polymer characterstics

1. Composite material

2. Introduction; constitution and classification of composites -
particle- reinforced, fiber- reinforced, metal matrix-fibre
composites, hybrid composites, structural composites and
their applications; processing of fibre reinforced composites;
application of composite materials

3. A materials system composed of two or more physically distinct phases
whose combination produces aggregate properties that are different
from those of its constituents.
or
Two or more chemically distinct materials which when combined have
improved properties over the individual materials. Composites could be
natural or synthetic.
What is a composite Material?

4. Composites
 A judicious combination of two or more materials that produces a
synergistic effect. A material system composed of two or more
physically distinct phases whose combination produces aggregate
properties that are different from those of its constituents.
 To obtain a more desirable combination of properties (principle of
combined action)
 e.g., low density and high strength
4

5. • Composites can be very strong and stiff, yet very light
in weight, so ratios of strength -to - weight and
stiffness -to - weight are several times greater than steel
or aluminum.
• Fatigue properties are generally better than for common
engineering metals.
• Toughness is often greater too
• Composites can be designed that do not corrode like
steel
• Possible to achieve combinations of properties not
attainable with metals, ceramics, or polymers

6. In selecting a composite material, an optimum combination of properties
is usually sought, rather than one particular property
Fuselage and wings of an aircraft must be lightweight and be strong,
stiff, and tough
Several fiber reinforced polymers possess this combination of
properties
Example: natural rubber alone is relatively weak; adding significant
amounts of carbon black to NR increases its strength dramatically.

7. 1. Traditional composites – composite materials that occur in nature or
have been produced by civilizations for many years
Examples: wood, concrete, asphalt
2. Synthetic composites - modern material systems normally associated
with the manufacturing industries, in which the components are first
produced separately and then combined in a controlled way to achieve
the desired structure, properties, and part geometry

8. Nearly all composite materials consist of two phases:
1. Primary phase - forms the matrix within which the secondary
phase is imbedded
2. Secondary phase - imbedded phase sometimes referred to as a
reinforcing agent, because it usually serves to strengthen the
composite
The reinforcing phase may be in the form of fibers, particles, or
various other geometries

9. 9
:
-- Matrix - is continuous
-- Dispersed - is discontinuous and
surrounded by matrix
Fig.1

10. Composite Structural Organization: the design
variations

11. Functions of matrix
 Binds fibre
 Act as medium
 Protect fibre
 Prevent propagation of cracks.

12. Essentials of matrix phase
 It should be ductile
 Bonding strenth should be high
 Corrosion resistant

13. Classification of dispersed phase
 The dispersed phase can be fibre particle etc.
 Fibres:
1.Glass fibres
2.Carbon fibres
3.Aramid fibres(Aromatic)
 Particles (metallic or non metallic)
 Flakes : 2-d particles
 Whiskers: thin crystals with high impact ratio e.g. graphite,
silicon carbide etc.

14. Provides the bulk form of the part or product made of the composite material.
Holds the imbedded phase in place, usually enclosing and often concealing it.
When a load is applied, the matrix shares the load with the secondary phase, in
some cases deforming so that the stress is essentially born by the reinforcing agent.

15. Function is to reinforce the primary phase
Imbedded phase is most commonly one of the following shapes:
Fibers
Particles
Flakes
In addition, the secondary phase can take the form of an infiltrated phase
in a skeletal or porous matrix
Example: a powder metallurgy part infiltrated with polymer

16. Composite Survey
Large-
particle
Dispersion-
strengthened
Particle-reinforced
Continuous
(aligned)
Aligned Randomly
oriented
Discontinuous
(short)
Fiber-reinforced
Laminates Sandwich
panels
Structural
Composites

17. Classification of Composite Materials
by Matrix:
• Ceramic matrix composites (CMC):
– Silicon carbide-silicon carbide (SiC-SiC)
– Same material both matrix and filler BUT filler
different form such as whickers, chopped fibers
or strands to achieve preferred properties.

18. Incorporation of two or more fibres within a single
matrix resulted in formation of hybrid composite.

19. Hybrids: configuration
a b c
d e f

20. Hybrid materials are composites consisting of two
constituents at the nanometer or molecular level.
Commonly one of these compounds is inorganic
and the other one organic in nature. Thus, they
differ from traditional composites where the
constituents are at the macroscopic (micrometer to
millimeter) level. Mixing at the microscopic scale
leads to a more homogeneous material that either
show characteristics in between the two original
phases or even new properties.
HYBRID COMPOSITES

21. Classification:
Hybrid materials can be classified based
on the possible interactions connecting the
inorganic and organic species.
Class I hybrid materials are those that
show weak interactions between the two
phases, such as van der Waals, hydrogen
bonding or weak electrostatic interactions.
Class II hybrid materials are those that
show strong chemical interactions between
the components such as covalent bonds.

22. Advantages of hybrid materials overtraditional composites
•Inorganic clusters or nanoparticles with specific optical,
electronic or magnetic properties can be incorporated in
organic polymer matrices.
•Contrary to pure solid state inorganic materials that often
require a high temperature treatment for their processing,
hybrid materials show a more polymer-like handling,
either because of their large organic content or because of
the formation of crosslinked inorganic networks from
small molecular precursors just like in polymerization
reactions.

23. Structural Composites
The properties of structural composites depend on
 Constituents
 Geometrical design

24. Types of Structural Composites
Laminar: Is composed of two-dimensional sheets or panels that
have a preferred high strength direction such as is found in wood
and continuous and aligned fiber-reinforced plastics. The layers
are stacked and cemented together such that the orientation of
the high-strength direction varies with each successive layer. One
example of a relatively complex structure is modern ski and
another example is plywood.

25. Structural Composites:
Sandwich Panels: Consist of two strong outer sheets
which are called face sheets and may be made of
aluminum alloys, fiber reinforced plastics, titanium
alloys, steel. Face sheets carry most of the loading and
stresses. Core may be a honeycomb structure which has
less density than the face sheets and resists
perpendicular stresses and provides shear rigidity.
Sandwich panels can be used in variety of applications
which include roofs, floors, walls of buildings and in
aircraft, for wings, fuselage and tailplane skins.

27. Applications of HYBRID COMPOSITES
•Scratch-resistant coatings with hydrophobic or anti-fogging properties.
•Nanocomposite based devices for electronic and optoelectronic applications
including light-emitting diodes, photodiodes, solar cells, gas sensors and field
effect transistors.
•Fire retardant materials for construction industry.
•Nanocomposite based dental filling materials.
•Composite electrolyte materials for applications such as solid-state lithium
batteries or supercapacitors.
•Corrosion protection

28. 1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals,
such as cemented carbides and other cermets
2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with
fibers to improve properties, especially in high temperature
applications
The least common composite matrix
3. Polymer Matrix Composites (PMCs) - thermosetting resins are widely
used in PMCs
Examples: epoxy and polyester with fiber reinforcement, and phenolic
with powders

29. 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

30. One-dimensional reinforcement, in which maximum strength and stiffness are
obtained in the direction of the fiber
Planar reinforcement, in some cases in the form of a two-dimensional woven
fabric
Random or three-dimensional in which the composite material tends to possess
isotropic properties

31. Fiber materials in fiber reinforced composites:
Glass – most widely used filament
Carbon – high elastic modulus
Boron – very high elastic modulus
Polymers - Kevlar
Ceramics – SiC and Al2O3
Metals - steel
The most important commercial use of fibers is in polymer composites

32. There is always an interface between constituent phases in a composite material
For the composite to operate effectively, the phases must bond where they join at
the interface
Figure 9.4 - Interfaces between phases in a composite material: (a)
direct bonding between primary and secondary phases

33. A metal matrix reinforced by a second phase.
Reinforcing phases:
1. Particles of ceramic (these MMCs are commonly called cermets)
2. Fibers of various materials: other metals, ceramics, carbon, and
boron

34. • Metal matrix composites (MMC):
– Metal matrix: Al, Mg, Fe, Cu, Ni
– Different metal or another material, such as a
ceramic or organic compound
– Example: Al-SiC (silicon carbide)
– Example: Al-Al2O3 (aluminum oxide)
High strength, high stiffness, dimensional
stability, high temperature and toughness.

35. Composition:
• MMCs are made by dispersing a reinforcing material into a metal
matrix.
•The reinforcement surface can be coated to prevent a chemical
reaction with the matrix.
•For example, carbon fiber are commonly used in aluminium matrix to
synthesize composites showing low density and high strength.
However, carbon reacts with aluminium to generate a brittle and
water-soluble compound Al4C3 on the surface of the fibre.
•To prevent this reaction, the carbon fibres are coated with nickel or
titanium boride.

36. A PMC consisting of a polymer matrix imbedded with high-strength fibers.
Polymer matrix materials:
Usually a thermosetting (TS) plastic such as unsaturated polyester or
epoxy
Can also be thermoplastic (TP), such as nylons (polyamides),
polycarbonate, polystyrene, and polyvinylchloride
Fiber reinforcement is widely used in rubber products such as tires and
conveyor belts

37. Fiber Reinforced Polymers (FRPs)
 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.

38. Note: Fiber composite
manufacturers often rotate layers
of fibers to avoid directional
variations in the modulus.

39. A fiber-reinforced composite (FRC) is a composite
building material that consists of three components:
(i) the fibers as the discontinuous or dispersed
phase, (ii) the matrix as the continuous phase, and
(iii) the fine interphase region, also known as the
interface. This is a type of advanced composite
group, which makes use of rice husk, rice hull, and
plastic as ingredients. This technology involves a
method of refining, blending, and compounding
natural fibers from cellulosic waste streams to form a
high-strength fiber composite material in a polymer
matrix. The designated waste or base raw materials
used in this instance are those of waste
thermoplastics and various categories of cellulosic
waste including rice husk and saw dust.

40. Most widely used form of FRP is a laminar structure, made by stacking and
bonding thin layers of fiber and polymer until desired thickness is
obtained.
By varying fiber orientation among layers, a specified level of anisotropy in
properties can be achieved in the laminate
Applications: parts of thin cross-section, such as aircraft wing and fuselage
sections, automobile and truck body panels, and boat hulls

41. 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

42. Aerospace – much of the structural weight of todays airplanes and
helicopters consist of advanced FRPs.
Automotive – somebody panels for cars and truck cabs
Continued use of low-carbon sheet steel in cars is evidence of its low
cost and ease of processing.
Sports and recreation
Fiberglass reinforced plastic has been used for boat hulls since the
1940s
Fishing rods, tennis rackets, golf club shafts, helmets, skis, bows and
arrows.

43. The two phases are typically produced separately before being combined
into the composite part.
Processing techniques to fabricate MMC and CMC components are similar
to those used for powdered metals and ceramics
Molding processes are commonly used for PMCs with particles and
chopped fibers
Specialized processes have been developed for FRPs.

44. • Particulate Methods: Sintering
• Fiber reinforced: Several
• Structural: Usually Hand lay-up and
atmospheric curing or vacuum curing

45. © 2000 The McGraw-Hill Companies, Inc.,
Irwin/McGraw-Hill

46. Open Mold Processes
Only one mold (male or female) is needed and may be made of
any material such as wood, reinforced plastic or , for longer runs,
sheet metal or electroformed nickel. The final part is usually very
smooth.
Shaping. Steps that may be taken for high quality
1. Mold release agent (silicone, polyvinyl alcohol, fluorocarbon, or
sometimes, plastic film) is first applied.
2. Unreinforced surface layer (gel coat) may be deposited for best
surface quality.

47. Hand Lay-Up: The resin and fiber (or pieces cut from
prepreg) are placed manually, air is expelled with squeegees
and if necessary, multiple layers are built up.
· Hardening is at room temperature but may be improved by
heating.
· Void volume is typically 1%.
· Foam cores may be incorporated (and left in the part) for
greater shape complexity. Thus essentially all shapes can
be produced.
· Process is slow (deposition rate around 1 kg/h) and labor-
intensive
· Quality is highly dependent on operator skill.
· Extensively used for products such as airframe
components, boats, truck bodies, tanks, swimming pools,
and ducts.

48. A spray gun supplying resin in two converging streams into
which roving is chopped
· Automation with robots results in highly reproducible
production
· Labor costs are lower
SPRAY-UP MOLDING

49. Cut and lay the ply or prepreg under computer control and
without tension; may allow reentrant shapes to be made.
· Cost is about half of hand lay-up
· Extensively used for products such as airframe components,
boats, truck bodies, tanks, swimming pools, and ducts.
Tape-Laying Machines
(Automated Lay-Up)

50. Filament Winding Characteristics
۰Because of the tension, reentrant shapes cannot be produced.
۰CNC winding machines with several degrees of freedom
(sometimes 7) are frequently employed.
۰The filament (or tape, tow, or band) is either precoated with
the polymer or is drawn through a polymer bath so that it picks
up polymer on its way to the winder.
۰Void volume can be higher (3%)
۰The cost is about half that of tape laying
۰Productivity is high (50 kg/h).
۰Applications include: fabrication of composite pipes, tanks, and
pressure vessels. Carbon fiber reinforced rocket motor
cases used for Space Shuttle and other rockets are made
this way.

51. Pultrusion
۰ Fibers are impregnate with a prepolymer, exactly positioned with
guides, preheated, and pulled through a heated, tapering die
where curing takes place.
۰Emerging product is cooled and pulled by oscillating clamps
۰Small diameter products are wound up
۰Two dimensional shapes including solid rods, profiles, or hollow
tubes, similar to those produced by extrusion, are made, hence its
name ‘pultrusion’

52. Vapor deposition
•Physical vapor deposition: The fiber is passed through a thick
cloud of vaporized metal, coating it.
In-situ fabrication technique
Controlled unidirectional solidification of a eutectic alloy can
result in a two-phase microstructure with one of the phases,
present in lamellar or fiber form, distributed in the matrix

53. • Properties of many important composites are anisotropic - the properties differ
depending on the direction in which they are measured – this may be an advantage
or a disadvantage
• Many of the polymer-based composites are subject to attack by chemicals or
solvents, just as the polymers themselves are susceptible to attack.
• Composite materials are generally expensive
• Manufacturing methods for shaping composite materials are often slow and costly

54. Books and references
1. Engineering Chemistry by Jain & Jain
2. A text book of Engineering Chemistry by Shashi Chawla
•en.wikipedia.org/wiki/Composite_material
•www.substech.com/dokuwiki/doku.php?id=classification_of_
composites