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The effect of journal misalignment on the performance of a big-end connecting-rod is analysed in this paper. The misalignment considered varies in magnitude and direction during all the cycle up to contact between the shaft and the bearing. The numerical procedure incorporates misalignment velocities. The technique used for bearing characteristics evaluation (minimum film thickness, friction torque, axial flow) is an extension of the mobility method of BOOKER.

Applying EHL theory, the paper derives the mathematical model for analysis of lubricating of cylinder sleeve and piston ring, and composes a general CAD program for computation of the thickness of lubricant film, by which anlyses can be made to the lubricating state of cylinder sleeve and piston ring for engines of various models with different operating mode. Tests of specific point on bench in specific conditions show that the computing method is feasible.

This paper reviews the major results of a recent study on lubrication and wear performance of a ceramic roller followers/cast iron camshaft system for automobile valve trains. The modified mobility method considering surface roughness effect was used for lubrication analysis of the ceramic roller/steel pin combination, and the relevant tests were conducted on both the two roller rig and the actual engine head. Results show that clearance and surface roughness play significant roles in lubrication, and dynamic load variation may improve lubrication because of the squeeze film effect. Wear rate tests for more than ten different ceramic materials and durability and fatigue tests on the engine head were also conducted, and the wear mechanisms were then explored. It was found that Si3N4 and TiC-Al2O3 have very high wear resistance in rolling contacts, and SIC and TiC-Al2O3 have superior antiwear performance in simple sliding. The major wear modes include grain pullout, microchipping, intergranular crack propagation leading, to delamination, etc. Contact stress analysis was also carried out in this study in order to optimize the design of contact geometry.

The continuing evolution of the internal combustion engine, together with required improvements in component design lead times and reliability, places increasing demands on improved design and applications engineering techniques. This paper charts the evolution of predictive design techniques for selected components within the engine and outlines the anticipated trends and developments necessary to meet the challenge of future design requirements.

A set of sapphire windows have been inserted in the cylinder liner of a Petter AVI diesel engine. This has enabled the temperatures of the piston ring and piston land surfaces to be measured at various points in the cycle of a firing engine using an infrared emission microscope attached to a storage oscilloscope. In this paper the method is described and some results obtained at mid-stroke and top dead centre are presented. These are compared to previous measurements of the bulk temperature of piston rings taken by other workers.

Traction drive CVT (Continuously variable transmission) for automobile use requires a big torque capacity, and the temperature of the traction fluid filled in CVT sometimes rises to 140 °C. To achieve stable power transmitting under this condition, it is necessary that traction coefficient of the fluid is sufficiently higher than the designed value of CVT. For the purpose of developing the excellent CVT fluid which enables stable power transmitting even at high temperature, we have studied the quantitative correlation between the molecular structures and traction coefficients at high temperature. In this paper, we describe the relationship mentioned above and experimental result of practical CVT test.

The paper deals with the results of experimental and theoretical research carried out within the Laboratory of Mechanical Seals from Machine Elements and Tribology Department of the Polytechnical Institute in Bucharest, special attention being paid on the studies concerning engine water-pumps mechanical seals.

Fibers such as fabric and bristles can be readily fabricated into a variety of configurations that are compliant and responsive to high-speed or lightly loaded systems. These configurations can be linear, circular, or contoured linear or circular. In this paper visualization and characterization of the complex flow fields in simulated linear bristle configurations as applied to brush seals (bearings) are explored. The full-field flow tracking (FFFT) method is used to visualize the flow field and bristle dynamics, which were nonintrusively determined and graphically reconstructed. Visualization of the flow field revealed regions that are characteristically river, jetting, vortical, cross, and edge flows and exist upstream, downstream, or within the brush. Such flows are caused by variations in fiber packing and stiffness that are both spatial and temporal and strongly influence leakage, stability, and load capacity. Potential applications of brush seals are described herein, and in the appendix a brush seal system design procedure is provided that compares favorably with brush seal leakage results.

This paper presents experimental measurements from laboratory dynamometers of the dependence of the life of automotive timing belts on belt torque and total tension in the transmission of power between two crankshaft sized (19 tooth) pulleys, each with an angle of wrap of 180°. Failure observations of tooth root cracking and of worn belt covers are also presented. Contact loads between belt and pulley teeth have been calculated and it is found that in the conditions of the present experiments tooth load at exit from the driven pulley is the critical load controlling life by tooth root cracking: assuming that this remains the critical load, predictions are made of the effect on life of changing belt tension, pulley size and angle of wrap.

The purpose of this paper is to reveal the relation between flexibility and clearance of oil film by a co-rotating bearing (bush is rotating together with shaft in the same direction and rotation rate), which can be used for sharing load equally in planetary transmission of vehicle. The authors have adopted a theoretical approach of infinite width bearing and explained the characteristics of oil film for co-rotating bearing. Using the numerical calculation to solve the non-linear equation, the authors have gotten the results on finite width co-rotating bearing. By experiments, the relations between flexibility and clearance of oil film for co-rotating bearing are presented by charts in different clearance, rotation rate and load. A good consistency of the results between experimental and numerical calculation result is gotten.

This paper gives the General Motors (GM) perspective in vehicle tribology. Tribology plays an important role in vehicle durability, reliability, and fuel efficiency. While several areas in the vehicle are included, major emphasis is given to engine tribology. Piston skirt, piston rings, crankshaft and its bearings, and the valve train are identified as the most critical reciprocating engine components for tribological investigation. In addition to discussing these, engine friction, engine lubricants, clutches and brakes, and sheet metal forming are briefly covered. In each case the tribological state-of-the-art, as applied in design, is identified. GM's analytical and experimental capabilities are discussed, and areas where more work is needed are identified.

The purpose of this paper is to clarify a universal method to calculate the speed ratio and the power transmission efficiency of rolling contact continuously variable transmissions with planetary cones (differential type CVT). The authors present a new method in which the instantaneous center of rotation and the speed and torque efficiencies were effectively used. This method can be used to derive the equations for calculating the ratio and the efficiency of any types of CVT's and gear drives with complex mechanism. Using the equations obtained in the present investigation, numerical calculations were conducted in the case of a differential CVT with planetary cones. The calculated results agreed well with the experimental ones when the oil churning and bearing losses were taken into account.

This paper surveys and itemizes the various elastohydrodynamic interactions which occur when a pneumatic tyre rolls and slides on a wetted pavement texture. The following treatment includes brake and drive slip, free-rolling, cornering and pure sliding behaviour.

It is well known that the microstructure of physical vapour deposited (PVD) coatings controls many of the properties (hardness, adhesion, residual stress) which are important in tribological applications. However, it is not generally recognised that the coating microstructure dictates the operating wear mechanism, both indirectly through determining the range of properties of a particular coating, and directly through its promotion of wear mechanisms that depend purely on the morphology of the coating. In this paper the effects of microstructure on hardness, internal stress and adhesion are briefly reviewed and the relevance of these properties to wear applications is discussed for titanium nitride coatings.

This paper measured the P-V diagram of 52100 steel/1045 steel rubbing pair under lubrication with and without oxide coating on the “ball-on-disc” testing machine. The oxide coating was pretreated on the steel surface by heating in the atmosphere of CO 2 gas. The effect of coating thickness and hardness of substrate on the P-V diagram was examined, and an optimum condition had been obtained, by which the load bearing capacity can vbe increased significantly. The microanalyses of oxide film were conducted by AES and XPS as well, and a model of three-sublayer structure of oxide coating had been proposed

Many coatings have been developed in recent years but their use in machinery is hampered by the lack of design methods for coated elements. While it is quite clear that the limitations in design methods of homogeneous elements used in rubbing contacts, and which relate essentially to the surface as opposed to the bulk aspects of the problem, apply also to coated elements, it is possible to develop methods which will help choose coating/substrate combinations that can withstand the mechanical and thermal loads applied to the contact by the mechanism under study. This paper discusses these methods and suggests that if they were applied to the rubbing elements or first-bodies, they could identify non compatible combinations under the working conditions envisaged and thus eliminate a large part of the trial and error process which is current today in the choice of coatings. Mechanical and thermal characteristics, thin layer solid mechanics theories along with a general pluridisciplinary approach are needed if these methods are to be developed.

The morphologies of particles generated during the grinding of metals are analyzed. The ground materials include several steels, titanium, and copper while aluminum oxide, cubic boron nitride, and diamond abrasive grinding wheels are used. Interest is focused on spherical particles of which three distinct morphologies have been typically observed. The occurrence of these particles is related to the different grinding induced temperatures and arguments are advanced to suggest that the spherical particles are formed by frictionally induced melting and subsequent solidification. Finally, it is suggested that analysis of chip morphology may afford a simple means of determining whether the grinding process is thermally “out of control.”

The aim of this study was to characterize the tribological behavior of a flame sprayed anti-wear Molybdenum, coating in dry and lubricated conditions (temperature: -10°C to +120°C). The different parameters which could lead to a variation of the lubrication mode, friction coefficient and wear rate were studied using a pin-and-disk tribometer. The influence of applied load, sliding velocity, lubricant temperature and oil additives were investigated. Different oils, with additives or not, were used. An important section of the molybdenum coating (0.6 mm thick) was removed during sliding in the additive-free lubricants, whereas only slight polishing was observed on top of summits in the case of sophisticated lubricants (

Damage, be it breakage, deformation or wear is initiated by overstraining or overstressina. Full modelling of both these causes is not possible today and one resorts to “simulation” to produce the data needed by design engineers to predict function loss. The question then is: how reliable is the data furnished by simulation? The answer is brought by the analysis of data produced in fretting tests which show that even very small variations in running conditions, in this case in amplitude, can change the nature of the damage. Simulation tests have to be undertaken with the utmost care.

A phenomenological mathematical description will be given of three body contact which is based on the condition that the third body is much weaker and more pliable than the two first bodies. It will be applied to wheel-rail rolling contact, where it results in the occurrence of a single extra material constant in the two-body equations which must be determined experimentally. It is found that with the aid of this constant the experiments fit a theoretical line. Also, this third body description can account for the empirical reduction factor of the creepage and spin coefficients C ij (see Kalker (1990) App. E) used by vehicle dynamicists in their calculation of the critical speed of railway vehicles.

Spall detachment in coatings is modelled as a cracked coated medium submitted to contact loading. Few models analyse the role of interfacial cracks between coating and substrate. The existing models are limited in use, due to assumptions on number and location of displacement zones (stick, slip, open) along crack faces. Further only ones crack is analysed at a time. A spall detachment is analysed as a combination of an interfacial crack that propagates at the interface and a surface breaking crack that propagates normally to the interface. These two cracks are analysed simultaneously. The energy release rate G is determined at crack tips. The method employed is half-analytical and half-numerical. Results show that, for the case studied, crack interaction favours crack propagation. The following spall detachment process is proposed: the surface breaking crack propagates down to the interface and the interfacial crack propagates at the interface in a direction opposite to that of the load displacement.

Friction and wear characteristics of PVD TiN, (Ti 50 ,Al 50 )N and (Ti 70 ,Nb 30 )N coated disks sliding against DIN 100Cr6 (AISI D3) hardened chromium steel balls were investigated. The coefficient of friction and the arm displacement were measured on-line whereas the worn-off volume of the ball after the test was optometrically determined. In most cases a reddish brown transfer layer of Fe and Fe 2 O 3 was left on the disk. The on-line measured friction and displacement were found to be a result of debris formation, trapping and ejection. In the steady state a dynamic equilibrium exists between particle formation (F), adhesion (A) and escape (E). It is suggested that the coefficient of friction originates mainly from the shear force between the particles in the third-body layer. The experiments show that care must be taken when interpreting the on-line measurements for studying the wear behaviour of (Ti,X)N coatings vs steel.

A technique is presented for measurement of skidding of roller followers on camshafts using optical scanners to determine rotational velocities. To investigate the role of surface finish in roller/cam skidding, a Tappet Roller Skid Machine was designed and constructed. Tests were conducted with two surface finishes, two temperatures, two simulated oil supply pressures and three rotational speeds. The study was then extended to perform in-situ experiments on a diesel engine. The cam follower housing and an injector follower lever of a complete six-cylinder diesel engine were modified and instrumented for the tests. Computer codes were developed for data acquistion and reduction. It was found that skidding is reduced by increasing temperature, base circle loading and surface roughness. The greatest difference in surface velocity was, however, found on the base circle of the cam where surface distress would not be expected.

Traction drive contact optimisation requires the investigation of trends in performance and durability to find the best combination for a given application. While information relating to contact efficiencies and capacities has been around for some time, it is not immediately obvious which practical steps the designer should take to improve his creation. The results of the parametric study presented here should help to clarify matters and the brief review of factors which influence rolling component life will give an appreciation of the ‘other half’ of the optimisation process.

A mass-conserving simulation algorithm for cavitating hydrodynamic lubrication has been described elsewhere. The algorithm, which is particularly well adapted to finite element implementation, is outlined qualitatively and demonstrated quantitatively through real and ideal engine bearing applications studied previously by others. Present simulation results and previous data agree reasonably closely for these applications, providing a limited validation of the present algorithm and demonstrating the importance of mass conservation in engine bearing design analysis.

The running-in wear of auto-motive cam-follower systems is assessed from tests carried out using a motored PSA TU3 cylinder head. The changes in surface topography occurring through wear is examined as a basis for establishing an objective method of wear evaluation. The effects of variations in the Initial surface finish and hardness of cams and followers is evaluated using a specially instrumented MIRA Test Machine in which the effect of hardness difference between cam and follower is highlighted and the implications of surface finish variation are examined.

Taper bushing, so-called the taper lock bush, on the market are commonly used with a key. If the limit of the transmissible torque by the taper bushing without a key is made clear, the use of the taper bushing would be more widespread. In this study, the maximum static transmission torque of the taper bushing without a key was experimentally discussed. The experimental data was considered in terms of the multiple regression analysis, and a regression equation for the transmissible torque was obtained.

The modern concept of a car wheel bearing is a complete unit that is ready to use, greased and sealed for life. Thus today the lubricant and the seal form an integral part of the bearing. With ongoing improvement in bearing internal geometry and materials, the performance of the seal can even replace rolling contact fatigue as the limiting factor for bearing service life. At the same time, demands for reliability and long, service-free running periods are continuously increasing. Systematic efforts during recent years have resulted in improved seal designs and have provide deeper insight into their functioning and the tribology effects involved. Seals for grease lubricated bearings are defined as active hydrodynamic engineering elements, with a preferential outward pumping effect to prevent penetration of foreign matter into a bearing unit. Seal life is thus governed by the existence of preferential pumping effects. When these have vanished, the seal transforms from an active into a passive engineering element. Bearing life from then depends on environmental factors only. Several mechanisms were identified which influence these effects negatively and thus restrict seal life: of these ageing of the seal lip material and counterface abrasive wear are described. Limiting factors were found and incorporated in a seal life model.

This Keynote Address list eight questions relating to tribological aspects of reciprocating engines. The questions have been chosen to highlight areas where a deeper insight of the phenomena may enable small improvements in friction and wear.

Experimental investigations on connecting-rod bearings in operating engines required the use of a mechanical scissor linkage to support the wires carrying the electronic signals. In many applications, one end of the linkage is attached to the big-end bearing cap by a yoke, the other end being fixed to the engine frame. The mass and inertia of the linkage modify the load acting to the bearing and change the bearing characteristics. The effect of the mechanical linkage is estimated by carrying out both rigid and elastic bearing calculations with and without a contribution from the linkage to the connecting-rod load. The loads arising from the yoke and links on the connecting-rod were calculated as a function of crankangle for different crankshaft speeds. The calculations showed that the linkage and yoke increase the inertial part of the load diagramm by about 10% and modify the orbit of the bearing center at small eccentricity ratios.

In recent years, the great improvement in the materials for the rolling elements and the development of the new traction oil has increased the reliability of the traction drive CVT (Continuously Variable Transmission) for automotive use. The authors began the research and development of the Half Toroidal CVT in 1978, and have made types of prototypes. Traction coefficient and efficiency were measured and life tests were carried out succesfully. As a result of these studies, we conclude that traction drive CVT has the potential for application to automotive transmission.

Methods of calculating oil flow in connecting rod big end bearings are discussed and a numerical example typical of engine practice is presented. The commonly used oil feed arrangement for connecting rod bearings, consisting of a single hole emerging from the crank pin, results in small flows and the bearing oil film may be depleted. It is therefore necessary to consider a rigorous ‘oil film history’ model where the transportation and availability of oil in the bearing clearance is allowed for. Cycle-averaged oil flow results for over 150 bearing cases are summarized in design chart and equation form. The design charts are of two types, one relating the flow from the rigorous oil film history method with the oil flows based on rapid methods. The other type considers directly the many engine and bearing parameters involved thus making this technique suitable for general use. Also included are sensitivity charts showing the effect on oil flow of changes in particular parameters.

Synopsis Previous work on brake noise and vibration problems is reviewed from its beginnings up to the present day. An underlying theme is revealed; namely that the inadequacy of analytical approaches in leading to satisfactory designs has forced the industry to develop empirical fixes when brake noise and vibration problems occur in practice. Despite having developed skills in tackling practical noise and vibration problems, the brake industry has a pressing need for design tools to avoid such problems from the outset. The growing importance of customer complaints of brake noise and vibration - against a background of increased overall vehicle refinement - provides an obvious commercial motivation. Suggestions are made of how to enhance FE models of the brake assembly in order to develop such design tools.

This work presents a forecasting model of the wear risk for an automotive overhead camshaft and its confrontation to experimental results. This model was built on the specific oil film thickness calculation and on the subsequent calculation of the coefficients of friction and stresses, the corresponding values being then compared with threshold values. Organized as a piece of computer software, the model permits the calculation of overall wear factors; the most significant parameters are thus presented as curves related to the cam profiles in such a way that the occurence and localization of wear is predicted with a rather good agreement with results obtained on rigs, for different operating conditions.

In practice rotary shaft seals will experience a small-amplitude dynamic excitation. It is shown that under periodic excitation circumferentially nonuniform clearances develop due to viscous seal material behaviour. The nearby fluid will fill these gaps, so entrainment and squeeze effects can develop fluid pressures which are sufficiently high to overcome the radial preload. Viscous seal properties are essential in this type of EHD lubrication. Hence it is designated viscoelastohydrodynamic (VEHD) lubrication. At present, this lubrication concept is the only macrohydrodynamic theory that explains the existence of a consistent circumferentially nonuniform film geometry of appreciable dimensions. Moreover, calculated values of film thickness and friction are in agreement with experimental data.

Empirically-derived correlations of dimensionless flow and load are presented as a direct means of predicting cycle-averaged feed pressure and hydrodynamic flows in ungrooved connectingrod bearings which are pressure-lubricated through a crankpin feed hole. The correlations allow quick estimation of flow sensitivity to small engine/bearing dimensional variations, as well as provide a simple relation that indicates when feed pressure flow can be a good indicator of actual flow.

Synopsis The durability of the cam and follower contact of the valve train of automobile engines has proved to be suspect in recent times. The received wisdom as to the mechanism of operation is that boundary lubrication pertains during the loading cycle. This view may well have delayed the application of fluid film lubrication theory in the study of the device. Modern thinking would lead to the view that some element of elastohydrodynamic lubrication must be occurring and that the mode of lubrication would be better described as ‘mixed’. The situation is reviewed and it is concluded that the use of lubrication theory as a design tool, alongside traditional tribological approaches, has much merit.

Friction clutches and brakes are analysed by the methods of computer-aided analysis. Clutch/brake rotational dynamics and friction and wear are considered jointly. Mathematical model and numerical algorithm for computer solution of dynamic equations are developed. Computer programmes provide generation and detailed analysis of design variants. An optimum design variant can be selected according to a specified criterion. The computer programmes developed are tested with transport engineering problems and some of the numerical results are presented.

Synopsis Developing a high-performance engine requires the capabilities for simultaneously predicting and studying the desired functions and quality of the entire engine at the initial stage of the development process. Vigorous effects have been under way at Nissan to advance the use of tribological technology in R&D activities for new engines and their components. Approaches used up to now have generally treated engine technology in terms of two categories: component technology and assembly technology. Crankshaft bending analysis, which takes into account the oil film pressure distribution, and cylinder bore distortion analysis, based on bolt tightening torque, are examples of techniques used in the component technology category. Engine friction prediction model and lubrication system model are typical tools used in the assembly technology category. It is expected that computer-aided tribology will continue to advance as various technological issues are overcome in the future.

ispartof: Journal Of Energy Chemistry vol:76 pages:165-174 status: published

For hard brittle coatings on hard substrates single pass scratch testing is shown to produce shallow tracks whose depth prior to fatal damage does not exceed one third of the coating thickness. The singular cause for fatal damage (chipping, spalling) is tensile type surface cracks generated behind the trailing edge of the indenter. The crack features observed correspond to a quasi-bulk mechanical response of the coating. By increasing the tip radius of the indenter the measured critical load for crack generation becomes increasingly sensitive to coating/substrate interface brittleness and flaws. Multipass sclerometric wear experiments done on the same scratch tester provide for more realistic testing of fatigue wear likely to be dominant for hard coatings on hard substrates. They reveal delamination in the substrate/coating interface region. Friction is shown to amplify brittle surface damage both for scratch and multipass wear testing. Damage caused by both techniques appears to be controlled by the same basic mechanism of surface crack generation and propagation.

The scratch test was analysed. Experiments and FEM calculations were performed on a PVD TiN coating on substrates with different hardnesses. Experiments indicated that at a critical load the coating fails through brittle fracture. FEM calculations showed that at this load the tensile stresses inside the coating become large enough to cause brittle failure. Although an Increase in shear stress across the interface at critical load was established, spalling of the coating was not the failure-determining mechanism. The results presented imply that the scratch test should not only be considered as an adhesion test, but also as a test for the strength of a material.

Piston ring/cylinder contacts in modern automotive engines are being exposed to increasingly high temperatures, gas pressure loading and combustion contamination. Conventional ferrous materials and wear-resistant coatings appear to be reaching their limit of reliability and a variety of novel materials, notably ceramics, are being applied to combat the tribological problems resulting from these developments. The tribological behaviour of ceramics in an engine environment is, as yet, not well understood. In particular, there is inadequate knowledge of how lubricants can affect the wear processes, and hence the durability, of ceramics in these applications. As a first step in clarifying these questions, the wear of an alumina-based plasma coating has been compared with that of conventional chromium plating in the Plint reciprocating wear machine. The temperatures, contact loadings and sliding speeds pertaining close to the top reversal point in a high temperature, heavy-duty diesel engine were closely simulated, and the experimental specimens were prepared from real engine components. The wear of the two piston ring coatings responded differently to lubricant additives. The alumina-based coating gave generally lower wear than the chromium plating. Examination of the worn surfaces by scanning electron microscopy and electron probe microanalysis revealed markedly different material removal processes for the two coatings. In these thick coatings damage appeared always to have been initiated at the surface rather than at the interface with the substrate. The possible influences of film formed on the surface by the lubricant are discussed.

A series of rolling contact fatigue tests were conducted on TIN coated 4118 carburized steel rollers against AISI 52100 steel disc using a two disk machine. Morphological pictures display features of shell pattern at the edge of spalls showing signs of crack propagation. The number and size of spalls are evaluated quantitatively and illustrate progressive damage of contact surfaces. Cross-sectional microstructure exhibits micro-crack propagation in the coating layer. Fatigue damage data indicates that thinner coatings result in a substantial improvement in the rolling contact fatigue life, and thicker coatings generate debonding or delamination more readily. Based on the patterns of micro-cracks and the morphology of spalled areas, failure mechanism of coated contact is suggested.

Numerical solutions developed by Chen and Engel for the elastic deformation of layered elastic half spaces are recast in the form of correction factors. These correction factors apply to the load and area at a circular microcontact computed using the Hertz equations when both contacting bodies are composed entirely of the coating material. The values thus corrected are the load and area applicable to the composite material consisting of the coating and the substrate. The correction factors depend on the ratio of the coating thickness to the uncorrected microcontact radius. The amount of the correction thus varies with the height of individual asperities. Using approximating functions for the correction factors and the Greenwood-Williamson microcontact model, a simulation scheme is outlined for determining the total microcontact load and area for coated surfaces. Results are obtained using representative surface characteristics and four values of the ratio of the elastic modulus of the coating to the elastic modulus of the substrate. The values of these ratios are E 1 /E 2 = 1/10, 1/3, 3 and 10, and span the range from very soft to very hard coatings.

The tribological behavior of TiN-coated Inconel 625 rings in dry sliding contact with carbon graphite was investigated with the aid of ring-on-ring sliding tests, computer-assisted profilometry, optical microscopy and scanning electron microscopy. Residual stresses and preferred orientations in TiN coatings were determined by X-ray diffractometry methods. Both hardness and Young's modulus of the TiN coatings were measured by nanoindentation hardness testing. Friction, wear, and spalling results were related to the hardness, residual stress, preferred crystallographic orientation, and thickness of the coating. To better understand the effects of coating and substrate properties on coating performance, thermal and thermoelastic models of the sliding contact were developed. Finite element methods were used to study the thermomechanical behavior of the thin TiN coatings.

The substrate Young's modulus is identified by using the first natural flexural frequency of a rectangular sample. The simulation of the “free-free” boundary conditions makes the reproductibility of the experimental conditions possible. Taking the geometrical irregularities, mainly the thickness variations, into consideration when interpreting the frequency spectra, gives Young's modulus of the material very accurate. Young's modulus of the film deposited on the substrate is measured using the same method of identification. All that is needed is to interpret the shift of the first natural flexural frequency of the sample after coating.

Photothermal radiometry is a promising method for the non destructive testing and the characterization of thin materials and has already been suggested to study various kinds of layered materials. A bonding defect at the interface of two materials leads to a thermal contact resistance which is usually low and hardly detectable with the existing NDT techniques. We wish to present here the results of three studies of modulated photothermal radiometry for which such defects can be observed. At first, we have studied several metallic-electrochemically induced deposits. A statistical treatment allows to distinguish various samples, when prepared in different conditions. Then, a similar coating (black polyurethane paint) has been deposited on two plates (steel and glass), for which the bonding strength is known as different. Evidence is given of the existence of an interface thermal resistance for the coating deposited on glass. At last, we have studied the mechanical contact quality between two coaxial metallic pipes. A mathematical model has been developed, including a focalized laser excitation. We were thus able to measure very low contact resistances (about 10-5 S.I.).

The current state of advancement of the analysis of layered media, subject to repeated contact loading, and containing a flaw, is given. References are included to contributions to component parts of the analysis of this configuration, and an indication made of how they might be amalgamated to form the desired solution. The goal of such an analysis is the determination of the conditions under which a layered surface might fail, when subject to rubbing or rolling contact. Also, the rate of detachment of a badly-adhered layer should be predictable, and the combination of materials which elastically give rise to a mild state of internal stress found.