Discontinuous Fiber Reinforcement

Fiber-Matrix Composites. As shown in Figure 1.75, there are two main classifications of FMCs those with continuous fiber reinforcement and those with discontinuous fiber reinforcement. Continuous-flber-reinforced composites are made from fiber rovings (bundles of twisted filaments) that have been woven into two-dimensional sheets resembling a cloth fabric. These sheets can be cut and formed to a desired shape, or preform, that is then incorporated into a composite matrix, typically a thermosetting resin such as epoxy. Metallic, ceramic, and polymeric fibers of specific compositions can all be produced in continuous fashions, and the properties of the... 

Calculate axial and transverse modnli and strengths for nnidirectional, continuous and discontinuous, fiber-reinforced composites and laminate composites. Describe the structure of soft and hard biologies that give rise to their unique mechanical properties. 

A.2.3 Composite Moduli Halpin-Tsai Equations. Derivations of estimates for the effective moduli (tensile E, bulk K, and shear G) of discontinuous-fiber-reinforced composite materials are extremely complex. The basic difficulty lies in the complex, and often undefined, internal geometry of the composite. The problem has been approached in a number of ways, but there are three widely recognized... 

The rule of mixtures generally provides a poor estimate of the bulk and shear moduli in both the axial and transverse directions, respectively, in unidirectional, discontinuous-fiber-reinforced composites. 

A.2.4 Discontinuous-Fiber-Reinforced Polymer-Matrix Composites Sheet Molding Compound. Of the parameters influencing the mechanical properties in short-fiber-reinforced polymer-matrix composites, fiber composition, matrix composition, fiber geometry, and manufacturing method will be elaborated upon here. 

Stress Distribution and High Temperature Creep Rate of Discontinuous Fiber Reinforced Metals, Acta Metallurgies et Materialia, 38, 1941-1953 (1990). 26. A. G. Evans, J. W. Hutchinson, and R. M. McMeeking, Stress-Strain Behavior of Metal Matrix Composites with Discontinuous Reinforcements, Scripta Metallurgica et Materialia, 25, 3-8 (1991). 

The surface is molten during forming, so the surface finish tends to have a fibrous finish. Fiber separation could occur for extremely complex parts. The use of braided woven fabrics and continuous fiber mat reinforcements practically eliminates separation (Chapter 7). Discontinuous fiber reinforced composites, such as those made by the slurry process, can be molded into complex shapes without separation. 

B. F. Blumentritt, B. T. Vu, and S. L. Cooper, The Mechanical Properties of Oriented Discontinuous Fiber-Reinforced Thermoplastics. 1. Unidirectional Fiber Orienta-... 

Due to their different nature and mechanical behavior, continuous and discontinuous fiber-reinforced composites are discussed separately in this section. 

Mechanical Properties of Discontinuous Fiber-Reinforced Composites... 

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. 

Petersen, R.C., Discontinuous fiber-reinforced composites above critical length, /. Dent. Res., 84(4), 365-370, 2005. 

K. Boustany, A.Y. Coran (to Monsanto Co). Preparation of discontinuous fiber reinforced elastomer. U.S. Patent 3,836,412,1974. 

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