KTU 2019 MECH

1. MODULE -1

2. 2
Composite
• Combination of two or more individual
materials
• Design goal: obtain a more desirable
combination of properties (principle of
combined action)
– e.g., low density and high strength

3. COMPOSITES
-Composite materials are engineered materials made from two
or more constituent materials that remain separate and distinct
while forming a single component
-Generally, one material forms a continuous matrix while the
other provides the reinforcement
- The two materials must be chemically inert with respect to each
other so no interaction occurs upon heating.

4. What is a composite?
• A composite is a structural
material which consists of
combining two or more
constituents
• Examples:
– Flesh in your leg reinforced
with bones
– Concrete reinforced with steel
– Epoxy reinforced with graphite
fibers.

5. 5
• Composite:
-- Multiphase material that is artificially
made.
• Phase types:
-- Matrix - is continuous
-- Dispersed(Reinforcement) - is discontinuous and
surrounded by matrix
Terminology/Classification
Adapted from Fig. 16.1(a),
Callister & Rethwisch 8e.

6. Fibrous Composites
• Generally there are two phases
– Fiber as a reinforcement
– Matrix as a binder

7. Historical Perspective
• 4000 B.C. Fibrous composites were used in
Egypt in making laminated writing
materials
• 1300 BC: “You are no longer to supply the
people with straw for making bricks; let
them go and gather their own straw”
• 1700 AD: French Scientist, Reumer talked
about potential of glass fibers

8. Historical Perspectives (continued)
• 1939: Glass fiber manufactured commercially
for high temperature electrical applications
• 1950s: Boron and carbon fibers were produced
to make ropes.
• 1960s: Matrix added to make polymeric matrix
composites.

9. Historical Perspectives (continued)
• 1970s: Cold war forces development of metal
matrix composites for military aircrafts and
missile guidance systems
• 1990s: High temperature ceramic matrix
composites are being aggressively researched
for use in next generation aircraft engines and
power plant turbines

10. ADVANATGES OF COMPOSITES
 The prime advantage of composites is their high specific stiffness and strength.
Therefore, the component weight can be drastically reduced by using composites.
 The second advantage of composites is their energy efficiency. Most of the composites
currently used are polymer-based composites. The polymer composites can be
produced at ambient temperature or slightly above ambient temperature and may be
a few hundred degrees above ambient temperature. Hence, very little energy is
required for the production of composites.
 Complex shapes can be made very easily with composites. Processing methods of
composites, at least polymer composites are matured enough to produce any complex
shape.
 It is possible to produce composites with combination of desired properties. In some
of the applications, like automobile body parts, it is necessary to have good
mechanical properties with better thermal insulation and aesthetics.

11. DISADVANATGES
 Composites are more expensive than conventional materials on a cost to cost basis.
The composites are approximately 5 and 20 times costlier than aluminum and steel,
respectively, on weight basis.
 The chances of formation of defects at the interface are high, since composites are
made with entirely different kind of materials.
 The production rate of composites is generally low. Composites may not be suitable
for high volume production industries like automobile industries.
 Recycling is another hurdle for the wide usage of composites. The recycling of
composites is difficult compared to the conventional metallic materials.

13. BOEING 787-DREAMLINER AIRCRAFT
Aerospace structures such as space antennae, mirrors and optical instrumentation make
use of lightweight and extremely stiff graphite composite.

14. High stiffness high strength and low density make composites highly desirable in primary
and secondary structures of both military and civilian aircraft.

15. STEALTH BOMBER
The stealth characteristics of carbon/epoxy composites are highly desirable in military
aircraft, such as B2 bomber.

16. UNMANNED AIRCRAFT
Small unmanned air vehicles are also made almost entirely of composites.

17. SOLAR POWERED FLYING WING-HELIOS
Solar powered flying wing Helios used by NASA for environmental research was made
of carbon and Kevlar fiber composites. It weighed only 708kg.

18. COBRA TRAM IN ZURICH
Cobra tram in Zurich incorporates composite sandwich construction

19. Ship structures incorporate composites in various forms, thick section glass and carbon
fiber composite and sandwich construction. It consists of thin composite face-sheets
bonded to a thicker lightweight core.
Less corrosion ship building, lower maintenance, lower manufacturing cost
Composites in ship building

21. COMPOSITE WIND TURBINE BLADE
Wind turbine completely made out of composite materials

22. FOOT & LEG PROSTHESES
Incorporates carbon/epoxy components

23. HIP PROSTHESIS
Incorporates Carbon / polysulfone

24. COMPOSITE PIPES
Chlorinated polyvinyl chloride

25. FOOT BRIDGE AT ABERFELDY -SCOTLAND
Uses Composite Decking Sections

28. Composite materials are commonly classified at following two
distinct levels:
1. The first level of classification: is usually made with respect to the
matrix constituent.
 Metal Matrix Composites (MMCs)
 Ceramic Matrix Composites (CMCs)
 Polymer Matrix Composites (PMCs)
 Carbon matrix composites

29. The second level of classification: refers to the reinforcement form –
Fibre reinforced composites
 Discontinuous
 Continuous fibres.
 Laminar composites
 Particulate composites.

32. 1. Fibers as the reinforcement (Fibrous Composites):
a. Random fiber (short fiber) reinforced composites
b. Continuous fiber (long fiber) reinforced composites
2. Particles as the reinforcement (Particulate composites):
3. Flat flakes as the reinforcement (Flake composites):
Common Categories of Composite Materials based on fibre length

33. Fibre Reinforced Composites are composed of fibres embedded in matrix
material. Such a composite is considered to be a discontinuous fibre or short
fibre composite if its properties vary with fibre length.
On the other hand, when the length of the fibre is such that any further
increase in length does not further increase the elastic modulus of the
composite, the composite is considered to be continuous fibre reinforced.
Fibres are small in diameter and when pushed axially, they bend easily although
they have very good tensile properties. These fibres must be supported to keep
individual fibres from bending and buckling.

34. Laminar Composites: are composed of layers of materials held together by
matrix. Sandwich structures fall under this category.
 Particulate Composites: are composed of particles distributed or embedded in
a matrix body. The particles may be flakes or in powder form. Concrete and wood
particle boards are examples of this category.
Metal Matrix Composites (MMCs): A metal matrix composite (MMC) is a type
of composite material with at least two constituent parts, one being a metal. The other
material may be a different metal or another material, such as a ceramic or organic
compound. When at least three materials are present, it is called a hybrid composite.

36. Although it is undoubtedly true that the high strength of composites is largely due
to the fibre reinforcement, the importance of matrix material cannot be
underestimated as it provides support for the fibres and assists the fibres in carrying
the loads. It also provides stability to the composite material.
In selecting matrix material, following factors may be taken into consideration:
The matrix must have a mechanical strength commensurate with that of the
reinforcement i.e. both should be compatible. Thus, if a high strength fibre is used as
the reinforcement, there is no point using a low strength matrix, which will not
transmit stresses efficiently to the reinforcement.
The resultant composite should be cost effective.
SELECTION OF MATRIX MATERIAL

37. The matrix must stand up to the service conditions, viz., temperature, humidity,
exposure to ultra-violet environment, exposure to chemical atmosphere, abrasion
by dust particles, etc.
 The matrix must be easy to use in the selected fabrication process.
Aluminium and magnesium alloys are regarded as widely used matrices due to low
density and high thermal conductivity.
Reducing the tensile ductility of the composite.

38. Functions of Matrices in Composites
Transfer stresses between the fibers.
Provide a barrier against an adverse environment.
Protect the surface of the fibers from mechanical abrasion.
 Determine inter-laminar shear strength. (determines the load-bearing capacity of
thick-walled composite elements)
 Determine damage tolerance of composites.
Determine the processibility of composites.
 Determine heat resistance of composites.

39. In composites intended for use at elevated temperatures, an additional consideration is
the difference in melting temperatures between the matrix and the reinforcements.
A large melting temperature difference may result in matrix creep.
However, creep in both the matrix and reinforcement must be considered when there
is a small melting point difference in the composite.
The needs or desired properties of the matrix which are important for a composite
structure are as follows:
Reduced moisture absorption.
 Low shrinkage.
Low coefficient of thermal expansion.
 Good flow characteristics so that it penetrates the fibre bundles completely and
eliminates voids during the compacting/curing process.
 Must be elastic to transfer load to fibres.

40. In the last few years, research has been conducted in the area of advanced
composites to be used as smart materials for smart structures. Smart structures and
materials are defined as systems which have two basic functions: the first is to sense
any external stimuli and the second to respond to that stimuli in some appropriate
ways in real or near real time.
SMART COMPOSITES
Shape-memory polymers (SMPs) are polymeric smart materials that have the
ability to return from a deformed state (temporary shape) to their original
(permanent) shape induced by an external stimulus (trigger), such as temperature
change

41. Shape-memory polymer composites (SMPCs)---which could be obtained by
incorporating small amounts of active fillers in the polymer matrix, which have
unique electrical and magnetical properties as well as biofunctionality.
In most cases the pure SMP can be thermally-actuated by increasing the
environmental temperature (direct heating)

42. Shape memory polymers (SMPs) have promising applications in the field of
 sensors and actuators
 aerospace engineering
 textile engineering
 automobile engineering, packaging
 self-healing, self-peeling reversible adhesive
 biomedical field

43. Similarly, the SMPC containing magnetic particles, such as iron oxide or nickel zinc
ferrite, could be inductively-actuated by exposure to an alternating magnetic field. The
latter approach had the advantage of wireless/remote operation.
Polymer composites with carbon compounds as fillers such as carbon black (CB),
carbon fibers, carbon nanotubes, or graphite were highly conductive materials. The
carbon compounds significantly reduced the electric resistance and resulted in
conductive SMPC, which could be triggered by means of Joule heat as an indirect
actuation method. Joule heating is the physical effect by which the pass of current
through an electrical conductor produces thermal energy.
The outstanding properties of SMPCs as well as their light weight, low cost, easy
processibility and very high recoverable strain make SMPCs good candidates for
many potential applications. SMPCs are recognized as extraordinarily versatile
materials and enabling technology for future space and interplanetary missions

44. For example, SMPCs have been explored to prepare trusses and torus-shape
structures for lightweight satellite supports, antenna reflectors, and deployable
wings for unmanned aerial vehicles. In this case, the SMPC materials allowed users
to pack large, lightweight structures tightly into small volumes for later use on orbit
or in the atmosphere.
SMPCs prepared from biodegradable matrix and active fillers are potential
candidates for biomedical applications such as orthopedic, dental, and
maxillofacial applications. Shape stability, excellent recovery stress and strain,
biocompatibility, and biodegradability (for in vivo biomedical application) or
inductively actuation as well as ease of processing are vital factors for the
acceptance of SMPC in these potential applications

45. Continuous fiber reinforced SMPCs currently cover a broad range of application
areas ranging from outer space to automobiles.
Recently, they are being developed and qualified especially for deployable hinges,
trusses, antennas and smart mandrels, as well as morphing skin.

46. Interfaces
Interface between a reinforcement and a matrix act as the bounding surface
between the two across which a discontinuity in some parameter occur.
An interface is the region through which material parameters such as concentration of
element, crystal structure density e.t.c change from one side to another.
Behavior of a composite material is the result of combined behavior of following
three entities.
Reinforcing phase(Fibre)
Matrix
Fibre/Matrix Interface

47. Microscopic view of interface

48. Wettability
It is the ability of a liquid to spread on solid surafce.
The liquid drop will spread and wet the surface completely only when it results in
net reduction of surface free energy.
(Surface free energy can be considered as the surface tension of a solid)
Wetting of solid surface by a liquid surface is made possible when a solid/vapor
interface is replaced by a solid/liquid interface.
Contact angle ϴ is an important parameter that characterize wettability.
Contact angle is obtained from the tangents along the three interfaces ;
Solid/Liquid, Liquid/Vapor and Solid/Vapor

49. Low contact angles are indicative of good wetting, whereas high contact angles point
to unsatisfying wetting .
Good wettability means that the liquid (matrix) will flow over the reinforcement
covering the rough surface completely and removing all air.

50. Partial wetting, on the other hand, relates to the situation when the surface
energy of the substrate is low and hence a finite contact angle is obtained in which
case the liquid retains its drop shape which is restricted at the solid surface by a
contact line where the solid, liquid and vapor phases meet.

51. Wettability describes the extent of intimate contact between a liquid and a solid; It
does not mean a strong bond at interface.
Wettability also depends upon following factors,
Time and Temperature of contact
Interface reactions
Surface Geometry
Heat of Formation
Electronic configurations

52. BONDING
It is important to be able to control the degree of bonding between the matrix and
reinforcement.
The important types of interfacial bonding are
Mechanical Bonding
Physical Bonding
Chemical Bonding

53. MECHANICAL BONDING
Simple Mechanical Keying or Interlocking effects between two surfaces can lead to
considerable degree of bonding.
Mechanical bonding is a low energy bonding.
Incase of mechanical bonding matrix must fill the pores and surface roughness of the
reinforcement.
Rather than pure mechanical bonding; mechanical bonding along with reaction
bonding contributes to overall strength of the bonding.
Surface roughness plays an important role in determining strength of mechanical
bond. It is utilized in CMCs, PMCs & MMCs.

54. (a) Good mechanical bond. (b) Lack of wettability can make a liquid polymer or metal
unable to penetrate the asperities on the fiber surface, leading to interfacial voids

55. 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, approximately 8–16 kJ/mol.

56. CHEMICAL BONDING
Atomic or molecular transport, by diffusional processes, is involved in chemical
bonding.
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.
Chemical bonding involves primary forces and the bond energy is in the range of
approximately 40–400 kJ/mol.

57. 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.
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.

58. Interface zone in a metal matrix composite
showing solid solution and intermetallic
compound Formation