Composite materials: Engineering and science

Books and publications ideal for handling the transformations, is introduced and further explained in an appendix. This leadsto the matheF. L. Matthews and R. D. Rawlings matical treatment of anisotropicmateriChapman & Hall, 1994, als, non-axial properties and classical ISBN 0 412 55970-9, paperback, f24.99 laminate theory. A usefulfeature is the worked exampleswhich help flesh out CeramicMatrix Composites the results for the beginner. The stanK. K. Chawlu dard resultsfor the micro-mechanicsof Chapman & Hall, 1993, unidirectional composites based on ISBN 36740-8, hardback, f42.00 seriesand parallel modelsare derived and there is a brief discussion of Expertise in composite materiais requires familiarity with several compressivestrength and failure criteria branches of science and engineering, for laminates.The treatment, however, is too conciseand severaltopics includincluding the chemistry of resins and ing compressiveand thermal properties polymers and their interaction with and the effects of edgeson laminates moisture, the behaviour of fibres and would have benefited from more solidsespeciallyfracture and the effects of defects, interfaces, strength of madetails. Many commercialsystemsare based terials, stressanalysisand elasticity to on short fibres randomly dispersedin a a combination of reinforcement and matrix in both static and dynamic situaplane or in three dimensions.Problems arise in injection moulding becauseof tions. If other types of matrix are weld lines and unwanted fibre orientainvolved a knowledge of ceramicsand metals is called for. Common to all tion. These and other topics are discussed together with the simple types of compositematerialsis the vital area of fabrication so often regarded theory of the stressdistribution along the length of a fibre, which, it is pointed mistakenly asof little consequence. Composite Materials: Engineering and out, can now be readily measured. Fibre composites,like most materials, Science gives a balanced,detailed treatment of the whole field of composite have their weaknesses. Theseare often associatedwith impac~fracture performaterials. The scene is set with the evolution of materialsthrough the ages mance and appropriately two chapters are devoted to fracture and toughening and the benefits of combining two or more materials. The reinforcements mechanismsand impact. Unfortunately considered include natural, renewable the performanceof, particularly, carbon fibres, asbestos, synthetic organics, fibre compositesin this respectand as ceramic,glass,boron and carbon fibres. regardshot, wet, compressionstrength Representativepropertiesand structural is still poor though the authors believe detailsare includedaswell as figureson that a much-improvedunderstandingof the production capacity for carbon toughening mechanisms and higher fibres. It would have beeninterestingto strain to failure fibres backed by have similar information for glassand tougher matriceswill improve the situaceramicfibres aswell assomecomparation This is clearly an area for much tive cost data. more research input and the aspiring The fibre matrix interface has a worker could do a lot worse than to marked effect on composite performstart by reading thesetwo chapters. anceand it is not alwaysapparentto the Fatigue and environmental effects user as to what is the optimum bond make a brief appearanceand the book strength. Wetting, bonding mechanisms finisheswith an account of jointing and and strength tests are discussedgenerrepair and NDT. While both may be ally. Before going on to the details of necessary for a good structure the micro-mechanicsand laminate theory former is an extremely important topic there are three useful chapters dealing which is (like manufacturing)sometimes with the processingand overall propplayed down. However, it can make a erties of metal, ceramic (including considerabledifference to the commercarbon/carbon), and polymer matrix cial successof compositestructures. composites.The mathematicaltheory of Each chapter finishes with a brief compositebehaviour is prefacedwith an summary,referencesfor further reading, elementaryaccount of stressand strain, some problemsand a number of selfthe effects of transforming the axesand assessment questions. the behaviour of thin-walled spheres Overall, this is an attractive, welland cylinders. Matrix notation, which is produced, first account of composite Composite Materials: Science

0261-3~9/95/02011~7~1995

Engineering and

Elsevier

ScienceLtd

materials which is very competitively priced and should prove useful in university courses.Depth can be added later by referring to the many specialist journals. Regarding ProfessorChawla’sbook, Ceramic Matrix Composites, I must immediately declare my interest. I did suggestsomeyears ago that the author wrote a book on ceramic matrix materials and this fact is acknowledgedin the Preface. However, I had no further input to the work and I feel that I can review the resulting volume quite objectively. In many ways Ceramic Matrix Composites mirrors Composite laterals: Engineering and Science. The same issuesoccur - manufacturing, the interface micro- and macro-mechanics, toughness, laminate theory, etc. thereby illustrating the underlying unity common to all composite materials. Ceramic matrix composites(Iike their polymer matrix cousins)are bedevilled by fracture failure but their ability to survive high temperaturesand their relatively low density comparedwith metals are considerableadvantagesand make the systemswell worth developing. The book comments with a useful review of the basic characteristicsof ceramicsand processingtechniquesfor glassand ceramics. Reinforcing fibres for this type of matrix include glass, boron, carbon, ceramics based on carbides,nitrides and oxidesand metals. There is a lengthy account of these fibres plus a useful description of the statistics of fibre strength based on Weibull’s approach. Again processingis accordedits proper placewith a consideration of both conventional and novel techniques. Wetting and bonding are vital if the resulting compositeis to have integrity. Methods of measuring the bond strength by pull-out and push-out are discussed followed by the standard micro-mechanicsand thermal performanceof composites,load transfer to the fibre, creep and fatigue. Thermal stresseswhether due to the fabrication route or subsequentoperating conditions are very important in composite materialsbecausethey can causecracking in the matrix and then possiblylead to premature fibre failure in hostile atmospheres.The cracking may be exacerbated in ceramicsbecausethe materials usually have a lower strain to failure than polymers. On the other hand, ceramicshave a lower coefficient

Materials & Design Volume 16 Number 2 1995

Ii9

Books and publications of thermal expansion than polymers. The discussion is backed by a concise mathematical analysis. Toughness (or lack of it!), as was mentioned earlier, is a problem with all composites and toughening mechanisms and interface engineering (or the coating of fibres) are described. Finally, there is a conventional treatment of macromechanics and an account of some applications of fibre-reinforced ceramics. The emphasis tends to be on uses in which temperature resistance is a prime consideration. This is a very well-produced book and happily the author, although working in North America, unashamedly uses SI units. It would be excellent for anyone working in the field of reinforced ceramics but could equally profitably be read by the student of polymer composites. N.L. Hancox

Design for Practice

Assembly

Principles

and

Alan Redford and Jan Chal McGraw-Hill International (UK) 1994, ISBN 0 07 707838 1. 202 pp, hardback,

f29.95 The book is divided into four parts. In Methods and Processesessential assemblyprocesses(manual, dedicated, flexible) are defined, followed by a discussionof the mostimportant factors that causeprocessfailure. The second part dealswith Product DesignFactors affecting the assemblyof a product. The authors critically discussdesignfactors which are both independent of and dependent on assemblymethods and processes.In addition, the secondpart dealswith product designfactors affecting automatedassembly.In Designfor Assembly Methods (DFA) first the requirements of DFA systems and methods are consideredand these are followed by a description of the key methodsinvolved in designfor assembly. As a special feature, the authors give a rated comparisontable of several DFA methodsto enablepotential users to select the best DFA method for their purposes.This is followed by a detailed descriptionof three commercially used DFA systems: The Hitachi Assemblability Evaluation, the Lucas the Evaluation and DFA Boothroyd-Dewhurst DFA. Simple product examplesillustrate the functionality of the DFA systems.In the fourth part, Design for Assembly and Conceptual Design, the authors emphasize the benefits of using DFA during the conceptual design phase rather than after, as in conventional DFA systems. 120

The evaluation and selectionof concept variants in the conceptual phase requiresfundamentaldecisionsconceming the assemblabilityof the developed product. The utilization of simpleDFA rules and principles in the conceptual phase(i.e. reducingthe numberof parts, choosingan appropriate product structure for assembly or using fasteners which easeassembly)lays the foundations for successfuloptimization of the assemblyof the product in succeeding design phases(embodiment and detail design).Although the benefits of DFA in the conceptualphaseare evident, the main applications for DFA are the embodiment design phase and detail design phase. In several product examples analysis and optimization of concept variants relating to design for assemblyis carried out. The book is easyto read and includes several examples to illustrate the advantagesof design for assembly.It emphasizes the importance of the utilization of DFA at all phasesof the design and production process. To satisfy this strategy, the authors discuss a generalapproachto designfor assembly that shows correlations between design for assemblyand other design principles (for example, design for production). However, there are some points for criticism. Above all, the book does not offer a systematiccompilation of DFA rules and principles. In addition, brief summarieswould be useful. There are almost no literature referencesin the text even though someillustrations are taken directly from other authors. In conclusion,the book is suitablefor studentsand practising engineerswho would like an introduction to the methods and principles of DFA. Without further literature, the book is only of limited use for undertaking DFA. W. Beitz Technische Universitat Berlin Germany

Multicriteria Engineering

Optimization

and

Roman B. Statnikov and Joseph B. Matusov Chapman & Hall, 1995, ISBN O-41299231-0 hardback, 236 pp, f35 Multicriteria Optimization and Engineering is a well-presentedand strongly

bound book aimed at helping the practising engineerin applying multicriteria optimization techniques to real-world designproblems.Its style is a combination of the mathematical,with numerous theorems,proofs and formulae, and

Materials & Design Volume 16 Number 2 1995

the practical with many examplesand fully worked casestudies.Its approach to multicriteria evaluation is to delay the comparison of criteria until the designspacehasbeenthoroughly investigated and the best alternativesidentified. Thus multicriteria optimization becomesfirst the searchfor the design envelope and then the selectionof the best solution. While this seemsa relatively straightforward approach, it has the effect of dramatically increasingthe time required to investigate the design space. The book divides into six chapters where each topic is introduced and examined with supporting theories, proofs and formulae. While this rather heavy mathematical approach can be difficult to work through, each chapter contains several fully worked case studies. Indeed, the most interesting aspectof the book liesin the discussions of how best to model complex technical systems. Chapter 1: Multicriteria optimization and the parameter space method. The

parameterspaceinvestigationmethodis an approach to determining regionsof feasiblesolutionswithin a design(parameter) space.Rather like a highly structured gameof Battleships whereany hits are simply logged, the user investigates solutions acrossthe whole multidimensional spaceand notes if theseturn out to be feasibleor unfeasible.Thus for a problem containing five parameters, over 4000 trials may produce only 35 feasiblesolutions. This approach makesno use of the knowledge about the design space provided either by the designer (i.e. aluminium is lighter than steel) or by previous trials (i.e. trials 34, 35 and 36 were feasible)and can be describedasa structured random search. Chapter 2: Approximation of feasible solutions and Pareto optimal sets. By

introducing a method of approximation the boundariesof feasibleregionsin the designspacemay be definedwith fewer trials. Based on a simple margin of error, the approachmay work in one of two ways; either each trial solution can provide information about its immediate neighboursor the searchprocesscan be halted when a pre-specifiedspreadof feasiblesolutions have been identified. While this helps reduce searchtime, it does not overcome the redundancy inherent in the method. Chapter 3: Decomposition and aggregation of large-scale systems. This

chapter addresses the inherent complexity of real engineering problems by decomposingthe problem into smaller and easier-to-handle tasks. Three approachesare proposed based on: a simplifiedanalysisof the wholedesign,a sequenceof sub-systemswhere only feasible solutions are passedon for further analysis, or a division and