TAILIEUCHUNG - Mechanical Engineer´s Handbook P10

Polymer Matrix Composites There are a large and increasing number of processes for making PMC parts. Many are not very labor-intensive and can make near-net shape components. For thermoplastic matrices reinforced with discontinuous fibers, one of the most widely used processes is injection molding. However, as discussed in Section , the stiffness and strength of resulting parts are relatively low. This section focuses on processes for making composites with continuous fibers. Many PMC processes combine fibers and matrices directly. However, a number use an intermediate material called a prepreg, which stands for preimpregnated material, consisting of fibers embedded in a. | APPLICATIONS 163 Polymer Matrix Composites There are a large and increasing number of processes for making PMC parts. Many are not very labor-intensive and can make near-net shape components. For thermoplastic matrices reinforced with discontinuous fibers one of the most widely used processes is injection molding. However as discussed in Section the stiffness and strength of resulting parts are relatively low. This section focuses on processes for making composites with continuous fibers. Many PMC processes combine fibers and matrices directly. However a number use an intermediate material called a prepreg which stands for preimpregnated material consisting of fibers embedded in a thermoplastic or partially cured thermoset matrix. The most common forms of prepreg are unidirectional tapes and impregnated tows and fabrics. Material consolidation is commonly achieved by application of heat and pressure. For thermosetting resins consolidation involves a complex physical-chemical process which is accelerated by subjecting the material to elevated temperature. However some resins undergo cure at room temperature. Another way to cure resins without temperature is by use of electron bombardment. As part of the consolidation process uncured laminates are often placed in an evacuated bag called a vacuum bag which applies atmospheric pressure when evacuated. The vacuum-bagged assembly is typically cured in an oven or autoclave. The latter also applies pressure significantly above the atmospheric level. PMC parts are usually shaped by use of molds made from a variety of materials steel aluminum bulk graphite and also PMCs reinforced with E-glass and carbon fibers. Sometimes molds with embedded heaters are used. The key processes for making PMC parts are filament winding fiber placement compression molding pultrusion prepreg lay-up resin film infusion and resin transfer molding. The latter process uses a fiber preform which is placed in a mold. Metal Matrix

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