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FIBROUS REINFORCEMENT

FIBROUS REINFORCEMENT . Structure: 1. Continuous bundles of fibers. 2. Woven fabrics. 3. Chopped fiber. Normally their diameters in the range of 5-15 µm and produce in two or bundles consist of large number of filaments (1000-10000).

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FIBROUS REINFORCEMENT

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  1. FIBROUS REINFORCEMENT • Structure: • 1. Continuous bundles of fibers. • 2. Woven fabrics. • 3. Chopped fiber.

  2. Normally their diameters in the range of 5-15 µm and produce in two or bundles consist of large number of filaments (1000-10000). • A critical feature of fibers used for reinforcement is the coating of size applied to the surface during the manufacturing process. • Sizing is designed to: • 1. Hold the fibre together as a coherent bundle • 2. Protect the fibre surface from mechanical and environmental damage. • 3. Improve the chemical bonding between fibres and matrix in the composite.

  3. TYPES OF FIBROUS REINFORCEMENT • Three types are dominate the reinforced plastics. • 1. Glass fibers. • 2. Carbon fibers. • 3. Oriented polymeric fibers (Kevlar). Figure. 5 Stress strain curves for reinforcing fibers compared with 0.1%plane steel: (a) Stress vs. strain; and (b) specific stress vs. strain.

  4. GLASS FIBRE. • Widely used fibre for reinforcement of plastic • Moderate prices. • Desirable properties for reinforcement • Based on silica (SiO2) + some other smaller quantities of other inorganic oxides.

  5. MANUFACTURING • Glass fibre are manufactured by extruding molten glass at high velocity through a large number (100-1000) of holes in a platinum plate. (Bushing). • The resulting filaments are then wound up at an even faster rate as they cool through their glass transition and solidity.  • Fibre are cooled rapidly through Tg during drawing to ensure that there are no crystallinity. • Crystals act as stress raisers in glass and greatly weaken the fibers.

  6. ADVANTAGE OF GLASS FIBRE • 1. Resistance to high temperature (softening point as about 850oC). • 2. Transparency to visible light. • 3. Isotropy (thermal expansion is identical in axial and radical direction).

  7. DISADVANTAGE • Very susceptible to surface damage. Such as rubbings or action of moisture. • Therefore sizing is important.

  8. CARBON FIBRES • Less widely used compared to glass fibre because of their higher cost. • Carbon fibers prepared from polyacryonitrile (PAN) by converting the polymer into graphite through a sequence of carefully controlled heat treatment operations. • Carbon fibers are preferred due to their high degree of orientation and strong covalent bonding between the carbon atoms.

  9. Advantages: • 1. Chemical innerness (resist moisture) • 2. High electrical and thermal conductivity • 3. Dimensional stability • V. Low thermal expansion. • Disadvantage: • 1. They are black and impart this colors to the composite.

  10. H H C C N N n O O AREMID POLYMER (FIBRE) • Contain both aromatic and amide groups in the molecular chain. • Example • Kevlar 49. • It is the most widely used aramid fibre for reinforcement. Poly (paraphenylene tetephthalamide)

  11. …...... C = O N H H C N O • The molecules is rigid because of the benzene rings. • No chain folds. • The rod-like molecules pack together like pencils and bond firmly to their neighbors by the amide groups present, providing an excellent glue. • Their high degree of orientation is achieve by extruding the Kevlar fibre from solution and stretched in order to a sign the molecules parallel to the fibre axis.

  12. The structure is of a disordered crystal without discrete amorphous regions.  • The properties of Kevlar fibers show two drawbacks • 1. Weakness in axial shear • 2. Yellow coloration (imparts thing color to its composite) • Because of their high cost their are considered only where their outstanding mechanical properties are really needed.

  13. ADVANTAGES • 1. Fatigue resistance (but carbon fibre is better) • 2. Elevated temperature resistances • 3. Chemical resistance • 4. Weathering resistance

  14. PLATELET REINFORCEMENT • Commonly are minerals such as talc and mica • Talc: 3 MgO.4SiO2.H2O • Mica: k2O.3Al2O3.6SiO2.2H2O • Never obtained in pure form • Talc and Mica both are crystalline • Their dimension after crushing and grinding are in the order of 10-1000 m across and 1-5 m in thickness.

  15. ADVANTAGE • 1. Low price. • 2. Stiffness and strength are greater than plastics • 3. Provide reinforcement in all directions and not merely in direction as with uniaxially aligned fibre.

  16. Thank You See You Next Lecture

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