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From atoms to systems
Tribology research at Osaka University From atoms to systems N. Ohmae and T. Tsukizoe*
Fundamental study of tribology is carried out at Osaka University in the Department of Precision Engineering. Our research is concerned with microscopic analysis of tribological phenomena occurring on metal surfaces. An attempt is also being made to establish a computer-based tribo-engineering system.
to the practical system. These operations should, of course, be done by computer in order to save time, money and man-power.
The tribometric system enables us to perform on-line data collection and data processing of friction force, normal force, electrical contact resistance and vertical displacement. By analysing the Tribo-engineering disturbances introduced to the system, Tribologists believed that the differences it is possible to estimate the "true" friction force and the "true" normal existing between tribology in the force at any instant in time. A protolaboratory and that in industry was so type of the tribo-engineering system great that the experimental results was introduced in the IRG-OECD obtained in the laboratory could not Documentation 79/3 by Dr Salomon = be extended directly to practical as a promising beginning to the systems problems. What is needed is a bridge approach to tribology, especially for between the two, not only a systedecision makers. matical programming of research projects in laboratories, but also communiBesides dynamic systems analysis cation with industry to determine the involved in tribometry, even a static most present and urgent problems. system modelling of friction and wear The aim of tribo-engineering 1 is to of frp 3 revealed that multi-regression design an information system in which analysis and autoregression analysis an exchange of science-oriented knoware effective for the explanation of ledge and technology-oriented knowfriction and wear processes. Some of ledge is pursued. The tribometric the companies in this country began to system, located at the centre of the estimate the important explanatory overall system, exists to interpret variables of a sliding system, for examlogical reasons for tribological ple, maximum torque transmission phenomena. Tribometry is, therefore, between wheel and rail, through the systematic treatment of tribological multi-regression analysis. Modelling variables. and simulation of tribo-processes are Laboratory experiments supply triboin progress in our laboratory, and the logical outputs such as wear, friction report on the fundametals of tribo(sometimes lubrication), fatigue, corrometry will be published in the near sion, temperature, noise, vibration and future. other variables. The tribometric system measures these outputs, and Microscopic considerations then simulates, evaluates, optimises, predicts and finally controls the The other side to our work is contribological system. The processed cerned with the microscopic analyses data are stored in the data bank and of tribology. Until the 1970's, the when demands are made by a practical deformation and fracture of asperities tribology system, the tribometric system were the central research interest of supplies suitable information through tribologists. Mathematical and statistical the data bank. In case the tribometric treatments of the asperity model presystem is not able to answer the dicted the amount of wear and the questions immediately, the operating magnitude of friction rather well. Still, command is made to the laboratory one simple question arises. Why and tribology system to simulate the practical how does the material wear? The tribological situations. The tribometric asperity model may not be able to system transmits the analysed results answer this question. Obviously, a *Department of Precision Engineering, Faculty surface asperity is not a fundamental of Engineenng, Osaka University, Yamada-Kami, quantity, because an asperity naturally consists of material which has physicalSuita, Osaka 565, Japan
mechanical constants and electronic structures. Real surfaces do not have steep peaks and valleys as obtained by profilometry, caused by the vertical magnification being much greater than the horizontal. Realistic contact occurs between slightly wavy surfaces. Dislocations
On a smaller scale, deformation of materials is determined by the interaction of dislocations. Transmission electron microscopy is the most powerful tool for observing dislocation structure; a high-voltage transmission electron microscopical observation was carried out to investigate the frictioninduced deformations of copper and aluminium single crystals. It was found that the greater the degree of deformation, ie the smaller the dislocation cell size, the larger the friction coefficient. From the point of view of dislocation arrangements, there is no difference between adhesion and abrasion. Adhesion and abrasion are thus morphologically determined. Friction is the resistance to deformation, whatever the macroscopic processes may be. A further study on the cross-sections of a friction track verified that the microscopic constitution of a workhardened layer contained a texture, a distorted region, a compressed zone and an undisturbed matrix 4,s. Thus by analysing the dislocation structures of a friction track, it becomes clear that friction is primarily a resistance to deformation during sliding. For the process of wear debris formation, fracture of materials was studied. For this purpose, we are using the finite element method. Twodimensional elastic programming is used to estimate the principal stresses acting on each element and a two-dimensional elastic-plastic program will estimate the progress in plastic deformation as well as the onset and process of fracture. The dimensions of triangular elements were of the order of the dislocation cell sizes, eg 0.5/~m, based on the results of transmission electron microscopical observations 6 . Yielding of material
TRIBOLOGY international August 1980 181
was initiated by sliding, and a heavily deformed region originated below the surface. Simulations of void nucleation and crack propagation determined wear sheet formation as demonstrated by Suh. A further finite element method analysis using a large-scale computer is being conducted in order to investigate the deformation processes due to sliding and the mechanism of wear. Field ion m i c r o s c o p y
On the atomic scale, an in situ field ion microscopical study on frictioninduced deformations is being carried out. The change in the arrangement of tungsten atoms was observed before and after friction experiments inside the field ion microscope. The depth of induced damage was examined using a field evaporation technique. When a tungsten tip slid against a gold plate, the damage was limited to about 10 to 20 atomic layers from the surface and the parallel slip systems to the surface occurred on the {011.} or the {112 plane. Sliding contact with a tungsten plate caused severe damage of more than 100 atomic layers in depth, and slip on the {011} and the {112} planes occurred normal to the surface. Results of the field ion microscopical
Link-belt roller bearings Positive roller retention and precise roller guidance are the main benefits claimed for a range of high capacity spherical roller bearings now available on the European market. The selfaligning self-contained bearings have retainer roller pockets double contoured to the shape of the roller giving large hi~h-conformity contact areas above the centre line. According to FMC, these bearings are particularly suited for heavy-duty high-precision applications, including particular earth moving equipment, vibrating screens, steel and paper mills, embossing rollers, printing presses, and torque converters. They are available in shaft sizes from 40mm to 300mm. Symmetric roller design permits natural roller positioning and distribution of loading in roller raceways which are contoured to provide controlled stress distribution. Controlled raceway curvatures on inner and outer rings provide precise clearance and prevent roller
study on sndmg contact will be published in the near future.
Electronic structure The nature of adhesion is being studied from the standpoint of the electronic structures of solids. Adhesion experiments of copper single crystals at light loads were conducted in the ultra-high vacuum of an Auger emission spectrometer. The adhesive coefficient of copper single crystals was found to be strongly dependent on crystallographic orientations. Research effort is being extended to analyse the nature of adhesion from the standpoint of electronic energy bands of solids. A preliminary analysis of the influence of electronic structure on the friction of 3d transition metals against copper has been interpreted by the filling of the d-bands~
Acknowledgements Much of the research work reviewed in this paper is carried out by graduate and undergraduate students in our laboratory; the role of electronic structure in metallic adhesion by T. Okuyama and T Mori; field ion microscopy of sliding contact by K. Nishizaki and K. Tsubouchi; finite element method analysis of wear
edge loading. Outer ring raceways are spherically finished to provide freedom of alignment under variable dynamic conditions. Bearings are available with outer ring variations to suit design requirements. A grooved outer ring with three lubrication holes drilled through at 120 ° is standard.
FMC Power Transmission Group, 172 Sterrebeekbaan, 1930 Zaventem, Belgium
Wear teach-in A highly successful one day Wear Workshop was recently held at the Department of Metallurgy, Brunel University, organised by Dr T. Eyre. The objective of the Workshop was to provide an opportunity for representatives from industry to gain a broader, practical experience of ~,ome wear problems of technological importance and of experimental techniques and services which are now
182 TRIBOLOGY international August 1980
processes by E. Yamamoto and A. Sakakura,the fundamentals of tribometry by S. Ishikawa and H. Funasho.
References l. Ohmae N. An Introduction to Triboengineering. Proc. International Conference on Fundamentals o f Tribology, MIT, Cambridge, June 1978, in press
2. SalomonG. CommunicationProblems of IRG Activities. IRG-OECD Documentation 79/3
3. Ohmae N., Yukumoto M. and Tsukizoe T. Analysis of Systems Structure in the Wear of FRP. Proc. Eurotrib '77. Diisseldorf, October'1977, No. 57
4. Ohmae N. Transmission Electron Microscope Study of the Inter-relationship Between Friction and Deformation of Copper Single Crystals.Proc. International Conference on Fundamentals o f Tribology, MIT, Cambridge, June 1978, in press
5. Ohmae N., Tsukizoe T. and Akiyama F. On the MicroscopicProcesses Involved in Metallic Friction. Philosophical Magazine A, 1979, 4 0 , 8 0 3
6. Ohmae N. and Tsukizoe T. The Wear Process Analysedby Finite Element Method. Wear, #t press 7. Ohmae N., Okuyama T. and Tsukizoe T.
The Influence of Electronic Structure on the Friction in Vacuum of 3d Transition Metals in Contact with Copper. Tribology International, 1980, 13(4), 1 7 7 - 1 8 0
available for studying these problems, which in turn will lead to a better understanding of the underlying wear mechanisms. The various types of wear which occur in bearings and cams and tappets were reviewed and many test specimens were available to illustrate the different failure modes. Demonstrations were given on the rigs currently being used in the Metallurgy Department for the study of friction and wear problems. Analytical techniques for investigating wear processes and for condition monitoring were also covered in the Workshop. In particular, the application of the sem to ring and cylinder liner Wear was reviewed, and the technique of specimen preparation and use of acetate replicas for sem were demonstrated. The technique of ferrography was demonstrated, along with the use of the bichromatic microscope and sem for examination of the separated particles.
Fundamental study of tribology is carried out at Osaka University in the Department of Precision Engineering. Our research is concerned with microscopic analysis of tribological phenomena occurring on metal surfaces. An attempt is also being made to establish a computer-based tribo-engineering system.
to the practical system. These operations should, of course, be done by computer in order to save time, money and man-power.
The tribometric system enables us to perform on-line data collection and data processing of friction force, normal force, electrical contact resistance and vertical displacement. By analysing the Tribo-engineering disturbances introduced to the system, Tribologists believed that the differences it is possible to estimate the "true" friction force and the "true" normal existing between tribology in the force at any instant in time. A protolaboratory and that in industry was so type of the tribo-engineering system great that the experimental results was introduced in the IRG-OECD obtained in the laboratory could not Documentation 79/3 by Dr Salomon = be extended directly to practical as a promising beginning to the systems problems. What is needed is a bridge approach to tribology, especially for between the two, not only a systedecision makers. matical programming of research projects in laboratories, but also communiBesides dynamic systems analysis cation with industry to determine the involved in tribometry, even a static most present and urgent problems. system modelling of friction and wear The aim of tribo-engineering 1 is to of frp 3 revealed that multi-regression design an information system in which analysis and autoregression analysis an exchange of science-oriented knoware effective for the explanation of ledge and technology-oriented knowfriction and wear processes. Some of ledge is pursued. The tribometric the companies in this country began to system, located at the centre of the estimate the important explanatory overall system, exists to interpret variables of a sliding system, for examlogical reasons for tribological ple, maximum torque transmission phenomena. Tribometry is, therefore, between wheel and rail, through the systematic treatment of tribological multi-regression analysis. Modelling variables. and simulation of tribo-processes are Laboratory experiments supply triboin progress in our laboratory, and the logical outputs such as wear, friction report on the fundametals of tribo(sometimes lubrication), fatigue, corrometry will be published in the near sion, temperature, noise, vibration and future. other variables. The tribometric system measures these outputs, and Microscopic considerations then simulates, evaluates, optimises, predicts and finally controls the The other side to our work is contribological system. The processed cerned with the microscopic analyses data are stored in the data bank and of tribology. Until the 1970's, the when demands are made by a practical deformation and fracture of asperities tribology system, the tribometric system were the central research interest of supplies suitable information through tribologists. Mathematical and statistical the data bank. In case the tribometric treatments of the asperity model presystem is not able to answer the dicted the amount of wear and the questions immediately, the operating magnitude of friction rather well. Still, command is made to the laboratory one simple question arises. Why and tribology system to simulate the practical how does the material wear? The tribological situations. The tribometric asperity model may not be able to system transmits the analysed results answer this question. Obviously, a *Department of Precision Engineering, Faculty surface asperity is not a fundamental of Engineenng, Osaka University, Yamada-Kami, quantity, because an asperity naturally consists of material which has physicalSuita, Osaka 565, Japan
mechanical constants and electronic structures. Real surfaces do not have steep peaks and valleys as obtained by profilometry, caused by the vertical magnification being much greater than the horizontal. Realistic contact occurs between slightly wavy surfaces. Dislocations
On a smaller scale, deformation of materials is determined by the interaction of dislocations. Transmission electron microscopy is the most powerful tool for observing dislocation structure; a high-voltage transmission electron microscopical observation was carried out to investigate the frictioninduced deformations of copper and aluminium single crystals. It was found that the greater the degree of deformation, ie the smaller the dislocation cell size, the larger the friction coefficient. From the point of view of dislocation arrangements, there is no difference between adhesion and abrasion. Adhesion and abrasion are thus morphologically determined. Friction is the resistance to deformation, whatever the macroscopic processes may be. A further study on the cross-sections of a friction track verified that the microscopic constitution of a workhardened layer contained a texture, a distorted region, a compressed zone and an undisturbed matrix 4,s. Thus by analysing the dislocation structures of a friction track, it becomes clear that friction is primarily a resistance to deformation during sliding. For the process of wear debris formation, fracture of materials was studied. For this purpose, we are using the finite element method. Twodimensional elastic programming is used to estimate the principal stresses acting on each element and a two-dimensional elastic-plastic program will estimate the progress in plastic deformation as well as the onset and process of fracture. The dimensions of triangular elements were of the order of the dislocation cell sizes, eg 0.5/~m, based on the results of transmission electron microscopical observations 6 . Yielding of material
TRIBOLOGY international August 1980 181
was initiated by sliding, and a heavily deformed region originated below the surface. Simulations of void nucleation and crack propagation determined wear sheet formation as demonstrated by Suh. A further finite element method analysis using a large-scale computer is being conducted in order to investigate the deformation processes due to sliding and the mechanism of wear. Field ion m i c r o s c o p y
On the atomic scale, an in situ field ion microscopical study on frictioninduced deformations is being carried out. The change in the arrangement of tungsten atoms was observed before and after friction experiments inside the field ion microscope. The depth of induced damage was examined using a field evaporation technique. When a tungsten tip slid against a gold plate, the damage was limited to about 10 to 20 atomic layers from the surface and the parallel slip systems to the surface occurred on the {011.} or the {112 plane. Sliding contact with a tungsten plate caused severe damage of more than 100 atomic layers in depth, and slip on the {011} and the {112} planes occurred normal to the surface. Results of the field ion microscopical
Link-belt roller bearings Positive roller retention and precise roller guidance are the main benefits claimed for a range of high capacity spherical roller bearings now available on the European market. The selfaligning self-contained bearings have retainer roller pockets double contoured to the shape of the roller giving large hi~h-conformity contact areas above the centre line. According to FMC, these bearings are particularly suited for heavy-duty high-precision applications, including particular earth moving equipment, vibrating screens, steel and paper mills, embossing rollers, printing presses, and torque converters. They are available in shaft sizes from 40mm to 300mm. Symmetric roller design permits natural roller positioning and distribution of loading in roller raceways which are contoured to provide controlled stress distribution. Controlled raceway curvatures on inner and outer rings provide precise clearance and prevent roller
study on sndmg contact will be published in the near future.
Electronic structure The nature of adhesion is being studied from the standpoint of the electronic structures of solids. Adhesion experiments of copper single crystals at light loads were conducted in the ultra-high vacuum of an Auger emission spectrometer. The adhesive coefficient of copper single crystals was found to be strongly dependent on crystallographic orientations. Research effort is being extended to analyse the nature of adhesion from the standpoint of electronic energy bands of solids. A preliminary analysis of the influence of electronic structure on the friction of 3d transition metals against copper has been interpreted by the filling of the d-bands~
Acknowledgements Much of the research work reviewed in this paper is carried out by graduate and undergraduate students in our laboratory; the role of electronic structure in metallic adhesion by T. Okuyama and T Mori; field ion microscopy of sliding contact by K. Nishizaki and K. Tsubouchi; finite element method analysis of wear
edge loading. Outer ring raceways are spherically finished to provide freedom of alignment under variable dynamic conditions. Bearings are available with outer ring variations to suit design requirements. A grooved outer ring with three lubrication holes drilled through at 120 ° is standard.
FMC Power Transmission Group, 172 Sterrebeekbaan, 1930 Zaventem, Belgium
Wear teach-in A highly successful one day Wear Workshop was recently held at the Department of Metallurgy, Brunel University, organised by Dr T. Eyre. The objective of the Workshop was to provide an opportunity for representatives from industry to gain a broader, practical experience of ~,ome wear problems of technological importance and of experimental techniques and services which are now
182 TRIBOLOGY international August 1980
processes by E. Yamamoto and A. Sakakura,the fundamentals of tribometry by S. Ishikawa and H. Funasho.
References l. Ohmae N. An Introduction to Triboengineering. Proc. International Conference on Fundamentals o f Tribology, MIT, Cambridge, June 1978, in press
2. SalomonG. CommunicationProblems of IRG Activities. IRG-OECD Documentation 79/3
3. Ohmae N., Yukumoto M. and Tsukizoe T. Analysis of Systems Structure in the Wear of FRP. Proc. Eurotrib '77. Diisseldorf, October'1977, No. 57
4. Ohmae N. Transmission Electron Microscope Study of the Inter-relationship Between Friction and Deformation of Copper Single Crystals.Proc. International Conference on Fundamentals o f Tribology, MIT, Cambridge, June 1978, in press
5. Ohmae N., Tsukizoe T. and Akiyama F. On the MicroscopicProcesses Involved in Metallic Friction. Philosophical Magazine A, 1979, 4 0 , 8 0 3
6. Ohmae N. and Tsukizoe T. The Wear Process Analysedby Finite Element Method. Wear, #t press 7. Ohmae N., Okuyama T. and Tsukizoe T.
The Influence of Electronic Structure on the Friction in Vacuum of 3d Transition Metals in Contact with Copper. Tribology International, 1980, 13(4), 1 7 7 - 1 8 0
available for studying these problems, which in turn will lead to a better understanding of the underlying wear mechanisms. The various types of wear which occur in bearings and cams and tappets were reviewed and many test specimens were available to illustrate the different failure modes. Demonstrations were given on the rigs currently being used in the Metallurgy Department for the study of friction and wear problems. Analytical techniques for investigating wear processes and for condition monitoring were also covered in the Workshop. In particular, the application of the sem to ring and cylinder liner Wear was reviewed, and the technique of specimen preparation and use of acetate replicas for sem were demonstrated. The technique of ferrography was demonstrated, along with the use of the bichromatic microscope and sem for examination of the separated particles.