FIBROUS REINFORCEMENTFIBROUS REINFORCEMENTStructure: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).

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.

TYPES OF FIBROUS REINFORCEMENTTYPES 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.

GLASS FIBRE.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.

MANUFACTURING 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.

ADVANTAGE OF GLASS FIBRE 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).

DISADVANTAGEDISADVANTAGE

Very susceptible to surface damage. Such as rubbings or action of moisture.

Therefore sizing is important.

CARBON FIBRES 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.

Advantages:1. Chemical innerness

(resist moisture)2. High electrical and

thermal conductivity3. Dimensional stability

– V. Low thermal expansion.

Disadvantage:1. They are black and

impart this colors to the composite.

AREMID POLYMER (FIBRE)AREMID POLYMER (FIBRE)Contain both aromatic and amide groups

in the molecular chain.ExampleKevlar 49.It is the most widely used aramid fibre

for reinforcement.

nC

O

C

O

N

H

N

H

Poly (paraphenylene tetephthalamide)

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.

C = O N HC

O

N

H

…......

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.

The structure is of a disordered crystal without discrete amorphous regions. 

The properties of Kevlar fibers show two drawbacks

1. Weakness in axial shear2. 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.

ADVANTAGESADVANTAGES

1. Fatigue resistance (but carbon fibre is better)

2. Elevated temperature resistances3. Chemical resistance4. Weathering resistance

PLATELET REINFORCEMENT PLATELET REINFORCEMENT Commonly are minerals such as talc and mica Talc: 3 MgO.4SiO2.H2O

Mica: k2O.3Al2O3.6SiO2.2H2O

Never obtained in pure formTalc and Mica both are crystallineTheir dimension after crushing and grinding are

in the order of 10-1000 m across and 1-5 m in thickness.

ADVANTAGEADVANTAGE1. Low price.2. Stiffness and strength are greater than

plastics3. Provide reinforcement in all directions and

not merely in direction as with uniaxially aligned fibre.

Thank YouThank You

See You Next Lecture