Evaluation of Tribological Performance of PTFE Composite Filled with Rare Earths Treated Carbon Fibers under Water-Lubricated Condition

Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites filled with carbon fibers treated with different treatment methods. Tribological properties of the PTFE composites, sliding against GCr15 steel under water-lubricated condition, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the composites were examined using scanning electron microscopy. Experimental results reveal that RE treatment is superior to air oxidation in promoting tribological properties of CF reinforced PTFE （CF/PTFE） composite. The friction and wear properties of PTFE composite filled with RE treated CF are the best of the PTFE composites. RE treatment is more effective than air oxidation to improve the tribological properties of CF/PTFE composite owing to the effective improvement of interfacial adhesion between carbon fibers and PTFE matrix.

Vibration Reduction Performance of Damping-Enhanced Water-Lubricated Bearing Using Fluid-Saturated Perforated Slabs

As the first link element for the transmission of shaft vibration to the pedestal and even to the hull,water-lubricated bearing plays a key role in suppressing vibration.Although the porous structure is considered as one of the main methods for improving the wideband vibration and noise reduction performance of materials in many industrial fields,the studies in the field of water-lubricated bearing remain insufficient.To enhance vibration reduction performance,a fluid-saturated perforated slab is designed in this study,and via the establishment of a fluid-solid coupled vibration model,the influence law and impact levels were analyzed and verified by simulation and experiments.The results obtained verified that the total vibration amplitude of damping-enhanced stern bearing in the vertical direction was smaller than that of the normal stern bearing,and the reduction amplitude of the characteristic frequency agreed with the optimal value at approximately 0.1 of the volume fraction of the liquid phase when the solid-fluid phase was rubber–water.Additionally,the increase in fluid fraction did not enhance the damping effect,instead,it unexpectedly reduced the natural frequency of the raw material significantly.This research indicates that the design of the fluid-saturated perforated slab is effective in reducing the transmission of the vibration amplitude from the shaft,and presents the best volume fraction of the liquid phase.

Steady Characteristics of the Water-Lubricated Conical Bearings

The water-lubricated conical bearing has attracted attentions of researchers for its simple structure,easily adjusted gap ( film thickness ) , lower friction loss, and less pollution in application. A mathematic model with consideration of the effects of turbulence,two-phase flow,and temperature on the pressure field at bearing surface is proposed here. Using this model,the Reynolds' equation and energy equation are solved in which the thermo-physical properties of the water as lubricant are taken into account. The dependency of characteristics of bearing,such as load-carrying capacity,flow rate ( pumping losses ) ,and frictional losses,on angular velocity, conical angle, and radial eccentricities, is presented. The research results are beneficial to the improvement of the efficiency of conical bearing and the environmental protection.

Review of the evolution and prevention of friction,wear,and noise for water-lubricated bearings used in ships

With the development of green tribology in the shipping industry,the application of water lubrication gradually replaces oil lubrication in stern bearings and thrust bearings.In terms of large-scale and high-speed ships,water-lubricated bearings with high performance are more strictly required.However,due to the lubricating medium,water-lubricated bearings have many problems such as friction,wear,vibration,noise,etc.This review focuses on the performance of marine water-lubricated bearings and their failure prevention mechanism.Furthermore,the research of marine water-lubricated bearings is reviewed by discussing its lubrication principle,test technology,friction and wear mechanism,and friction noise generation mechanism.The performance enhancement methods have been overviewed from structure optimization and material modification.Finally,the potential problems and the perspective of water-lubricated bearings are given in detail.

智能水润滑轴承的设计与可行性综述

Water-lubrication bearings are critical components in ship operation.However,studies on their maintenance and failure detection are highly limited.The use of sensors to continually monitor the working operation of bearings is a potential approach to solve this problem,which is collectively called intelligent bearings.In this literature review,the recent progress of electrical resistance strain gauges,Fiber Bragg grating,triboelectric nanogenerators,piezoelectric nanogenerators,and thermoelectric sensors for in-situ monitoring is summarized.Future research and design concepts on intelligent water-lubrication bearings are also comprehensively discussed.The findings show that the accident risks,lubrication condition,and remaining life of water-lubricated bearings can be evaluated with the surface temperature,coefficient of friction,and wear volume monitoring.The research work on intelligent water-lubricated bearings is committed to promoting the development of green,electrified,and intelligent technologies for ship propulsion systems,which have important theoretical significance and application value.

Insight into the Lubrication Performance of Biomimetic Porous Structure Material for Water-lubricated Bearings

Water-lubricated bearings have great advantages in the application of ship tail bearings due to the characteristics of green,pollution-free,and sustainable.However,the poor wettability of water-lubricated materials,as well as the low viscosity and poor load-carrying capacity of water,resulting in poor lubricating film integrity and short material service life under low-speed,heavy-load,start-stop conditions,which limits its application.To study the relationship between wettability and lubrication state and improve the lubrication performance of Si_(3)N_(4) under water lubrication conditions,the characteristic parameters that determine the hydrophilicity of Sphagnum were detected and extracted,and the bionic Si_(3)N_(4) model was established using Material Studio.Then,the molecular dynamic behavior and tribological properties of different Si_(3)N_(4) models were simulated and analyzed.Pore structure affects the spreading and storage of water on the material surface and changes the wettability of the material.Under the condition of water lubrication,better wettability and water storage promote the formation of water film,effectively improve the lubrication state of the material,and improve its bearing performance.

Wear monitoring method of water-lubricated polymer thrust bearing based on ultrasonic reflection coefficient amplitude spectrum

The water-lubricated thrust bearings of the marine rim-driven thruster(RDT)are usually composed of polymer composites,which are prone to serious wear under harsh working conditions.Ultrasonic is an excellent non-destructive monitoring technology,but polymer materials are characterized by viscoelasticity,heterogeneity,and large acoustic attenuation,making it challenging to extract ultrasonic echo signals.Therefore,this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient.The effects of bearing parameters,objective function,and algorithm parameters on the identification results are simulated and analyzed.Taking the correlation coefficient and root mean square error as the matching parameters,the thickness,sound velocity,density,and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm(DEA),and the wear measurement system is constructed.In order to verify the identification accuracy of this method,an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-etherketone(PEEK)fixed pad and stainless-steel thrust collar as the object.The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system,respectively.Ultimately,the results demonstrate that the thickness identification error of this method is approximately 1%,and in-situ monitoring ability will be realized in the future,which is of great significance to the life prediction of bearings.

Water-Lubricated Ni-Based Composite(Ni-Al_2O_3,Ni-SiC and Ni-ZrO_2)Thin Film Coatings for Industrial Applications

In this work, pure nickel and Ni-based nanocomposite coatings （Ni-AI2O3, Ni-SiC and Ni-ZrO2） were pro- duced on steel substrate by using pulse electrodeposition technique. The industrial performance tests were conducted to evaluate the wear resistance, corrosion resistance, adhesion strength and wettability behaviour of newly developed coat- ings. Rolling contact ball-on-disc tribometer was used to assess anti-wear behaviour of these coatings under water- lubricated contacts. The results showed that the wear- and corrosion resistance properties of nickel alumina and Ni-SiC composite coatings significantly improved than that of pure Ni and Ni-ZrO2 coatings. The adhesion and wettability results of Ni-A1203 composite showed better performance when compared to the rest of the coatings. The effects of incorporating nanoparticles on the surface microstructure, interface adhesion and distribution of the particles were also investigated. The coatings were characterized by using scanning electron microscopy, X-ray diffraction analysis and 3D white light inter- ferometry. The wear failure behaviour of these coatings was further examined by post-test surface observation under optical microscope.

Friction and wear behavior of different seal materials under water-lubricated conditions

The shaft mechanical face seal in a high-speed turbopump of a liquid rocket engine often operates under extremely harsh conditions.For example,a low-temperature and low-viscosity fluid(such as liquid oxygen or liquid hydrogen)is used as a lubricant.The performance of the seal rings,especially the friction and wear behavior,directly determines whether the seal functions normal.In this study,the friction and wear behavior of several ring materials are tested using a pin-on-disk tribo-tester,and the wear morphology of the ring is investigated.The friction coefficients(COFs)and mass-wear rates under dry-friction and water-lubricated conditions,which are used to simulate low-viscosity conditions,are obtained.The results show that at a pressure-velocity(PV)value of 2.4 MPa-(m/s),the COF between the copper graphite(stator)and copper-chrome alloy disk(rotor)is low(with a value of 0.18)under the dry-friction conditions,and the 5-min wear mass of the copper graphite is approximately 2 mg.Under the water-lubricated conditions,compared with other materials(such as copper-chrome alloy,S07 steel,alumina ceramic coating,and nickel-based calcium fluoride),the S07 steel with a diamond-like carbon film is preferred for use in a high-speed turbopump under extreme conditions.The results of this study can provide theoretical and experimental guidance in the design of mechanical face seals in liquid rocket engines.

Application of Bionic Tribology in Water-Lubricated Bearing:A Review

Water-lubricated bearing has become the development trend in the future because of its economy and environmental friendliness.The poor friction performance under low speed and heavy load seriously limits the popularization and application of water-lubricated bearings.Learning from nature,the phenomenon of low friction and wear in nature has aroused great interest of scientists,and a lot of research has been carried out from mechanism analysis to bionic application.In this review,our purpose is to provide guiding methods and analysis basis for the bionic design and theoretical research of anti-friction and anti-wear of water-lubricated bearings.The development of water-lubricated bearing materials are described.Some typical examples of natural friction reduction and drag reduction are introduced in detail,and several representative preparation methods are listed.Finally,the application status of bionic tribology in water-lubricated bearings is summarized,and the future development direction of water-lubricated bearings is prospected.

Energy flow characteristics of friction-induced nonlinear vibrations in a water-lubricated bearing-shaft coupled system

Based on the energy flow theory of nonlinear dynamical system,the stabilities,bifurcations,possible periodical/chaotic motions of nonlinear water-lubricated bearing-shaft coupled systems are investigated in this paper.It is revealed that the energy flow characteristics around the equlibrium point of system behaving in the three types with different friction-para-mters.(a)Energy flow matrix has two negative and one positive energy flow factors,constructing an attractive local zero-energy flow surface,in which free vibrations by initial disturbances show damped modulated oscillations with the system tending its equlibrium state,while forced vibrations by external forces show stable oscillations,(b)Energy flow matrix has one negative and two positive energy flow factors,spaning a divergence local zero-energy flow surface,so that the both free and forced vibrations are divergence oscillations with the system being unstable,(c)Energy flow matrix has a zero-energy flow factor and two opposite factors,which constructes a local zero-energy flow surface dividing the local phase space into stable,unstable and central subspace,and the simulation shows friction self-induced unstable vibrations for both free and forced cases.For a set of friction parameters,the system behaves a periodical oscillation,where the bearing motion tends zero and the shaft motion reaches a stable limit circle in phase space with the instant energy flow tending a constant and the time averaged one tending zero.Numerical simulations have not found any possible chaotic motions of the system.It is discovered that the damping matrices of cases(a),(b)and(c)respectively have positive,negative and zero diagonal elements,resulting in the different dynamic behavour of system,which gives a giderline to design the water-lubricated bearing unit with expected performance by adjusting the friction parameters for applications.

Investigation on the stability and anti-eccentric load margin of a novel structure bearing lubricated by low viscosity medium

The paper studies the anti-eccentric load margin of a novel structure bearing lubricated by low viscosity medium. The lubrication dynamic model considering journal inclination angle is established. The effects of different speeds, loads, and tilted angles on the interface attributes of the bearing under typical working conditions are studied. The results show that the special structure bearing has self-stability margin of anti-tilted and anti-eccentric load. Particularly under different speed conditions, analyses show that the eccentric load has little influence on the static/dynamic characteristics of the bearing. Under the same conditions, the stability margin of the bearing is higher than that of traditional bearings. The research provides a theoretical basis for the application of such kinds of special structure bearings.