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Massimiliano Pau - One of the best experts on this subject based on the ideXlab platform.
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estimation of wheel rail adhesion coefficient under wet condition with measured boundary friction coefficient and Real Contact Area
Wear, 2011Co-Authors: Hua Chen, Koan Sok Baek, Tsunamitsu Nakahara, Akira Namura, Bruno Leban, Makoto Ishida, Massimiliano PauAbstract:Abstract This paper describes how to improve the prediction method of the adhesion coefficient by means of the experimentally estimated boundary friction coefficient obtained by two kinds of twin-disc rolling Contact machines and the ratio of Real Contact Area to nominal Contact Area ( RCA / NCA ) obtained by ultrasonic measurement. The previous prediction method that the authors had already proposed in the last paper was based on Greenwood–Tripp's rough surface Contact model; however, in this study, the authors adopted Lee & Ren's rough surfaces Contact model and focused on the RCA / NCA measured by ultrasonic wave in order to predict the adhesion coefficient under wet conditions with the actual surface Contact conditions. As a result, regarding the tendency of adhesion coefficient decreasing with an increase of running speed, a good agreement has been obtained between the results obtained by the prediction method proposed in this study and the measured results obtained by the field-test of Japanese Shinkansen vehicle (series 200).
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Estimation of wheel/rail adhesion coefficient under wet condition with measured boundary friction coefficient and Real Contact Area
Wear, 2010Co-Authors: Koan Sok Baek, Massimiliano Pau, Akira Namura, Bruno Leban, Hua Chen, Makoto Ishida, Tsunamitsu NakaharaAbstract:This paper describes how to improve the prediction method of the adhesion coefficient by means of the experimentally estimated boundary friction coefficient obtained by two kinds of twin-disc rolling Contact machines and the ratio of Real Contact Area to nominal Contact Area (RCA/NCA) obtained by ultrasonic measurement. The previous prediction method that the authors had already proposed in the last paper was based on Greenwood-Tripp's rough surface Contact model; however, in this study, the authors adopted Lee & Ren's rough surfaces Contact model and focused on the RCA/NCA measured by ultrasonic wave in order to predict the adhesion coefficient under wet conditions with the actual surface Contact conditions. As a result, regarding the tendency of adhesion coefficient decreasing with an increase of running speed, a good agreement has been obtained between the results obtained by the prediction method proposed in this study and the measured results obtained by the field-test of Japanese Shinkansen vehicle (series 200).
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Estimation of Real Contact Area in a wheel-rail system by means of ultrasonic waves
Tribology International, 2003Co-Authors: Massimiliano PauAbstract:The application of an ultrasonic technique to estimate the Real Contact Area (RCA) in a wheel-rail system is proposed. The method is based on the analysis of the reflection of ultrasonic waves which are sent over the Contact region and reflected by it according to the state of Contact. The interaction of the experimental data with a theoretical model formulated in the early 1990s by Krolikowski allows us to calculate the RCA for the Area illuminated by the ultrasonic beam. By varying the external load and the surface conditions of the Contacting elements, it is possible to obtain the trend of the RCA with increasing load (for a certain roughness) as well to explore changes in RCA for different roughness while the load is kept fixed. Results showed that RCA grows almost linearly with the applied load and that an increase of one order of magnitude in combined roughness of the wheel-rail system leads to a roughly sevenfold reduction in RCA under a given load.
Isami Nitta - One of the best experts on this subject based on the ideXlab platform.
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Measurement of Real Contact Area on thermal print head using a laser microscope with a wide field of view
Tribology International, 2014Co-Authors: Isami Nitta, Yosuke Tsukiyama, Tsuyoshi Tsukada, Hirotoshi TeraoAbstract:Abstract In a dye-sublimation printer, a thermal print head presses and heats a dye-based ribbon to diffuse ink dyes to the desired positions into the receiving layer of paper. The print quality will deteriorate if the Contact condition between the thermal print head and the paper is insufficient. Thus, it is necessary to analyze the Contact condition for finer printing. Direct observation of the Contact Area with an optical microscope is effective to clarify the Contact conditions of the thermal print head. However, conventional optical microscopes take too much time to observe the whole apparent Contact Area, because their fields of view are not sufficiently wide. Previously, we developed a laser microscope with a wide field of view and applied this laser microscope to observe the whole apparent Contact Area of rubber elements. In this study, we examined the Contact conditions between the thermal print head and the paper. In general, when we observe the Contact Area of two solid surfaces, one is restricted to a transparent material such as a glass plate. Instead of the thermal print head, a glass head of the same shape as an existing thermal print head was pressed on the paper and observed through the glass head. This allowed us to clearly determine the Contact situations of the interface and measure the Contact widths and distributions of Real Contact Area. In this method, it was confirmed that the Contact width and the Real Contact Area changed in accordance with the type of paper used, steps of the printing process, and density of color printing.
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Thorough Observation of Real Contact Area of Copper Gaskets Using a Laser Microscope With a Wide Field of View
Journal of Tribology, 2013Co-Authors: Isami Nitta, Yoshio Matsuzaki, Yosuke Tsukiyama, Motoshi Horita, Shuichi SakamotoAbstract:To quantitatively predict the leakage rates of static metal seals, it is important to observe the Real Contact Area at seal surfaces because the leakage path consists of the nonContact portions between the flange and gasket surfaces. In a previous study, we observed the Real Contact situation using a thin polymer film 1 μm in thickness. In the present study, we observed the Real Contact Area on gasket surfaces using a laser microscope with a wide field of view. With this method, observation time over the whole gasket surface could be greatly reduced compared with conventional methods. The observations indicated that the leakage paths on the gasket surfaces were in the radial direction perpendicular to a lathe-turned groove and the circumferential direction along the groove. As the closing loads increased, the leakage paths in the radial direction disappeared and only the leakage path in the circumferential direction remained. When the closing loads increased further, the widths of the leakage paths at both the inside and outside on the gasket surface became narrower. The critical Contact pressure where the leakage paths in the radial direction disappear was determined from the observation of the Contact surface of the gasket. The leakage rates obtained from the experiments showed good agreement with the calculated values under the assumption of laminar flow along the turned groove over the critical Contact pressure.
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Evaluation of tribological properties of pick up roller measured using a laser microscope with a wide field of view
Tribology International, 2013Co-Authors: Isami Nitta, Yosuke Tsukiyama, Tsuyoshi Tsukada, Hirotoshi TeraoAbstract:Abstract Analysis of Contact conditions between rubber rollers and printing paper is important for stable paper feeding operation. Direct observation of apparent Contact Area is necessary to understand Contact conditions, such as distributions of Real Contact Area and micro-slips. However, conventional optical microscopy takes too long to observe the whole apparent Contact Area because the field-of-view is too narrow. We developed a wide field-of-view laser microscope, and applied it to determine the distributions of Real Contact Area of rubber rollers against glass plates. Critical torques at which micro-slips of the rubber rollers occurred were proportional to total Real Contact Area.
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Observation of Real Contact Area Using Laser Microscope with Wide Field of View
Journal of Advanced Mechanical Design Systems and Manufacturing, 2011Co-Authors: Isami Nitta, Rintaro Ebuchi, Yukiko Yasuda, Hirotoshi TeraoAbstract:In tribology, a Contact condition between mating surfaces is very important to reduce friction and raise their lifetime. Direct observation of apparent Contact Area is necessary for a better understanding of the Contact condition. We examined the distribution of Real Contact Area between a platen rubber roller and a glass plate using a laser microscope with wide field of view. Based on these observations, the distribution of Real Contact Area ratio, which is the ratio of Real Contact Area to the apparent Contact Area at each point, was calculated. Micro-slips over the whole apparent Contact Area were measured with several torques applied to the platen roller. The relationship between Real Contact Area ratio and micro-slips on the Contact Area are discussed.
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observation of Real Contact Area using laser microscope with wide field of view
Transactions of the Japan Society of Mechanical Engineers. C, 2011Co-Authors: Isami Nitta, Rintaro Ebuchi, Yukiko Yasuda, Hirotoshi TeraoAbstract:In tribology, a Contact condition between mating surfaces is very important to reduce friction and raise their lifetime. Direct observation of apparent Contact Area is necessary for a better understanding of the Contact condition. However, it takes a lot of measurement time to observe the whole apparent Contact Area with the existing Contact microscope. Thus, another technique is required for a faster method to observe the Real Contact Area. So, the laser microscope with a wide field of view we developed has been used to observe the whole apparent Contact Area for a very short time. A rubber disk specimen of a diameter of 5mm was pressed on a glass plate at several different loads and their Contact Areas were observed through the glass plate. The same Contact Areas were observed with the Contact microscope. Both the measured results by two different methods were compared with each other. It was found that they were similar with each other. Considerably wide apparent Contact Area between a platen rubber roller and the glass plate was observed with the laser microscope with a wide field of view. The distribution of Real Contact ratios and micro-slips on the Contact Area were obtained. A Relationship between the Real Contact ratios and the micro-slips on the Contact Area was discussed.
Takashi Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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measurement of Real Contact Area and analysis of stick slip region
Tribology International, 2009Co-Authors: Masao Eguchi, Takashi Shibamiya, Takashi YamamotoAbstract:The Real Contact Area obtained between a rough rubber hemisphere and a glass plate, under unlubricated conditions, was visualized by white light interferometry. The Contacting friction condition of the Real Contact Area in the starting friction process was analyzed using interference intensity. The Real Contact Area was extracted by fitting the intensity histogram of interference images to Gaussian distribution. This was seen to decrease with the increase of the applied tangential force, and it became approximately constant after initiation of macroscopic sliding. Real shear stress increased linearly in the micro-sliding regime and then became constant in the macro-sliding regime with the increase of the glass plate's displacement. The statistical ratio of stick region to Contact Area was estimated with the use of a differential histogram of the interference image intensity based on a tangential force coefficient of zero. This ratio showed a tendency to be more than a theoretical solution offered by Mindlin. In addition, we performed particle image velocimetry analysis, which assumed Real Contact spots as chase markers, and succeeded in the mapping of the stick/slip region within the Real Contact Area.
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Measurement of Real Contact Area and analysis of stick/slip region
Tribology International, 2009Co-Authors: Masao Eguchi, Takashi Shibamiya, Takashi YamamotoAbstract:The Real Contact Area obtained between a rough rubber hemisphere and a glass plate, under unlubricated conditions, was visualized by white light interferometry. The Contacting friction condition of the Real Contact Area in the starting friction process was analyzed using interference intensity. The Real Contact Area was extracted by fitting the intensity histogram of interference images to Gaussian distribution. This was seen to decrease with the increase of the applied tangential force, and it became approximately constant after initiation of macroscopic sliding. Real shear stress increased linearly in the micro-sliding regime and then became constant in the macro-sliding regime with the increase of the glass plate's displacement. The statistical ratio of stick region to Contact Area was estimated with the use of a differential histogram of the interference image intensity based on a tangential force coefficient of zero. This ratio showed a tendency to be more than a theoretical solution offered by Mindlin. In addition, we performed particle image velocimetry analysis, which assumed Real Contact spots as chase markers, and succeeded in the mapping of the stick/slip region within the Real Contact Area.
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Mechanism of Friction and Real Contact Area
2007Co-Authors: Takashi YamamotoAbstract:Friction is a representative phenomenon of tribology caused by sliding motion and rolling motion. The function and operational performance of mechanical components are remarkably infl uenced by friction. The role of boundary lubrication is dominant in the operation of tribo-mechanical components since severe operating conditions can be allowed due to the improvement of processing accuracy in the surface fi nishing of mechanical components. Therefore, the clarifi cation of the generation mechanism of friction with a relative motion in which a viscous effect is not included is important in analyzing the performance of mechanical components. It is the Real Contact Area that becomes a starting point when the generation mechanism of the boundary friction is discussed. Therefore, more detailed discussion of the concept of Real Contact Area is required. In this paper, we introduce mainly the content discussed in our research group regarding this subject.
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measuring a Real Contact Area using white light interferometry for a low reflecting rough surface under nonlubricated conditions
Japanese journal of tribology, 2005Co-Authors: Masao Eguchi, Takashi YamamotoAbstract:A method of measuring Real Contact Area for low reflectivity rough surface Contacted against a glass plate under nonlubricating and static Contact was proposed based on a white light interference image obtained using a stereomicroscope. First, under a Hertzian Contact for a steel ball against a glass plate, the correspondence of the magnitude of the Real Contact Area using Hertz theory to the result by the proposed method with the binary threshold determining method (threshold method) was confirmed. Also, in the case of Contact for paper material against a glass plate, by compensating image processing for a nonuniformly illuminated background of the optical interference image was obtained, it was made clear from the result of the Contact pressure dependency of an intensity histogram and a Real Contact ratio that this threshold method was effective. Furthermore, the Real Contact Area has been extracted simply and correctly without specifying an strict threshold value by extracting the pixel portion darker than the illuminated background average of each RGB interference color images and with performing logic operation AND (RGB-AND method) between each of those images. Both the threshold and RGB-AND methods were also applied to the measurement of a Real Contact ratio for phenol resin against a glass plate, and then the same result was obtained. By using the RGB-AND method, we clearly showed that the measurement of a Real Contact Area for low reflectivity rough surface against a glass plate under nonlubricating and static Contact is possible without setting a clear threshold value for binarization.
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Shear characteristics of a boundary film for a paper-based wet friction material: friction and Real Contact Area measurement
Tribology International, 2005Co-Authors: Masao Eguchi, Takashi YamamotoAbstract:Abstract A paper-based wet friction material lubricated with automatic transmission fluids (ATFs) produces plateau and positive slope regions in the friction–sliding velocity diagram. This feature observed at less than 1 mm/s of sliding velocity is discussed in this paper. The relationship between the friction and Contact pressures of less than 5 MPa was determined by a reciprocating friction test rig lubricated with mineral oil including phosphoric acid ester, one of the additives for ATFs. The Real Contact Area for dry condition was also determined by optical interferometry. The consistency of the Real Contact pressure dependency of the shear strength of the boundary film was indicated at pressures of less than 1 GPa obtained by steel-on-steel boundary friction (oiliness) test. This suggests that the generation of the positive slope region is due to thin film lubrication. To the plateau region, possibility of application of the phase transition model is considered.
Julien Scheibert - One of the best experts on this subject based on the ideXlab platform.
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evolution of Real Contact Area under shear and the value of static friction of soft materials
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Rahel Sahli, G Pallares, Christophe Ducottet, Al S Akhrass, Marcel Guibert, Julien ScheibertAbstract:The frictional properties of a rough Contact interface are controlled by its Area of Real Contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the Real Contact Area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various Contacts involving elastomers or human fingertips, we show that the Real Contact Area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the Area-reduction rate of individual Contacts obeys a scaling law valid from micrometer-sized junctions in rough Contacts to millimeter-sized smooth sphere/plane Contacts. For the class of soft materials used here, our results should motivate first-order improvements of current Contact mechanics models and prompt reinterpretation of the rate-and-state parameters. Area of Real Contact | rough Contact | elastomer | static friction | rate-and-state friction R ough solids in dry Contact touch only at their highest asper-ities, so that Real Contact consists of a population of individual microjunctions (Fig. 1B), with a total Area A R. A R is usually much smaller than the apparent Contact Area, A A , that one would expect for smooth surfaces. Since the seminal work of Bowden and Tabor (1), it is recognized that the frictional properties of such multiContact interfaces are actually controlled by A R rather than by A A. In particular, direct measurements of A R on transparent interfaces have been developed (2, 3) and repeatedly found proportional to the friction force, both for multiContacts (4–10) and for single Contacts between smooth bodies (1, 11, 12), with the proportionality constant being the Contact's frictional shear strength, σ. A R is a dynamic quantity with three major causes for variations. First, A R is roughly proportional to the normal load applied to multiContacts (5, 6, 10). This result, which provides an explanation for Amontons–Coulomb's law of friction (friction forces are proportional to the normal force), has been reproduced by many models of weakly adhesive rough Contacts under purely normal load (1, 4, 13–16). In the case of independent elastic microjunctions, although each of them grows nonlinearly with normal load, proportionality arises statistically due to random-ness in the surface asperities' heights (13). Second, in static conditions , A R slowly increases, typically logarithmically, with the time spent in Contact (5, 17). This phenomenon, so-called geometric aging (18), is interpreted as plastic (5, 19, 20) or viscoelas-tic (21) creep at the microjunctions, depending on the materials in Contact, and is different from Contact strengthening with time at constant Contact Area (18, 22), so-called structural aging. Third, at the onset of sliding of the interface, the population of already aged microjunctions gradually slips and is replaced by new, smaller microjunctions. Slip inception is thus accompanied by a drop of A R (5, 17), by up to a few tens of percent. This effect is often considered to be the origin of the difference between the peak (static) and steady sliding (kinematic) friction forces (18). Accounting for these three dependencies together has been a major success in the science of friction because it provides a consistent picture of the physical mechanisms underlying the ubiquitous state-and-rate friction law (5, 18, 20–31), which is obeyed by multiContacts in a variety of materials, from polymer glasses to rocks, through rubber and paper. However, a series of experimental observations reported here and there in the literature over recent decades suggest that the picture may not be fully comprehensive yet. These observations, made on smooth Contacts, have repeatedly indicated that the Area of apparent Contact, A A , depends on the value of the tangential load, Q, applied to the interface. For instance, smooth metallic sphere/plane Contacts typically grow as Q increases (1, 2), due to plastic deformations in the vicinity of the Contact (1, 32). Conversely, A A decreases when smooth elastomer-based sphere/plane Contacts as well as fingertip Contacts are increasingly sheared (9, 33–38), presumably due to viscoelastic and/or adhesion effects (33, 36, 38–40). It is therefore tempting to hypothesize that not only smooth but also rough interfaces have a dependence of their Contact Area on the tangential load, Q. Such a dependence would directly affect the resistance to sliding of a rough Contact, the way we use current Contact and friction models to predict the static friction force, and the physical meaning of the parameters of the rate-and-state friction law. To test this hypothesis, we carried out experiments to monitor, in multiContacts involving elastomers or human fingertips, the evolution of A R when Q is increased from 0 to macroscopic sliding. Significance We investigate the origin of static friction, the threshold force at which a frictional interface starts to slide. For rough Contacts involving rubber or human skin, we show that the Real Contact Area, to which static friction is proportional, significantly decreases under increasing shear, well before the onset of sliding. For those soft materials, our results will impact how we use and interpret current Contact mechanics and friction models.
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evolution of Real Contact Area under shear and the value of static friction of soft materials
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Riad Sahli, G Pallares, Christophe Ducottet, Al S Akhrass, I Ben E Ali, Matthieu Guibert, Julien ScheibertAbstract:The frictional properties of a rough Contact interface are controlled by its Area of Real Contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the Real Contact Area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various Contacts involving elastomers or human fingertips, we show that the Real Contact Area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the Area-reduction rate of individual Contacts obeys a scaling law valid from micrometer-sized junctions in rough Contacts to millimeter-sized smooth sphere/plane Contacts. For the class of soft materials used here, our results should motivate first-order improvements of current Contact mechanics models and prompt reinterpretation of the rate-and-state parameters.
Tsunamitsu Nakahara - One of the best experts on this subject based on the ideXlab platform.
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estimation of wheel rail adhesion coefficient under wet condition with measured boundary friction coefficient and Real Contact Area
Wear, 2011Co-Authors: Hua Chen, Koan Sok Baek, Tsunamitsu Nakahara, Akira Namura, Bruno Leban, Makoto Ishida, Massimiliano PauAbstract:Abstract This paper describes how to improve the prediction method of the adhesion coefficient by means of the experimentally estimated boundary friction coefficient obtained by two kinds of twin-disc rolling Contact machines and the ratio of Real Contact Area to nominal Contact Area ( RCA / NCA ) obtained by ultrasonic measurement. The previous prediction method that the authors had already proposed in the last paper was based on Greenwood–Tripp's rough surface Contact model; however, in this study, the authors adopted Lee & Ren's rough surfaces Contact model and focused on the RCA / NCA measured by ultrasonic wave in order to predict the adhesion coefficient under wet conditions with the actual surface Contact conditions. As a result, regarding the tendency of adhesion coefficient decreasing with an increase of running speed, a good agreement has been obtained between the results obtained by the prediction method proposed in this study and the measured results obtained by the field-test of Japanese Shinkansen vehicle (series 200).
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Estimation of wheel/rail adhesion coefficient under wet condition with measured boundary friction coefficient and Real Contact Area
Wear, 2010Co-Authors: Koan Sok Baek, Massimiliano Pau, Akira Namura, Bruno Leban, Hua Chen, Makoto Ishida, Tsunamitsu NakaharaAbstract:This paper describes how to improve the prediction method of the adhesion coefficient by means of the experimentally estimated boundary friction coefficient obtained by two kinds of twin-disc rolling Contact machines and the ratio of Real Contact Area to nominal Contact Area (RCA/NCA) obtained by ultrasonic measurement. The previous prediction method that the authors had already proposed in the last paper was based on Greenwood-Tripp's rough surface Contact model; however, in this study, the authors adopted Lee & Ren's rough surfaces Contact model and focused on the RCA/NCA measured by ultrasonic wave in order to predict the adhesion coefficient under wet conditions with the actual surface Contact conditions. As a result, regarding the tendency of adhesion coefficient decreasing with an increase of running speed, a good agreement has been obtained between the results obtained by the prediction method proposed in this study and the measured results obtained by the field-test of Japanese Shinkansen vehicle (series 200).
