40207_appa - TYPICAL PROPERTIES FOR ADVANCED COMPOSITES...

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APPENDIX A ADVANCED COMPOSITES Kenneth R. Berg A.l INTRODUCTION For a company or institution that is designing composite material structures, or embarking for the first time into the application of advanced composite materials for structural purposes, it is imperative that material prop- erties be available. Of course it would be desirable to have a complete set of statistical Design Allowables, such as the statistical 'A' values for properties, or even the 'B' values, (see Chapter 33 for detailed definitions of these values and Neal and Spiridgliozzi, 1987). Since complete statistical Design Allowables are not available, the next sought after mater- ial properties would be 'typical' properties. However 'typical' properties are not defined statistically and may be defined in many dif- ferent ways. Therefore it is important to discuss typical material properties and also discuss the means to achieve a set of typical proper ties. The purpose of having a complete set of typical properties is to be able to design com- posite structures with a minimum of testing confirmation. Having a complete set of typical properties will allow design optimization, pre- liminary design, cost and weight optimization and other trade-offs with a number of different materials and candidate laminates with differ- ent fiber orientations. Once an optimum Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 material and configuration is selected, a mini- mum test program would then be initiated. Having a set of typical composite materials has advantages and disadvantages. For exam- ple, if one were to design a structure utilizing only typical material properties, without the knowledge of the scatter that may occur in those properties, structural failure may occur. Perhaps not immediately, nor on every struc- ture produced, but on an unknown statistical basis, at some point in time. However, prior to a final design for a structure, the normal engi- neering procedure is to initiate the test program. The purpose of the test program is threefold: one, confirmation of the design; two, determine the scatter that occurs due to variations in materials and the manufacturing process; and three, over a period of time, either to confirm the material properties data- base being used, or to accumulate test data for a material properties database. A.2 TYPICAL PROPERTIES - CONSTITUENTS A.2.1 FIBERS One of the problems of determining typical properties is the variations that occur in the materials making up laminates. In the case of glass fiber, the types of glass fiber and number of manufacturers is considerably less than with carbon fiber. However, even with
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40207_appa - TYPICAL PROPERTIES FOR ADVANCED COMPOSITES...

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