4. Composite
• A composite,in the present context,is a multiphase material
that is artificially made, as opposed to one that occurs or
forms naturally. In addition, the constituent phases must be
chemically dissimilar and separated by a distinct interface.
5. We shall call a material that satisfies the following conditions
a composite material:
• It is manufactured (i.e., naturally occurring composites,such
as wood, are excluded).
• It consists of two or more physically and/or chemically
distinct, suitably arranged or distributed phases with an
interface separating them.
• It has characteristics that are not depicted by any of the
componentsin isolation.
6. • A composite is a structural material that consists of two or more
combined constituents that are combined at a macroscopic level
and are not soluble in each other.
• One constituent is called the reinforcing phase and the one in which
it is embedded is called the matrix.
• The reinforcing phase material may be in the form of fibers,
particles, or flakes. The matrix phase materials are generally
continuous.
• Examples of composite systems include concrete reinforced with
steel and epoxy reinforced with graphite fibers, etc.
7. • Many compositematerials are composed of just two phases; one
is termed the matrix, which is continuous and surrounds the
other phase, often called the dispersed phase(Reinforcement).
8. • The advantage of composite materials is that, if well designed,
they usually exhibit the best qualities of their components or
constituentsand often some qualities that neither constituent
possesses.
9. Some of the properties that can be improved by forming a
composite material are
• strength
• fatigue life
• stiffness
• temperature dependent
behavior
• corrosion resistance
• thermal insulation
• wear resistance
• thermal conductivity
• attractiveness
• acoustical insulation
• weight
10. Examples for Composite
• Concrete. Also called “concrete”,it is the compositematerial
most used in construction at the same time, it is a
combination of various substances: cement, sand, gravel or
gravel and water.
• Plywood: Also called multilaminate, plywood, plywood or
plywood, it is a board of thin sheets of wood glued to each
other with their fibers in transverse orientation, with
synthetic resins, pressure and heat.
11. • Adobe. They are uncooked bricks, that is, fillings for
construction,made of clay and sand or other masses of mud,
mixed with straw and dried in the sun.
• Glass reinforced plastic. Known as GFRP (Glass-Fiber
Reinforced Plastic in English), is a composite material formed
by a plastic or resin matrix, reinforced with glass fibers.
12. Naturally found composites
• Examples include wood, where the lignin matrix is reinforced
with cellulose fibers and bones in which the bone-salt plates
made of calcium and phosphate ions reinforce soft collagen.
13. Example for advantages of using composites over
metals
• In many cases, using composites is more efficient. For
example, in the highly competitive airline market, one is
continuously looking for ways to lower the overall mass of the
aircraft without decreasing the stiffness* and strength† of its
components. This is possible by replacing conventional metal
alloys with composite materials.
14. How are composites classified?
• Composites are classified by the geometry of the
reinforcement — particulate, flake, fibers etc— or by the type
of matrix — polymer, metal, ceramic, and carbon.
17. Particulate composites
• Particulate composites consistof particles immersed in
matrices such as alloys and ceramics.
• They are usually isotropic because the particles are added
randomly.
• Particulate composites have advantages such as improved
strength, increased operating temperature, oxidation
resistance, etc.
• Typical examples include use of aluminum particles in rubber;
silicon carbide particles in aluminum; and gravel, sand, and
cementto make concrete.
18. Flake composites
• Flake composites consist of flat reinforcements of matrices.
Typical flake materials are glass, mica, aluminum, and silver.
Flake composites provide advantages such as high out-of-
plane flexural modulus,* higher strength, and low cost.
However, flakes cannot be oriented easily and only a limited
number of materials are available for use.
19. Fiber composites
• Fiber composites consist of matrices reinforced by short
(discontinuous) orlong (continuous) fibers.
• Fibers are generally anisotropic† and examples include carbon
and aramids.
• Examples of matrices are resins such as epoxy, metals such as
aluminum, and ceramics such as calcium–alumino silicate.
20. • Aramid fibers, short for aromatic polyamide, are a class of
heat-resistant and strong synthetic fibers. They are used in
aerospace and military applications
21.
22. • Laminar Composites - layers of
materials held together by matrix
(Sandwich structures)
23.
24. Nanocomposites
• Nanocomposites consist of materials that are of the scale of
nanometers . The accepted range to be classified as a
nanocomposite is that one of the constituentsis less than 100
nm.
25. Polymer Matrix Composites
• The most common advanced composites are polymer matrix
composites (PMCs) consisting of a polymer (e.g., epoxy,
polyester, urethane) reinforced by thin diameter fibers (e.g.,
graphite, aramids, boron).
• For example, graphite/ epoxy composites are approximately
five times stronger than steel on a weight for-weight basis.
• The reasons why they are the most common composites
include their low cost, high strength, and simple
manufacturing principles.
26. Metal matrix composites (MMCs)
• Metal matrix composites (MMCs), as the name implies, have a
metal matrix.
• Examples of matrices in suchcomposites include aluminum,
magnesium, and titanium.
• Typical fibers include carbon and silicon carbide.
• Metals are mainly reinforced to increase or decrease their
properties to suit the needs of design.
27. • Examples include continuous alumina fibers in an aluminum
matrix composites used in power transmission lines,
• Nb–Ti filaments in a copper matrix for superconducting
magnets,
• tungsten carbide (WC)/cobalt (Co) particulate composites
used as cutting tool and oil drilling inserts.
28. Ceramic matrix composites (CMCs)
• Ceramic matrix composites (CMCs) are a special type of
composite material in which both the reinforcement
(refractory fibers) and matrix material are ceramics. In some
cases, the same kind of ceramic is used for both parts of the
structure, and additional secondary fibers may also be
included. Because of this, CMCs are considered a subgroup of
both composite materials and ceramics.
29. Typical reinforcing fiber materials include the following:
• Carbon, C
• Silicon Carbide, SiC
• Alumina, Al2O3
• Mullite or Alumina Silica, Al2O3-SiO2
30. Reasons Why Composites Are Replacing
Traditional Materials
• Composites have a high strength-to-weight ratio.
• Composites are durable.
• Composites open up new design options
• Composites are now easier to produce
• Meet the demands of today’s advanced technologies
• Using composites is more efficient
31. Characteristics
31
• Composite materials show good maintenance of very high strength
even at extremely high temperature.
• They provide product design flexibility.
• High toughness and also show impact and shock resistance.
• Can withstand high mechanical stress and temperature and show
exceptionally high potential for abrasion and deformation resistance.
• Posses very high resistance to the effect of fire and chemical attacks.
• Being light weight and easily fabricable, composites are also cost
efficient.
• Least affected by the effect of nature for example weathering.
32. Functions
32
Composites should provide following functions:
• Enhance Strength
• Reduced weight
• Improve stiffness
• Improve durability
• Easy maintenance
33. Functions of a reinforcement:
• Provide superior levels of strength and stiffness to the
composite.
• Reinforcing materials (graphite, glass, SiC, alumina) may also
provide thermal and electrical conductivity, controlled
thermal expansion, and wear resistance in addition to
structural properties.
• Transfer the strengthto matrix.
34. Functions of a matrix
• Holds the fibers together
• Protects the fibers from environment
• Protects the fibers from abrasion (with each other)
• Helps to maintain the distribution of fibers
• Distributes the loads evenly between fibers
• Enhances some of the properties of the resulting material and
structural component.
• Provides better finish to final product
35. • The ability of composities to withstand heat, or to conduct
heat or electricity depends primarily on the matrix properties
since this is the continuous phase.
• Prevents the propagation of brittle cracks from fiber to fiber,
which could result in catastrophic failure; in other words, the
matrix phase serves as a barrier to crack propagation.
36. APPLICATION OF COMPOSITE
MATERIALS
• AIRCRAFT AND MILITARY APPLICATIONS
The major structural applications for compositesare in the
field of military and commercial aircrafts, for which weight
reduction is critical for higher speeds and increased payloads .
• Eg. carbon fiber reinforced epoxy
37. • AUTOMOTIVE APPLICATONS
• Applications of fiber-reinforced composites in the automotive
industry can be classified into three groups: body components,
chassis components, and engine components.
• Exterior body components , such as the hood or door panels,
require high stiffness and damage tolerance (dent resistance ) as
well as a ‘‘Class A’’ surface finish for appearance. The composite
material used for these components is E-glass fiber -reinforced
sheet molding compound (SMC) composites.
38. • SPORTING GOODS APPLICATIONS
• The advantages of using fiber-rein forced polymers a re
weight reduction, vibration damping , and design flexibility.
• Weight reduction achieved by substitutingcarbon fiber-
reinforced epoxies for metals leads to higher speeds and quick
maneuvering in competitive sports, such as bicycle races.
39. • Tennis rackets
• Racket ball rackets
• Golf club shafts
• Fishing rods
• Bicycle frames
• Snow and water skis
• Ski poles, pole vault poles
• Hockey sticks
• Baseball bats
• Sail boats and kayaks
• Oars, paddles
• Canoe hulls
• Surfboards, snow boards
• Arrows
• Archery bows
• Javelins
• Helmets
• Exercise equipment
• Athletic shoe soles and heels
40. • MARINE APPLICATIONS
• Glass fiber-reinforced polyesters have been used in different
types of boats.
• The principal advantage is weight reduction, which translates
into higher cruising speed, acceleration, maneuverability, and
fuel efficiency.
41. • INFRASTRUCTURE
• Fiber- reinforced polymers have a great potential for replacing
reinforced concrete and steel in bridges , buildings, and other
civil infrastructures.
• The principal reason for selecting these composites is their
corrosion resistance, which leads to longer life and lower
maintenance and repair costs.
42. • fiber-reinforced polymer is also used for upgrading,
retrofitting, and strengtheningdamaged, deteriorating, or
substandardconcrete or steel structures
43. • Fiber- reinforced polymer composites are also used in
electronics (e.g., printed circuit boards) ,building construction
(e.g ., floor beams), furniture (e.g., chair springs), power
industry (e.g., transformer housing), oil industry (e.g., offshore
oil platforms and oil sucker rods used in lifting underground
oil), medical industry (e.g., bone plates for fracture fixation,
implants, and prosthetics), and in many industrial products,
such as step ladders, oxygen tanks, and power transmission
shafts.
44. Advantages of composites
• Lower density (20 to 40%)
• Higher directional mechanical properties (specific tensile strength
(ratio of material strength to density) 4 times greater than that of
steel and aluminium.
• Higher Fatigue endurance .
• Higher toughness than ceramics and glasses.
• Versatility and tailoring by design.
• Easy to machine.
• Can combine other properties (damping, corrosion).
• Cost.
45. Drawbacks and limitationsin use of composites
• High cost of fabrication of composites.
• Mechanical characterization of a composite structure is more
complex than that of a metal structure. Unlike metals,
composite materials are not isotropic, that is, their properties
are not the same in all directions. Therefore, they require
more material parameters.
• Repair of composites is not a simple process compared to that
for metals. Sometimes critical flaws and cracks in composite
structuresmay go undetected.
46. • Composites do not necessarily give higher performance in all
the properties used for material selection.
47. Smart composites
• Smart material are the materials which have the ability to change
their physical properties in response to specific stimulus input or
environmental changes.
• These stimulus could be pressure, temperature, electric, magnetic
filed ,chemical, mechanical stress, radiation etc.
• Piezo Electric Materials: Materials that produce a voltage when
stress is applied.
• Photovoltaic or Optoelectronics materials: Converts Light to
electrical current.
• Shape memory materials: Induce deformation due to
temperature, stress change.
48. • Smart composites are defined as the Systemic
composition of smart materials to provide enhanced
dynamic sensing, communicating, and interacting
capabilities via Interactive Connected Smart Materials.
• Smart Composites can be explained simply as these
are designed materials ,where smart materials are
embedded in polymer, metal or concrete etc.. to sense,
control, communicate etc.
49. Examples for Smart Composites
• PH Sensitive polymers: Material which changes in
volume when PH of surrounding medium changes.
• Halochromic materials: Change their color as a result
of changing acidity.
• Temperature response polymers: Materials which
undergo changes upon temperature.
• Thermoelectric materials: Convert temperature
difference to electricity & Vice versa.
• Di Electric elastomers: Produce large strains (up to
500%) under the influence of an electric field.
50. Smart
Composites
50
• FOUR General classification of Smart
composites are;
• Structural smart composites
• Composites for actuation
• Novel functional composites
• Nanocomposites that are
functions.
enablers of novel
51. Smart
Composites
51
• Structural Smart composites are materials
that have the sensing capability to detect stress,
strain, fatigue and damage. monitor the health
conditions of structures that are difficult to
inspect or repair, such as wind turbine blades,
underground pipes and long-span bridges.
• Smart material
integrated design that is more reliable
into structural material is an
and
compact. Several types of smart materials or
sensors have been adopted in sensitive
structural composites. Among them, fiber optic
sensors, piezo electric have been widely studied
and adopted.
52. Smart
Composites
52
• Smart Composites for Actuation: Materials
being used as actuators were referred to as
induced strain actuators in the 1980s.
• The actuation was based on
mechanisms that
natural
cause actuation strains,
including thermal expansion, piezoelectricity,
material phase change and moisture
absorption.
• Shape-memory materials were proposed and
developed based on the above mechanisms.
53. Smart
Composites
53
• Smart Composites with Novel
Functionalities: Smart composites can also be
composites with unusual properties (additional
to sensing and actuation).
• Self-healing composites are composite
materials that can recover automatically after
damage.
• Nano Composites Enabling Novel
Functions: Many actuation, sensing and other
functions discussed above are enabled by the
incorporated nanoparticles. Functional nano
composites are also occasionally referred to as
smart composites.
54. Interface
• Interface is the boundary between matrix and reinforcement
• The behavior of a composite material is a result of the
combined behavior of the following three entities:
• Fiber or the reinforcing element
• Matrix
• Fiber/matrix interface
55. • An interface is the region through which material parameters,
such as concentration of an element, crystal structure,atomic
registry, elastic modulus, density, coefficient of thermal
expansion, etc., change from one side to another.
56. Wettability
• Wettability tells us about the ability of a liquid
to spread on a solid surface.
• Wettability is very important in PMCs because
in the PMC, manufacturing the liquid matrix
must penetrate and wet fiber tows.
57. • Contact angle, y,of a liquid on the solid surface fiber is a
convenient and important parameter to characterize
wettability. Commonly, the contact angle is measured by
putting a sessile drop of the liquid on the flat surface of a solid
substrate.
• The contactangle is obtained from the tangents along three
interfaces: solid/liquid, liquid/vapor, and solid/vapor.
58.
59. • It is important to realize that wettability and bonding are not
synonymous terms. Wettability describes the extent of
intimate contact between a liquid and a solid; it does not
necessarily mean a strong bond at the interface. One can have
excellent wettability and a weak van der Waals-type low-
energy bond. A low contact angle, meaning good wettability,
is a necessary but not sufficient condition for strong bonding.
60. • Although the contact angle is a measure of wettability, the
reader should realize that its magnitude will depend on the
following important variables: time and temperature of
contact; interfacial reactions; stoichiometry, surface
roughness and geometry; heat of formation; and electronic
configuration.
61. Types of Bonding at the Interface
• It is important to be able to control the degree of bonding
between the matrix and the reinforcement.To do so, it is
necessary to understand all the different possible bonding
types, one or more of which may be acting at any given
instant.We can conveniently classify the important types of
interfacial bonding as follows:
– Mechanical bonding
– Physical bonding
– Chemical bonding
• Dissolution bonding
• Reaction bonding
63. • Simple mechanical keying or interlocking effects between two
surfaces can lead to a considerable degree of bonding. In a
fiber reinforced composite, any contractionof the matrix onto
a central fiber would result in a gripping of the fiber by the
matrix. Imagine, for example, a situation in which the matrix
in a composite radially shrinks more than the fiber on cooling
from a high temperature. This would lead to a gripping of the
fiber by the matrix even in the absence of any chemical
bonding
64. • In general, mechanical bonding is a low-
energy bond via chemical bond, i.e., the
strength of a mechanical bond is lower
than that of a chemical bond.
65. • In the case of mechanical bonding, the matrix
must fill the hills and valleys on the surface of
the reinforcement. Rugosity, or surface
roughness, can contribute to bond strength
only if the liquid matrix can wet the
reinforcement surface.
66. • (a) Good mechanical bond. (b)Lack of wettability can makea liquid polymer or metal
• unableto penetrate the asperitieson the fiber surface, leadingto interfacial voids
67. Physical bonding
• Any bonding involving weak, secondary or van
der Waals forces, dipolar interactions, and
hydrogen bonding can be classified as physical
bonding. The bond energy in such physical
bonding is very low
68. • Atomic or molecular transport, by diffusional processes, is
involved in chemical bonding. Solid solution and compound
formation may occur at the interface, resulting in a
reinforcement/matrix interfacial reaction zone having a
certain thickness. This encompasses all types of covalent,
ionic, and metallic bonding.
69. • There are two main types chemical bonding:
• 1. Dissolution bonding. In this case, interaction between
components occurs at an electronic scale. Because these
interactions are of rather short range, it is important that
the components come into intimate contact on an atomic
scale. This implies that surfaces should be appropriately
treated to remove any impurities. Any contamination of
fiber surfaces, or entrapped air or gas bubbles at the
interface, will hinder the required intimate contact
between the components.
70. • 2. Reaction bonding. In this case, a transport of molecules,
atoms, or ions occurs from one or both of the components to
the reaction site, that is, the interface. This atomic transport is
controlled by diffusional processes. Such a bonding can exist
at a variety of interfaces, e.g., glass/polymer, metal/metal,
metal/ceramic, or ceramic/ceramic.
71. Questions
• What are the conditions to be satisfied for a material to be
called as a compositematerial.
• Classify the composite according to type of matrix and
reinforcement
• Explain about the function of reinforcementand matrix in
composite
72. • What are the advantages and disadvantages of composites
• Discuss about smart composites
• Explain about types of bonding at interface
• Explain about wettability of composites
• What are the advantages of composite materials over the
conventional engineering materials?
