TAILIEUCHUNG - Ebook Engineering materials (2nd edition - Volume 2): Part 2
(BQ) Part 2 book "Engineering materials 2" has contents: Polymers, the structure of polymers, mechanical behaviour of polymers, design with materials, case studies in design, production, forming and joining of polymers, Special topic - Wood. | Polymers C. Polymers and composites 217 218 Engineering Materials 2 Polymers 219 Chapter 21 Polymers Introduction Where people have, since the industrial revolution, used metals, nature uses polymers. Almost all biological systems are built of polymers which not only perform mechanical functions (like wood, bone, cartilage, leather) but also contain and regulate chemical reactions (leaf, veins, cells). People use these natural polymers, of course, and have done so for thousands of years. But it is only in this century that they have learned how to make polymers of their own. Early efforts (bakelite, celluloid, formaldehyde plastics) were floppy and not very strong; it is still a characteristic of most simple synthetic polymers that their stiffness (for a given section) is much less than that of metal or, indeed, of wood or bone. That is because wood and bone are composites: they are really made up of stiff fibres or particles, embedded in a matrix of simple polymer. People have learned how to make composites too: the industries which make high-performance glass, carbon, or Kevlar-fibre reinforced polymers (GFRP, CFRP, KFRP) enjoy a faster growth rate (over 10% per year) than almost any other branch of materials production. These new materials are stiff, strong and light. Though expensive, they are finding increasing use in aerospace, transport and sporting goods. And there are many opportunities for their wider application in other fields like hiking equipment, medical goods and even apparently insignificant things like spectacle frames: world-wide, at least 1,000,000,000 people wear spectacles. And the new polymers are as exciting as the new composites. By crystallising, or by cross-linking, or by orienting the chains, new polymers are being made which are as stiff as aluminium; they will quickly find their way into production. The new processing methods can impart resistance to heat as well as to mechanical deformation, opening up new ranges of application for
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