Wang Liqin

Nonlinear Dynamics Behaviors of a Rotor Roller Bearing System with Radial Clearances and Waviness Considered

Abstract A rotor system supported by roller bearings displays very complicated nonlinear behaviors due to nonlinear Hertzian contact forces, radial clearances and bearing waviness. This paper presents nonlinear bearing forces of a roller bearing under four-dimensional loads and establishes 4-DOF dynamics equations of a rotor roller bearing system. The methods of Newmark-β and of Newton-Laphson are used to solve the nonlinear equations. The dynamics behaviors of a rigid rotor system are studied through the bifurcation, the Poincare maps, the spectrum diagrams and the axis orbit of responses of the system. The results show that the system is liable to undergo instability caused by the quasi-periodic bifurcation, the periodic-doubling bifurcation and chaos routes as the rotational speed increases. Clearances, outer race waviness, inner race waviness, roller waviness, damping, radial forces and unbalanced forces—all these bring a significant influence to bear on the system stability. As the clearance increases, the dynamics behaviors become complicated with the number and the scale of instable regions becoming larger. The vibration frequencies induced by the roller bearing waviness and the orders of the waviness might cause severe vibrations. The system is able to eliminate non-periodic vibration by reasonable choice and optimization of the parameters.

Effect of two-phase liquid lubricant on fatigue life

Abstract This paper investigates experimentally the effect of two-phase liquid lubricating oil with solid additives of carbon or graphite or polytetrafluoroethene (PTFE) powder on contact fatigue life. The results show that the greater the amount of the three additives mentioned above, the longer the contact fatigue life becomes, but after the amount of graphite is greater than 0.5%, the contact fatigue life becomes almost a constant value. It is thought that the mechanism to prolong the fatigue life exists in four aspects: increasing effect of viscosity, decreasing effect of Hertzian contact stress, wedge effect of additive grains and adherent effec of additives on the contact surface.

Effect of external loads on cage stability of high-speed ball bearings

In high-speed ball bearings, external load has a great effect on cage stability and sliding ratio, especially for the bearings at work in the starting process. For this paper, a dynamic model of high-speed ball bearings was developed, and cage stability both under steady conditions and during the starting process was analyzed based on the model. The effect of external load on cage stability was evaluated taking into consideration the two different working conditions. The results show that cage stability is worse in the beginning of the bearing starting process. According to the investigation of cage stability on different external loads, it can be concluded that the axial load greatly influences cage dynamic performance in the bearing starting process. In addition, while ball bearings worked under steady conditions, axial load and radial load both have a great influence on cage dynamic performance. The effects of axial load on cage dynamic performance during the bearing starting process are opposite from the effects under steady conditions.

Effects of axial misalignment of rings on the dynamic characteristics of cylindrical roller bearings

Axial misalignment of bearing rings has an effect on the loading characteristics and stability of cylindrical roller bearings. Based on the kinematic relationship between bearing elements, a dynamic model of cylindrical roller bearings was developed. The effect of axial misalignment of rings on the contact pressure distribution of cylindrical roller bearings with a Lundberg logarithm modified profile roller was analysed. The vibration of the contact pressure and the cage stability during bearing operation were also analysed. The results show that a tilt between the inner ring and outer ring leads to stress concentration along the roller generatrix of the roller in the loaded zone. At the same time, when the bearing in operation, the cage sliding ratio and swing amplitude of the rollers in the loaded zone increase with the increasing tilt angle of the inner ring. The stress concentration of the rollers in the loaded zone that results from the tilt between the inner ring and outer ring could be improved by increasing the Lundberg logarithm modified coefficient.

Microstructure and properties of Nb/Ta multilayer films irradiated by a high current pulse electron beam

Nb/Ta multilayer films deposited on Ti6Al4V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by a high current pulse electron beam (HCPEB) to prepare Nb—Ta alloyed layers. The microstructure and the composition of the outmost surface of melted alloyed layers were investigated using a transmission electron microscope (TEM) equipped with an X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was ~ 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface layer.

Study on the Characteristics of Transferred Lubricating Thin Films on Ceramic Surfaces Generated in Liquid Nitrogen

The ceramic bearings operated in liquid nitrogen are mainly lubricated by the thin films transferred from the PTFE based composite retainers. The thin films on silicon nitride balls surfaces are generated by the friction and interaction among the composite retainer, the balls and the ANSI 440C stainless steel rings.

Study on loading capacity of the coating-substrate system of vapour-deposited TiN and TiC on bearing balls II. Rubbing method in experiments and analysis

Abstract The critical load of failure Lc is an important index for the loading capacity of a coating-substrate system. In consideration of the fact that a coating-substrate system in practice may take any one form of the four failure modes, coating failure, substrate yielding, interfacial failure or the mixed failure, this paper defines the critical load of failure of a coating-substrate system as the maximum normal load under a certain friction coefficient before any failure occurs. It also puts forward a new method, the rubbing method, to measure Lc. A multifunctional tester, Model CM-1, is developed on the basis of this method. The critical loads of bearing balls with physical vapor deposited (PVD) TiN or chemical vapor deposited (CVD) TiC or CVD TiC + Ti(CxNy) + TiN coatings under different friction coefficients are tested on this machine and their failing processes are analysed. The results show that the rubbing method is a sound new method for the measurement of Lc, and the results agree well with the those of field effect microscopy. The Lc of the CVD coating is greater than that of the PVD coating, and the Lc under smaller friction coefficient f is greater than that under larger f.