Composites are also particularly susceptible to

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Unformatted text preview: ymers, metals, and ceramics facilitates the achievement of both high strength and flexibility, while retaining high modulus. Matrix materials may be polymers, metals, or ceramics. The matrix provides lateral support to the fibers in continuous-fiber composites and also transfers the load to the fibers through the fiber-matrix interface in short-fiber composites. The fiber architecture determines the strength and modulus of the composite in various directions. The optimal fiber arrangement depends primarily on the intended application. The properties of composites also depend on the interfacial characteristics. The interfacial strength determines how efficiently the stress is transferred to the fibers, which is especially critical in short-fiber composites. It controls the fracture toughness and the fatigue resistance of all composites. Interfacial strength is derived from mechanical bonding, chemical bonding, or both. Important properties such as elastic modulus in various directions, tensile strength, coefficient of thermal expansion, and thermal and electrical conductivity of composites can be estimated from the fiber arrangement and the properties and volume fractions of the matrix and reinforcing materials. Properties that do not depend on the spatial arrangement can be determined using the rule of mixtures. The mechanisms of fracture and fatigue of composites are different from those in conventional materials. Composite fracture originates in the brittle phase and is slowed from spreading by either the ductile phase or interfacial failure. The high fracture toughness in these systems is derived from spreading the damage over a large area in front of the main crack as opposed to relying solely on plastic deformation of the ductile phase. Composite laminate fatigue failure occurs in three stages: ply cracking, delamination, and fiber fatigue. Composites are also particularly susceptible to thermal fatigue failures. Although most applications for composites are in high-performance structures, their use is growing rapidly in the electrical and electronic industries. Examples include superconducting cables and electronic package casings. KEY TERMS ........................................................................................................................................................................... isostrain reinforcing phase composites isostress rule of mixtures concrete laminate composites specific modulus critical aspect ratio matrix phase specific strength critical fiber length l0 particulate composites thermal fatigue | v v aggregate composites | e-Text Main Menu | unidirectional fiber-reinforced composites Textbook Table of Contents pg608 [V] G12 7-27060 / IRWIN / Schaffer 608 Part III iq 13.01.98 plm QC3 rps MP Properties HOMEWORK PROBLEMS ........................................................................................................................................................................... SECTION 14.2 History and Classification of Composites 1. Most...
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