Academic literature on the topic 'Flat Face Friction'

The flat end face mechanical seals are widely used in shaft sealing at moderate rotational speed. The thermal deformation of the rotating and stationary rings initiated by friction heat of fluid film should be primarily considered in the design of mechanical seal. In consideration of the coupling effect among the thermal deformation of sealing rings, the fluid flow in the gap composed by end faces of sealing rings and the heat transfer from fluid film to sealing rings, the optimum design method for flat end face mechanical seal is established. The end faces are fabricated to form a divergent gap at the inner side of the sealing rings, and a convergent gap will occur at the outer side and a parallel gap will be obtained at where the original divergent gap is due to the thermal deformation. After optimization, the leakage rate can be reduced while the bearing force of fluid film is still large enough to keep the fluid lubrication of the end faces.

Friction stir welding is a solid-state welding technique for joining metals such as aluminum alloys quickly and reliably. This article presents a design of experiments approach (central composite face–centered factorial design) for predicting and optimizing the process parameters of dissimilar friction stir welded AA6351–AA5083. Three weld parameters that influence weld quality were considered, namely, tool shoulder profile (flat grooved, partial impeller and full impeller), rotational speed and welding speed. Experimental results detailing the variation of the ultimate tensile strength as a function of the friction stir welding process parameters are presented and analyzed. An empirical model that relates the friction stir welding process parameters and the ultimate tensile strength was obtained by utilizing a design of experiments technique. The models developed were validated by an analysis of variance. In general, the full impeller shoulder profile displayed the best mechanical properties when compared to the other profiles. Electron backscatter diffraction maps were used to correlate the metallurgical properties of the dissimilar joints with the joint mechanical properties as obtained experimentally and subsequently modeled. The optimal friction stir welding process parameters, to maximize ultimate tensile strength, are identified and reported.

Multistage centrifugal pumps and compressors are among the most widely used pieces of rotating machinery in industry. A typical application demands the arrangement of several impellers or wheels mounted on a shaft that spins within a stationary case. Annular seals are the most common sealing devices used in this type of machinery. The annular seal design affects both (i) machinery performance in terms of energy conversion efficiency, and (ii) stability due to the interaction within the rotor and the stator through the fluid flow within the seals. Traditionally, the “bulk-flow” theory due to Hirs (ASME J. Lubrication Technol., pp. 137–146) has been used to estimate annular seals leakage and dynamic coefficients. To predict the flow behavior through the seal, this theory relies on empirical friction factor correlations. While leakage is well predicted, the dynamic coefficients are not. The discrepancy is attributed to the friction factor model. Several experiments have produced seal leakage data indicating that friction factor increases as the seal clearance is increased, contradicting predictions based on Moody’s pipe-friction model. A Computational Fluid Dynamics (CFD) commercial code was used to simulate flat-plate-channel-flow experimental tests of water flowing with deliberately roughened surfaces, showing an increase of friction factor with clearance increase. The higher friction factor characteristics of these deliberately roughened surfaces are governed by their ability to develop a high static pressure in the trailing face of each roughness cavity, while the wall shear stresses on the smooth land play a secondary role. In a certain Reynolds number range, the maximum friction factor observed on a specific roughness pattern size is independent of the actual clearance, which we have referred to as the friction-factor-to-clearance indifference behavior. This phenomenon is found to be related to the roughness cavity size and its length-to-clearance ratio.

The aim of this study is to analyze how the process parameters affect the mechanical properties of butt joints obtained by friction stir welding (FSW). The experimental study was performed by the FSW of sheets having a thickness equal to 6 mm and made of aluminum alloys AA2024 T351, varying the process parameters, namely rotational speed and welding speed. The following welding parameters were used: the rotation speed of the tool did not change and amounted to 750 rpm, and the welding speed was 73, 116,150 mm / min. The welds were obtained without the presence of errors and with an acceptable flat surface of the compound. Tensile tests were performed orthogonally to the welding direction on specimens having the welding nugget placed in the middle of gage length. Vickers hardness measurement was conducted perpendicular to the welding direction, a cross-section of the weld joint. The hardness profiles were obtained along 3 horizontal and 63 vertical directions. Bend testing was carried out according to EN 910 The bending specimens were tested using face and root side of the joint in tension.

Air lubrication to reduce hull skin friction is an idea that originated more than a century ago. There are few implementations of this concept, and there are even fewer systematic investigations at high Reynolds numbers. To address this, an experimental investigation was performed at the W. B. Morgan Large Cavitation Channel that examined the drag-reducing effects of a ventilated partial cavity at high Reynolds numbers. The design was accomplished using both linear gravity wave theory and a two-dimensional inviscid numerical model via Fluent. The physical model was a 12 m long flat plate with a plenum on the bottom. The plenum was formed by an abrupt step near the nose and a long sloping reattachment region toward the rear. Air was injected from the aft face of the step to create a cavity approximately 17.8 cm deep. Friction loads, air flow, and cavity pressure were measured over a range of air fluxes and speeds near the cavity design speed of 3.4 m/s. Cavities were shown to be stable with respect to large changes in air flux and slow perturbations in tunnel speed and pressure. Stable cavities were produced that reduced the skin drag by more than 95% over the extent of the cavity, including the cavity closure.

AbstractThis work is a computational study of a rarefied non-reacting hypersonic flow past a forward-facing step at zero-degree angle of attack in thermal non-equilibrium. Effects on the flow field structure and on the aerodynamic surface quantities due to changes in step frontal-face height are investigated by employing the direct simulation Monte Carlo method. The work focuses the attention of designers of hypersonic configurations on the fundamental parameter of surface discontinuity, which can have an important impact on even initial design. The results presented highlight the sensitivity of the primary flow field properties, velocity, density, pressure and temperature, to changes in the step frontal-face height. In addition, the behaviour of heat transfer, pressure and skin friction coefficients with variation of the step frontal-face height is detailed. The analysis shows that hypersonic flow past a forward-facing step in the transition flow regime is characterized by a strong compression ahead of the frontal face, which influences the aerodynamic surface properties upstream and adjacent to the frontal face. The analysis also shows that the extension of the upstream disturbance depends on the step frontal-face height. It was found that the recirculation region ahead of the step is also a function of the frontal-face height. A sequence of Moffatt eddies of decreasing size and intensity is observed in the concave step corner. Locally high heating and pressure loads were observed at three locations along the surface, i.e. on the lower surface, on the frontal face and on the upper surface. The results showed that both loads rely on the frontal-face height. The peak values for the heat transfer coefficient on the frontal-face surface were at least one order of magnitude larger than the maximum value observed for a smooth surface, i.e. a flat plate without a step. A comparison of the present simulation results with numerical and experimental data showed close agreement concerning the wall pressure acting on the step surface.

An analysis of a coupled plane elasticity problem of crack/contact mechanics for a coating/substrate system with functionally graded properties is performed, where the rigid flat punch slides over the surface of the coated system that contains a crack. The graded material is treated as a non-homogeneous interlayer between dissimilar, homogeneous phases of the coated medium and the crack is assumed to exist along the interface between the interlayer and the substrate. Based on the Fourier integral transform method and the transfer matrix approach, formulation of the current coupled mixed boundary value problem lends itself to the derivation of a set of three simultaneous Cauchy-type singular integral equations. In the numerical results, the emphasis is placed on the investigation of interactions between the contact stress field and the crack-tip behaviour for various combinations of material, geometric and loading parameters of the coated system. Specifically, effects of interfacial cracking on the distributions of the contact pressure and the in-plane stress component along the coating surface are examined and the mixed-mode stress intensity factors evaluated from the crack-tip stress field with the square-root singularity are provided as a function of punch location. Further addressed is the quantification of the singular character of contact pressure distributions at the trailing and leading edges of the flat punch in terms of the punch-edge stress intensity factors. Implicit in this particular analysis of the coupled crack/contact problem presented henceforth is that the crack closure behaviour under the compressive contact stress field is not taken into account, ignoring the influence of crack-face contact and friction.

In this work, the resistance to scratch and wear (pin-on-flat) tests of five different porous TiO2 films were compared. Such tribological tests were carried out under dry conditions. The coatings were electrodeposited on commercially pure-Ti by anodic oxidation method in different electrolyte solutions at constant voltages. The scratch tests were conducted by applying increasing normal loads up to 400 mN. The coefficient of friction (COF) varied from 0.2 up to 0.5, and increased at larger penetrations depths. When the electrolyte concentration was changed from 0.5 into 1.0M H2SO4, the COF slightly decreased. Scanning electron microscopy indicated that the coatings produced in H2SO4/150V and Na2SO4/100V did not have their substrates revealed. In addition, the samples anodized in H2SO4/150V had the highest elastic recoveries. Therefore, such coatings seem to be more resistant to scratch tests than the others. The wear tests were carried out with Berkovich tip as counter-face under constant normal loads of 10 mN in 10 forward-backward cycles. The coatings deposited in H2SO4/150V had the lowest wear volume rates. The findings suggest that the porous Ti oxide coatings electrodeposited above their rupture voltages are more suitable to both scratch- and wear-resistance compared to those prepared at the lowest voltage (H2SO4/100V).

In this study, a numerical model is developed to show the performance improvement of a cam–follower mechanism when using a roller type follower compared to the flat-faced follower. Nonconformal geometry besides the thermal effects due to the shearing of the lubricant film results in formation of a thin film in which the asperities contribute in carrying the load. The numerical model is developed in which the geometry, load, speed, lubricant properties, and the surface roughness profile is taken as input and the film thickness and friction coefficient as a function of cam angle are predicted. The asperities are assumed to have elastic, elasto-plastic, and plastic deformation. Simulation results indicated that the thermal effects cannot be neglected. Surface roughness is also a key parameter that affects the pressure distribution, film thickness, and friction coefficient. Finally, asperity and hydrodynamic pressure is reported and the performance of the two mechanisms is compared. Roller follower has a considerable preference in terms of friction coefficient compared to flat-faced follower. The minimum film thickness, however, is slightly larger in the flat follower.

This article develops a student effort model that considers several uncertainties students face: the chance of missing an exam as well as the uncertainty associated with translating knowledge into an exam grade. The model suggests that student effort increases when makeup exams are offered and when grading protocols are adopted that reduce knowledge-to-grade frictions; effects on student utility depend on time endowments, and leisure preferences. JEL Classifications: A20, D81, I21

The sheet metal forming process basically involves the shaping of sheet metal of various thickness and material properties into the desired contours. This metal forming process has been extensively used by the automotive industry to manufacture both car panels and parts. Over the years numerous investigations have been conducted on various aspects of the manufacturing process with varied success. In recent years the requirements on the sheet metal forming industry have headed towards improved stability in the forming process while lowering environmental burdens. Therefore the overall aim of this research was to identify a technique for developing lubricant formulations that are insensitive to the sheet metal forming process. Due to the expense of running experiments on production presses and to improve time efficiency of the process the evaluation procedure was required to be performed in a laboratory. Preliminary investigations in the friction/lubricant system identified several laboratory tests capable of measuring lubricant performance and their interaction with process variables. However, little was found on the correlation between laboratory tests and production performance of lubricants. Therefore the focus of the research switched to identifying links between the performance of lubricants in a production environment and laboratory tests. To reduce the influence of external parameters all significant process variables were identified and included in the correlation study to ensure that lubricant formulations could be desensitised to all significant variables. The significant process variables were found to be sensitive to die position, for instance: contact pressure, blank coating of the strips and surface roughness of the dies were found significant for the flat areas of the die while no variables affected friction when polished drawbeads were used. The next phase was to identify the interaction between the significant variables and the main lubricant ingredient groups. Only the fatty material ingredient group (responsible for the formation of boundary lubricant regimes) was found to significantly influence friction with no interaction between the ingredient groups. The influence of varying this ingredient group was then investigated in a production part and compared to laboratory results. The correlation between production performance and laboratory tests was found to be test dependant. With both the Flat Face Friction test and the Drawbead Simulator unaffected by changes in the lubricant formulation, while the Flat Bottom Cup test showing similar results as the production trial. It is believed that the lack of correlation between the friction tests and the production performance of the lubricant is due to the absence of bulk plastic deformation of the strip. For this reason the Ohio State University (OSU) friction test was incorporated in the lubricant evaluation procedure along with a Flat Bottom Cup test. Finally, it is strongly believed that if the lubricant evaluation procedure highlighted in this research is followed then lubricant formulations can be developed confidently in the laboratory.

Doctoral Thesis in Mechanical Engineering, Surface Engineering Branch, submitted to the Department of Mechanical Engineering, Faculty of Science and Technology of the University of Coimbra.
Transition-metal-dichalcogenide coatings (such as MoS2) provide low friction due to its characteristic low shear strength along the basal plane of the lamellar structure; however, the material can easily degrade through exfoliation and poor adhesion to the metallic substrates. Furthermore, its low load-bearing capacity leads to high wear and high coefficient of friction (COF). All these issues prevent these coatings for a wide range of applications meant for dry or solid lubrication. Physical vapour deposition (PVD) has provided new insights into the field of tribology and lubrication with the possibility to deposit tailored thin coatings based on the application requirements. The present work is aimed towards the development and optimization of direct current (DC) magnetron sputtered Mo-S-N coatings for low friction applications, particularly for space components. Then coatings with high adhesion to the substrate, high hardness and a stable tribological performance in vacuum environment are deposited. Initially, in this work, an innovative approach was employed to improve the coating's adhesion. A secondary plasma source was used during deposition to generate an additional charged particle flux which was directed to the growing coating independently of the magnetron cathode. Therefore, Mo-S-N solid lubricant coating were deposited by DC magnetron sputtering from a single molybdenum disulphide (MoS2) target in a reactive atmosphere. Nitrogen was introduced during the deposition with increasing partial pressures, resulting in a high N content in the alloyed coatings (37 at. %). The variation in the incident ion energy and flux of the energetic species bombarding the growing coating allows for the control of the S/Mo ratio through the selective re-sputtering of sulphur from the coating. The S/Mo ratio was progressively increased, with a gradient-like effect, up to the range of 1.2 - 1.8, i.e., from an almost metallic Mo(N) layer up-to-the lubricious sulphide. The coatings were nanocrystalline from 0 to 28 at. % N and, further addition, led to the amorphous structure. Combining the ion bombardment with nitrogen incorporation, the cohesive critical load (Lc1) reached 38 N, one order of magnitude higher than MoS2 coating. The adhesion at coating-substrate was above 80 N. A maximum hardness of 8.9 GPa was measured for the 37 at. % N-alloyed coating. For high N content coatings, high-resolution transmission electron microscopy (HR-TEM) revealed an amorphous structure as well as a perfect bonding with the substrate, with zones with epitaxial growing. Afterwards, the tribological performance of Mo-S-N coatings were analysed in vacuum (10-4 Pa) and room (20 - 25 °C, 20 - 30 % RH) conditions. The tribological tests were performed at relatively low contact stresses to replicate real industrial needs using a cylinder-on-flat reciprocating tribometer. The interaction between different mating surfaces (coating versus steel, coating versus coating) was carried out. Additionally, the effects of loads on the sliding properties were also studied for coating versus coating interactions, and endurance testing for one of the Mo-S-N coatings with coating versus steel interaction. In all mating conditions, the pure MoS2 coating had COF in the range of 0.1 – 0.25 and the least specific wear rates were found to be 3.0 × 10-6 mm3/N.m for flat and 2.5 × 10-6 mm3/N.m for the cylinder. As compared to MoS2 coating, the COF and specific wear rates decreased with N additions. The COF lied in the range of 0.05 – 0.1 for Mo-S-N coatings, while coating versus coating displayed the lowest specific wear rates (8.6 × 10-8 mm3/N.m for flat and 4.4 × 10-8 mm3/N.m for cylinder). The increase in the load resulted in lower COF but higher wear rate. The Mo-S-N coatings performed for longer duration at low COF without any failures compared to pure MoS2. Finally, one of the Mo-S-N coatings tested for different mating conditions in ambient air resulted in an increasing trend of COF, reaching the maximum value of 0.3. The detailed mechanism behind the COF behaviour for the different mating conditions was also presented and discussed. This work brings some important issues when testing transition metal dichalcogenides based coatings under low contact stress conditions more appropriated for simulating real service applications. In the final part of this thesis, the aim was to investigate the tribological behaviour of an amorphous Mo-S-N coatings, especially, (i) the role of nitrogen incorporation, (ii) the formation mechanism of MoS2 tribo-film at the sliding interface and, (iii) the changes in the friction behaviour under different environments. One of the Mo-S-N coatings (30 at. % N) was tested using standard ball-on-disc rotating tribometer with high contact stresses. The coating was predicted to have either a Mo-S-N phase with N filling some of the S sites or a MoS2(N2) structure where the gas molecules prevent the formation of a crystalline lamellar structure. The tribological studies performed in vacuum and ambient air resulted in steady-state COF values of 0.03 and 0.15, respectively. HR-TEM analysis performed on the wear-tracks revealed that the low coefficient of friction (COF) in vacuum was attributed to the formation of a thick and continuous lamellar tribo-film with a low amount of nitrogen. Contrarily, in ambient air, the surface oxidation disturbed the formation of a continuous MoS2 tribo-film from the amorphous coatings, leading to an increase in the COF and wear rate. This study shows through indirect measurements of the chemical composition of the as-deposited coating and wear debris that nitrogen is stored in gaseous form (N2) within the amorphous matrix and is released from the contact during sliding.
RESUMO: Os revestimentos de dicalcogenetos de metais de transição (como p.ex. o MoS2) mostram baixo atrito devido à resistência reduzida ao corte característica dos planos basais da estrutura lamelar; no entanto, o material pode degradar-se facilmente devido à sua esfoliação e má adesão aos substratos metálicos. Além disso, devido à baixa resistência a cargas de contato, estes revestimentos podem apresentar coeficientes de atrito (COF) e desgaste muito elevados. Estes problemas têm tido um impacto negativo que os tem impedido de serem utilizados numa gama mais alargada de aplicações onde é requerida lubrificação sólida. Com o advento das técnicas de deposição física em fase de vapor (PVD), abriram-se novas possibilidades para as áreas de tribologia e lubrificação, já que é possível ajustar as propriedades dos revestimentos finos aos requisitos impostos pela aplicação. O presente trabalho visa o desenvolvimento e otimização de revestimentos Mo-S-N depositados por pulverização catódica magnetrão em corrente contínua (CC) para aplicações de baixo atrito destinadas a componentes espaciais. O objetivo é depositar revestimentos com elevada adesão ao substrato, maior dureza e desempenho tribológico estável em condições ambientais e de vácuo. Inicialmente, neste trabalho, foi utilizada uma abordagem inovadora para melhorar a adesão do revestimento. Foi usada uma fonte secundária de plasma durante a deposição para gerar um fluxo adicional de partículas carregadas eletricamente que foi direcionado para o filme em crescimento independentemente do cátodo magnetrão. Assim, o revestimento de lubrificante Mo-S-N foi depositado por pulverização catódica CC magnetrão a partir de um único alvo de bissulfureto de molibdénio (MoS2) em atmosfera reativa. O azoto foi introduzido durante a deposição com pressões parciais crescentes, resultando num teor elevado de N nos revestimentos (37 at. %). A variação na energia e no fluxo dos iões que bombardeiam o revestimento em crescimento permite o controlo da relação S / Mo por meio de uma repulverização seletiva do enxofre do filme. A razão S / Mo foi aumentada progressivamente, dando origem a um gradiente de composição, até um valor na faixa de 1,2 - 1,8, desde um camada quase metálica até ao bissulfureto lubrificante. Combinando o bombardeamento iónico com a incorporação de azoto, a carga crítica coesiva (Lc1) atingiu 38N, uma ordem de grandeza maior do que o revestimento MoS2. A adesão ao substrato de revestimento atingiu valores acima de 80 N. A dureza máxima atingida foi de 8,9 GPa e foi medida para o revestimento com 37 at. %N. A microscopia eletrónica de transmissão de alta resolução (HR-TEM) dos revestimentos com elevado teor de N revelou uma estrutura amorfa e uma ligação perfeita com o substrato, com zonas onde pode ser detetado um crescimento epitaxial. Numa fase posterior, foi analisado o desempenho tribológico dos revestimentos Mo-S-N em vácuo (10-4 Pa) e ao ar ambiente (20 - 25 ° C, 20 - 30% UR) . Os testes tribológicos foram realizados com tensões de contato relativamente baixas, para replicar as necessidades industriais reais, num tribómetro alternativo usando uma geometria de cilindro / plano. Foi variada a interação entre diferentes superfícies de contato (revestimento versus aço, revestimento versus revestimento). Além disso, também foram estudados o efeitos da carga aplicada nas propriedades tribológicas para a interação revestimento vs. revestimento assim como testes de resistência para um dos revestimentos Mo-S-N para a interação de revestimento versus aço. Em todas as condições de pares de deslizamento, o revestimento de MoS2 puro mostrou COF na faixa de 0,1 - 0,25 e taxas de desgaste específicas de 3,0 × 10-6 mm3 / Nm, para o plano, e 2,5 × 10-6 mm3 / Nm, para o cilindro. Em comparação com o revestimento MoS2, os COF e as taxas de desgaste específicas diminuíram com a adição de N. O COF ficou na faixa de 0,05 - 0,1 para revestimentos Mo-S-N, enquanto que na configuração revestimento vs. revestimento foram exibidas as menores taxas de desgaste específico (8,6 × 10-8 mm3 / Nm, para o plano, e 4,4 × 10-8 mm3 / Nm, para o cilindro). O aumento da carga resultou numa diminuição do COF, mas foi observado um aumento na taxa de desgaste. Os revestimentos Mo-S-N mostraram uma vida mais longa com COF reduzido, e sem qualquer falha, em comparação com o MoS2 puro. Finalmente, um dos revestimentos Mo-S-N testados para diferentes configurações de contato em ar ambiente mostrou uma tendência crescente do COF atingindo um valor final de 0,3. O mecanismo que está por trás deste comportamento do COF nas diferentes configurações, foi apresentado e discutido. Este trabalho traz algumas questões importantes ao testar revestimentos à base de dicalcogenetos de metais de transição sob condições de baixa tensão de contato mais adequadas para simular aplicações reais em serviços. Na parte final desta tese, o objetivo foi investigar o comportamento tribológico de revestimentos amorfos de Mo-S-N, especialmente, (i) o papel da incorporação de nitrogênio, (ii) o mecanismo de formação da tribo-camada MoS2 na interface de contato e, (iii) as variações do comportamento de atrito em diferentes ambientes de ensaio. Para tal, foi testado um dos revestimentos Mo-S-N com 30 at. % N num tribómetro tradicional tipo pino-disco, sob tensões de contato elevadas. O revestimento poderia ser constituído por uma fase Mo-S-N, onde o N preenchia alguns dos sítios S, ou por uma estrutura MoS2 onde as moléculas de N2 estavam incorporadas evitando a formação de uma estrutura lamelar cristalina. Os estudos tribológicos realizados em vácuo e atmosfera ambiente resultaram em valores de COF em estado estacionário de 0,03 e 0,15, respetivamente. A análise HR-TEM realizada nas pistas de desgaste revelou que o baixo coeficiente de atrito em vácuo era atribuído à formação de um tribo-filme lamelar espesso e contínuo com uma baixa quantidade de azoto. Pelo contrário, em atmosfera ambiente, a oxidação da superfície perturbava a formação do tribo-filme de MoS2 contínuo, a partir dos revestimentos amorfos, levando a um aumento no COF e na taxa de desgaste. Este estudo mostrou por meio de medições indiretas da composição química do revestimento como depositado e dos detritos de desgaste que uma parte do azoto é armazenado na forma gasosa (N2) dentro da matriz amorfa e é liberado do contato durante o deslizamento.

Frictional force microscopy (FFM) was applied to the detection of frictional asymmetry due to molecular tilt, and anisotropy at various atom-flat surfaces of ionic crystals. Less tilted S=O bonds at CaSO4(100) face and more tilted C=O bonds at (10–14) face of calcite gave contrasting results of asymmetry, which are explained by describing the bonds as mass-spring systems. Frictional anisotropy arises from different periodicity of atoms depending upon the scan directions of the probe. Alkali halide surfaces showed anisotropy due to arrangement of electric charges. Surface geometry also causes anisotropy at corrugated CaSO4(001), etc. Adsorbed water can reduce or enhance friction depending upon the relative humidity and the nature of the surfaces.

The behavior and life of a tilted flat thrust washer bearing is modeled by a comprehensive numerical code. The goal is to investigate the conditions that distress thrust washer bearings through numerical techniques. This work includes thermo-mechanical deformations (which have been neglected in previous studies). The thrust washer bearing supports non-axisymmetric loads within the planetary gear sets of automatic transmissions and consists of flat-faced washers placed between an idle helical gear and its contacting face. Various coupled numerical schemes model sliding friction, boundary lubrication, asperity contact, thermo-mechanical deformation, thermo-viscous effects, and full film lubrication. The model provides predictions of frictional torque, bearing temperature, hydrodynamic lift and other indicators of bearing performance. The experimental and numerical results show that the bearing is very susceptible to the mechanism of thermoelastic instability (TEI). Theoretical predictions indeed predict that the washer may operate in the range of TEI.

For the clarification of the lubrication and thermal problems between ring and liner of internal combustion engines, an unsteady thermohydrodynamic lubrication model considering the ring temperature and the ring movement in the piston ring groove was developed. Then using the method of thermohydrodynamic lubrication, the effect of the profile of top ring sliding face on the oil film thickness and friction losses was analyzed. The ring is width of 3mm and thickness of 4.5mm. Profiles in sliding face of the ring used are two types. Ring 1 has a flat in the middle and a roundness in the corner, and Ring 2 has a barrel face. The ring temperature on the sliding surface shows the characteristic temperature distribution, and the temperature difference between ring lower face and middle of ring has about 19 °C. The oil film thickness changed in a cycle increases with increase of barrel height. The friction mean effective pressure FMEP decreases with the increase of barrel height both Ring 1 and Ring 2. FMEP of Ring 2 is more effective than that of Ring 1.

Abstract Test results are presented involving axial rubbing of a test rotor with an overhung disk to investigate test results cited by Den Hartog [1]. Point rubbing was introduced via a rod on the inside (motor-drive side) and outside faces of the overhung disk for multiple operating conditions (running speeds below and above the critical speed) and multiple shaft configurations. For supercritical running speeds, no change in the response spectrum was observed. For subcritical running speeds, a slight increase of response at twice running speed was observed. “Face” axial rubbing was introduced by forcing a contact between the outside face of the disk and a flat surface. Rubbing at running speeds below the critical speed produced: (i) a small backwards component at the running speed frequency, (ii) a large backward-whirl component at twice running speed, and (iii) a very large, twice-running-speed, forward-whirl component. Rubbing at running speeds well above the critical speed produced a subsynchronous forward component near the critical speed. The large twice-running-speed results due to rubbing at the outside face were comparable to Den Hartog’s. However, point rubbing on the inside face did not produce the subsynchronous backward-whirl response cited by Den Hartog. Analysis of a nonslipping kinematic whirl condition (comparable to classical dry friction whipping) for the face of an overhung disk against a stationary surface predicts reverse asynchronous whirl; however, testing over a wide range of parameters failed to produce this response. None of the present test results produced the types of very high vibration levels and grave consequences that have been produced in test rigs for conventional, radial dry-friction whirl and whip.

A mechanism with a cam and a flat-faced follower is considered for distinct angular velocities. The dynamic analysis presents follower linkage displacement driven by a cam rotating at a uniform angular velocity. The system has clearances between the flat-faced follower and the guides and the effect of clearance is analyzed. The cam-follower linkage mechanism is simulated using Solidworks program taking into account the impact and the friction between the cam, flat-faced follower, and the guides. The non-linear analysis tools are employed for the movement of the flat-faced follower. An experimental set up is established to capture the motion of the follower. High-resolution optical marker is mounted on the follower stem to capture the follower motion in the y-direction. The simulation and experimental results are compared and verified for largest Lyapunov exponent.

A theoretical approach for calculating the movement of liquid water following deposition onto a turbomachine rotor blade is described. Such a situation can occur during operation of an aero-engine in rain. The equation of motion of the deposited water is developed on an arbitrarily oriented plane triangular surface facet. By dividing the blade surface into a large number of facets and calculating the water trajectory over each one crossed in turn, the overall trajectory can be constructed. Apart from the centrifugal and Coriolis inertia effects, the forces acting on the water arise from the blade surface friction, and the aerodynamic shear and pressure gradient. Non-dimensionalisation of the equations of motion provides considerable insight and a detailed study of water flow on a flat rotating plate set at different stagger angles demonstrates the paramount importance of blade surface friction. The extreme cases of low and high blade friction are examined and it is concluded that the latter (which allows considerable mathematical generalisation) is the most likely in practice. It is also shown that the aerodynamic shear force, but not the pressure force, may influence the water motion. Calculations of water movement on a low-speed compressor blade and the fan blade of a high bypass ratio aero-engine suggest that in low rotational speed situations most of the deposited water is centrifuged rapidly to the blade tip region.

Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. They are generally made of a carbon ring mounted in a steel ring for preserving their integrity. Low leakage is ensured by the small clearance of the annular space between the carbon ring and the rotor. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor may occur when the annular seal is locked up against the stator and the amplitude of rotor vibrations are larger than the radial clearance. This situation is prohibited because it rapidly leads to the destruction of the carbon ring. The present work presents experimental results obtained for floating ring annular seals of 38 mm, tandem mounted in a buffer seal arrangement. The rotation speed was comprised between 50 Hz and 350 Hz and maximum pressure drop was 7 bar. For these operating conditions the floating ring follows the rotor vibrations without any impacts. Comparisons were made with a theoretical model based on the equations of motion of the floating ring driven by mass inertia forces, hydrostatic forces in the (main) annular seal and by friction forces on its radial face (also named the “nose” of the seal). The friction coefficient on the nose of the floating ring was estimated from Greenwood and Williamson’s model for mixed lubrication. The present analysis validates the theoretical model used for predicting the dynamic response of the floating ring for a given rotor motion.

This paper reports the findings of a flutter investigation on a low-pressure turbine rotor having an integrally machined tip shroud with different type of constraints. Two types of tip shroud constraints, namely fully constrained and tangentially free, were used, representing two extreme conditions: (a) a typical integrated shroud design with a tight interlocking and no wear on contact surface; and (b) an extremely smooth contact surface design or the most severe wear of a fully constrained interface, or changes in the manufacturing process that result in almost no friction across the shroud surface. The tangentially free constraint is unusual in that it seeks to explore how sensitively the contact constraint could cause blades to response. The mode shapes and corresponding frequency characteristic are presented for both shroud constraints using a standard finite element analysis. The flutter analysis was firstly undertaken by considering all vibration modes of interest in a single calculation using a whole-annulus model of the rotor. It was found that the removal of the tip constraints in the tangential direction was responsible for introducing the unstable first flap family under condition of zero mechanical damping. Of considerable interest was the fact that instability in the first flap mode occurred in forward-travelling nodal diameter modes, which is considered as somewhat different from classical low-pressure turbine flutter where instability exists in backward-travelling nodal diameter modes. The flutter mechanism was verified by undertaking a detailed investigation on the forward-travelling nodal diameter modes of the first flap family using a single-passage analysis. It was concluded that tip shroud constraints are highly sensitive for turbine blade interlock designs and unusual response could be excited under extremely severe wear condition.

Over the last few years, lateral buckling has gone from a secondary issue to one of the major concerns in pipeline design. Not many years ago pipelines were thought of as flexible elements, which could absorb virtually any kind of displacement, but due to the trend to increase fluid temperatures and after a few major environmental accidents, it seems that lateral buckling became the major design issue. Burial was then assumed to be the only safe solution. This is the normal reaction to every traumatic experience, but now that there is alertness and that accidents are being prevented, it is once again time to re-evaluate and see where caution has become excessive and what cheaper alternatives can be used. Several papers have been written over the last 3 or 4 years addressing this issue, [10–13] for instance, and, in general, one could say that there is a consensus regarding the need to know more about how pipelines move, when they buckle laterally, and to what extent they should be allowed to do so. Still another issue, which has been discussed along with this one, is related to how cyclic motions (due to cycles of heating and cooling) can aggravate the problem. Attention is drawn to the fact that the buckling analyses are usually performed based on models conceived to simplify the design, while, on the other hand, construction and installation pay a penalty, because of unnecessary conservatism, which could be avoided if a bit more effort was put into the design. Just to illustrate what is being said, let us consider a typical lateral buckling problem and how the practice has decided it should normally be treated: 1. Determine the pipeline embedment length (that for which the pipeline will build up sufficient axial friction to anchor the axial force due to the temperature variation). 2. Build a model twice that size, embedded at both ends; using a program, which can model axial and lateral friction (this is a nonlinear analysis). 3. Build a prop type lateral installation deviation at the center of the model. 4. Analyze the pipeline assuming that the expansion from both sides will build into that deviation, thus causing the pipeline to buckle at that section. In spite of having become a traditional design approach, it is associated with a conservative model. The bottom is assumed flat, the soil model is a simple elasto-plastic spring and, also, that there is only one lateral imperfection, which will concentrate all the axial expansion. The object of this paper is to show that it can be very advantageous to spend more time and money, on the design, using more detailed analysis models, in order to save much more on the construction and installation. This will be done by sharing the experience gained based on the use of such models, during several recent pipeline projects, handling over 300km of pipes, with diameters varying between 6 and 34 inches in water depths ranging from 0 to 2000m.