Preface
Science-led or design-led? Two approaches to materials teaching
Most things can be approached in more than one way. In teaching this is especially true. The way to teach a foreign language, for example, depends on the way the student wishes to use it—to read the literature, say, or to find accommodation, order meals and buy beer. So it is with the teaching of this subject, Materials.
The figure shows the enrolment in engineering and materials-related departments in US universities in 2006. Mechanical, Civil and Chemical Engineering account for two-thirds of the total. Aerospace, Manufacturing and General Engineering account for a further 20%. The more science-related subjects—Materials Science, Engineering Science and Physics—total 3%. All of these courses carry requirements for Materials teaching, but the way the students in some courses will use it differs from those in others.
The traditional approach to Materials teaching starts with fundamentals: the electron, the atom, atomic bonding, and packing, crystallography and crystal defects. Onto this is built alloy theory, the kinetics of phase transformations and the development of microstructure on scales made visible by electron and optical microscopes. This sets the stage for the understanding and control of properties at the millimeter or centimeter scale at which they are usually measured. This science-led approach emphasises the physical basis but gives little emphasis to the behavior of structures and components in service or methods for material selection and design.
The alternative approach is design-led. The starting point is the requirements that materials must meet if they are to perform properly in a given design. To match material to design requires a perspective on the range of properties they offer, how these properties combine to limit performance, the influence of manufacturing processes on properties and ways of accessing the data needed to evaluate all of these. Once the importance of certain properties is established there is good reason and a clear context from which to ‘drill down’, so to speak, to examine the science that lies behind them—valuable because an understanding of the fundamentals itself informs material choice, processing and usage.
Each approach has its place. The choice depends on the way the student will wish to use the information. If the intent is pure scientific research, the first is the logical way to go. If it is engineering design and applied industrial research, the second makes better sense. This book follows the second.
What is different about this book?
There are many books about the science of engineering materials; many more about design. What is different about this one?
First, its design-led approach, specifically developed to guide material selection and understanding for a wide spectrum of engineering courses. The approach is systematic, leading from design requirements to a prescription for optimised material choice. The approach is illustrated by numerous case studies. Practice in using it is provided by worked examples in the text and exercises at the end of each chapter.
Second, its emphasis on visual communication through a unique graphical presentation of material properties as material property charts and numerous schematics. These are a central feature of the approach, helpful in utilising visual memory as a learning tool, understanding the origins of properties, their manipulation and their fundamental limits, and providing a tool for selection and for understanding the ways in which materials are used.
Third, its breadth. We aim here to present the properties of materials, their origins and the way they enter engineering design. A glance at the contents page will show sections dealing with
- • Physical properties
- • Mechanical characteristics
- • Thermal behavior
- • Electrical, magnetic and optical response
- • Durability (expanded in this 2nd edition with tools for selection)
- • Processing and the way it influences properties (also expanded in this 2nd edition)
- • Environmental issues
Throughout we aim for a simple, straightforward presentation, developing the materials science as far as it is helpful in guiding engineering design, avoiding detail where this does not contribute to this end.
The fourth feature is new to this 2nd edition. Certain topics lend themselves to self-instruction with embedded exercises to build systematic understanding. It works particularly well for topics that involve a contained set of concepts and tools. Thus Crystallography, as an example, involves ideas of symmetry and 3-dimensional geometry that are most easily grasped by problem-solving. And an introduction to Phase Diagrams and Phase Transformations relies on interpreting graphical displays of chemical and thermodynamic information. Their use to understand and predict microstructure follows procedures that are best learned by application. Both topics can be packaged, so to speak, into self-contained units, with each new concept being presented and immediately tested with exercises, thereby building confidence. Students who have worked through a package can feel that they have mastered the topic and know how to apply the ideas it contains. We have chosen to present Crystallography, and Phase Diagrams and Phase Transformations, in this way here. Both topics appear briefly in the main text. The Guided Learning Units provide for those courses that require a deeper understanding.
This book and the CES Materials and Process Information software
Engineering design today takes place in a computer-based environment. Stress analysis (finite element method, or FEM, codes for instance), computer-aided design (CAD), design for manufacture (DFM) and product data management (PDM) tools are part of an engineering education. The CES Materials and Process Information software1 for education (the CES EduPack) provides a computer-based environment for optimised materials selection.
This book is self-contained and not dependent on computer support for its use. But at the same time it is designed to interface with the CES application, which implements the methods developed in it. Using the CES EduPack enhances the learning experience. It allows realistic selection studies that properly combine multiple constraints on material and processes attributes, and it enables the user to explore the ways in which properties are manipulated. The CES EduPack contains an additional tool to allow the science of materials to be explored in more depth. The CES Elements database stores fundamental data for the physical, crystallographic, mechanical, thermal, electrical, magnetic and optical properties of all 111 stable elements of the periodic table. It allows interrelationships between properties, developed in the text, to be explored in depth.
The approach is developed to a higher level in three further textbooks, the first relating to mechanical design2, the second to design for the environment3, the third to industrial design4.
For information on obtaining the CES EduPack for your school, see the ‘Resources’ section following the ‘Acknowledgements’ section.
1 The CES EduPack, Granta Design Ltd., Rustat House, 62 Clifton Court, Cambridge CB1 7EG, UK. www.grantadesign.com.
2 Ashby, M. F. (2005), Materials selection in mechanical design, 3rd edition, Butterworth-Heinemann, Oxford, UK, Chapter 4. ISBN 0-7506-6168-2. (A more advanced text that develops the ideas presented here in greater depth.)
3 Ashby, M. F. (2009), Materials and the environment, Butterworth-Heinemann, Oxford, UK. ISBN 978-1-85617-608-8. (A teaching text that provides the resources, background, methods, data—to enable environmental issues to be introduced into the Materials courses.)
4 Ashby, M. F. and Johnson, K. (2002), Materials and design—the art and science of material selection in product design, Butterworth-Heinemann, Oxford, UK. ISBN 0-7506-5554-2. (Materials and processes from an aesthetic point of view, emphasising product design.)