FIBROUS REINFORCEMENT

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 0.1plane 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
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

• 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