1. Introduction To Composite
Materials
Mr. S. G. Kulkarni
SVNIT SURAT

2. Tutorial
 What is metal ?
 What is non metal ?
 What is alloy ?
 What are drawbacks of metals ?
 What is engineering ?
 Why we are studying practical ?

3. Introduction to Composites
1. What is the matrix in a composite and what materials are commonly
used as a matrix?
2. What is reinforcement in composites ?
3. Be able to decide different factors responsible for properties of
composite.
4. Know the equation for the critical length (Lc) of a fiber..
Reading:

4. Composites in Action

5. Composite Material
Two inherently different materials
that when combined together produce
a material with properties that exceed
the constituent materials.

6. What is a composite Material?
A broad definition of composite is: Two or more chemically distinct
materials which when combined have improved properties over the
individual materials. Composites could be natural or synthetic.
Wood is a good example of a natural composite, combination of
cellulose fiber and lignin. The cellulose fiber provides strength
and the lignin is the "glue" that bonds and stabilizes the fiber.
Bamboo is a very efficient wood composite structure. The components are
cellulose and lignin, as in all other wood, however bamboo is hollow. This
results in a very light yet stiff structure. Composite fishing poles and golf
club shafts copy this natural design.
The ancient Egyptians manufactured composites! Adobe bricks are a good
example. The combination of mud and straw forms a composite that is
stronger than either the mud or the straw by itself.
6

7. Tutorial
Revise the concept of
Hardness
Toughness
Stiffness
Yield strenth
Ultimate tensile strength
Compressive strenth
Tensile Strenth
Shear strength
Ductileness
Brittleness

8. Strength
For metals the most common measure of strength is the yield strength. For
most polymers it is more convenient to measure the failure strength, the
stress at the point where the stress strain curve becomes obviously non-
linear. Strength, for ceramics however, is more difficult to define. Failure in
ceramics is highly dependent on the mode of loading. The typical failure
strength in compression is fifteen times the failure strength in tension. The
more common reported value is the compressive failure strength.
Yield Strength
The yield strength is the minimum stress which produces permanent
plastic deformation. This is perhaps the most common material property
reported for structural materials because of the ease and relative accuracy
of its measurement. The yield strength is usually defined at a specific
amount of plastic strain, or offset, which may vary by material and or
specification. The offset is the amount that the stress-strain curve deviates
from the linear elastic line. The most common offset for structural metals
is 0.2%.

9. Ultimate Tensile Strength
The ultimate tensile strength is an engineering value calculated by dividing the maximum load on a material
experienced during a tensile test by the initial cross section of the test sample. When viewed in light of the other tensile
test data the ultimate tensile strength helps to provide a good indication of a material's toughness but is not by itself a
useful design limit. Conversely this can be construed as the minimum stress that is necessary to ensure the failure of a
material.
Ductility
Ductility is a measure of how much deformation or strain a material can withstand before breaking. The most common
measure of ductility is the percentage of change in length of a tensile sample after breaking. This is generally reported
as % El or percent elongation. The R.A. or reduction of area of the sample also gives some indication of ductility.
Toughness
Toughness describes a material's resistance to fracture. It is often expressed in terms of the amount of energy a material
can absorb before fracture. Tough materials can absorb a considerable amount of energy before fracture while brittle
materials absorb very little. Neither strong materials such as glass or very ductile materials such as taffy can absorb
large amounts of energy before failure. Toughness is not a single property but rather a combination of strength and
ductility.
The toughness of a material can be related to the total area under its stress-strain curve. A comparison of the relative
magnitudes of the yield strength, ultimate tensile strength and percent elongation of different material will give a good
indication of their relative toughness. Materials with high yield strength and high ductility have high toughness.
Integrated stress-strain data is not readily available for most materials so other test methods have been devised to help
quantify toughness. The most common test for toughness is the Charpy impact test.
In crystalline materials the toughness is strongly dependent on crystal structure. Face centered cubic materials are
typically ductile while hexagonal close packed materials tend to be brittle. Body centered cubic materials often display
dramatic variation in the mode of failure with temperature. In many materials the toughness is temperature dependent.
Generally materials are more brittle at lower temperatures and more ductile at higher temperatures. The temperature at
which the transition takes place is known as the DBTT, or ductile to brittle transition temperature. The DBTT is
measured by performing a series of Charpy impact tests at various temperatures to determine the ranges of brittle and
ductile behavior. Use of alloys below their transition temperature is avoided due to the risk of catastrophic failure.

10. Composites Offer
High Strength
Light Weight
Design Flexibility
Strenthen of Parts
Net Shape Manufacturing

11. Composites
Composites are combinations of two materials in which one of the material
is called the reinforcing phase, is in the form of fibers, sheets, or
particles, and is embedded in the other material called the matrix phase.
Typically, reinforcing materials are strong with low densities while the matrix is
usually a ductile or tough material. If the composite is designed and fabricated
correctly, it combines the strength of the reinforcement with the toughness of the
matrix to achieve a combination of desirable properties not available in any single
conventional material.
Components of composite materials
Reinforcement: fibers Matrix materials Interface
Glass Polymers Bonding
Carbon Metals surface
Organic Ceramics
Boron
Ceramic
11
Metallic

12. Why Composites are Important
 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 alone

13. Fiber Reinforced Polymer Matrix
Matrix
•Transfer Load to Reinforcement
•Temperature Resistance
•Chemical Resistance
Reinforcement
•Tensile Properties
•Stiffness
•Impact Resistance

14. Matrix Considerations
End Use Temperature
Toughness
Cosmetic Issues
Flame Retardant
Processing Method
Adhesion Requirements

15. Matrix Materials
 Functions of the matrix
– Transmit force between fibers
– arrest cracks from spreading between fibers
 do not carry most of the load
– hold fibers in proper orientation
– protect fibers from environment
 mechanical forces can cause cracks that allow environment to
affect fibers
 Demands on matrix
– Interlaminar shear strength
– Toughness
– Moisture/environmental resistance
– Temperature properties
– Cost

16. Types of Composite Materials
There are five basic types of composite materials:
Fiber, particle, flake, laminar or layered and filled
composites.

17. A. Fiber Composites
In fiber composites, the fibers reinforce along the line of their
length. Reinforcement may be mainly 1-D, 2-D or 3-D. Figure
shows the three basic types of fiber orientation.
 1-D gives maximum strength in one
direction.
 2-D gives strength in two directions.
 Isotropic gives strength equally in all
directions.

18. B. Particle Composites
 Particles usually reinforce a composite equally in all directions (called
isotropic). Plastics, cermets and metals are examples of particles.
 Particles used to strengthen a matrix do not do so in the same way as
fibers. For one thing, particles are not directional like fibers. Spread at
random through out a matrix, particles tend to reinforce in all
directions equally.
 Cermets
(1) Oxide–Based cermets
(e.g. Combination of Al2O3 with Cr)
(2) Carbide–Based Cermets
(e.g. Tungsten–carbide, titanium–carbide)
 Metal–plastic particle composites
(e.g. Aluminum, iron & steel, copper particles)
 Metal–in–metal Particle Composites and Dispersion
Hardened Alloys
(e.g. Ceramic–oxide particles)

19. C. Flake Composites - 1
 Flakes, because of their shape, usually
reinforce in 2-D. Two common flake
materials are glass and mica. (Also
aluminum is used as metal flakes)

20. D. Laminar Composites - 1
Laminar composites involve two or more layers of
the same or different materials. The layers can be
arranged in different directions to give strength
where needed. Speedboat hulls are among the very
many products of this kind.

21. D. Laminar Composites - 4
 A lamina (laminae) is any
arrangement of unidirectional or
woven fibers in a matrix. Usually
this arrangement is flat, although
it may be curved, as in a shell.
 A laminate is a stack of lamina
arranged with their main
reinforcement in at least two
different directions.

22. F. Combined Composites
 It is possible to combine several
different materials into a single
composite. It is also possible to
combine several different
composites into a single
product. A good example is a
modern ski. (combination of
wood as natural fiber, and layers
as laminar composites)

23. E. Filled Composites
 There are two types of filled composites. In
one, filler materials are added to a normal
composite result in strengthening the composite
and reducing weight. The second type of filled
composite consists of a skeletal 3-D matrix
holding a second material. The most widely used
composites of this kind are sandwich structures
and honeycombs.

24. Figure (a) Model of a fiber-reinforced composite material showing
direction in which elastic modulus is being estimated by the rule of
mixtures (b) Stress-strain relationships for the composite material and
its constituents. The fiber is stiff but brittle, while the matrix
(commonly a polymer) is soft but ductile.

25. Types of Composites
Matrix Metal Ceramic Polymer
phase/Reinforc
ement Phase
Powder metallurgy Cermets (ceramic- Brake pads
Metal parts – combining metal composite)
immiscible metals
Ceramic Cermets, TiC, TiCN SiC reinforced Fiberglass
Cemented carbides –
used in tools Al2O3
Fiber-reinforced Tool materials
metals
Polymer Kevlar fibers in
an epoxy matrix
Elemental Fiber reinforced Rubber with
metals carbon (tires)
(Carbon, Bor Boron, Carbon
on, etc.) Auto parts
reinforced plastics
aerospace
MMC’s CMC’s PMC’s
Metal Matrix Composites Ceramic Matrix Comp’s. Polymer Matrix Comp’s

26. Composites – Metal Matrix
The metal matrix composites offer higher modulus of
elasticity, ductility, and resistance to elevated temperature
than polymer matrix composites. But, they are heavier
and more difficult to process.
Ken Youssefi Mechanical Engineering Dept. 26

27. Introduction to Composites
1. What is the matrix in a composite and what materials are commonly
used as a matrix?
2. What is reinforcement in composites ?
3. Be able to decide different factors responsible for properties of
composite.
4. Know the equation for the critical length (Lc) of a fiber..
Reading:

28. Design Objective
Performance: Strength, Temperature, Stiffness
Manufacturing Techniques
Life Cycle Considerations
Cost

29. Matrix Types
Epoxy
Epoxies have improved strength and stiffness properties
over polyesters. Epoxies offer excellent corrosion
resistance and resistance to solvents and alkalis. Cure
cycles are usually longer than polyesters, however no
by-products are produced.
Flexibility and improved performance is also achieved
by the utilization of additives and fillers.

30. Reinforcement
Fiber Type
Fiberglass
Carbon
Aramid
Textile Structure
Unidirectional
Woven
Braid

31. Fiberglass
E-glass: Alumina-calcium-borosilicate glass
(electrical applications)
S-2 glass: Magnesuim aluminosilicate glass
(reinforcements)
Glass offers good mechanical, electrical, and thermal
properties at a relatively low cost.
E-glass S-2 glass
Density 2.56 g/cc 2.46 g/cc
Tensile Strength 390 ksi 620 ksi
Tensile Modulus 10.5 msi 13 msi
Elongation 4.8% 5.3%

32. Aramid
Kevlar™ & Twaron™
Para aramid fiber characterized by high tensile strength and modulus
Excellent Impact Resistance
Good Temperature Resistance
Density 1.44 g/cc
Tensile Strength 400 ksi
Tensile Modulus 18 Msi
Elongation 2.5%

33. Carbon Fiber
PAN: Fiber made from Polyacrylonitrile precursor fiber
High strength and stiffness
Large variety of fiber types available
Standard Modulus Intermediate Modulus
Density 1.79 g/cc 1.79 g/cc
Tensile Strength 600 ksi 800 ksi
Tensile Modulus 33 Msi 42 Msi
Elongation 1.8 % 1.8 %

34. Woven Fabrics
Basic woven fabrics consists of two systems of yarns
interlaced at right angles to create a single layer with
isotropic or biaxial properties.

35. Components of a Woven Fabric

36. Basic Weave Types
Plain Weave

37. Basic Weave Types
Satin 5HS

38. Basic Weave Types
2 x 2 Twill

39. Basic Weave Types
Non-Crimp

40. Braid Structure

41. Types of Braids

42. Triaxial Yarns
A system of longitudinal yarns can be introduced which are held in
place by the braiding yarns
These yarns will add dimensional stability, improve tensile
properties, stiffness and compressive strength.
Yarns can also be added to the core of the braid to form a solid braid.

43. MANUFACTURING PROCESSES
OF COMPOSITES
 Composite materials have succeeded remarkably in their
relatively short history. But for continued growth, especially in
structural uses, certain obstacles must be overcome. A major
one is the tendency of designers to rely on traditional materials
such as steel and aluminum unless composites can be
produced at lower cost.
 Cost concerns have led to several changes in the composites
industry. There is a general movement toward the use of less
expensive fibers. For example, graphite and aramid fibers have
largely supplanted the more costly boron in advanced–fiber
composites. As important as savings on materials may be, the
real key to cutting composite costs lies in the area of
processing.

44. B. Molding Operations
Molding operations are used in making a large number of
common composite products. There are two types of processes:
A. Open–mold
(1) Hand lay–up
(2) Spray–up
(3) Vacuum–bag molding
(4) Pressure–bag molding
(5) Thermal expansion molding
(6) Autoclave molding
(7) Centrifugal casting
(8) Continuous pultrusion and pulforming.

45. 1. Hand Lay-up
Hand lay–up, or contact molding, is the oldest and simplest
way of making fiberglass–resin composites. Applications are
standard wind turbine blades, boats, etc.)

46. 2. Spray-up
In Spray–up process, chopped fibers and resins are sprayed
simultaneously into or onto the mold. Applications are lightly
loaded structural panels, e.g. caravan bodies, truck
fairings, bathtubes, small boats, etc.

47. 7. Centrifugal Casting
Centrifugal Casting is used to form round objects such as pipes.
8. Continuous Pultrusion and Pulforming
Continuous pultrusion is
the composite counterpart
of metal extrusion.
Complex parts can be
made.

48. Weight Considerations
Aramid fibers are the lightest
1.3-1.4 g/cc
Carbon
1.79 g/c
Fiberglass is the heaviest
2.4 g/cc

49. Strength Considerations
Carbon is the strongest
600-800 ksi
Fiberglass
400-600 ksi
Aramids
400 ksi

50. Stiffness Considerations
Carbon is the stiffest
30-40 msi
Aramids
14 msi
Fiberglass
10-13 msi

51. Cost Considerations
Fiberglass is cost effective
$5.00-8.00/lb.
Aramids
$20.00/lb
Carbon
$30.00-$50.00/lb

52. Fabric Structures
Woven: Series of Interlaced yarns at 90 to each other
Knit: Series of Interlooped Yarns
Braided: Series of Intertwined, Spiral Yarns
Nonwoven: Oriented fibers either mechanically,
chemically, or thermally bonded

53. Applications of Reinforced Plastics
Phenolic as a matrix with asbestos fibers was the first reinforced plastic
developed. It was used to build an acid-resistant tank. In 1920s it was
Formica, commonly used as counter top., in 1940s boats were made of
fiberglass. More advanced developments started in 1970s.
Consumer Composites
Typically, although not always, consumer composites involve products that
require a cosmetic finish, such as boats, recreational
vehicles, bathwear, and sporting goods. In many cases, the cosmetic finish
is an in-mold coating known as gel coat.
Industrial Composites
A wide variety of composites products are used in industrial
applications, where corrosion resistance and performance in adverse
environments is critical. Generally, premium resins such as isophthalic and
vinyl ester formulations are required to meet corrosion resistance
specifications, and fiberglass is almost always used as the reinforcing fiber.
Industrial composite products include underground storage
tanks, scrubbers, piping, fume hoods, water treatment components, pressure
Mechanical Engineering Dept. 53
vessels, and a host of other products.

54. Applications of Reinforced Plastics
Advanced Composites
This sector of the composites industry is characterized by the use of
expensive, high-performance resin systems and high strength, high stiffness
fiber reinforcement. The aerospace industry, including military and
commercial aircraft of all types, is the major customer for advanced
composites.
These materials have also been adopted for use in sporting goods, where
high-performance equipment such as golf clubs, tennis rackets, fishing
poles, and archery equipment, benefits from the light weight – high strength
offered by advanced materials. There are a number of exotic resins and fibers
used in advanced composites, however, epoxy resin and reinforcement fiber
of aramid, carbon, or graphite dominates this segment of the market.
Mechanical Engineering Dept. 54

55. Composites – Ceramic Matrix
Ceramic matrix composites (CMC) are used in applications where
resistance to high temperature and corrosive environment is desired.
CMCs are strong and stiff but they lack toughness (ductility)
Matrix materials are usually silicon carbide, silicon nitride and
aluminum oxide, and mullite (compound of aluminum, silicon and
oxygen). They retain their strength up to 3000 oF.
Fiber materials used commonly are carbon and aluminum oxide.
Applications are in jet and automobile engines, deep-see
mining, cutting tools, dies and pressure vessels.
Mechanical Engineering Dept. 55

56. Ken Youssefi Mechanical Engineering Dept. 56

57. Application of Composites
Lance Armstrong’s
2-lb. Trek
bike, 2004 Tour de
France
Pedestrian bridge in
Denmark, 130 feet
long (1997)
Swedish
Navy, Stealth
(2005)
Ken Youssefi Mechanical Engineering Dept. 57

58. Application of Composites in
Aircraft Industry
20% more fuel
efficiency and
Ken Youssefi Mechanical Engineering Dept.lbs. lighter
35,000 58

59. Advantages of Composites
Higher Specific Strength (strength-to-weight ratio)
Composites have a higher specific strength than many other materials. A distinct
advantage of composites over other materials is the ability to use many
combinations of resins and reinforcements, and therefore custom tailor the
mechanical and physical properties of a structure.
The lowest properties for each material are associated with simple manufacturing processes
and material forms (e.g. spray lay-up glass fibre), and the higher properties are associated
with higher technology manufacture (e.g. autoclave moulding of unidirectional glass
fibre), the aerospace industry. 59

60. Advantages of Composites
Design flexibility
Composites have an advantage over other materials because they can be
molded into complex shapes at relatively low cost. This gives designers the
freedom to create any shape or configuration. Boats are a good example of
the success of composites.
Corrosion Resistance
Composites products provide long-term resistance to severe chemical and
temperature environments. Composites are the material of choice for
outdoor exposure, chemical handling applications, and severe environment
service.
Mechanical Engineering Dept. 60

61. Advantages of Composites
Low Relative Investment
One reason the composites industry has been successful is because of
the low relative investment in setting-up a composites manufacturing
facility. This has resulted in many creative and innovative companies in
the field.
Durability
Composite products and structures have an exceedingly long life span.
Coupled with low maintenance requirements, the longevity of composites is a
benefit in critical applications. In a half-century of composites
development, well-designed composite structures have yet to wear out.
In 1947 the U.S. Coast Guard built a series of forty-foot patrol
boats, using polyester resin and glass fiber. These boats were used until
the early 1970s when they were taken out of service because the design
was outdated. Extensive testing was done on the laminates after
decommissioning, and it was found that only 2-3% of the original
strength was lost after twenty-five years of hard service.
Mechanical Engineering Dept. 61

62. Disadvantages of Composites
Composites are heterogeneous
properties in composites vary from point to point in the material.
Most engineering structural materials are homogeneous.
Composites are highly anisotropic
The strength in composites vary as the direction along which we
measure changes (most engineering structural materials are isotropic).
As a result, all other properties such as, stiffness, thermal
expansion, thermal and electrical conductivity and creep resistance are
also anisotropic. The relationship between stress and strain (force and
deformation) is much more complicated than in isotropic materials.
The experience and intuition gained over the years about the behavior of
metallic materials does not apply to composite materials.
Mechanical Engineering Dept. 62

63. Disadvantages of Composites
Composites materials are difficult to inspect with conventional
ultrasonic, eddy current and visual NDI methods such as radiography.
American Airlines Flight 587, broke apart over
New York on Nov. 12, 2001 (265 people died).
Airbus A300’s 27-foot-high tail fin tore off.
Much of the tail fin, including the so-called
tongues that fit in grooves on the fuselage and
connect the tail to the jet, were made of a
graphite composite. The plane crashed because
of damage at the base of the tail that had gone
undetected despite routine nondestructive
testing and visual inspections.
Mechanical Engineering Dept. 63

64. Disadvantages of Composites
In November 1999, America’s Cup boat “Young America”
broke in two due to debonding face/core in the sandwich
structure.
Mechanical Engineering Dept. 64

65. SUMMARY
 What is the matrix in a composite and what materials are
commonly used as a matrix?
 What are the possible strengthening mechanisms for particle
reinforced composites (there are 2)?
 Be able to calculate upper and lower bounds for the Young’s
modulus of a large particle composite.
 Know the equation for the critical length (Lc) of a fiber.
 Know the stress distribution on fibers of various lengths w/r
Lc in a composite.
Reading for next class

66. Conclusions
Composite materials offer endless design
options.
Matrix, Fiber and Preform selections are
critical in the design process.
Structures can be produced with specific
properties to meet end use requirements.