This work aimed to investigate the effect of the burnishing surface treatment on the tribocorrosion resistance related to Ti6Al4V specimens, in the framework of the head-neck tribo-pair characterising a total hip replacement. The experimental procedure carried out started by choosing the specimens referred to different burnishing conditions together with specimens not treated or treated only with the turning process. Then, tribocorrosion experiments with fixed load and two frequencies were conducted through a reciprocating tribometer equipped with a potentiostat able to measure the electrochemical corrosion potential and current associated to the synergistic wear phenomenon analysed together with the coefficient of friction. Furthermore, optical topographical acquisitions were performed before and after the experiments. The results showed that the non-burnished specimens exhibited unexpected oscillations of the coefficient of friction approximately in the middle of the rubbing phase and the same happens for the cell potential; the wear volume was measured after the tribocorrosion test. This allowed to estimate the wear factor related to all the analysed configurations, showing a greater mean value in correspondence of greater sliding frequencies in the non-burnished cases, while the opposite happens in the burnished cases. Finally, the burnished sample at the lower burnishing force resulted to have the noblest corrosion potential, while the non-burnished samples exhibited the lowest corrosion current density.
Aiming to solve the problem of the gear lubrication of unmanned aerial vehicles (UVAs), a grease mixed Thermal-elastohydrodynamic lubrication (TEHL) model is established, and the lubrication state of the gearbox of oil-powered heavy-duty UAVs is numerically analyzed. In this study, grease is regarded as a non-Newtonian fluid whose properties change nonlinearly with respect to pressure, temperature, and other conditions. The complex meshing state of a spiral bevel gear tooth surface is analyzed using the loaded tooth contact analysis (LTCA) method, and three points on the tooth surface are selected as samples to describe the lubrication state of the entire tooth surface. The thickness of grease film and the temperature rise of the tooth surface are studied in detail, considering the natural roughness of the tooth surface and influence of different greases. The results show that the established model agrees with results from the literature. The dangerous point of tooth surface lubrication is at the meshing midpoint. Under cruise conditions, the lubricating grease viscosity significantly influences the temperature rise of the tooth surface.
Copper-based functionally gradient composite material is developed using powder metallurgy processing technique, as a potential wind turbine brake pad material. The developed composite has a gradient composition of Cu, CeO2, Al2O3, Fe, and C-g to enable joint strength at the interface (brake calliper) and wear resistance at the contact surface (brake disc). The article presents a comprehensive analysis on the microstructure, microhardness, and tribological performance of the developed composite. The wear mechanism is deduced through surface morphology, elemental composition, and phase composition analysis using field emission scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and X-ray photoelectron spectroscope. A maximum hardness of 198.2 HV was obtained at the contact surface. Experimental values from tribology tests show that a decreasing trend was obtained with a wear rate of 2.013 x 10(-7) g N-m(-1) and a friction coefficient was 0.215.
The tribological characteristics of stir cast Al-15%Si-10%Zn matrix with 15%ZrO2 reinforced composite were investigated. The microstructure of the Al-15Si alloy consisted of coarse primary Si and acicular eutectic Si phases randomly distributed in the Al dendrites. The Al-15%Si-10%Zn/ZrO2 composite showed spherical Si with a size between 25 and 75 & mu;m; fragmented eutectic Si phase and uniform dispersion of ZrO2 particles in the matrix. The wear test was conducted using in a pin-on-disc method at different loads and sliding velocities. It was found reduced coefficient of friction, significant increase in the hardness and wear resistance of the composite compared to the matrix alloy. High wear resistance in the composite due to the effect of solid lubrication provided by Zn, and good fracture toughness and wear resistance by the reinforced ZrO2 particles. The predominant oxidative and abrasive wear were identified as the mechanisms leading to material failure through plastic deformation and delamination.
The machinability studies for the Inconel 718 alloy with the coated cemented carbide cutting tool having 0.4 and 1.2 mm nose radius, varying cutting speeds (65, 81, 95 and 106 m/min) with a constant feed rate of (0.15 mm/rev) and a depth of cut (0.2 mm) were conducted. The cutting force decreases with the increase in cutting speed due to the thermal softening of the work surface at a high temperature. With the increase in nose radius a decrease in the cutting force is observed due to the increase in the cutting edge of the tool. The formation of residual stress has a profound effect on the change in the tool morphology during the machining of the alloy. Furthermore, the chip analysis in terms of chip morphology is carried out in detail. The detailed tool fracture studies are conducted and are explained for the various machining processes.
Systematic planning of an activity is a key factor for the success of any event. It is well said that ‘If Well planned, 90% of the work is completed’. But planning a successful activity depends on how sustainable the solutions would be. For machinery too, the maintenance planning is to be sustainable, particularly the lubrication. Additionally, with the concern of the environment now industries are looking for sustainable but environment-friendly economical solutions. Lubricants which form one of the major mechanical elements need to be taken into high consideration. However, it is important to understand the role of these lubricants in mechanical applications and choose the correct lubricant for specific applications. The special issue focuses on various tribological systems from nano to macro scale. This issue brings together interesting contributions both from industry and academia covering applications such as wind turbines, nano-bio-lubricants, self-lubricating nanocomposites, coatings, and natural composite brake pads. The topics covered diverse topics highlighting innovative scientific approaches covering modern lubrication techniques. The special issue is divided into two sections: initial articles focus on the lubrication aspects of industrial applications and later articles focus on the composites and coatings, thus, covering several dimensions in the field of tribology. The issue begins with an interesting manuscript ‘Investigating the effect of temperature and time on the starvation of lubricants for the wind turbine industry’ where Georgiou et al. developed a validation test procedure and reported the effect of temperature and time on lubrication starvation in windmills. Sustainable lubricants are the need of the hour. Biodegradable lubricants are lubricants of interest to the environmental policies of all nations. In ‘Performance Assessment of Some Selected Vegetable Oils as Lubricants in Turning of AISI 1045 Steel Using a Taguchi-Based Grey Relational Analysis Approach’, Abegunde et al. reported the efficacy of vegetable oil in turning AISI 1045. The incorporation of nanotechnology in lubricants had exhibited an improvement in the tribological properties of lubricants. Srivyas et al. evaluated the tribological properties of a hybrid nanoparticle added poly alpha olefin oils in ‘Enhanced Extreme Pressure and Tribological Performance of Hybrid Nano Lubricant’ and reported a significant reduction in frictional coefficient. Furthermore, in ‘Tribological Evaluation of Rice Bran Oil Based Ionanolubricants Containing Ionic Liquids and Nanoparticles’. Garg et al. reported an improvement in the tribological properties of rice bran oil by introducing ionic liquids along with nanoparticles. Recent advances in self-lubricating composites have also been an area of interest in this issue. In several applications, composites need to be wear-resistant and one of the most exciting topics is self-lubricating composites. ‘Investigations on the temperaturedependent tribological behavior of spark plasma sintered CNT304 SS self-lubricating nanocomposites’ by Radhamani et al., report the results on the enhanced tribological properties of CNT-incorporated 304 stainless steel at high temperatures, particularly for applications of oil and gas industry. The results are quite interesting as they reported a significant reduction in wear at high temperatures. Additionally, the process of incorporating CNTs in steel by sintering is also noteworthy. Natural composites are also being used in brake pads. The manuscript ‘Recent Progress in the Research on Natural Composite Brake Pads: A Comprehensive Review’ by Bharath KN et al. thoroughly reviewed the recent progress in natural composites. The manuscript further discussed the wear mechanisms involved in various materials of brake pads and concluded with the possibility of manufacturing such natural composite brake pads using modern techniques. An excellent anti-wear property of WS2 solid lubricant coating on the aluminium substrate was reported in ‘Wear characteristics and sustainability of WS2 solid lubricant deposited layer on Al 6061-T6 substrate under the dry sliding conditions’ by Rajeshshyam R. The manuscript reported the wear reduction property of WS2 coatings and hence, is suitable for several industrial applications. Hence, it can be seen that the special issue has focused not only on regular academic research but also on industrial applications. This Special Issue came to light after a series of positive discussions with the Journal’s Editorial Board, particularly with Prof. Tomasz Liskiewicz. I
The demand for magnesium (Mg) alloys is increasing in many industries, such as automotive and aerospace, thanks to their low density and high specific strength. However, the poor tribological performance of Mg alloys is one of the most important disadvantages that limit their widespread use. Researchers have developed different approaches to improve the wear performance of Mg alloys, such as alloying, coatings, surface modifications and composite production. Wear performance of systems with sliding parts are crucial for a lifetime and energy efficiency. The development of Mg matrix composites can significantly reduce energy loss by reducing damage from friction and wear. For this reason, it is crucial to understand the wear behaviour of recent Mg matrix composites. The effect of different parameters such as load, sliding speed, reinforcement content, reinforcement type and temperature on the wear performance of Mg matrix composites were investigated.
Cardiovascular implants have been widely used as a treatment for various cardiovascular diseases. However,the contact between implant surface and blood will cause thrombus that leads to significant morbidity and mortality worldwide. To reduce the risk of thrombus, immobilizing anticoagulant coatings on the implant surface is a common method to realize anticoagulation. In this review, we focus on the anticoagulant coatings on different cardiovascular implants in the past 10 years. We review the advance on the anticoagulant coatings of four typical cardiovascular implants including artificial heart valves, vascular stents, ventricular assist devices, and catheters. In the end, we conclude the ideal design for each implant and look ahead to the future of the cardiovascular anticoagulant coatings. It is of great significance to improve the design and application of cardiovascular implants.
The service life of products is significant for ensuring stable and reliable performance of these products, such as spacecraft, military equipment and electronic equipment. Such service life is generally evaluated by measuring the working duration of products before losing efficacy or breaking down through tests under the same working condition with the real working condition. However, with the rapid increasing improvements in reliability and of products, the service life of products had been lengthen remarkably, the corresponding time and financial costs of the conventional simulated products life tests were continuously increasing, and such costs were becoming too high to be accepted. On this basis, the concept of accelerated test was suggested as a potential solution in which appropriate equivalent of products service life should be selected. The tests were accelerated by adjusting the changing rate of the equivalent, so that the test durations were shortened under a certain equivalent. In 1980s, the Accelerate Life Test（ALT） and the Accelerate Degradation Test（ADT） based on ALT, which estimated the reliability and service life of products under common stress levels through the accelerate test data under higher stress levels were suggested. ALT and ADT were the most common accelerated test methods, in which the failure possibility function were regarded as the equivalent. In other accelerated tests, the selected equivalent also included surface topography and condition parameters. As for accelerated wear test, there were numerous models for quantitative prediction of wear, which was a typical form of the degradation process of materials, the equivalent of wear could be selected based on these quantitative wear models. This paper aimed to propose an accelerated wear test method based on an accurate quantitative wear model. The investigations were conducted based on friction and wear with experiment condition of surface contact and mixed lubrication by the standard apparatus for typical mechanical seal material pair 9Cr18Mo/M234A0. The structure of tested seal ring was modified to reduce temperature rise and strengthen the fluid dynamic pressure effect. In this paper,the accelerated wear model was established with the entropy increase as equivalent of wear, based on the dissipation wear model which considered the wear as an irreversible thermodynamic process. The dissipation wear model was verified with the mentioned seal pair, revealing a linear relationship between wear rate and entropy increase. By modifying the entropy increase rate under the same entropy increase, the wear test duration was shortened. On this basis,this accelerate wear model was verified with equivalent wear tests with long time/low entropy increase and short time/high entropy increase. This model was also compared with accelerate wear model based on Archard model. The result of which revealed that wear test of 200 min duration could be equally replaced by a wear test of 10 min duration with an error of 2.22%, and the maximum relative error of other time was 4.75%. The feasibility and the accuracy of this accelerate wear model was proved preliminarily by the test results of this study. Further investigation revealed that the wear mechanism was invariable during the tests in this paper.
Floating foil seal is a new non-contact seal structure,which is proposed to meet the sealing requirements of the rocket turbine pump and the main bearing of aero-engines.Specifically,elastic foil with adaptive deformation ability is designed based on the cylindrical gas film seal,with the rigid sealing surface being replaced.In this way,the anti-interference ability of the system can be improved.Research in this regard mostly takes the sealing friction pair as a smooth surface,but in practice,a completely smooth surface does not exist,as any friction interface is composed of many different micro convex bodies and micro pits.On the surface of the friction pair,the dynamic pressure pits or dynamic pressure grooves are usually designed to improve the dynamic pressure effect and friction performance.After re-processing,the working surface tends to exhibit varied surface characteristics,meaning that the accurate control of the groove shape and roughness remains a topic of exploration for high-precision machining technology. In fact,whether it is a gas seal or other mechanical parts,the true shape of the friction pair surface should not be completely ignored under certain circumstances.In order to investigate how the surface topography of the sealing pair affecting the floating foil sealing performance,this work studied the textured floating foil gas film seal of one end fixed bump foil.The detailed experiments were as follows:the rough flat foil surface with triangular texture was characterized by the three-dimensional W-M fractal function.The pressure control equation for the synchronous rotation of the wedge-shaped gas film and the moving rotor was established,with the micro-channel scale effect,the fluid-solid interface step effect,and the elastic surface deformation had been taken into account.The finite diference method was used to solve the coupling problem,then,the effects of fractal parameters on the lubricating state of the flow field and sealing characteristics were obtained.By changing the characteristic scale coefficient and fractal dimension,this work further analyzed how the real surface characteristics were correlated to the static and dynamic sealing performances. The research results showed that changing fractal parameters within a certain range did not affect the overall distribution of gas film thickness and pressure,but the influence of fractal parameters on sealing performance could not be ignored in the following three cases:the average thickness was small,the amplitude of surface roughness peak was intense,or the fluctuation was dense.The effect of surface roughness had a monotonic relationship with the sealing performance,while the effect of surface density was irregular.The increase of the characteristic scale factor G and the decrease of the fractal dimension D within a certain range could improve the sealing dynamic pressure effect and reduced the leakage rate,and vice versa,which helped to reduce friction and stabilize the sealing system.The influence of the real surface of the friction pair on sealing characteristics could not be ignored,but the degree of effect could be gradually weakened as the gas film thickness increased.The dynamic characteristic coefficient showed a relatively complex correlation with the thickness change,but with the increase of gas film thickness,the system tended to be more unstable,and the best dynamic characteristics might be the best at 20 μm.This paper brought the theoretical research on the floating foil gas film seal closer to the actual working conditions,and also provided reference for later manufacturing of the elastic foil.
The new self-impact seal has been widely concerned and recognized by peer scholars and industry experts since its introduction.In this paper,the thermodynamic effect and flow field characteristics of the seal were analyzed,the mathematical relationship between the thermodynamic effect and the leakage was established,and the influence of working condition and geometric parameters on them were investigated.The results showed that the established leakage equation agreed well with the simulation results(the error is 7.59％at variable rotational speeds).The entropy increasing effect of the seal varied most obviously with the sealing clearance when sealing clearance h ≤200 μm.The leakage was significantly affected by medium pressure and sealing clearance,but was largely independent of rotational speed.Along with the sealed medium flowing into the clearance,the temperature of the flow field was rising step by step,and reached the highest at the outlet.The outlet temperature increased with the increase of pressure and sealing clearance,and decreased slowly with the increase of the number of stages.The effect of rotational speed on the outlet temperature was small.The thermodynamic effect was the main reason for the sealing tightness,while the stream contraction effect and the friction effect also favored the conversion of kinetic energy to internal energy to some extent.Compared with the existing non-contact gas seals(clearance,spiral,labyrinth,dry gas seal,etc.),the gas permeability effect after the self-impact could be basically ignored.When the gas passed through the flow paths of the three-dimensional Tesla valve of the seal,the gas in the sealing cavity was divided into two paths,and ultimately impacted each other in the intersection area of each sealing stage,and the kinetic energy of the gas was gradually converted into thermal energy and dissipated by impacting step by step,which leaded to the increase of temperature and entropy.The impulse and devision between the streams created an impact blockage effect,strongest at the intersection position,which was also the key position of pressure energy(kinetic energy)converting into thermal energy,and at the same time,the gas flow through the position was exceptionally intense.The gas flow rate in general tended to decrease due to the thermal dissipation after the impact.How to relieve pressure,control temperature and select the appropriate high-temperature resistant materials was the key to the new seal as soon as possible to realize the industrialization of the application.
The application of carbon dioxide to thermal power generation expected to develop a new type of high-efficiency thermal power generation system,which has the advantages of compact cycle system structure and high cycle efficiency.However,material failure caused by fretting wear has become one of the key problems restricting the development of its system.Therefore,it is of great significance to study the fretting wear properties of materials to ensure the stable operation of thermal power systems.In this study,the fretting wear test of 904L stainless steel heat transfer tube at different temperatures and environmental media(room temperature atmosphere,room temperature carbon dioxide,350 ℃ atmosphere,350 ℃ carbon dioxide)was carried out on the controllable atmosphere fretting wear test equipment.The displacement amplitude of the test was 60 pm,the normal load was maintained at 10 N,and 105 test cycles were performed at a frequency of 10 Hz.Subsequently,the dynamic characteristics of the friction displacement curve and the friction coefficient curve were analyzed,and the wear scar morphology was observed and analyzed by a super-depth-of-field microscope.The wear scar three-dimensional morphology was characterized by an optical 3D surface profilometer.The cross-sectional profile,wear area and wear volume of the wear scar were measured.Scanning electron microscope and energy dispersive spectrometer were used to analyze the microscopic morphology and element composition of the surface and cross-section of the wear scar.The fretting wear mechanism of 904L stainless steel was further explored in different environments.The results showed that,the friction force displacement curve was an obvious parallelogram shape and the fretting wear running in the gross slip zone under room temperature conditions.The friction coefficient in the atmospheric environment was greater than that in the carbon dioxide environment.Significant material spalling and wear debris appeared in the fretting damage area,and accompanied by the initiation and propagation of cracks.The wear mechanisms of fretting wear under room temperature atmosphere and carbon dioxide environment were mainly delamination and oxidative wear.When the temperature raised to 350 ℃,the friction force displacement curve changed from a parallelogram to an ellipse,and the fretting running in the mixed zone.Compared with the room temperature,the friction coefficient of fretting wear under 350 ℃ was reduced.However,the friction coefficient in the carbon dioxide environment was greater than that in the atmospheric environment.The wear debris generated by wear forms a"glaze layer"on the wear surface through the adhesion and sintering process,which inhibits the increase of wear.The highest oxygen content was detected on the wear surface in the atmospheric environment.The wear mechanisms in the atmospheric environment of 350℃ were mainly adhesive wear and oxidative wear.In the same carbon dioxide environment,a wear debris accumulation layer was formed on the surface of the wear scar,which inhibits the wear.However,due to the difference in tribochemistry,a compact"glaze layer"was not formed on the worn surface,and the wear debris tended to flow to the edge of the wear scar.Under the room temperature conditions,the wear amount of carbon dioxide was reduced compared with the atmospheric environment.When the temperature is increased to 350 ℃,the wear amount was significantly smaller,and the wear amount in the carbon dioxide environment was slightly smaller than that in the atmospheric environment.
Energetic materials,which can be generally simplified as EMs,have been widely applied in many cutting-edge areas such as the defense weaponry and its systems as well as the solid propellants for aerospace field.During their manufacturing and in-service process such as production,pressing,manufacturing,usage,and storage of energetic materials,the tribological properties of energetic materials interfaces have gradually become one of the most predominated common issues that is affecting their safety and stability during their manufacturing and in-service processes.In special,the safety of energetical material under various frictional stimulations conditions has become an extreme issue that is affecting the safety of mechanical equipment and operate engineers.Therefore,in order to improve the safety and stability of energetic materials under various frictional stimulation conditions,it is of critical importance to scientifically and comprehensively understand the common tribological behaviors of energetic materials,for instance,the friction behavior of energetic materials interfaces,the formation of friction-induced hot-spots at of energetic materials interfaces,the sensitivity to frictional stimulation of energetic materials,and other problems of energetic materials interfaces under different frictional stimulation conditions.It should be noted that those fundamental questions about the tribological behaviors of energetic materials have gradually become one of the important topics in the fundamental and application research in the research field of energetic materials during various manufacturing and in-service processes.Aiming to answer those important questions,first of all,this review paper analyzes the key tribological problems of energetic materials during their manufacturing and in-service processes involving the production,pressing,manufacturing and usage process,and expounds the research connotation of tribological behaviors of energetic materials.On basis of this,the latest research progresses of related research method and fundamental theory about the tribological behaviors of energetic materials in recent years are reviewed.To be more specific,in addition to the commonly used methods and equipment for both the fundamental and application of tribological properties of energetic materials,the fundamental mechanism of tribological behavior of energetic materials under various conditions are discussed,for instance,as the most important frictional parameter,the evolution and its mechanism of friction coefficient of energetic materials interfaces are discussed,the formation and its mechanism of the formation of friction-induced hot-spots at energetic materials interfaces are discussed,and as most important parameter during actual applications,how to reduce frictional sensitivity of energetic materials by various treatments are also discussed.Finally,some future research prospectives are proposed based on the existing research progress and development trend of research on tribological behaviors of energetic materials.
As the key component of mine hoisting system,hoisting wire rope is responsible for lifting coal,gangue,personnel and equipment.In the working process,the fretting wear between steel wires will aggravate the fatigue damage of hoisting wire rope,reduce the service life of wire rope,and seriously threaten the safety of the mine hoisting.In order to study the influence of strand structure on the fretting friction and wear characteristics of spiral contact steel wires,the fretting wear tests of steel wires under tension-torsion coupling force were carried out on a self-made test rig.The micro wear characteristics of steel wire surface were observed by the scanning electron microscope(SEM),and the fretting wear mechanism and fracture failure behavior of spiral contact steel wires under different strand structures were revealed.The results show that with the increase of contact force,the frictional coefficient between steel wires under the same diameter contact pairs decreases from 0.748 to 0.646,while that under different diameter contact pairs decreases from 0.941 to 0.911.The friction degree between steel wires under different diameter contact pairs is obviously greater than that under the same diameter contact pairs.In addition,in the stable stage,the friction coefficient between steel wires under the same diameter contact pairs presents a horizontal change trend,while that under different diameter contact pairs shows a slight upward trend.Under different working conditions,the depth and width of wear scars increase with increasing the contact force.For the same contact force,the wear depth of steel wires under the convex contact pairs is significantly greater than that under the concave contact pairs,and the greater the contact force is,the more obvious the difference of wear depth of steel wires under different contact forms is.Whether the diameter of the loading wire and the fatigue wire is the same or not,the wear coefficient of steel wires under different contact forms decreases with the increase of the contact force.The wear depth and coefficient of steel wires under different diameter contact pairs are significantly greater than that under the same diameter contact pairs.For the microscopic wear characteristics of steel wires,compared with the same diameter contact pairs,the worn surface of steel wires under the different diameters contact pairs presents more serious wear characteristics,and the worn surface of steel wires under the concave contact pairs is rougher than that under the convex contact pairs.Furthermore,there are a lot of wear characteristics on the surface of worn steel wire,such as wear debris,material adhesion,plastic deformation,fine scratches,material delamination,micro cracks and furrows.Therefore,the main wear mechanisms between steel wires are abrasive wear,adhesive wear and fatigue wear,and the fatigue wear of steel wires under different diameter contact pairs are more serious,which is caused by the"cutting"effect between thin steel wire and thick steel wire.As the contact force increases,the fatigue life of steel wires under different strand structures decreases gradually.And for the same contact force,the fatigue life of steel wires under different diameter contact pairs is obviously smaller than that under the same diameter contact pairs.The fracture surface of steel wires is obviously divided into fatigue source region,crack propagation region and final fracture region.Abundant secondary cracks and dimples exist in the final fracture region,and the fatigue fracture failure mechanism of steel wires is mainly ductile fracture.
Aerostatic bearings are widely used in ultra-precision manufacturing equipment due to their noncontact,near-zero friction,high accuracy,and pollution-free characteristics.Loading capacity,stiffness and stability are the important parameters of aerostatic bearings.Traditionally,the load capacity and stiffness of aerostatic bearings are improved by adding the pocket.However,turbulent vortices in the pocket can cause the pressure fluctuation of the aerostatic bearing flow field and induce the micro-vibration of aerostatic bearings,which seriously affects the stability and positioning accuracy.In order to improve the stability of the aerostatic bearing and its positioning accuracy,the transient flow characteristics of a classical orifice restriction aerostatic bearing are analyzed,and the formation mechanism of the vortex inside the pocket is described.According to the formation mechanism of the turbulent vortices inside the pocket,a novel aerostatic bearing with an inclined orifice restrictor(IOR)is designed.The IOR structure can suppress the generation of turbulent vortices by changing the direction of airflows in the pocket,which can reduce the micro-vibration of aerostatic bearings.In the simulation calculation,the airflow calculational field is divided into 4 parts due to the symmetry of the aerostatic bearing structure,and a quarter structure is utilized as the airflow computational field to improve the computational efficiency.To improve the mesh quality and ensure calculation accuracy,structured grids are used in the CFD model.In order to capture the turbulent flow structures inside the pocket the grid is refined in the orifice and the pocket.The large eddy simulation method is utilized to analyze the flow field inside the aerostatic bearing with the IOR.In order to verify the proposed numerical model,the simulation results of the aerostatic bearing are compared with the existing experimental data.Furthermore,the influence of the working condition and structure parameters of the aerostatic bearing with IOR on its performance is analyzed,such as the angle of the inclined orifice,the height of the inclined orifice,the diameter of the inclined orifice and the supply pressure of the aerostatic bearing with IOR.The simulation results show that the micro-vibration of the aerostatic bearing with IOR decreases first and then increases as the angle of the inclined orifice increases,while the loading capacity remains basically unchanged.When the inclined orifice angle is 110°,the aerostatic bearing with IOR has the weakest amplitude of micro-vibration and the best stability.The micro-vibration of the aerostatic bearing with IOR increases as the inclined orifice height decreases,and the loading capacity remains basically unchanged.When the orifice height is increased to 0.4 mm,further increase of the inclined orifice height has little effect on the micro-vibration of the aerostatic bearing with IOR.The micro-vibration of the aerostatic bearing with IOR decreases as the diameter of the inclined orifice increases,and the loading capacity increases as the diameter of the orifice increases.The micro-vibration and the loading capacity of the aerostatic bearing with IOR both increase as the increasing of supply pressure.The formation of turbulence can be inhibited by changing the structural parameters of the aerostatic bearings,thus improving the stability of the aerostatic bearings.The research results can provide a theoretical reference for the design of high-stability aerostatic bearings.
Mechanical seal is a key component in industrial production,and its safe and reliable operation are very important for the continuity of industrial production.There are many problems with the maintenance time of mechanical seals.Premature replacement of seals will increase production costs,and vice versa,it will cause security risks due to failure.Given the lack of an effective state monitoring method for the performance degradation caused by face wear of contact mechanical seals in the process of use,a method for measuring the tribological behavior of mechanical seals by face vibration acceleration was proposed.The test rig of the mechanical seal was built,the original waveform data of vibration acceleration of the stationary ring face was collected,and the tribological performance test of the mechanical seal was carried out.By replacing four rotating rings with different face surface roughness to simulate the operation to failure test of mechanical seal,the relationship between sensitive characteristic parameters of seal face acceleration and the increase of wear degree of the face was explored.By changing the rotational speed,the variation law of the sensitive characteristic parameters of the seal face acceleration with the rotational speed was explored,and then the evolution law of the sensitive characteristic parameters of the mechanical seal face vibration with the tribological regime was discussed.Based on the test data,the performance degradation evaluation method based on k-medoid clustering was attempted to establish,and the evaluation standard of mechanical seal performance degradation was established.The results showed that the face vibration acceleration monitoring method could be used to monitor the tribological regime of mechanical seals.Fuzzy entropy,mean entropy and permutation entropy were three face vibration-sensitive characteristic parameters that were sensitive to tribological regimes.With the increase of face wear degree,the face tribological regime gradually transiteds from the mixed friction state to the boundary tribological regime.The fuzzy entropy,mean value,and entropy of face vibration acceleration showed good sensitivity to the increase of face wear degree,among which the fuzzy entropy was more sensitive to the change of face wear degree than the mean value and entropy of arrangement.The fuzzy entropy,mean value,and permutation entropy of the face vibration of the stationary ring increased linearly with the increase of rotating speed under the mixed friction state of the mechanical seal.The fundamental frequency amplitude of the face vibration waveform increaseed with the increase of rotating speed,and the change of the fundamental frequency amplitude of the radial vibration waveform was more sensitive.The failure evaluation method of the mechanical seal was established.The three-dimensional vector coordinates of the original mean value of axial,radial,and tangential face vibration data were calculated in real-time.The Euclidean distance between the coordinates and the cluster center corresponding to the degenerate state was calculated.When the mechanical seal performance degradation level reached IV,it indicated that the mechanical seal might fail.The above conclusions could be used in engineering applications of seals.It was proved that the face vibration acceleration signal contained abundant information about the change of microstructure in the dynamic process and was sensitive to the change of microscopic motion in the elastic deformation.The face vibration acceleration measurement method monitoring of mechanical seals could help workers assess the status of seals and determine whether and what interventions were needed.This had great engineering value for the safe operation and life management of seals.
Dynamic pressure seal is widely used in high-speed fluid machinery,and its groove shape is the key factor to determine its steady-state characteristics(such as opening force,film thickness and leakage rate)and dynamic characteristics(such as dynamic stiffness and dynamic damping),and a reasonable groove shape can greatly improve the fluid lubrication performance of the seal end face and ensure the safe and stable long-life operation of dynamic pressure seal.Therefore,the study of groove optimization accounts for a large part of the research on dynamic pressure seals.Groove optimization is mainly divided into amorphous groove research and fixed shape groove research,of which fixed shape optimization research accounts for a large part.This is because it is relatively easy to optimize the study of fixed shape groove patterns,and a large number of studies and experiences have shown that most of the engineering needs can be met by optimizing the widely used fixed shape groove patterns(such as logarithmic spiral grooves,T-shaped grooves,tree grooves,etc.). In order to improve the fluid lubrication performance of fixed shape dynamic pressure seal,an optimization method of dynamic pressure seal groove type based on the principle of fluid dynamic pressure was proposed:taken the typical parameters of spiral groove sealing performance under constant closure force as the initial value,the number of grooves,groove width ratio,groove dam ratio and spiral angle of dynamic pressure seal spiral groove as the optimization variables,and minimized the ratio of leakage rate to opening force as the optimization objective. Established a slot optimization model to obtain a series of optimized slot types,and the optimization results showed that the proposed optimization method had good stability for different rotational speeds and optimized number of slots,and the optimized slots were concentrated on two structural parameters A and B,which were 15°,0.5,0.55 and 22.5°,0.55,0.55 in the order of helix angle β,slot width ratioγ1and slot dam ratio γ2,respectively;further comparison analysis showed that the inner mechanism of the slot optimization process was that by adjusting the helix angle,slot width ratio and slot dam ratio,shifting the peak pressure and homogenizing the circumferential pressure to achieve the goal of reducing the leakage rate by maintaining a high opening force while reducing the fluid transfer in the slot and dam area and lowering the fluid outlet flow rate. Compared the opening performance of typical spiral groove and A and B groove types,the results showed that in the small film thickness section,the fluid film formation rate was larger,so the typical spiral groove with high film thickness was the preferred groove type,while in the large film thickness section,the B groove with lower leakage rate was the preferred groove type,while the performance of A groove in the full film thickness section was between the two.It was noticeable that differences in performance between the optimized and typical grooves at different rotational speeds were indicative of the important influence of rotational speed on the optimized groove parameters.Obviously,for a given sealing parameter,optimization at the actual working speed could further improve the actual sealing performance.Meanwhile,the sealing performance of a typical spiral groove was not inferior to that of the new groove obtained from optimization,and it was wise to optimize the groove with typical parameters as the initial design for a spiral groove dynamic seal with a given optimization target.
Contact-type mechanical seals are widely utilized across various industries,including aviation,maritime,and chemical engineering,owing to their exceptional sealing capabilities.During their operational lifespan,these seals are subjected to diverse frictional states,namely dry friction,boundary lubrication,and hybrid lubrication.In the context of dry friction and boundary lubrication,the predominant mode of friction between the seal faces is attributed to direct contact between microasperities,which significantly contributes to seal wear and impairs its longevity.However,when operating under hybrid lubrication conditions,both fluid film lubrication and microasperity contact play substantial roles in the overall frictional behavior.Given the prevalence of hybrid lubrication as the dominant operating state for contact-type mechanical seals,it becomes imperative to thoroughly investigate the intricate frictional mechanisms governing such conditions.Understanding the underlying phenomena will shed light on the fundamental aspects of friction in hybrid lubrication,thereby facilitating the development of effective strategies to optimize seal performance and enhance their reliability. In order to investigate the friction mechanism under hybrid lubrication conditions,a comprehensive study was conducted by integrating a rough surface elastoplastic model and solving the Reynolds equation considering the influence of seal face roughness.The impact of various operating conditions,such as rotational speed and fluid pressure,on the friction parameters governing the sealing performance in the hybrid lubrication state was thoroughly examined.Furthermore,an energy formula for the emitted acoustic waves during sealing was derived to quantify the energy distribution.To experimentally validate the findings,a specialized test rig for contact-type mechanical seal friction was developed.Concurrently,the collection of seal face temperature data and acoustic emission signal data was performed.By analyzing the acquired seal face temperature data,the hybrid lubrication state was categorized into distinct wear and stable periods.Subsequently,utilizing the 1.5-dimensional spectral theory,the acoustic emission signals were processed to extract the characteristic frequencies associated with the sealing behavior,thereby unraveling the frictional evolution patterns prevalent in the hybrid lubrication state.The outcomes of this investigation underscored the significant influence of friction parameters on the energy amplitude of the emitted acoustic waves,and established that the form of seal friction underwent alterations throughout the hybrid lubrication state.Specifically,during the wear period,a rapid rise in seal face temperature was observed,accompanied by a pronounced amplitude of characteristic frequencies related to microasperity contact,signifying that microasperity contact dominated the seal face friction.Conversely,during the stable period,the seal face temperature fluctuated within a stabilized range,concomitant with an increased amplitude of characteristic frequencies associated with viscous shear friction of the fluid film.This observation suggested an intensified viscous shear effect,with localized microasperity contact exclusively presented on the seal faces.The conclusions derived from this comprehensive investigation beared crucial theoretical implications for the study of friction mechanisms governing contact-type mechanical seals operating under hybrid lubrication conditions.
There is also a growing need for internal combustion engines to improve fuel efficiency and reduce polluting emissions in the fight against global climate change.Efficient supercharging,antifriction coating,low viscosity lubricating oil and other energy saving technologies have appeared.The requirements of higher mechanical stress,higher speed and higher operating temperature in the new technology make it difficult for existing commercial internal combustion engine oil additives to meet.Nano additives have a broad application prospect in energy saving engine oils due to their high anti-wear and anti-friction effects.The co-effect mechanism between nano additives and commercial additives in engine oils is a key issue in developing the formula of nano additive engine oils.Quartz crystal microbalance(QCM-D)was used to study the synergistic adsorption behavior of oleylamine modified CeO2 nanoparticles and commercial engine oil additives on metal surfaces,and the effect mechanism on anti-friction and anti-wear properties of CeO2 nanoparticles.It was found that the formation of dense CeO2 friction film on the surface of the friction pair by CeO2 nanoparticles is the fundamental mechanism to achieve antifriction and anti-wear properties.When CeO2 nanoparticles are mixed with commercial internal combustion engine oil additives,Dispersant(AD)interferes with the formation of CeO2 friction film,resulting in its antifriction and antiwear properties lower than that of a single additive,showing an antagonistic effect.Other additives,such as Detergent(DE),Friction Modifier(FM),Antioxidant(AO)and Viscosity Index Improver(VII),can form friction films together with CeO2 nanoparticles,making the anti-wear performance better than that of a single additive,showing a synergistic effect.Both CeO2 nanoparticles and the involved commercial additives are able to co-adsorb on metal surfaces.For Viscosity Index Improver(Ⅶ),Antioxidant(AO),Detergent(DE)and Dispersants(AD),the degree of co-adsorption of CeO2 nanoparticles decreased with the increase of alkyl chain length in the additive.The polyisobutene(FIB)with molecular weight of 1300 in the Dispersant(AD)molecule greatly hindered the adsorption of CeO2 nanoparticles,which could not be deposited on the surface of the friction pair to form a film,leading to a significant antagonistic effect.For the multi-layer viscoelastic adsorption of Friction Modifier(FM),the adsorption of CeO2 nanoparticles on the metal surface increased significantly,resulting in the maximum adsorption mass.The wear resistance of CeO2 nanoparticles combined with organic molecular additives is proportional to the adsorption mass of the adsorption layer.The combination with the Friction Modifier(FM)has the maximum adsorption mass and the smallest diameter of the grinding spot.The combination with Dispersant(AD)has the lowest adsorption quality,resulting in the grinding diameter of AD is larger than that of other additives.The friction film formed by the Detergent(DE)with inorganic nuclei and CeO2 nanoparticles has stronger anti-wear ability than the single CeO2 friction film.
