40207_21 - FILAMENT WINDING Yu.M Tarnopollskii S.T Peters...

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FILAMENT WINDING 21 Yu.M. Tarnopollskii, S.T. Peters, A.I. Bed’ 21.1 INTRODUCTION A winding operation is the basic fabrication technique for forming load-bearing structural elements made of polymer matrix-based fibrous composites, which have the shapes of bodies of revolution. A semifabricated product (uncured preform) of previously impregnated filaments, strands, tapes and fabrics is wound layer by layer with controlled tension onto the mandrel or previous layers. By varying the angle of filament or tape placement, it is possi- ble to control the reinforcement fiber angles within the same layer and through the thick- ness of the composite wall. During winding, fiber tension generates pressure between lay- ers of uncured composite; this pressure influences the compaction and void content of the article and contributes to more complete utilization of the strength and stiffness of the reinforcing fibers. If the contact pressure is insufficient for compaction of the material, additional layer-by-layer compaction of a semifabricated product must be employed. The wound article must be converted by chemical and/or thermal means to the fin- ished article. With heat treatment, the usual method, the temperature can be constant or can vary with time. The mandrel defines the internal shape of the article. It is removed after curing if the mandrel is not an element of the structure. The winding process is illustrated in Fig. 21.11,*. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 Filament winding is a natural way to com- bine two-dimensional reinforcement and, with additional processes and devices, three- dimensional reinforcement. Advanced processes, combining filament winding and braiding, allow fabrication of spatially sewn structures. The most important groups of wound arti- cles are: thin-walled shells (their thickness is negligible compared to their radius); com- pound structures, including three-layered and multi-layered shells with a light foam or hon- eycomb plastic filler; and thick-walled structural elements. For thin-walled shells, it is most important to optimize the reinforcement configuration. For compound surfaces, contact pressure on the interface is a design parameter. Also, there is the problem of monolithicity for thick-walled structural elements, which is closely related to the problem of control of residual stresses. Most composites cannot sus- tain a significant internal pressure over time without leaking (weeping) through the other- wise sound composite wall. The use of internal liners made from rubber, plastic or metal can provide a leak tight structure. The semifabri- cated (uncured) article has extremely low strength in the radial direction. Thus, the ratio of elastic modulii along and across fibers can reach lo3.
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40207_21 - FILAMENT WINDING Yu.M Tarnopollskii S.T Peters...

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