are discussed, and the relations between the uneven loading conditions and sound radiation are investigated. This study proposes a method for the study of uneven loading conditions, and provides theoretical basis for the optimal design of full ceramic bearings.

The proton exchange membrane (PEM) fuel cell is one of the most promising fuel cells for wide applications, and the proton exchange membrane is one of its key components. However, the proton transfer mechanism in perfluorinated sulfonic acid polytetrafluoroethylene remains unclear for the research on PEM fuel cells. In this paper, the model of the proton transfer mechanism in perfluorinated sulfonic acid polytetrafluoroethylene is developed based on the fundamentals of the molecular dynamics, particularly the principle of energy and radial distribution function. The proton transfer process in perfluorinated sulfonic acid polytetrafluoroethylene is simulated, whereas the effects driven by the water content in the membrane and fuel cell temperature are analyzed. The results show that the water bridges developed by free water are the passage for proton transfer from one sulfonic group to its adjacent sulfonic group in perfluorinated sulfonic acid polytetrafluoroethylene. The proton transfers along the water bridge by the formation and cleavage of the H–O bond between the water from the water bridge and the proton; the increases in the water content in the membrane and the fuel cell temperature speed up the proton transfer, causing the decrease in the resistance of proton transfer. These findings are remarkably helpful to understand the working mechanism of PEM fuel cells.

Experimental purpose is to test gravity influence on water discharged in PEM fuel cell cathode. Through changing the way of placement of the cathode and anode, it takes adjusting the electronic load to test the output of voltage and current. Corresponding to the position of the cathode-upward and the anode-upward, different humidification condition, draws the polarization curve using the voltage and current density. According to the placing position of the cathode and anode, cell temperature, humidification temperature of the cathode and anode gas, 4 groups of experimental results are obtained. The experimental conclusion is: when a PEM fuel cell is placed anode-upward, gravity is advantageous to discharge the liquid water in PEM fuel cell cathode. On the contrary, gravity is disadvantageous to discharge the liquid water.