40207_26 - 26 CONTROL 26.1 INTRODUCTION Consolidation is an important step that occurs in almost every process used to make an advanced composite

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26 CONTROL Fig. 26.1 Schematic of the prepreg lay-up used in autoclave cure (Springer, 1986). lay-up used in autoclave cure. In a traditional lay-up process, prepregs with different fiber orientation and architecture are placed in cer- tain order forming a near-net-shape composite structure. During the lay-up operation, whether it is done manually or using a robot, the trapping of air pockets within the structure is unavoidable. Thus a consolidation step after the lay-up operation is necessary. Prepregs are usually provided with relatively low fiber vol- ume fraction. With the consolidation step, the fiber volume fraction of the composite product can be increased and excessive resin can be removed. The basic mechanisms involved in a consol- idation process are the fiber deformation and resin flow, which are coupled with thermal effects and the resin cure reaction. A similar consolidation process can also be seen in soil mechanics such as the settlement of a founda- tion. However, the deformation behavior of fibrous materials is substantially different from that of granular structures and resin flow behavior is strongly affected by thermal effects 26.1 INTRODUCTION Consolidation is an important step that occurs in almost every process used to make an advanced composite article. Consolidation is usually brought about by the application of pressure at a boundary which squeezes air and resin out of the composite thereby changing both its microstructure and dimensions. Improper consolidation can lead to voids, residual stresses, warping and other unwanted effects which could ultimately lead to the rejec- tion of the part. A comprehensive discussion of consolidation in composites would include many complex phenomena. Simultaneously, there is heat, momentum and mass transfer, accompanied by the chemical curing reaction of the resin and the deformation and motion of fibers. Consolidation techniques have been used in the fabrication of both thermoset and thermo- plastic composite parts, but are more crucial steps in thermoset composite processing. The traditional composite manufacturing process for aerospace industry products usually starts with the B-stage impregnated prepregs con- sisting of fiber preforms and staged resin matrix. Usually the resin content is relatively high. In order to achieve the required compos- ite material properties which are dominated by the fibers, consolidation is used as an important processing step. Figure 26.1 shows a setup of the prepreg Handbook of Composites. Edited by S. T. Peters. Published in 1998 by O1apman & Hall, London. ISBN 0412 540207
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Introduction 577 and chemical reaction of the resin. Thus, the study of the consolidation process of fibrous composite materials involves many disciplines. To effectively control a consolidation process, the selection of the equipment and tooling materials is crucial. Major process parameters for a consolidation process include pressure and temperature and both are func- tions of time and are usually set as operation cycles. Thus the system setup should be able
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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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40207_26 - 26 CONTROL 26.1 INTRODUCTION Consolidation is an important step that occurs in almost every process used to make an advanced composite

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