The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
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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assessment of Nominal Contact Area parameters by means of ultrasonic waves
Journal of Tribology-transactions of The Asme, 2004Co-Authors: Francesco Aymerich, Massimiliano PauAbstract:In this paper the application of an ultrasonic method to evaluate size and shape of the Nominal Contact Area between two Contacting bodies is studied. The technique is based on the analysis of the quota of the ultrasonic wave reflected by the interface, which may be related to the level of Contact between the surfaces. A simple deconvolution procedure is applied to the raw ultrasonic data so as to remove the blurring effect introduced by the ultrasonic beam size. The ultrasonic data acquired on a simple sphere-plane Contact interface are compared with those obtained by means of a commercial pressure sensitive film and the results are discussed to evaluate the capability of the ultrasonic technique to capture the main Contact patch features correctly.
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evaluation of Nominal Contact Area and Contact pressure distribution in a steel steel interface by means of ultrasonic techniques
Jsme International Journal Series C-mechanical Systems Machine Elements and Manufacturing, 2003Co-Authors: Francesco Aymerich, Massimiliano Pau, Francesco GinesuAbstract:Analysis of Contact interfaces represents one of the most critical engineering problems and involves a huge number of practical applications such as roller bearings, tooth gears, wheel-rail interaction, electrical and thermal couplings, biomechanics etc. While theoretical and numerical approaches to the problem have been extensively studied over the years, only a few experimental techniques have been devised either to validate analytical results, or to infer information non invasively about the state of Contact. From the late 1950s onwards, when a relationship was discovered between the amount of energy reflected or transmitted through the Contact region and the charac· teristics of Contact, researchers have been employing ultrasonic waves to inspect Contact interfaces. Since then, many efforts have been directed towards improving the experimental technique and enhancing the theoretical understanding of ultrasonic waves propagation over an incomplete Contact interface. In the light of these consider· ations, the application of a simple 'pulse-echo' technique able to investigate the elastoplastic Contact of a steel sphere-plate system is proposed in this paper. The main purpose of the analysis is to assess the reliability of the ultrasonic method as a useful tool for assessing a number of Contact parameters such as size and shape of Contact Area, distribution of Contact pressure and so on. Experimental data were compared with numerical results obtained using a Finite Element Model (FEM) code. Ultrasonic reflection data were in· good agreement with calculated values, thus confirming the effectiveness of the ultrasonic technique as a fast, reliable and non invasive method in evaluating Contact parameters in loaded metallic interfaces.
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ultrasonic measurements of Nominal Contact Area and Contact pressure in a wheel rail system
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2000Co-Authors: Massimiliano Pau, Francesco Aymerich, Francesco GinesuAbstract:AbstractFor more than a century, the Contact between wheel and rail has been the subject of careful investigation by scientists and railway technicians. Many efforts have been made to understand a series of phenomena (wear, pitting, fatigue, failures, etc.) that are closely related to processes occurring in such a small Contact patch. A huge amount of numerical and theoretical research work (starting from Hertz's theory) has been carried out, but there is a noteworthy lack of experimental tests, which is probably due mainly to difficulties in accessing the Contact Area with conventional techniques. In the present paper, an experimental investigation dealing with the evaluation of the Contact Area and stresses transmitted across it is proposed: the technique employed is based on a non-invasive ultrasonic method that analyses the reflection of ultrasonic waves by the Contact interface. By using a set-up commonly employed in many non-destructive testing (NDT) analyses it was possible to obtain graphic maps o...
Vesa Saikko - One of the best experts on this subject based on the ideXlab platform.
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effect of type of Contact counterface surface roughness and Contact Area on the wear and friction of extensively cross linked vitamin e stabilized uhmwpe
Journal of Biomedical Materials Research Part B, 2020Co-Authors: Vesa SaikkoAbstract:Novel extensively cross-linked, vitamin E stabilized polyethylene (VEXLPE) materials are expected to provide improved wear and oxidation resistance in orthopedic implants. Noncyclic, multidirectional pin-on-disk (POD) wear tests were performed for VEXLPE with flat-on-flat (FoF) and ball-on-flat (BoF) specimen configurations against CoCr counterfaces of varying surface roughness (Sa = 0.02-0.74 μm). In addition, wear tests (FoF) were performed for VEXLPE pins of varying Nominal Contact Area (7.07-113 mm2 ) with consistent load regimen against polished CoCr disks. All specimen couples were also friction tested with a multidirectional, circularly translating POD device. In all tests, calf serum was used as the lubricant. In comparison with earlier, similar tests for conventional, gamma-sterilized ultra-high molecular weight polyethylene (UHMWPE) and for extensively cross-linked, heat treated UHMWPE (XLPE), the tribological findings for the present VEXLPE appeared promising with respect to its possible clinical use in prosthetic joints, particularly as an acetabular liner against large-diameter femoral heads, and in nonconforming Contacts. Contrary to the well-known, paradoxical behavior of conventional UHMWPE, the VEXLPE wear factor decreased with increasing Contact Area.
M. Bahaaddini - One of the best experts on this subject based on the ideXlab platform.
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effect of Contact surface Area on frictional behaviour of dry and saturated rock joints
Journal of Structural Geology, 2020Co-Authors: M A Pirzada, M S Andersen, Ahmadreza Hedayat, J. Oh, Hamid Roshan, M. BahaaddiniAbstract:Abstract Frictional behaviour of joints/faults is of great importance in many geo-engineering applications across different scales. It is known that the joint surface roughness is one of the critical parameters controlling the frictional behaviour of rock joints. While Nominal normal and shear stresses acting across the joint asperities are calculated based on overall shearing Area, the actual normal and shear stresses can be much greater due to smaller actual Contact Area. The actual Contact Area on the other hand is known to be related to the joint surface roughness. In order to investigate the effect of Contact Area on the shear behaviour of rock joints, an extensive set of direct shear experiments at different normal stresses on dry and saturated shale, limestone and sandstone tensile joints were undertaken. To compare the frictional properties of natural and artificial samples, synthetic samples were also fabricated, and their frictional properties were evaluated. Results of this study revealed that the predominant parameter controlling the frictional strength is the actual Contact Area. While the common models in predicting the shear strength of rock joints were unable to fit the experimental data based on Nominal Contact Area, the results based on actual Contact Area fit the measured values accurately. In addition, it was observed that when the actual Contact Area is considered, Mohr-Coulomb criterion is sufficient to fit the experimental data irrespective of the rock type, joint surface roughness or whether dry or saturated. This highlights that the Mohr-Coulomb criterion can appropriately predict the frictional strength if the actual Contact Area can be estimated. More importantly, the results showed that the surface roughness cannot dictate the shear behaviour of rock joints without considering the actual Contact Area.
Francesco Ginesu - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on Contact between cylindrical conformal surfaces
Journal of Strain Analysis for Engineering Design, 2004Co-Authors: Antonio Baldi, Pier Francesco Orru, Francesco GinesuAbstract:The application of an experimental technique based on ultrasonic waves to investigate Contact parameters for a cylinder versus cylinder system in conformal configuration is proposed. The method analyses the ultrasonic reflection from the Contact interface (or the transmission through it) and yields direct information about the size and shape of the Nominal Contact Area; it also gives a qualitative indication of the Contact pressure value, which is a parameter not explicitly related to the characteristics of the reflected wave.In order to assess the reliability of the technique as regards its ability to give a good reproduction of Contact Areas, the processed ultrasonic data, which can be easily represented as ‘Contact maps’, were compared with the results of the application of a commercial pressure-sensitive film (Fuji Prescale HS). At the same time, a finite element model of the tested Contact configuration supplied a further comparison term useful in assessing the effectiveness of the ultrasonic techniq...
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evaluation of Nominal Contact Area and Contact pressure distribution in a steel steel interface by means of ultrasonic techniques
Jsme International Journal Series C-mechanical Systems Machine Elements and Manufacturing, 2003Co-Authors: Francesco Aymerich, Massimiliano Pau, Francesco GinesuAbstract:Analysis of Contact interfaces represents one of the most critical engineering problems and involves a huge number of practical applications such as roller bearings, tooth gears, wheel-rail interaction, electrical and thermal couplings, biomechanics etc. While theoretical and numerical approaches to the problem have been extensively studied over the years, only a few experimental techniques have been devised either to validate analytical results, or to infer information non invasively about the state of Contact. From the late 1950s onwards, when a relationship was discovered between the amount of energy reflected or transmitted through the Contact region and the charac· teristics of Contact, researchers have been employing ultrasonic waves to inspect Contact interfaces. Since then, many efforts have been directed towards improving the experimental technique and enhancing the theoretical understanding of ultrasonic waves propagation over an incomplete Contact interface. In the light of these consider· ations, the application of a simple 'pulse-echo' technique able to investigate the elastoplastic Contact of a steel sphere-plate system is proposed in this paper. The main purpose of the analysis is to assess the reliability of the ultrasonic method as a useful tool for assessing a number of Contact parameters such as size and shape of Contact Area, distribution of Contact pressure and so on. Experimental data were compared with numerical results obtained using a Finite Element Model (FEM) code. Ultrasonic reflection data were in· good agreement with calculated values, thus confirming the effectiveness of the ultrasonic technique as a fast, reliable and non invasive method in evaluating Contact parameters in loaded metallic interfaces.
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ultrasonic measurements of Nominal Contact Area and Contact pressure in a wheel rail system
Proceedings of the Institution of Mechanical Engineers Part F: Journal of Rail and Rapid Transit, 2000Co-Authors: Massimiliano Pau, Francesco Aymerich, Francesco GinesuAbstract:AbstractFor more than a century, the Contact between wheel and rail has been the subject of careful investigation by scientists and railway technicians. Many efforts have been made to understand a series of phenomena (wear, pitting, fatigue, failures, etc.) that are closely related to processes occurring in such a small Contact patch. A huge amount of numerical and theoretical research work (starting from Hertz's theory) has been carried out, but there is a noteworthy lack of experimental tests, which is probably due mainly to difficulties in accessing the Contact Area with conventional techniques. In the present paper, an experimental investigation dealing with the evaluation of the Contact Area and stresses transmitted across it is proposed: the technique employed is based on a non-invasive ultrasonic method that analyses the reflection of ultrasonic waves by the Contact interface. By using a set-up commonly employed in many non-destructive testing (NDT) analyses it was possible to obtain graphic maps o...
M A Pirzada - One of the best experts on this subject based on the ideXlab platform.
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effect of Contact surface Area on frictional behaviour of dry and saturated rock joints
Journal of Structural Geology, 2020Co-Authors: M A Pirzada, M S Andersen, Ahmadreza Hedayat, J. Oh, Hamid Roshan, M. BahaaddiniAbstract:Abstract Frictional behaviour of joints/faults is of great importance in many geo-engineering applications across different scales. It is known that the joint surface roughness is one of the critical parameters controlling the frictional behaviour of rock joints. While Nominal normal and shear stresses acting across the joint asperities are calculated based on overall shearing Area, the actual normal and shear stresses can be much greater due to smaller actual Contact Area. The actual Contact Area on the other hand is known to be related to the joint surface roughness. In order to investigate the effect of Contact Area on the shear behaviour of rock joints, an extensive set of direct shear experiments at different normal stresses on dry and saturated shale, limestone and sandstone tensile joints were undertaken. To compare the frictional properties of natural and artificial samples, synthetic samples were also fabricated, and their frictional properties were evaluated. Results of this study revealed that the predominant parameter controlling the frictional strength is the actual Contact Area. While the common models in predicting the shear strength of rock joints were unable to fit the experimental data based on Nominal Contact Area, the results based on actual Contact Area fit the measured values accurately. In addition, it was observed that when the actual Contact Area is considered, Mohr-Coulomb criterion is sufficient to fit the experimental data irrespective of the rock type, joint surface roughness or whether dry or saturated. This highlights that the Mohr-Coulomb criterion can appropriately predict the frictional strength if the actual Contact Area can be estimated. More importantly, the results showed that the surface roughness cannot dictate the shear behaviour of rock joints without considering the actual Contact Area.