By mixing large and small particles the volume

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Unformatted text preview: be obtained polymers of other polymers, metals, and also display isotropic by random orientation to discontinuous fibers. These compositesceramics and propertiesalsoare less expensivecomposites. counterparts. Their properties, howand for bonding than their woven ever, are inferior to those of woven composites because of the short fiber length and aggregate composites Composites containing inherent low fiber volume fraction. reinforcements in the aggregate form such as sand and 14.3.6 Strengthening in Aggregate Composites gravel. If, in contrast to a fiber, the reinforcing phase that precipitates a second direcaging A heat treatment has roughly equal dimensions in all tions, the material is known as an aggregate composite. As shown in Figure 14.2–1, an phase from a is concrete, which is a mixture of fine aggregate in the form example of such a composite supersaturated solid solution. of sand and coarse aggregate in the formA material a matrix of cement (calcium of gravel, in that lacks the amorphous material aluminosilicate). By mixing large and small particles, the volume fraction of reinforcelong-range order that particles can fit into of a crystalline ment can be increased because the smallis characteristicthe cavities among the large solid. Amorphous materials are either rubbers or glasses. particles. Typical total aggregate (fine plus coarse) volume fractions in concrete are 0.60 to 0.75. The aggregate strengthens the composite in two ways. First, the inherent compresanisotropic Having properties that vary with direction. sive strength of the aggregate is higher than that of the matrix. Second, the high volume fraction of irregularly shaped process by which the surface of a anodizing A aggregate particles provides strength in compression through mechanical interlocking. As an added bonus, the aggregate is less expensive than component is converted into a hard oxide by an the cement, so high aggregate volume fractions reduce the composite cost. Similarly, asphalt onelectrochemical action. aggregate and 10% tar, is a low cost material the highway, which is about 90% that serves its purpose. antiferromagnetic A class of materials in which Concrete is one of the most common structural materials. Its use, however, is someadjacent tensile strength is much equal strength point in what limited, since itsmagnetic dipoles oflower than its compressive strength. A opposite directions. These materials show weak response to external magnetic fields. Arrhenius equation Textbook Table of Contents form | | e-Text Main Menu | Any equation of the C C0 exp Q RT . This equation states that the variable C increases exponentially as the temperature increases. artificial aging The precipitation of a second phase from a supersaturated solid solution at a temperature above room temperature. atactic Configuration of a vinyl polymer whose side groups are randomly positioned during polymerization. v Two-dimensional fabric weave architecture: (a) plain weave, and (b) five-harness satin weave. (Source: K. K. Chawla, Composites Material Science and Engineering, 1987, Springer-Verlag, New York. Reprinted with permission of Springer-Verlag, New Yor...
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