Showing papers in "Journal of Tribology-transactions of The Asme in 1995"

Frictional Heating of Tribological Contacts

Abstract: Wherever friction occurs, mechanical energy is transformed into heat. The tem­ perature rise associated with this heating can have an important influence on the tribological behaviour of the contacting components. Apart from determining per­ formance, thermal phenomena affect reliability and may cause failure of the con­tact. In the first part of this thesis the emphasis will be on the numerical calculation of the contact temperature given a heat source distribution, e.g. by means of a measured coefficient of friction. In order to calculate this contact temperature, a multilevel algorithm has been derived which allows for a non-uniform division of the heat generated in the contact and different bulk temperatures. Simulations for elliptic heat sources with uniform and semi-ellipsoidal distribu­ tions, which are of specific importance for contacts operating under conditions of dry and boundary lubrication, have resulted in accurate function fits for the average and maximum contact temperature. These function fits are based on asymptotic solutions for small and large Peclet numbers and are valid for arbitrary Peclet numbers. The function fits enable simple treatment of tribological contacts as part of a thermal network. The second part of this thesis deals with the EHL-line contact problem. First a model, which allows for Non-Newtonian lubricant behaviour and thermal effects, is described. For this model a multilevel algorithm is developed. The algorithm has been applied to a moderately loaded case, using a simplified energy equation. For this case, results show a significant decrease in minimum film thickness for increasing slip. Finally this thesis is concluded with some recommendations for future research.

Optical Surface Analysis of the Head-Disk-Interface of Thin Film Disks

Abstract: This paper describes the design, operation, theory, and data interpretation of an Optical Surface Analyzer (OSA). The OSA can measure carbon wear, lubricant depletion/accumulation, surface roughness, and lubricant alteration on carbon coated thin film disks. This device can measure an Angstrom of carbon wear or lubricant depletion/accumulation. The OSA can also measure debris generation and lubricant degradation through a measurement of optical index change. The lateral resolution of the OSA is approximately 5 by 10 microns and the bandwidth of the device is 2 MHz. The small device size allows it to be used within a test stand environment

Conditions for Scuffing Failure of Ground and Superfinished Steel Disks at High Sliding Speeds Using a Gas Turbine Engine Oil

Abstract: This paper describes the results of an experimental investigation to compare the scuffing performance of conventionally ground and superfinished hardened steel disks operating at sliding speeds of up to 26 m/s and lubricated with a gas turbine engine oil at a temperature of 100° C. The ground disks were finished in the axial direction to simulate the orientation of surface finish found on involute gears. Superfinishing was found to give a significant increase in the load at which scuffing occurred. Frictional traction was also measured in the experiments and was found to be significantly lower for the superfinished disks in the loading stages preceding scuffing failure.

EHD Analysis, Including Structural Inertia Effects and a Mass-Conserving Cavitation Model

Abstract: The dynamic behavior of two elastic connecting-rod bearings is studied. The Newton-Raphson method and 8-node isoparametric elements for the lubrication analysis are used. For the structural analysis, 3-D elasticity assumptions are made and 20 nodes isoparametric elements are used. Inertia forces due to the kinematics of the structure are incorporated with the effects of the hydrodynamic pressures in the elastic deformations of the bearing. Comparisons with Goenka‘s results are presented for the General Motors connecting-rod bearing. A mass-conserving model used in conjunction with Murty‘s algorithm is presented for the transient evolution of the cavitation area. This model is applied for the EHD study of a Renault connecting-rod bearing.

Numerical Simulation of a Ball Impacting and Rebounding a Lubricated Surface

Abstract: The case of a ball bouncing on a flat surface covered by a thin lubricant layer is analyzed theoretically. Both impact and rebound are studied. A Newtonian lubricant and perfect elastic solids are ...

A Transient Thermohydrodynamic Analysis Including Mass Conserving Cavitation for Dynamically Loaded Journal Bearings

Abstract: A comprehensive transient thermohydrodynamic analysis for dynamically loaded journal bearings such as engine crankshaft bearings has been developed. A key element in this analysis is consideration of different time scales for the oil film, journal and bushing. Another important element of this analysis is consideration of moving grids in the oil film. Mass conserving cavitation is included via the Elrod cavitation algorithm. Th 3-D energy equation is solved without any simplification in the oil film or the bushing. The journal is treated as a lumped thermal element. We found that the time scales for thermal transients in the oil film are of the same order as the period of the dynamic loading (one engine cycle for a crankshaft bearing); consequently, thermal transients in the oil film were considered. However, the time scales for thermal transients in the journal and bushing are several orders of magnitude greater than those for the oil film. Consequently, these elements were treated as if they were in quasi-steady state over one loading cycle. Results from this analysis are presented for an engine crankshaft main bearing under sinusoidal loading. Oil film temperatures are found to vary considerably over time and space

A Porous Media Model for Thin Film Lubrication

Abstract: A rheological model has been developed which can be applied to boundary lubrication. The model is applicable to thin films in which the molecular length scale is the same order as the film thickness. The micro structure is simulated by porous layers attached to the contact surfaces. The model contains three materal properties: (1) viscosity, (2) the thickness of the porous layer, and (3) a porosity parameter. A modified Reynolds equation is developed. Behavior in two types of contacts is calculated: squeezing flow between crossed cylinders (Chan and Horn's, 1985 drainage experiment) and a one-dimensional converging wedge contact. The effect of the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the porosity parameter value tends to reduce the magnitude of the load increase

On the Transitions in the Lubrication of Concentrated Contacts

Abstract: Friction experiments on lubricated concentrated contracts were performed to study; (a) the transitions between the different lubrication modes when operating in the lubricants liquid-state regime and (b) the frictional behavior of these contacts, under conditions of full-film lubrication, taking into account the lubricant liquid-state and solid-state behavior. On the basis of these results a flow diagram is presented for lubricated concentrated contacts, from which the lubrication mode as well as the frictional behavior can be obtained as a function of the operational conditions, under which these contacts are functioning

A Numerical Scheme for Static and Dynamic Simulation of Subambient Pressure Shaped Rail Sliders

Abstract: A numerical scheme based on the finite difference technique is developed to simulate the steady-state flying conditions and dynamic responses of subambient pressure sliders with shaped rails. In order to suppress numerical difficulties caused by the clearance discontinuities present in the subambient pressure sliders, the control volume formulation of the linearized generalized lubrication equation is utilized. For the shaped rail sliders, a method of averaging the mass flow across the rail boundaries is implemented. Furthermore, the power-law scheme by Patankar, is implemented in calculating the massflows. The resulting equation is solved using the alternating direction implicit method. For the simulation of steady-state flying conditions, a variable time step algorithm is implemented for the purpose of reaching the steady-state values as quickly as possible. This numerical scheme is very efficient in that the coarse finite difference mesh is sufficient for numerical stability, and that the time step changer very much improves the convergence rate. The static flying heights of the Transverse Pressure Contour and the «Guppy» slider are calculated for different disk velocities and slider skew angles. For the Guppy slider, the dynamic responses of the slider to a cosine bump and disk runout are simulated

A Fractal Theory of the Temperature Distribution at Elastic Contacts of Fast Sliding Surfaces

Abstract: The statistical temperature distribution at fast sliding interfaces is studied by characterizing the surfaces as fractals and considering elactic deformtion of the asperities. The fractions of the real contact area in the slow, transitional, and fast sliding regimes are determined based on the microcontact size distribution. For a smooth surface in contact with a rough surface, the temperature rises at the real contact area are determined under the assumption that most of the frictional heat is transferred to one of the surfaces. The interfacial temperature rises are bounded by the maxinum temperature rise at the largest microcontact when the fractal dimension is 1.5 or less, and are unbounded when it is greater than 1.5. Higher temperature rises occur at larger microcontacts when the fractal dimension is less than 1.5, and at smaller microcontacts when it is greater than 1.5. For a fractal dimension of 1.5, the maximum temperature rise at a microcontact is independent of its size. The maximum temperature rise at the largest microcontact is expressed as a function of the friction coefficient, sliding speed, elastic and thermal properties, real and apparent contact areas, and fractal parameters. The closed-form solutions for the distribution density function of the temperature rise can be used to calculate the fraction of the real contact area of fast sliding surfaces subjected to temperature rises in any given range. The present theory is applied to boundary-lubricated and dry sliding contacts to determine the fractions of the real contact area where lubricant degradation and thermal surface failure may occur

Theoretical and Experimental Comparisons for Rotordynamic Coefficients of a High-Speed, High-Pressure, Orifice-Compensated Hybrid Bearing

Abstract: Comparisons are presented between measurements and predictions for a 76.2 mm diameter, high-speed (24,600 rpm), high-pressure (7.0 MPa), hybrid bearings using warm (54°C) water as a test fluid. «Hybrid» refers to combined hydrostatic and hydrodynamic action. Test results are presented for an orifice-fed, square-recess configuration with five recesses. Data are provided for rotordynamic coefficients including direct and cross-coupled stiffness, direct damping, direct added-mass coefficients, and the whirl-frequency ratio. Experimental results are compared to predictions from an analysis by San Andres (1990a), which accounts for both temporal and convective acceleration terms in the fluid film. San Andres' development uses an orifice discharge coefficient to model the pressure drop from supply pressure to recess pressure. With experimentally determined discharge-coefficient values as input, good agreement is obtained between theary and experiment. However, predictions are sensitive to changes in the orifice discharge coefficients

An Analysis of Gas-Lubricated, Multileaf Foil Journal Bearings With Backing Springs

Abstract: This paper describes the development of a new analysis technique that was used to evaluate the performance of a class of gas-lubricated journal bearings. The surface of these bearings is made up of preformed, leaf-type, compliant foils that are anchored to the bearing housing by spacer keys. Each leaf overlaps an adjacent leaf. Beneath each foil and attached to the inside of the bearing housing is a strip of backing spring. The stiffnesses of various foil bearing structures are modeled and presented as influence coefficients. Unlike conventional approaches , the solution of the governing hydrodynamic equations dealing with compressible fluid is coupled with the structural resiliency of the bearing surfaces. The distribution of the fluid film thickness and pressures, as well as the shear stresses in a finite-width journal bearing, are computed. The solutions include values of bearing stiffness coefficients due to both structural and hydrodynamic stiffnesses. The analysis, which is conducted for multileaf configurations by varying the number of leaves, uncovers the effects that the various structural, geometric, and operational variables have on bearing behavior. Also discussed are design guidelines with regard to the number of leaves, the degree of compliance, and bearing operational parameters

Finite Element Analysis of Rolling Contact for Nonlinear Kinematic Hardening Bearing Steel

Abstract: A Mroz image point, two surface, nonlinear-kinematic-hardening-plastic (MNKP) representation of bearing steel is inserted into a finite element model of 2-dimensional, line contact for pure rolling. The calculations are compared with previous results for the same contact pressure derived for elastic-linear-kinematic-hardening-plastic (ELKP) behavior. The residual stress, deformation, and the connection between continuing cyclic deformation, etching bands, and cracks are analyzed. Unlike the ELKP constitutive properties, the MNKP behavior displays a distinct transient region which results in higher residual stresses.

Rheological Models for Thin Film EHL Contacts

Abstract: Rheological behavior in concentrated contacts has been studied extensively. In certain conditions such as a rough concentrated contact or sliding of nominally flat surfaces, films may be of molecular (nanometer) scale. The question arises as to whether the application of any viscous fluid model is appropriate. In this study, elastohydrodynamic lubrication analysis is performed on three candidate rheological models: (1) the classical case of viscosity variation with pressure, (2) an isoviscous model which idealizes porous layers on the solid surfaces representing the molecular microstructure, and (3) an isoviscous model which includes van der Waals and solvation surface forces. The latter two models predict behavior similar to classical behavior. The study is not sufficiently sensitive to determine which model best predicts experimental results, but some credence must be given to the latter two because experimental evidence suggests that Reynolds' equation is not valid for molecularly thin films

Friction Characteristics and Adhesion Force Under Low Normal Load

Abstract: The friction coefficient and adhesion force between steel balls and flat test pieces were measured during friction under low normal load in order to examine the tribological characteristics First, the friction coefficients were measured under a constant normal load of 08 to 2350 μN, and the adhesion forces were measured before and after each friction The result showed that the friction coefficient was highest at low normal loads, while the friction force divided by the sum of the normal load and the mean adhesion force was almost constant over the whole range of loads Second, when the normal load was reduced gradually during friction, friction still acted when the normal load became negative and a pulling off force was applied to the surface Thus an adhesion force acts during friction and this adhesion force affects the friction force in the same way as the normal load

The effects of three-dimensional pad deformations on tilting-pad journal bearings under dynamic loading

Abstract: Pad distorsions are generally not taken into account for the dynamic study of tilting-pad journal bearings. The objective of this paper is both to show the influence of the three-dimensional (3-D) pad deformations due to the pressure field on the bearing response and to analyse the bearing behavior for various unbalance eccentricities. Similar orbits are obtained using 2-D or 3-D pad deformations; however, due to the axial profile of the film thickness, the minimum film thickness obtained with the 3-D model is about 40 percent lower than the one obtained with the 2-D model for the greatest unbalance eccentricity. The maximum pressure is decreased by about 16 percent when the 3-D model is used but that value is nearly similar to the one obtained without deformation. The dynamic behavior of the bearing is largely modified when the dynamic load is greater than the static load

Mixed Lubrication Characteristics Between the Piston and Cylinder in Hydraulic Piston Pump-Motor

Abstract: This paper presents a method for evaluating the lubrication characteristics between the piston and cylinder in a swash-plate type axial piston pump-motor under mixed lubrication conditions. A numerical analysis is carried out in order to obtain the metal contact force between the piston and cylinder, and the contact ratio λ is shown to represent the mixed lubrication condition both for the pump and the motor strokes. The contact ratio, λ, is also obtained experimentally by detecting electric resistance between the piston and cylinder in a practical swash-plate type machine. The experimental result is expressed by a relationship between λ and S 0 (the ratio of dynamic pressure to supply pressure) as indicated by the numerical analysis. In conclusion, the mixed lubrication characteristics between the piston and cylinder in a swash-plate type pump-motor is expressed by λ − S 0 curve irrespective of the operating conditions such as the supply pressure or the rotation speed

Performance of Powder-Lubricated Journal Bearings With MoS2 Powder: Experimental Study of Thermal Phenomena

Abstract: Powder-lubricated, quasi-hydrodynamic journal bearings assist in controlling wear and hold promise for integration in outer space systems/mechanisms and in other hostile-environment applications where the use of conventional lubricants is impractical. Described herein are the termal phenomena and an assessment of the thermal stability, heat generation and dissipation characteristics of slider-type, powder-lubricated bearings. Powder lubricant films provide lift and separate bearing surfaces and cause side leakage. The reduction in friction coefficient and, consequently, in the heat generated in the bearings, drastically reduces wear of the tribomaterials. Further, bearing side leakage carries away most of the heat generated by shear, reducing the heat to the critical bearing surfaces. Also presented are the thermohydrodynamic effects of powder lubrication (MoS 2 ) on bearing performance criteria, i.e., temperature and friction coefficient as a function of speed and load, including the effect of powder flow rate on bearing performance and wear

Journal Orbits and Their Stability for Rigid Unbalanced Rotors

Abstract: With reference to a rigid symmetrical unbalanced rotor on lubricated journal bearings and adopting the short bearing theory, synchronous orbits and orbits with a 1/2 component described by the journal are determined as approximated solutions of the system of non-linear motion equations. The method also makes it possible to evaluate the stability of the above solutions and thus of the journal orbital motion. For different values of dimensionless unbalance of the rotor, examples of orbits thus obtained are given and, in the modified Sommerfeld number-stability parameter plane, the stability areas of the solutions are identified, in particular, the area of stability of the small synchronous orbits corresponding to the stable operating condition of the rotor-bearings system.

Boric Acid as an Additive for Core-Drilling of Alumina

Abstract: Interactions between chemical compounds added to cutting fluids and the workpiece surface in the cutting zone can have pronounced effects on the material removal process during abrasive machining. These interactions can influence the coefficient of friction, the wear of the abrasive grit, and the mechanical properties of the workpiece, thus affecting the machining rate. Experiments were conducted on sapphire and a high-purity polycrystalline alumina to evaluate the chemomechanical effects of boric acid mixed with distilled water. The machining tests were performed on a precision drill with metal-bonded diamond core-drills. Following the experiments, the drilled surfaces and the debris were examined by scanning electron microscopy to elucidate the material removal process. The results indicated that addition of boric acid to distilled water increases the rate of drilling of polycrystalline alumina by a factor of two. But, boric acid was found to be ineffective in improving the drilling rate of single crystal alumina, i.e., sapphire. Based on the results it is postulated that boric acid interacts with the amorphous oxide grain boundary phase in the polycrystalline alumina promoting intergranular fracture; thereby, increasing the drilling rate

Two-Dimensional Models of Boundary and Mixed Friction at a Line Contact

Abstract: Two-dimensional dynamic friction models at a lubricated line contact, operating in boundary and mixed lubrication regimes, are developed. The friction coefficient is shown to be a function of the sliding velocity and the instantaneous separation of the sliding bodies, normal to the sliding direction. The models are based on unsteady friction experiments carried out under constant normal loads and under time-varying sliding velocities. The normal motions at the sliding contact were detected indirectly by contact resistance measurements. The contact resistance is related to the theoretical central film thickness for smooth surfaces. An advanced system identification technique (Minimum Model Error) is implemented to identify the most important terms in a number of nonlinear friction models. Two friction models are then nondimensionalized and parameterized. The validity and range of application of the models are then tested, by comparing them with experiments and with selected models proposed by other researchers

Inlet pressure effects on the thermohydrodynamic performance of a large tilting pad journal bearing

Abstract: Inlet pressure effects on the thermohydrodynamic performance of a 4-pad large tilting pad journal bearing are investigated both theoretically and experimentally. The theory takes into account the inlet pressure and the three-dimensional variation of oil viscosity and eddy viscosity. Film pressure, film thickness, bearing metal temperature, load capacity, and eccentricity are measured by experiments. A noticeable inlet pressure rise is observed at the entrance of pads. It is shown that the inlet pressure increases not only the film pressure and the load capacity but also the supply flow rate, while it decreases the mixing and bearing surface temperature. The bearing characteristics predicted by the turbulent thermohydrodynamic theory, including the inlet pressure, are in good agreement with the experimental results. Therefore it can be suggested that the inlet pressure must be taken into account in theoretical calculations in order to predict the thermohydrodynamic performance of large tilting pad journal bearings accurately

Effects of the Feedline and the Hydrostatic Pocket Depth on the Flow Pattern and Pressure Distribution

Abstract: The paper treats on a comparative basis the development of the flow and pressure maps in deep, and respectively, shallow hydrostatic bearing pockets. The numerical simulation uses a dimensionless formulation of the Navier-Stokes equations written for a body fitted coordinates system, and applied through a collocated grid. The present work is a continuation of the simulations performed by Braun et al. (1993, 1994a, 1994b) to cases where the length and diameter of the restrictor feedline is of consequence to the flow in both the shallow and the deep pocket. The model includes the coupling between the pocket flow and a finite length feedline flow, on one hand, and the pocket and the adjacent lands on the other hand. Geometrically, all pockets have the same projected footprint, lands length, and capillary feedline. This numerical study uses the Reynolds numbe Re based on the runner velocity (laminar range only), and the inlet jet strength F as the dynamic similarity parameters, while the dimensionless clearance C is used as a geometric parameter. The flow structures, and the physical reasons underlying the causes of the pressure variation inside the deep and shallow pockets [either longitudinally (radially) or transversally (circumferentially)], are discussed quantitatively and comparatively. It is further shown that the transversal pressure distributions under the runner are highly dependent on whethr the flow is dominated by the rotation of the runner (hydrodynamic effects), or by the strength of the hydrostatic jet (F). Finally the longitudinal pressure curves in the depth of the pocket, and restrictor are presented and the nature of their variation discussed. The back step and Rayleigh step effects are also discussed on a comparative basis for the two types of pockets, and in conjunction with the Couette, and the jet dominated flow. the modification of the central vortical zones of the deep pockets into oblong vortical zones for the shallow pockets is presented, and its consequences are discussed

Experiment on Mixed Lubrication of Hydrostatic Thrust Bearings for Hydraulic Equipment

Abstract: Mixed lubrication characteristics of hydrostatic thrust bearings are examined experimentally. The effects of the surface roughness, supply pressure, loads, speed of rotation and size of restrictors on the frictional force, leakage-flow rate and power losses are clarified. Introducing the concept of mean pressure based on load-carrying capacity due to asperities, and the ratios of hydrostatic balance and leakage-flow rate, the experimental data can be normalized. Also good agreement is found between theoretical results based on a mixed lubrication model presented in a previous paper and the experiment.

Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part I—System Model

Abstract: The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic conditions, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of thes friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sliding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and asperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper , a fifth-order model is developed for the normal dynamics of the system, using both the Eigen-system Realization Algorithm (ERA) and classical experimental modal analysis techniques. In Part II, this system model is combined with a friction model, developed independently, to describe dynamic friction forces under both harmonic and impulsive applied normal loads

Turbulent Flow Foil Bearings for Cryogenic Applications

Abstract: Fluid film foil bearings are an innovative bearing technology proposed for rotor support in cryogenic turbomachinery. These bearings offer system life and rotor speeds currently unachievable with rolling element bearings alone. An isothermal analysis for the turbulent bulk-flow of a variable properties liquid in a foil bearing with a simple elastic matrix is introduced. Numerical predictions compare the static and dynamic force performance of a three pad foil bearing with a rigid surface bearing for a high speed application in liquid oxygen. The major advantages of the foil bearing are immediately apparent, namely linearity in the load versus eccentricity curve, uniform rotordynamic coefficients, and overall unsurpassed stability conditions. The effects of excitation frequency and the foil structural damping on the dynamic force coefficients are discussed

A Numerical Elastoplastic Model for Rough Contact

Abstract: Pressure distributions due to surface roughness in contact induce high-stresses just beneath the surface. These stresses can bring on crack initiation and micro-pitting. A purely elastic contact model to account for these effects is restrictive because stress fields often exceed the yield strength of the material. Plastic flow occurs and modifies the surface shape and material properties (work hardening). This paper presents a numerical model for elastoplastic rough contact. It allows the determination of real pressures and permanent surface displacements (flattening of asperities) as well as residual stress and plastic strains useful in fatigue analysis. The material is assumed to obey the Von-Mises yield criterion with linear kinematic hardening. Real surface profiles obtained from a measurement can be considered. In addition, simplified methods have been used to treat cyclic loading. Thus the ability of a rough surface to reach an elastic shakedown state can be investigated, even for a three-dimensional contact found, for instance, in roller bearings

Transient Analysis of Tilt Pad Journal Bearings Including Effects of Pad Flexibility and Fluid Film Temperature

Abstract: The paper considers vibration response of spinning shafts supported by flexible tilt pad journal bearings, to large mass imbalance (blade loss). A time transient study of the tilt pad journal bearing with thermal effects and without pad deformations, and with pad deformations and without thermal effects, is performed. Influence of the inclusion of thermal effects on the jurnal center's orbit, the minimum film thickness, and the maximum film temperature is evaluated, and also the influence of pad deformations due to the fluid film forces on the journal center's orbit and the minimum film thickness is studied. Inclusion of thermal effects had little effect on the orbit, while the inclusion of pad deformations had considerable effect on the journal orbit and the minimum film thickness. Three cases are studied in this paper; static load without imbalance, static load with low imbalance, and static load with high imbalance

Cavitation in Normal Separation of Square and Circular Plates

Abstract: The negative squeeze lubrication problem is investigated by means of a mass-conserving finite element cavitation algorithm (described elsewhere) within the context of a dimensionless study of lubricant film behavior between rigid, parallel separating surfaces. Appropriate mesh geometries which capture spatial and temporal mixture density history and satisfy JFO conditions on the cavitation interface are determined. Present simulation results agree qualitatively with previous experiments, supporting the validity of the algorithm and its utility in the bearing design process

A Study of the Durability of a Paper-Based Friction Material Influenced by Porosity

Abstract: The friction performance and thermal resistance of paper-based oil immersed friction materials are influenced by the material structure formed as a result of the combination of porosity and resiliency. In this paper, the effects of porosity on the thermal durability of paper-based frivtion materials were studied, of which the contents are varied but the geometries are the same as used in real applications. the relationship between the degree of carbonization and the durability was discussed in several terms of mechanical property changes of the material. the friction and thermal durability tests conducted by using an SAE No. 2 apparatus under a repeated engage-disengagement condition. To obtain the thermal durability performance the sliding surface temperature was also measured. Coefficients of friction of the low porosity material tend to decrease as the test cycle increases. And the total thickness loss of the low porosity material after durability test is bigger than that of the high porosity material. These durability performances were well correlated with the mechanical and physical property changes of the material, that is, variations of carbonization degree, permeability and hysteresis loss energy