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Glass fibers are made by letting molten glass drop through minute orifices and then atten-uating(lengthening) them by air jet. The standard glass fiber used in glass-reinforced com-posite materials is E-glass, a borosilicate type of glass. The glass fibers produced,with di-ameters from 5 to 25 ㄇ一ㄨm, are formed into strands having a tensile strength of 5 GPa. Chopped glass used as a filler material in polymeric resins for molding consists of glass fibers chopped into very short lengths.
E-glass is the first glass developed for use as continuous fibers. It is composed of 55% silica, 20% calcium oxide, 15% aluminum oxide, and 10% boron oxide. It is the stan-dard grade of glass used in fiber glass and has a tensile strength of about 3.45 GPa and high resistivity.
S-glass was developed for high-tensile-strength applications in the aerospace indus-try. It is about one-third stronger than E-glass and is composed of 65% silicon dioxide, 25% aluminum oxide, and 10% magnesium oxide.
Polymer matrix composites (PMCs)—Fiberglass-reinforced plass-tics (GRPs).
GRPs represent the earliest and the most widely used (over three- fourths of total fiber-reinforced composite production) fiber-resin composites. With glass fibers in various forms coupled with either a thermosetting or thermoplastic resin, these composites can be produced without the need for high curing temperatures or pressures. The product contains a very good balance of properties, has high corrosion resistance, and is low in cots for a multitude of uses as structural, industrial, and consumer-related prod-ucts, ranging in size from minute circuit boards to boat hulls. Using 20% to 40% fiber load-ings, the composites will, in general, double the strength and stiffness of the plastic resin used alone. Continuous fibers will increase these properties fourfold, with accompanying desirable decreases in thermal expansion and creep rate and with increases in impact strength, heat-deflection temperatures, and dimensional stability. These fibers may take the from of continuous filaments (monofilaments) or yarn. The disadvantages accompanying these composites arise, in the main, from the fact that they are especially two-phase structures. This leads to a degree of environmental degradation greater than that experienced by either component material alone. Residual stresses and electrochemical effects result from the marriage of two dissimilar materials. Furthermore, the diffusion of fiber materials into the matrix materials, and vice versa, may take place at several stages. Variation in the thermal expansion of these two materials leads.......
Posted on: 2010/12/6 22:38
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