40207_30 - LAMINATE DESIGN Jocelyn M . Seng 30 birch or...

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LAMINATE DESIGN 30 Jocelyn M. Seng 30.1 INTRODUCTION An early example of laminated composite materials is the de Havilland Mosquito fighter/bomber used by the British Royal Air Force during World War I1 (Fig. 30.1). This air- craft was built entirely out of wood because of limited metal supplies and the need for quick delivery. The wings, for example, were made as three-ply skins (each 1.5 mm (0.060 in) thick) of birch or spruce, laid over balsa core or fir stringers to form a sandwich structure1. This successful production aircraft (7781 units built) was designed without the analytical techniques described in this chapter and without fancy computer tools. With current laminate design and analysis techniques, today’s higher-perfor- mance composite aircraft are made possible; with the increase in speed and accuracy of com- putation results, designer confidence in Fig. 30.1 The de Havilland Mosquito, an all-wood WWII Production aircraft. Printed With Permission, Zokeisha Publications, Inc. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7
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Laminated plate theory 687 composites structures is increased. This chapter presents the basic mathematical tools used to design laminates and provides insight on the many options for optimizing the material for particular needs. Three distinct levels of benefit can be derived when using composites and laminate design. With equal fiber distribution in multi- ple directions, rendering an effectively quasi-isotropic material, composites can approximate metals while providing a weight savings due to the difference in material den- sities. In addition, however, designers opting to use composite parts enjoy the advantage of being able to tailor the properties of their material by orienting load-carrying fibers in the directions that there are loads. The result is an anisotropic material, which by definition is a material with different properties in different directions. Ultimately, the composites industry is finally beginning to see the development of unique structures that have never before been attempted and with material behavior that is only possible with distinct laminate designs. This is a result of coupled behavior, for exam- ple, an extensional load on an anisotropic material can yield extension coupled with bending and twisting deformations. The objective of this chapter is to outline a method to design ply layouts which achieve structural design goals for composite parts. This method is based on laminated plate the- ory used with the quadratic failure criterion2. This general discussion, which assumes famil- iarity with undergraduate mechanical engineering fundamentals, shows how the principles for isotropic materials (such as met- als) are extended to the analysis of advanced composites. The basic equations are presented and the analysis procedure is outlined.
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40207_30 - LAMINATE DESIGN Jocelyn M . Seng 30 birch or...

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