Types discontinuous fiber-reinforced

There are three basic types of engineered composites (1) laminates, (2) particle-reinforced composites, and (3) fiber-reinforced composites. In particle-reinforced composites, one can make the distinction between small (submicron) particle composites, where the particles are incorporated in the microstructure, vs. large particle composites, where the particles themselves actually do the work or carry the load. The reinforcing fibers can be discontinuous or continuous. The fibers in discontinuous fiber-reinforced composites can be randomly oriented to provide isotropic properties or aligned to enhance a specific property in a specific direction. Continuous fiber composites are generally designed for their unidirectional properties but can be crisscrossed to obtain multidirectional property enhancement such as in a filament-woimd pressure container. All possible permutations of metal, ceramic, and pol)uner are foimd in the laminated as well as in the reinforced composites. 

A composite material is defined as a material consisting of two or more distinct constituents or phases, which are insoluble in one another. The main types of reinforcement are particles, discontinuous fibers, continuous fibers (or filaments) and flakes. 

Silicone rubber Warrick et al. [29] reviewed the reinforcement of sUicone elastomers with various types of discontinuous fibers, some of which were generated in situ by graft polymerization. Polyester, cellulose and carbon fibers were also used to reinforce sUicone mbber [30,31]. 

Many fibers are used in laminates and reinforced plastics. The type of fiber used will depend on the cost, the properties required, and the nature of the polymeric system. Although glass fiber is the most common reinforcement, many others are used. Fiber reinforcements can also come in many forms such as discontinuous fibers, continuous fibers, mat and fabric. Fiber content is the amount of fiber present in reinforced plastics and composites, usually expressed as a percentage volume fraction or weight fraction. 

GRTP. Glass fiber reinforced thermoplastic a general term covering any type of discontinuous glass fiber reinforced thermoplastic material. 

The main types of reinforcements used in composite materials include aligned continuous fibers, discontinuous fibers, whiskers (elongated single crystals), particles, and numer-... 

Ceramic matrix composites (CMCs) can be thought of as an improved form of carbon matrix composite in which the carbon matrix is replaced with ceramics that are stronger and much more resistant to oxidation. CMCs employ a variety of reinforcements including continuous fibers, discontinuous fibers, whiskers, and particles. Continuous fibers provide the best properties. There are many different types of CMCs, and they are at various stages of development. 

Aerospace applications of ceramic matrix composites to date have been limited. Perhaps the most significant are the aircraft engine flaps used on a French fighter. There are two types. Both use silicon carbide matrices. One is reinforced with carbon fibers, and the other with a multifllament silicon carbide fiber. Another application is a missile diverter thruster made of carbon fiber-reinforced silicon carbide. Again, the process used to make this part is CVI. The Space Shuttle Orbiter thermal protection system (TPS) makes extensive use of tiles composed of a three-dimensional network of discontinuous oxide fibers with silicate surface layers. While there is no continuous matrix for most of the tile, the surface region is a form of CMC. In a sense, this can be considered to be a type of functionally graded material. 

Normally, when the fiber orientation is random, short and discontinuous fibers are used reinforcement of this type is schematically demonstrated in Figure 16.8c. Under these circumstances, a rule-of-mixtures expression for the elastic modulus similar to Equation 16.10a may be used, as follows ... 

Laminated MMCs. There are three types of laminated MMCs (/) metallic matrix-containing fibers oriented at different angles in different layers, similar to that of polymeric laminates (2) two or more different metallic sheets bonded to each other and (3) laminated metal/discontinuously reinforced MMC. 

The most commonly used theory used to model the stiffness of this type of composite was developed by Cox [1] and further improved by Krenchel [2, 3]. Cox s shear lag model was developed for aligned discontinuous elastic fibers in an elastic matrix. The applied load is transferred from the matrix to the fiber via interfacial shear stresses, with the maximum shear at the fiber ends decreasing to zero at the centre. Thus, the tensile stress in the fiber is zero at the ends and maximum in the middle. Thus, although the efficiency of stress transfer increases with fiber length, it can never reach 100%. In order to accommodate this dependence of reinforcement efficiency on fiber length, Cox introduced a fiber length efficiency factor -rij into the rule-of-mixtures equation for the composite modulus Eg. 

It is noteworthy that this new type of polymer-polymer composites, the microfibrillar reinforced composites (MFC), was developed during the last decade [32-35]. In contrast to the classical composites, i.e., those reinforced by discontinuous or continuous fibers, MFCs cannot be manufactured by conventional melt blending of the starting components, the matrix and the reinforcing materials. 

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