Accepted Manuscripts

Lijesh K.P., Mrityunjay Doddamani and Siddappa I. Bekinal
J. Tribol   doi: 10.1115/1.4037847
Passive Magnetic Bearing's (PMB) adaptability for both lower and higher speed applications demands, detailed and critical analysis of design, performance optimization and manufacturability. Optimization techniques for stacked PMB published in recent past are less accurate with respect to complete optimum solution. In this context, the present work deals with a pragmatic optimization of axially stacked PMBs for the maximum radial load using three-dimensional (3D) equations. Optimization for three different PMB configurations: monolithic, conventional and rotational magnetized direction (RMD) is presented based on the constraints, constants and bounds of the dimensions obtained from published literature. Further, to assist the designers, equations to estimate the mean radius and clearance, being crucial parameters are provided for the given axial length and outer radius of the stator with objective of achieving maximum load carrying capacity. A comparison of the load carrying capacity of conventional stacked PMB using the proposed equation with equation provided in literature is compared. Finally, effectiveness of the proposed pragmatic optimization technique is demonstrated by analyzing three examples with reference to available literature.
TOPICS: Optimization, Magnetic bearings, Load bearing capacity, Clearances (Engineering), Design, Dimensions, Stress, Stators
Keisuke Nagai, Satoru Kaneko, Hiroo Taura and Yusuke Watanabe
J. Tribol   doi: 10.1115/1.4037846
Numerical and experimental analyses were carried out to investigate the static characteristics of liquid annular seals with helical grooves in a seal stator. In the numerical analysis, the continuity equation and momentum equations with turbulent coefficients were averaged across the film thickness and numerically solved. To accurately define the location of the step between the groove and the land regions in the calculation domain, these governing equations were expressed using an oblique coordinate system in which the directions of coordinate axes coincided with the circumferential direction and the direction along the helical grooves. The numerical analysis includes the effect of both inertia and energy losses due to expansion during the passage of fluid from the land region to the helical groove region and due to contraction from the groove to the land region. In the experimental analysis, the helically grooved seals with different helix angles of helical groove were used. The numerical results for the leakage flow rate and the static pressure distributions agreed well with the experimental results, which demonstrated the validity of the numerical analysis. Under a low range of rotor spinning velocities, the leakage flow rate decreases with helix angle. On the other hand, under a high range of spinning velocities, the quantitative difference in the leakage flow rate due to the helix angle becomes small as compared with that under a lower range. The effects of the helix angle and rotor spinning velocity on the leakage flow rate were explained qualitatively using a simplified model.
TOPICS: Experimental analysis, Stators, Leakage flows, Spinning (Textile), Spin (Aerodynamics), Numerical analysis, Rotors, Energy dissipation, Inertia (Mechanics), Pressure, Momentum, Fluids, Turbulence, Film thickness
Wei Pu, Dong Zhu and Jiaxu Wang
J. Tribol   doi: 10.1115/1.4037844
In the present study, a modified mixed lubrication model is developed with consideration of machined surface roughness, arbitrary entraining velocity angle, starvation and cavitation. Model validation is executed by means of comparison between the obtained numerical results and the available starved EHL data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on starvation and cavitation, mixed EHL characteristics, friction and flash temperature in elliptical contacts is conducted in a wide range of operating conditions. In addition, the influence of roughness orientation on film thickness and friction is discussed under different starved lubrication conditions. Obtained results reveal that inlet starvation leads to an obvious reduction of average film thickness and an increase in inter-asperity cavitation area due to surface roughness, which results in significant increment of asperity contacts, friction and flash temperature. Besides, the effect of entrainment angle on film thickness will be weakened if the two surfaces operate under starved lubrication condition. Furthermore, the results show that the transverse roughness may yield thicker EHL films and lower friction than the isotropic and longitudinal if starvation is taken into account. Therefore, the starved Mixed EHL model can be considered as a useful engineering tool for industrial applications.
TOPICS: Friction, Lubrication, Temperature, Surface roughness, Cavitation, Film thickness, Model validation, Engineering instruments
Thella Babu Rao
J. Tribol   doi: 10.1115/1.4037845
One of the major advantages of metal matrix composites is that their tailorable properties meet the specific requirements of a particular application. This paper deals with the experimental investigations done on the effects of the reinforcement particulate size and content on the Al7075/SiC composite. The composites were manufactured using stir casting technique. The effect of SiC particle size (25, 50 and 75µm) and particulate content (5, 10 and 15wt.%) on the microstructural, mechanical properties and wear rate of the composites was studied and the results were analyzed for varied conditions of reinforcement. SEM examinations were used to assess the dispersion of SiC particles reinforced into the matrix alloy and was found with reasonably uniform with minimal particle agglomerations and with good interfacial bonding between the particles and matrix material. XRD analysis confirmed the presence of Al and SiC with the composite. The results of mechanical tests showed that the increasing SiC particle size and content considerably enhanced the ultimate tensile strength and hardness of the composites while the ductility at this condition was decreased. The highest UTS of 310MPa and hardness of 126 BHN were observed for the composites containing 15wt%. SiC at 75µm. Lower the wear resistance of the reference alloy while it was enhanced up to 40% with the composites. The wear resistance was increased up 1200m of sliding distance for all the composites, whereas for the composite containing 75µm SiC particles it was extended up to 1800m.
TOPICS: Wear, Composite materials, Particle size, Particulate matter, Alloys, Tensile strength, Wear resistance, Casting, Bonding, Metal matrix composites, Ductility, Mechanical properties, Mechanical testing
Yuechang Wang, Ying Liu, Gaolong Zhang and Yuming Wang
J. Tribol   doi: 10.1115/1.4037793
The simulated rough surface with desired parameters is widely used as an input for the numerical simulation of tribological behavior such as the asperity contact, lubrication, and wear. In this study, a simulation method for generating non-Gaussian rough surfaces with desired auto-correlation function (ACF) and spatial statistical parameters, including skewness (Ssk) and kurtosis (Sku), was developed by combining the fast Fourier transform (FFT), translation process theory, and Johnson translator system. The proposed method was verified by several numerical examples and proved to be faster and more accurate than the previous methods used for the simulation of non-Gaussian rough surfaces. It is convenient to simulate the non-Gaussian rough surfaces with various types of ACFs and large autocorrelation lengths. The significance of this study is to provide an efficient and accurate method of non-Gaussian rough surfaces generation to numerically simulate the tribological behavior with desired rough surface parameters.
TOPICS: Simulation, Surface roughness, Tribology, Wear, Lubrication, Computer simulation, Fast Fourier transforms
Manu Sam and N Radhika
J. Tribol   doi: 10.1115/1.4037767
A Functionally graded Cu-10Sn-5Ni metal matrix composite reinforced with 10 wt% of Al2O3 particles was fabricated using the centrifugal casting process with dimension Fout100 x Fin85 x 100 mm. The mechanical and wear resistance of the composite has been enhanced through heat treatment. Samples from of the inner zone (9-15mm) were considered for heat treatment, as this zone has higher concentration of less dense hard reinforcement particles. The samples were solutionised (6200C / 60mins) and water quenched followed by aging at different temperatures (400,450 and 5500C) and time (1, 2 and 3hrs). Optimum parametric combination (4500C, 3 hrs) with maximum hardness (269HV) was considered for further analysis. Dry sliding wear experiments were conducted based on Taguchi's L27 array using parameters such as applied loads (10, 20 and 30 N), sliding distances (500, 1000 and 1500 m) and sliding velocities (1, 2 and 3 m/s). Results revealed that wear rate increased with load and distance whereas it decreased initially and then increased with velocity. Optimum condition for maximum wear resistance was determined using Signal-to-Noise ratio. Analysis of Variance predicted the major influential parameter as load, followed by velocity and distance. Scanning Electron Microscope analysis of worn surfaces predicted the wear mechanism; observing more delamination due to increase in contact patch when applied load increased. Results infer 8% increase in hardness after heat treatment, making it suitable for load bearing applications.
TOPICS: Tribology, Composite materials, Heat treating (Metalworking), Stress, Wear, Particulate matter, Wear resistance, Delamination, Dimensions, Metal matrix composites, Temperature, Scanning electron microscopes, Centrifugal casting (Process), Signal to noise ratio, Bearings, Water
Mohammad Miraskari, Farzad Hemmati and Mohamed S. Gadala
J. Tribol   doi: 10.1115/1.4037730
To determine the bifurcation types in a rotor-bearing system, it is required to find higher order derivatives of the bearing forces with respect to journal velocity and position. As closed-form expressions for journal bearing force is not generally available, Hopf bifurcation studies of rotor-bearing systems have been limited to simple geometries and cavitation models. To solve this problem, an alternative nonlinear coefficient-based method for representing the bearing force is presented in this study. A flexible rotor-bearing system is presented for which bearing force is modeled with linear and nonlinear dynamic coefficients. The proposed nonlinear coefficient-based model was found to be successful in predicting the bifurcation types of the system as well as predicting the system dynamics and trajectories at spin speeds below and above the threshold speed of instability.
TOPICS: Bearings, Rotors, Journal bearings, Nonlinear dynamics, Bifurcation, Rotation, System dynamics, Cavitation, Spin (Aerodynamics), Particle spin
Mohammad Miraskari, Farzad Hemmati and Mohamed S. Gadala
J. Tribol   doi: 10.1115/1.4037731
The nonlinear stability of a flexible rotor-bearing system supported on finite length journal bearings is addressed. A perturbation method of the Reynolds lubrication equation is presented to calculate the bearing nonlinear dynamic coefficients, a treatment that is suitable to any bearing geometry. A mathematical model, nonlinear coefficient-based model, is proposed for the flexible rotor bearing system for which the journal forces are represented through linear and nonlinear dynamic coefficients. The proposed model is then used for nonlinear stability analysis in the system. A shooting method is implemented to find the periodic solutions due to Hopf bifurcations. Monodromy matrix associated to the periodic solution is found at any operating point as a by-product of the shooting method. The eigenvalue analysis of the Monodromy matrix is then carried out to assess the bifurcation types and directions due to Hopf bifurcation in the system for speeds beyond the threshold speed of instability. Results show that models with finite coefficients have remarkably better agreement with experiments in identifying the boundary between bifurcation regions. Unbalance trajectories of the nonlinear system is shown to be capable of capturing sub and super-harmonics which are absent in the linear model trajectories.
TOPICS: Bearings, Rotors, Journal bearings, Nonlinear dynamics, Bifurcation, Stability, Lubrication, Nonlinear systems, Eigenvalues, Geometry
Michael Giordano, Steven Schmid, Mohammadreza Arjmandi and Maziar Ramezani
J. Tribol   doi: 10.1115/1.4037728
Three-dimensional woven fabrics have been considered by biomedical researchers to be used as load-bearing surfaces in joint and ligament replacements. In this regard, wear is a crucial phenomenon that determines material failure as well as biological response of body to wear debris. The current study evaluates various micro-scale screening methods with the aid of Atomic Force Microscopy (AFM) for biocompatible polymer fibers that are used in 3D woven fabrics. Fibers in mono and multifilament forms were subjected to indentation, scratching and line wear testing in dry and soaked conditions and the effect of key parameters such as applied normal load, sliding velocity and number of wear cycles were investigated. The area of worn material was determined by geometric approximation superimposed on the measured residual scratch of line wear. Moisture was found to lower the indentation hardness of some fibers while increased the hardness of others. Line wear results clearly suggest ultra-high molecular weight polyethylene (UHMWPE) to be the primary material for further investigation and that monofilament fibers should be avoided.
TOPICS: Wear, Atomic force microscopy, Polymer fibers, Fibers, Textiles, Stress, Bearings, Microscale devices, Approximation, Cycles, Failure, Molecular weight, Biocompatible polymers, Wear testing, Biomedicine
Dongdong Gu, Jiubin Jue, Donghua Dai, Kaijie Lin and Wenhua Chen
J. Tribol   doi: 10.1115/1.4037729
The friction and wear properties of in-situ Al-matrix composites prepared by selective laser melting (SLM) were evaluated on a ball-on-disk tribometer by sliding against GCr15 steel at room temperature. The influence of the applied load, sliding speed and long-time continuous friction on the friction and wear properties of Al-matrix composites was systematically investigated. It showed that the wear rate and coefficient of friction (COF) increased when the applied load increased, due to the higher contact stress and larger extent of particle fracturing. As the sliding speed increased, the elevated rate of the formation of Al-oxide layer and the transfer of Fe-oxide layer from the counterface to the worn surface led to a significant reduction in wear rate and COF. As the sliding distance prolonged, the worn surface successively experienced the adhesive wear, the abrasive wear, the particle fracturing and crack nucleation, and the delaminated wear. The above processes were repeated on each exposed fresh surface, resulting in the fluctuation of COF. In the later stage of wear process, a large amount of oxides were produced on the worn surface, caused by the long-time accumulated frictional heat, which reduced the fluctuation of COF. The wear mechanisms of SLM-processed Al-matrix composite parts under various loads were dominated by abrasive wear and oxidation wear, whereas the predominant wear mechanisms were oxidation wear and delamination wear at different sliding speeds. For the long-time friction, all of these wear mechanisms were operational.
TOPICS: Lasers, Composite materials, Wear, Melting, Additive manufacturing, Friction, Stress, Particulate matter, oxidation, Fracture (Process), Disks, Nucleation (Physics), Fracture (Materials), Delamination, Tribometers, Heat, Temperature, Steel, Adhesives
Sitae Kim and Alan Palazzolo
J. Tribol   doi: 10.1115/1.4037699
This paper presents analytical bifurcations analysis of a "Jeffcott" type rigid rotor supported by five-pad tilting pad journal bearings (TPJBs). Numerical techniques such as non-autonomous shooting/arc-length continuation, Floquet theory and Lyapunov exponents are employed along with direct numerical integration to analyze nonlinear characteristics of the TPJB-rotor system. A rocker pivot type 5-pad TPJB is modeled with finite elements to evaluate the fluid pressure distribution on the pads, and the integrated fluid reaction force and moment are utilized to determine coexistent periodic solutions and bifurcations scenarios. The numerical shooting/continuation algorithms demand significant computational workload when applied to a rotor supported by a finite element bearing model. This bearing model may be significantly more accurate than the simplified infinitely short-/long-bearing approximations. Consequently, the use of efficient computation techniques such as deflation and parallel computing methods are applied to reduce the execution time. Loci of bifurcations of the TPJB-rigid rotor are determined with extensive numerical simulations with respect to both rotor spin speed and unbalance force magnitude. The results show that heavily loaded bearings and/or high unbalance force may induce consecutive transference of response in forms of synchronous to sub-synchronous, quasi-periodic responses and chaotic motions. It is revealed that the coexistent responses and their solution manifolds are obtainable and stretch out with selections of pad preload, pivot offset, and lubricant viscosity so that the periodic doubling bifurcations, saddle node bifurcations and corresponding local stability are reliably determined by searching parameter sets. In case the system undergoes an aperiodic state, the rate of divergence/convergence of the attractor is examined quantitatively by using the maximum Lyapunov exponent.
TOPICS: Rotors, Bifurcation, Journal bearings, Bearings, Finite element analysis, Approximation, Attractors, Computation, Manifolds, Rotation, Stability, Fluid pressure, Fluids, Viscosity, Computer simulation, Lubricants, Spin (Aerodynamics), Particle spin, Algorithms
Mürsel Ekrem, Hayrettin Duzcukoglu, Muhammet Ali Senyurt, Ömer Sinan Sahin and Ahmet Avci
J. Tribol   doi: 10.1115/1.4037698
In this study, the effects of addition of boron nitride nano platelets upon friction and wear behavior of epoxy resin have been investigated by using pin on disc test. It has been reported in the literature that certain percentages of boron nitride nano platelet addition can be usefull for enhancement of mechanical properties. So it is very important to obtain the effect of such addition upon friction and wear performance of epoxy resin. Boron nitride nano platelets have been incorporated at 0.3-0.5-0.7- 1 percent by weight. It is showed that boron nitride nano platelet additions has resulted in decrease in friction coefficient and wear loss. It is also showed that the best results have been obtained at 0.5% nano platelet addition. It is also observed that heat conduction of epoxy resin has enhanced by the nano platelet addition.
TOPICS: Friction, Wear, Epoxy resins, Boron, Platelets, Weight (Mass), Heat conduction, Mechanical properties, Disks
Vineet Tirth
J. Tribol   doi: 10.1115/1.4037697
AA2218-Al2O3(TiO2) composites are synthesized by stirring 2, 5 and 7 wt% of 1:2 mixture of Al2O3:TiO2 powders in molten AA2218 alloy. T61 heat-treated composites characterized for microstructure and hardness. Dry sliding wear tests conducted on pin-on-disc set-up at available loads 4.91 N to 13.24 N, sliding speed of 1.26 m/s up to sliding distance of 3770m. Stir cast AA2218 alloy (unreinforced, 0 wt% composite) wears quickly by adhesion, following Archard's law. Aged alloy exhibits lesser wear rate than unaged (solutionized). Mathematical relationship between wear rate and load proposed for solutionized and peak aged alloy. Volume loss in wear increases linearly with sliding distance but drops with increase in particle wt% at a given load, attributed to increase in hardness due to matrix reinforcement. Minimum wear rate is recorded in 5 wt% composite due to increased particles retention, lesser porosity and uniform particle distribution. In composites, wear phenomenon is complex, combination of adhesive and abrasive wear which includes the effect of shear rate, due to sliding action in composite, and abrasive effect (3 body wear) of particles. General mathematical relationship for wear rate of T61 aged composite as a function of particle wt%, load is suggested. Fe content on worn surface increases with increase in particle content and counterface temperature increases with increase in load. Coefficient of friction decreases with particle addition but increases in 7 wt% composite due to change in microstructure.
TOPICS: Wear, Composite materials, Alloys, Particulate matter, Stress, Disks, Porosity, Wear testing, Shear rate, Heat, Temperature, Adhesion, Adhesives, Friction
Janith Samarasinghe, Wyatt Culler, Bryan D. Quay, Domenic Santavicca and Jacqueline O'Connor
J. Tribol   doi: 10.1115/1.4037461
Fuel staging is a commonly used strategy in the operation of gas turbine engines. In multi-nozzle combustor configurations, this is achieved by varying fuel flow rate to different nozzles. The effect of fuel staging on flame structure and self-excited instabilities is investigated in a research can combustor employing five swirl-stabilized, lean-premixed nozzles. At an operating condition where all nozzles are fueled equally and the combustor undergoes a self-excited instability, fuel staging successfully suppresses the instability: both when overall equivalence ratio is increased by staging as well as when overall equivalence ratio is kept constant while staging. Increased fuel staging changes the distribution of time-averaged heat release rate in the regions where adjacent flames interact and reduces the amplitudes of heat release rate fluctuations in those regions. Increased fuel staging also causes a breakup in the monotonic phase behavior that is characteristic of convective disturbances that travel along a flame. In particular, heat release rate fluctuations in the middle flame and flame-flame interaction region are out-of-phase with those in the outer flames, resulting in a cancellation of the global heat release rate oscillations. The Rayleigh integral distribution within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the combustor pressure fluctuation. When staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities through a phase cancellation mechanism.
TOPICS: Fuels, Combustion chambers, Nozzles, Flames, Heat, Pressure, Fluctuations (Physics), Gas turbines, Flow (Dynamics), Oscillations
Fumitaka Yoshizumi, Yasuhiro Kondoh, Takahiro Moroi, Shinji Tamano and Yohei Morinishi
J. Tribol   doi: 10.1115/1.4037539
In a discharge reed valve for compressors, the oil stiction by the oil film between the reed and the valve seat is investigated experimentally, and a simulation model is developed. Through a model experiment, the initial oil film thickness is measured by an interferometry method, and the valve displacement and the bore pressure are measured from the stiction to the valve opening. The opening delay time together with the initial oil film thickness is measured while changing the contact area and the oil species. In the simulation model, the deformation of the reed and the pressure of the oil film as a result of cavitation are coupled. In order to take into account the tensile stress in the oil film, a cavitation model directly simulating the expansion of cavitation bubbles is developed (herein, dynamic cavitation model). In the experiment, a smaller contact area, a larger initial film thickness, and a smaller oil viscosity yield a shorter delay. In the simulation, the dynamic cavitation model is advantageous in representing the experimental delay time. In particular, with respect to the relationship between the initial film thickness and the delay time, the dynamic cavitation model with an initial bubble radius that depends on the oil film thickness yields results similar to the experimental results.
TOPICS: Compressors, Valves, Stiction, Cavitation, Film thickness, Delays, Simulation models, Bubbles, Pressure, Deformation, Interferometry, Viscosity, Simulation, Displacement, Tension
Moisés Brito, Luis Teixeira, Ricardo B. Canelas, Rui Miguel Lage Ferreira and Maria Graça Neves
J. Tribol   doi: 10.1115/1.4037464
Hydraulic cylinders are generally used as power take-off (PTO) mechanisms in wave energy converters (WECs). The dynamic behaviour of its PTO force, which integrates friction and pressure forces, is a difficult constraint to include in an analytical or in a numerical model. In this paper, the PTO force characteristics of a hydraulic cylinder are experimentally and numerically investigated under different magnitudes of controlled excitation force. In order to characterize the dynamic behaviours of PTO force the displacement, acceleration and pressure in the cylinder chamber for given excitation forces are measured. The pressure force is calculated using the measured value of the pressure, and the friction force is calculated based on the equation of motion using measured values of the pressure, excitation force and acceleration of the piston. Experimental results show clearly a strong nonlinear force-velocity characteristics, including stochastic and hysteretic behaviours. To model the hysteretic behaviour the modified LuGre model is used for the friction force and a new approach is proposed for the pressure force. To model the stochastic behaviour of the friction and pressure forces the spectral representation method is used. The systematically comparison between measured and simulated results shows that the numerical model captures most of dynamic behaviours of PTO force.
TOPICS: Cylinders, Pressure, Friction, Excitation, Computer simulation, Hydraulic cylinders, Equations of motion, Displacement, Pistons, Wave energy converters
Gengxiang Wang and Hongzhao Liu
J. Tribol   doi: 10.1115/1.4037463
Effect of flexible body and clearance spherical joint on the dynamic performance of 4-SPS/CU parallel mechanism are analyzed. The flexible moving platform is treated as thin plate element based on Absolute Nodal Coordinate Formulation (ANCF). In order to formulate the parallel mechanism's constraint equations between the flexible body and the rigid body, the tangent frame is introduced to define the joint coordinate. One of the spherical joints between moving platform and kinematic chains is introduced into clearance. The normal and tangential contact forces are calculated based on Flores contact force model and modified Coulomb friction model. The dynamics model of parallel mechanism with clearance spherical joint and flexible moving platform is formulated based on equation of motion. Simulations shows that the dynamic performance of parallel mechanism is not sensitive to the flexible body because of the inherent property of moving platform, however, when the clearance spherical joint is considered into the parallel mechanism with flexible body, the flexible moving platform exhibits cushioning effect to absorb the energy caused by clearance joint.
TOPICS: Dynamics (Mechanics), Clearances (Engineering), Parallel mechanisms, Kinematic chains, Engineering simulation, Friction, Coulombs, Simulation, Equations of motion
Ali Habbolahzadeh and Farahnaz Haftlang
J. Tribol   doi: 10.1115/1.4037465
For the first time, formation of cubic boron nitride (c-BN), besides Fe2B and iron nitrides, in bronitride coating was detected. Bronitride coating was applied on AISI 1045 steel substrates via duplex treatment of pack boriding and plasma nitriding (B-PN). Scanning electron microscope (SEM), X-ray diffractometer (XRD), and pin-on-disk wear test were utilized to evaluate microstructures, phases, and wear properties of the coatings. The surface of the as-coated sample exhibited a pebble-like and compact structure, and the cross-sectional morphology of the coatings showed a saw-tooth interface with substrate. Duplex treated sample revealed superior wear resistance in comparison with the borided one.
TOPICS: Tribology, Steel, Nitriding, Plasmas (Ionized gases), Surface finishing, Coatings, Wear resistance, Wear testing, Boron, Disks, Iron, Scanning electron microscopes, Wear, X-rays
Juan S Rudas, L. M. Gómez, A. Toro, J. M. Gutiérrez and A. Corz
J. Tribol   doi: 10.1115/1.4037467
Closure to "Discussion: Wear rate and entropy generation sources in a Ti6Al4V - WC/10Co sliding pair J. S. Rudas, L. M. Gomez, A. Toro, J. M. Guti´errez and A. Corz"
TOPICS: Wear, Entropy
Hisham A. Abdel-Aal
J. Tribol   doi: 10.1115/1.4037466
We discuss the preposition of Rudas et al of the generalization of the Degradation Coefficient for steady state tribological systems. We show that such a generalization markss a special case representing a passive stable thermodynamic steady state.
TOPICS: Tribology, Wear, Entropy, Steady state

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