In the past 250 years, natural resources have been consumed with very high speed and the earth is seriously damaged and polluted. Tribology supported powerful and high speed machinery in the period with technologies of energy and materials saving. Many kinds of resources reserves including those of energy and metals are now facing to deficiency within one hundred years. Revolutional technologies of sustainability and zero-emission are being strongly required in the world industries to establish new lifestyles of real health and sustainability for the eternal existence of human beings and other living things in symbiotic ways. Tribology is expected to support the revolutions by developing its science and technology for the demand of new values of industrial products.
Bump-type foil bearings have demonstrated excellent performance in service experiences in recent 30 years. Due to their special structures, the performance prediction models must couple the air pressure with the elastic deflection of the compliant foil structure. The solution of air pressure has been well settled in the hydrodynamic lubrication theory, while the deflection of foils now still cannot be accurately solved due to the mechanical complexity of the corrugated bump structure. A theoretical model, link-spring model, was developed to predict the structure characteristics of foil strips in a previous work. Effects of four factors, i.e., the elasticity of the bump foil, the interaction forces between bumps, the friction forces at contact surfaces, and the local deflection in the top foil, had been taken into consideration. In this investigation, based on the link-spring model, a perturbation approach is used to determine the dynamic characteristics of bump-type foil bearings. The calculations have been performed with different meshes. And the accordant results show that the calculation is independent on the mesh. The effects on the dynamic coefficients of the friction forces and radial clearance are also evaluated using the perturbation method.
A Molecular Dynamics (MD) technique is proposed to simulate the motion of water nanodroplets on wavelike nanorough surfaces and the contact angle is evaluated. Results obtained through MD simulations, in agreement with the experimental evidence, suggest that the contact angle can be increased by folding the base surface, to produce a wavelike nanoroughness. By considering the fraction of nonwetted area as a function of the ratio of true area to projected area, it becomes possible to fit the results obtained through MD simulations on a generalized Wenzel-Cassie model, even in the nanometer range. The physical meaning of such fitting technique is discussed. Results obtained are useful for the appropriate design of the hydrophobic or hydrophilic surfaces, and for the adequate design of nanorough surfaces with tribological applications.
Previously, we have reported tribological characteristics of a new unique Thermo-Reversible Gel-Lubricants (TR Gel-Lube), which consists of base fluids and gel agent. TR Gel-Lube has low friction property compared with conventional greases under mild lubricating conditions. However, under severe lubricating condition, extreme pressure (EP) property must be improved by some EP additives. In this study, addition of solid lubricants was investigated. Tribological properties were examined by some tribometers and various enhancements by Molybdenum disulfide, Melamine Cyanuric Acid and Boron Nitrides were observed. Mechanisms of the lubricity improvements were proposed by results of some chemical/physical analyses.
The objective of this study was to set forth guidelines for designing such an artificial knee joint that can make deep flexion. To this respect, we performed 2D model simulation for deep squatting in which the conventional posterior stabilized knee prosthesis was fitted. In the simulation we introduced a newly defined slip ratio in order to describe an over slipping phenomenon; the slipping and the rolling directions were mutually reversing. Then, the results demonstrated that the slip ratio was over 1 at high and deep flexion, indicating that the femoral rollback did not occur even though the post and the cam contacted. The relation also indicated that the conventional post-cam mechanism would not work appropriately at high/deep flexion. To overcome the above, and to promote femoral rollback even at high/deep flexion, we proposed a new design of the post-cam mechanism, which we called as a ball-ditch mechanism.
It is considered that cavitation plays an important role in maintaining the sealing performance of mechanical seals. However, there are not any studies that demonstrated how to control cavitation regions and take advantage of them to improve the sealing performance of mechanical seals. In this study, we have tried to demonstrate that the cavitation rings could be formed and maintained by taking advantage of the laser-textured surface. Furthermore, the effects of the cavitation rings on the frictional characteristics were also investigated. As a result, it was found that the sharp edge of the laser-textured surface could act as the geometric barrier to prevent the gas-liquid interface migration. Eventually, the gas-liquid interface maintained the steady fluid flow along the rows of dimples as the cavitation rings. Furthermore, it was also found that the friction coefficient of the textured surface fluctuated less than that of the plain surface.
The mechanism responsible for the effects of electric fields on the lubricant dip-coating process was investigated by comparing the lubricant film conformations obtained when applying an electric field for different durations. A QA-40 solution was prepared for dip-coating a magnetic disk under two conditions. The lubricant film thickness and surface free energy obtained under the two conditions were compared. It was found that the molecular conformation was changed by the electric field resulting in more end-groups being adsorbed on the disk surface when the electric field is applied during the withdrawal of the disk from the solution than during the normal dip process. As a result, the surface free energy decreased. As a consequence of applying the electric field during dipping and withdrawing, the thickness of the QA-40 layer increased 1 - 3 Å.
This paper proposes a new grease life predicting method which utilizes kinetics analysis of measured data obtained through thermogravimetry. The grease life is predicted by weight loss at a certain temperature. By separating effects of complex dynamics and physics in ball bearings to which the grease is applied, a static life of the grease can be predicted as a stand-alone evaluation within very short period of time.
This study demonstrates wear-protective tribofilms produced by an artificial supply of fine metal particles onto rubbing steel surfaces in vacuum. The supplied metal particles were Ag, Bi, Cu, Ni, Ti, and Fe, with the diameters of the particles ranging from 20 nm to 45 μm. The influence of the metal type of the supplied particles on the behavior of tribofilm formation as well as wear of the tribofilms were investigated. When Bi or Ti particles were supplied, the rubbed surfaces were almost entirely covered with the tribofilm. The thickness of the tribofilm produced by supplying Bi particles was 5 ∼ 8 μm. The tribofilms formed by supplying Ag, Bi or Cu particles showed initial low wear in wear tests, and the sliding distance of initial low wear was longer for the tribofilms formed by supplying finer particles. The tribofilms produced by supplying Bi (1.5 μm) particles showed the longest sliding distance of initial low wear.
Approximation of a third body proposes that a tribo-contact is conformed by two first bodies (that is to say; elements of a machine), and by an interface -or third body- of different composition, where velocity between the first two bodies accommodates tribo-chemically. In other words, the third body interface is a mecanochemical concept which has the ability to transmit mechanical power in speed. Correspondingly, thermodynamical activity of this third body friction, is of irreversible non-equilibrium, being more coherent to establish an exergetic analysis in order to conclude to a holistic and more advanced formulation for the so badly named Friction “Coefficient”. Concepts of Irreversible Non-Equilibrium Thermodynamics allow to establish a new formulation for third-body boundary friction. Microscopic analysis of tribo-fluctuations is applied to a generic contact to clarify the bond between friction and dissipation. The resulting mechanochemical formula for the 3rd-body’s boundary friction, falls in the scope of the Physics of the CHAOS and the phenomena of auto-organization of surfaces.
Fretting fatigue is a possible failure mode of rolling bearings, as well as for other machine elements with contacts. For a rotating bearing it normally can occur in the interfaces between outer ring/housing, and inner ring/shaft. For a non-rotating bearing subjected to small motion due to vibration, it can occur in the concentrated rolling element/ring contacts as well (mainly related to false brinelling). Detailed models for fretting-fatigue have been transferred and adapted to a bearing simulation framework called BEAring Simulation Toolbox (BEAST). It allows the use of the fretting-fatigue model to predict failures and be used by engineers in developing new solutions. Another important usage is to provide a platform for further development of other fretting-fatigue models, fretting-wear and false brinelling models. The results from two different examples are presented; one model with an oscillating body in contact with another, representing a concentrated contact, and one model with a Deep Groove Ball Bearing (DGBB) mounted inside a ring-like housing. Results are presented in terms of contact pressures, shear forces at the surfaces and a parameter representing the fretting risk according to the Dang-Van criterion. The model for the concentrated contact is used to verify the simulations against stand-alone computer code and experiments. The DGBB model shows how the fretting-fatigue related results are influenced by the ball pass frequency and the flexibility of the bearing and the housing.
This paper discusses various design aspects and experimental results regarding the selection of bearing materials in combination with different shaft materials utilized by electric water pumps. Acceleration tests have been conducted prior to endurance life tests which simulate actual automotive applications. The potential dangers of severe wear in certain material combinations is also discussed.
In the present work the evaluation of coconut and palm oil as lubricants in four-stroke engine was carried out and the performance was compared with commercially available engine oil. The tribological properties of oil samples collected from the engine at regular interval were evaluated by means of four ball tester. The emissions from engine were monitored by using exhaust gas analyzer. It was observed that antiwear properties of fresh vegetable base oils and engine oil were comparable at ambient conditions. The observed deviation with usage was linked to the oxidation and the absence of additives in vegetable oil. The increased wear with commercial engine oil was due to depletion of additives. Increased fuel efficiency and reduction in the concentration of oxides of carbon and nitrogen in the emission observed with vegetable oil based lubricant was linked to its high flash point.
It is essential to clarify the interaction between the magnetic head and the monolayer lubricant film coated on the magnetic disk in the design of next-generation hard disk drives with ultra-low flying height. However, with previous measuring methods such as AFM, it was difficult to measure the mechanical properties of molecularly thin lubricant films with a precisely controlled nanometer-sized gaps. In this study, we applied the fiber wobbling method to clarify the viscoelastic properties of monolayer lubricant films during touch-down and take-off behavior. The fiber wobbling method is the highly-sensitive measurement of shear force we developed and can control the shearing gap with sub-nanometer resolution. The gap dependence of viscoelastic properties was evaluated both in the approaching and the separating processes and their differences and dependencies on the types of lubricant films were discussed. As sample lubricants, we used non-polar and polar perfluoropolyether lubricants: Fomblin Z03 and Fomblin Zdol4000. Three different types of monolayer lubricant films were prepared. The first one consisted of mobile molecules of Z03 only. The second one contained both mobile and bonded molecules of Zdol4000. The third one was only made of bonded molecules of Zdol4000. Our experimental results indicated that the mobile molecules caused the formation of a liquid bridge between solid surfaces and it leads to the hysteresis of viscoelastic properties between approaching and separating processes. On the other hand, the sample only consisted of bonded molecules did not show such a hysteresis.
An advanced head disk interface (HDI) system assisted by gas perfluoropolyether (PFPE) lubrication is discussed in this paper. It is known that lubricant spins off at a high rotation speed and high temperature. Lubricant redistribution after long-term seeking operation with near-contact flying has been studied. The spin-off and redistribution of lubricant are serious problems for the reliability of hard disk drives (HDDs). An HDI system is proposed that exhibits high performance without lubricant spin-off and redistribution; that is, it allows only a small amount of lubricant to drip on the recirculation filter in the head disk assembly (HDA). This lubricant evaporates in the HDI at a high temperature, and the lubricant gas is adsorbed on the disk surface. Consequently, the thickness of the lubricant layer decreases because of spin-off or degradation. As a result, the spin-off, redistribution, and head contamination are significantly reduced. The lubricant can be maintained for a long time on the magnetic disk. In this study, we focused on the reduction of head contamination by gas lubrication. We confirmed that gas lubrication reduced head contamination caused by long-term HDD operation.
Original equipment manufacturers (OEMs) and end-users perceive “Zero Wear” differently. The “Zero Wear” approach will be put into a general relation for different applications and illuminated by individual paths, either based on monolithic materials, thin film coatings or alternative base oils, featuring triboactive materials and lubricious oxides for tribological engine components and dry running foil bearings or specific DLC, ta-C and novel Zirconium-based thin film coatings for concentrated contacts above FZG 14 and alternative engine oils (NoSAP & bio-no-tox). The associated tribometric test equipments for these examples will also be detailed.
For the optimization of polishing processes, the knowledge of the effectiveness of additives on the surface binding is essential. The nano-hardness was used as an indication for the most adequate acid used as additives. For analyzing the nano-hardness, nanoindentation tests were performed. This paper describes the investigations on the nano-hardness of NiFe affected by hydrochloric acid (HCl) and nitric acid (HNO3) used as liquid additives during a polishing process.