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Tribology of plastic materials
Rheology and elastohydrodynamic lubrication B. O. Jacobson This book is a cross between a collected works and a research monograph. The author refers to it hopefully as a textbook but it really is only suitable for very advanced students. His main idea is to present twenty-five years of his own work in a consistent manner with enough background material to make it intelligible. He does give a fairly full account of the early ideas of viscosity but the equivalent background material on elastohydrodynamic lubrication is mostly lacking. There is for example no mention of the seminal work of A. W. Crook. Like most investigators in this field the author has found that the existing viscometers, even the high shear rate ones, do not measure the right commodities for use in the ehl problem. He favours the idea of an oil with shear stress limit and associated glass transition which he holds in common with F. W. Smith and W. O. Winer. The alternative viewpoint favoured by K. L. Johnson, W. Hirst and others, of a model developed out of the Eyring theory, is not fully
Tribology Series Vol 19, Elsevier, 1991, ISBN 0-444-88146-8, xvi + 382 pp, $145.50 (US); Dfl. 255.00
explored. However, provided one has a consistent viewpoint when designing a suitable viscometer and when trying to account for the results from an ehl experiment, the agreement is normally fairly good. The trouble is that the accuracy with which one can make the ehl measurement is not sufficient to discriminate unambiguously between the various models. This problem is not discussed. The main meat in the book is the description of the various high pressure viscometers that the author has developed. The design of these has been improved over the years and it is now possible to get a full set of viscosity shear stress characteristics for an oil in return for a few days work. Perhaps the most pleasing development is the 'jumping ball' viscometer with which Jacobson is closely associated. This is used to show that the viscosity properties are quite different when stresses are only imposed for short periods of time. He also devotes a fair amount of space to the problem of solving ehl equations using the parameters derived from the viscometers. Armed with his model of the oil the author then goes on to reexamine a number of well-known
problems from the new point of view. These include pitting, ehl breakdown, lubricant contamination and the build-up of internal stresses. The most intellectually pleasing of these is the description of the processes which take place when lubrication finally breaks down. As he points out breakdown implies the onset of some non-linear effect and the model of an oil with a limiting shear stress provides just that. Again the problem is to obtain results which are sufficiently sensitive to test the theory. The book is beautifully produced on a very lavish scale. It is hardbacked with almost 400 pages and forms volume 19 of the well-known Elsevier series on tribology. My main complaint with the editorial side is that the book is chopped up into far too many chapters. This leads to a great deal of repetition. Likewise, the references which are put at the ends of each chapter are frequently repeated chapter after chapter. Thus there are six citations to the famous observations by Newton--all in the original Latin. But overall the book forms a very useful addition to the series. G. M. Hamilton
Tribology of plastic materials Y. Yamaguchi Polymers have always been regarded as interesting and useful materials for tribological applications. This is certainly reflected in the amount of published information on polymer tribology. However, the literature of polymer tribology, encompassing a variety of disciplinesand types of literature from scientific papers to Elsevier, 1990, 0-'!.448-7445-3, £75.00
TRIBOLOGY INTERNATIONAL
semi-technical material, requires careful searching and selection for practical information to be gained. It is, therefore, fortunate that Professor Yamaguchi's book on the tribology of polymers has been published as a sixteenth volume in the well-known Elsevier Tribology Series. The book consists of four chapters. The first two chapters introduce
the fundamentals of polymer tribology. Chapter one covers theories of polymer friction and parameters influencing frictional behaviour of polymers. Chapter two deals with wear and wearrelated topics. The two remaining chapters have a more practical and applied nature. Chapter three presents various ways to improve tribological performance of polymers through polymer blending 293
and composite production. Chapter four is devoted to the tribology of polymer machine elements such as bearings, gears, brake linings, and seals. The book contains a wealth of very detailed and specific information although there are attempts to generalize the data by introducing, where it is possible, some form of analytical description. There is a tendency to discuss topics from first principles and most of the links with engineering practice are in the terms of laboratory apparatus
rather than real engineering components. Nevertheless, engineers looking for guidance on problems involving the selection of specific polymers for a particular application or requiring information about the performance of a given polymer will find the book very useful. There are also certain shortcomings which ought to be mentioned. Diagrams showing experimental results are, in many cases, not very clear and it is rather difficult to extract the required information. Throughout
the book old cgs units are used instead of recommended SI units. The book is not entirely free of typographical errors. The lack of an index is unfortunate when one wants to find information on a particular polymer. Some diagrams showing testing equipment used often lack adequate explanation of the operating principles.
In summary, it is a useful reference book on polymer tribology containing a good deal of practical information. T. A. Stolarski
Modelling of the impact response of fibre-reinforced composites Edited by Y. Li, C. Ruiz and J. Harding This interesting, but rather small and expensive book describes in detail some advanced research work in modelling of the impact response of fibre-reinforced composites. The emphasis is on both experimental and theoretical approaches. Compared to many books on composites science and technology, in which normally some wider fields or general topics are covered, this volume concentrates on the topic of the mechanical response of fibrereinforced composites. It describes the progress of a project during a three-year programme about the subject mentioned in the title. Hence such a book is an attractive probe among the various forms of publication, but the success of these types of book has still to be demonstrated. On the experimental side, techniques of using Hopkinson-bar apparatus for determining the impact mechanical response of laminated composites in tension, compression and interlaminar shear are briefly described. A testing method is developed to determine the effect of strain rate on the interlaminar shear strength in composite materials. Research Technomic Publishing Co, 1991 (ca. £32) 128 pp
294
On the theoretical side the stress distribution in a hybrid carbon/glass tensile specimen is determined using a finite element package. The simulation indicates that under tensile loading the first step in the failure process is the tensile fracture of a carbon fibre tow aligned in the loading direction. By modelling such a failure in terms of reduced stiffness in the loading direction, the finite element method is used to determine the stress field around the failed tow. Stress distribution in the interlaminar plane is used to correlate failure modes, e.g. delamination and deplying. Further, the hybrid lay-up and its position within the specimen relative to the initial point of failure are discussed with respect to the effects on the stress distribution around the failed tow. The influence of stacking sequence on the failure of a woven hybrid laminate is also investigated.
description of the impact tensile response of woven-reinforced hybrid carbon-glass/epoxy laminates at an impact rate up to 1000 s 1, in terms of the experimental data obtained on woven carbon/epoxy and woven glass/epoxy laminates. The results show reasonable agreement with experimentally determined strength but the predicted failure strains are significant overestimates relative to the experimental values. This book contains no preface and index. It is composed of four individual chapters. Since the first gives an overview of the project, there is some repetition in the following chapters. In addition, it should be mentioned that some graphs are not printed clearly enough, especially those with small letters. However, the most serious defect is that the selection of topics is too narrow. This fact will, unfortunately, preclude many purchasers. Nevertheless, researchers in the field of mechanical characterization of composite materials would benefit from reading this volume to get a feeling for the difficulties in modelling the impact response of composite laminates.
Finally, the laminate theory used to predict the quasi-static tensile strength is extended to include a
K. Friedrich and L. Ye Institute for Composite Materials, Germany
results for a series of tensile impact tests on hybrid carbon/glass and carbon/Kevlar laminates as well as for a woven carbon/epoxy laminate at a quasi-static and an impact rate of loading are illustrated.
1992 Vol 25 No 4
Tribology Series Vol 19, Elsevier, 1991, ISBN 0-444-88146-8, xvi + 382 pp, $145.50 (US); Dfl. 255.00
explored. However, provided one has a consistent viewpoint when designing a suitable viscometer and when trying to account for the results from an ehl experiment, the agreement is normally fairly good. The trouble is that the accuracy with which one can make the ehl measurement is not sufficient to discriminate unambiguously between the various models. This problem is not discussed. The main meat in the book is the description of the various high pressure viscometers that the author has developed. The design of these has been improved over the years and it is now possible to get a full set of viscosity shear stress characteristics for an oil in return for a few days work. Perhaps the most pleasing development is the 'jumping ball' viscometer with which Jacobson is closely associated. This is used to show that the viscosity properties are quite different when stresses are only imposed for short periods of time. He also devotes a fair amount of space to the problem of solving ehl equations using the parameters derived from the viscometers. Armed with his model of the oil the author then goes on to reexamine a number of well-known
problems from the new point of view. These include pitting, ehl breakdown, lubricant contamination and the build-up of internal stresses. The most intellectually pleasing of these is the description of the processes which take place when lubrication finally breaks down. As he points out breakdown implies the onset of some non-linear effect and the model of an oil with a limiting shear stress provides just that. Again the problem is to obtain results which are sufficiently sensitive to test the theory. The book is beautifully produced on a very lavish scale. It is hardbacked with almost 400 pages and forms volume 19 of the well-known Elsevier series on tribology. My main complaint with the editorial side is that the book is chopped up into far too many chapters. This leads to a great deal of repetition. Likewise, the references which are put at the ends of each chapter are frequently repeated chapter after chapter. Thus there are six citations to the famous observations by Newton--all in the original Latin. But overall the book forms a very useful addition to the series. G. M. Hamilton
Tribology of plastic materials Y. Yamaguchi Polymers have always been regarded as interesting and useful materials for tribological applications. This is certainly reflected in the amount of published information on polymer tribology. However, the literature of polymer tribology, encompassing a variety of disciplinesand types of literature from scientific papers to Elsevier, 1990, 0-'!.448-7445-3, £75.00
TRIBOLOGY INTERNATIONAL
semi-technical material, requires careful searching and selection for practical information to be gained. It is, therefore, fortunate that Professor Yamaguchi's book on the tribology of polymers has been published as a sixteenth volume in the well-known Elsevier Tribology Series. The book consists of four chapters. The first two chapters introduce
the fundamentals of polymer tribology. Chapter one covers theories of polymer friction and parameters influencing frictional behaviour of polymers. Chapter two deals with wear and wearrelated topics. The two remaining chapters have a more practical and applied nature. Chapter three presents various ways to improve tribological performance of polymers through polymer blending 293
and composite production. Chapter four is devoted to the tribology of polymer machine elements such as bearings, gears, brake linings, and seals. The book contains a wealth of very detailed and specific information although there are attempts to generalize the data by introducing, where it is possible, some form of analytical description. There is a tendency to discuss topics from first principles and most of the links with engineering practice are in the terms of laboratory apparatus
rather than real engineering components. Nevertheless, engineers looking for guidance on problems involving the selection of specific polymers for a particular application or requiring information about the performance of a given polymer will find the book very useful. There are also certain shortcomings which ought to be mentioned. Diagrams showing experimental results are, in many cases, not very clear and it is rather difficult to extract the required information. Throughout
the book old cgs units are used instead of recommended SI units. The book is not entirely free of typographical errors. The lack of an index is unfortunate when one wants to find information on a particular polymer. Some diagrams showing testing equipment used often lack adequate explanation of the operating principles.
In summary, it is a useful reference book on polymer tribology containing a good deal of practical information. T. A. Stolarski
Modelling of the impact response of fibre-reinforced composites Edited by Y. Li, C. Ruiz and J. Harding This interesting, but rather small and expensive book describes in detail some advanced research work in modelling of the impact response of fibre-reinforced composites. The emphasis is on both experimental and theoretical approaches. Compared to many books on composites science and technology, in which normally some wider fields or general topics are covered, this volume concentrates on the topic of the mechanical response of fibrereinforced composites. It describes the progress of a project during a three-year programme about the subject mentioned in the title. Hence such a book is an attractive probe among the various forms of publication, but the success of these types of book has still to be demonstrated. On the experimental side, techniques of using Hopkinson-bar apparatus for determining the impact mechanical response of laminated composites in tension, compression and interlaminar shear are briefly described. A testing method is developed to determine the effect of strain rate on the interlaminar shear strength in composite materials. Research Technomic Publishing Co, 1991 (ca. £32) 128 pp
294
On the theoretical side the stress distribution in a hybrid carbon/glass tensile specimen is determined using a finite element package. The simulation indicates that under tensile loading the first step in the failure process is the tensile fracture of a carbon fibre tow aligned in the loading direction. By modelling such a failure in terms of reduced stiffness in the loading direction, the finite element method is used to determine the stress field around the failed tow. Stress distribution in the interlaminar plane is used to correlate failure modes, e.g. delamination and deplying. Further, the hybrid lay-up and its position within the specimen relative to the initial point of failure are discussed with respect to the effects on the stress distribution around the failed tow. The influence of stacking sequence on the failure of a woven hybrid laminate is also investigated.
description of the impact tensile response of woven-reinforced hybrid carbon-glass/epoxy laminates at an impact rate up to 1000 s 1, in terms of the experimental data obtained on woven carbon/epoxy and woven glass/epoxy laminates. The results show reasonable agreement with experimentally determined strength but the predicted failure strains are significant overestimates relative to the experimental values. This book contains no preface and index. It is composed of four individual chapters. Since the first gives an overview of the project, there is some repetition in the following chapters. In addition, it should be mentioned that some graphs are not printed clearly enough, especially those with small letters. However, the most serious defect is that the selection of topics is too narrow. This fact will, unfortunately, preclude many purchasers. Nevertheless, researchers in the field of mechanical characterization of composite materials would benefit from reading this volume to get a feeling for the difficulties in modelling the impact response of composite laminates.
Finally, the laminate theory used to predict the quasi-static tensile strength is extended to include a
K. Friedrich and L. Ye Institute for Composite Materials, Germany
results for a series of tensile impact tests on hybrid carbon/glass and carbon/Kevlar laminates as well as for a woven carbon/epoxy laminate at a quasi-static and an impact rate of loading are illustrated.
1992 Vol 25 No 4