Fiber-reinforced Composites

Fiber
Filaments of reinforcing material, usually circular in cross section-
- Diameters range from less than 0.0025 mm to about 0.13 mm, depending on material
- Filaments provide greatest opportunity for strength enhancement of composites
* The filament form of most materials is significantly stronger than the bulk form.
* As diameter is reduced, the material becomes oriented in the fiber axis direction and probability of defects in the structure decreases significantly.

Reinforcing fibers
- Reinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase the modulus of the matrix material. The strong covalent bonds along the fiber s length gives them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved. Fibers are difficult to process into composites which makes fiber-reinforced composites relatively expensive. Fiber-reinforced composites are used in some of the most advanced, and therefore most expensive, sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix. Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix.
- The arrangement or orientation of the fibers relative to one another, the fiber concentration, and the distribution all have a significant influence on the strength and other properties of fiber-reinforced composites. Applications involving totally multi directional applied stresses normally use discontinuous fibers, which are randomly oriented in the matrix material. Consideration of orientation and fiber length for a particular composites depends on the level and nature of the applied stress as well as fabrication cost. Production rates for short-fiber composites (both aligned and randomly oriented) are rapid, and intricate shapes can be formed which are not possible with continuous fiber reinforcement.
FRP Properties
-In most fiber-reinforced composites, the fibers are strong, stiff, and lightweight, If the composite is to be used at elevated temperature, the fiber should also have a high melting temperature. Thus the specific strength and specific modulus of the fiber are important charactaristics:
Specific strength=TS/P
Specific modulus = E/p
High strength to weight and modulus to weight ratios-
-Low specific gravity - a typical FRP weighs only about 1/5 as much as steel; yet, strength and modulus are comparable in fiber direction
Good fatigue strength-
-Good corrosion resistance, although polymers are soluble in various chemicals
-Low thermal expansion - for many FRPs, leading to good dimensional stability
Significant anisotropy in properties