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DESIGN ALLOWABLES SUBSTANTIATION 33 Christy Kirchner Lapp 33.1 INTRODUCTION Designing with composite materials requires knowledge of a significantly greater number of properties than for conventional isotropic metals. The selection of lamina and laminate allowables can be critical in the analysis of a composite structure. However, composite design allowables may not always be obtained from a single source of data. Several references must often be consulted to determine all the properties in the necessary directions, espe- cially if several fibers or matrices are being considered in the design. This can be a time- consuming effort, especially during the initial design phase. In addition, some organizations may not have easy access to all the necessary references required to collect the data. This chapter assembles lamina data from numerous sources so that the engineer may have a single reference point for initial design and analysis of composite structures. A broad range of fibers has been included since composites are increasingly being applied outside the aero- space community. Design allowables in this section are for both elastic and strength properties. Elastic properties are necessary for laminate design or the analysis of composite structures. These properties include elastic moduli and Poisson’s ratios. Strength properties are required to predict laminate strengths or per- form a failure analysis of the structure. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 Strength properties for compression, tension and shear must be determined. Both elastic and strength properties can be influenced by numerous variables such as the fiber, matrix, fiber volume and processing method. The test method used to determine the allowable can also affect the property. In addition, some allowables cannot be readily tested, especially properties through-the-thickness of the com- posite. Often, complete characterization of a fiber/matrix system may not be available and the engineer must estimate or assume proper- ties. It can be expensive and time-consuming to completely characterize a fiber /matrix sys- tem during the initial design phase, so it is important for the engineer to have allowables based on reliable data and to understand the limitations. This chapter concentrates on providing the material database and techniques for assem- bling the necessary composite allowables for preliminary design. Final design allowables may require additional testing. The allowables provided in this chapter should be considered preliminary design values. Allowables for both two dimensional (2-D) and three dimen- sional (3-D) properties are included. As a starting point, lamina allowables for com- monly used fiber/matrix systems are described and listed. The references for these allowables are included. Several references may be listed for a single material. Methods for estimating properties when data is not available or testing cannot be readily per- formed are also defined. The effects of
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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