COMPOSITES

1. Introduction to
Composite Materials
By
Bishwaraj Bhattarai
Institute Roll No 10/ME/134
Bishwaraj.Bhattarai@Outlook.com
Setobaadal@Gmail.com

2. Table of Contents 1
#. WHY STUDY COMPOSITE MATERIALS ?
1. Inception and History
• General Overview, Natural Occurrence and Anthropogenic History
2. Introduction
• Technical Definition
• Composition
3. Classification
• Based on Matrix Phase
• Based on Reinforcements
4. Mechanical Characterization
• Rule of Mixture and Loading Orientation
• Estimation of Various Properties
5. Advantages of Composite Materials
6. Disadvantages of Composite Materials
7. Conclusion

3. 2
Why Study Composite Materials ???
Lets take a closer look at our
lives….

4. 3
Why Study …contd.
• Composites make a great proportion of most of the materials we
use in our daily lives
• The use is ever increasing which makes it a must to understand
and explore these materials
THAT’S WHY …….

5. 1. Inception and History of Composite
Materials
4
• “Composite Material”
= Combination of two materials
• Natural Occurrences
1. Trees = Cellulose Fibers + Lignin (natural Polymer)
2. Muscles
3. Bones
4. Silky thread made by
spider
• Anthropogenic History
 Wood is the oldest known composite used by human beings
 Straw Bricks – as construction material, ~ 10000 BC ( Ashby et al)
 Modern development began before World War II with requirement of
strong but light material
 Glass Fiber Reinforced Plastic was the first commercial Composite
used in Havilland Mosquito Bomber aircraft of Royal British Navy
force

6. 2. Introduction to Composite
Materials
5
• Definition
 Combination of 2 different materials at macroscopic
level
 Identity of each component is retained
 Composites Vs. Alloys
• Basic Composition
 Composite = Ground Substance (Matrix Phase)
+ Reinforcements (Mostly
Fibers)
Fig – 1: Basic Components of a
Composite
 Various combinations of Matrix and
Reinforcing Materials can be used as per
the requirement of various properties
and the uses
 Various types based on various matrix
and reinforcement materials

7. 6
3. Classification of Composite
Materials
A. Based on Matrix Phase: Polymer/Metal/Ceramic
1. Polymer Matrix Composite,
PMC • Matrix is made from a Polymer like Resins
• The first commercial composite, Glass Fiber, was a PMC made with
Phenolic Resin
• May be a. Thermosetting ~ Epoxy Resin OR
b. Thermoplastic ~ Polycarbonate, PVC, Nylon, Polystyrene
 Light Weight
 Easy Processing
 Excellent Mechanical Properties
 Extensive use in Automobile and Aeronautical
Industries
2. Metal Matrix Composite, MMC
• Use metals like Aluminum, Magnesium, Iron, Cobalt etc. as
matrix phase
 Provide additional Strength, Fracture Toughness and Stiffness
than PMC
 Popular in Mobile Phone industries

8. 3.A Classification/Matrix Phase … contd.
3. Ceramic Matrix Composite, CMC
• Use Ceramic materials as the matrix phase and reinforce with short
fibers derived from Silicon Carbide, Boron Nitride, etc.
 High Melting Point
 Stability at elevated temperature ( ~ 1500 oC )
 Corrosion Resistant
 High Compressive Strength
7
 Favorite choice for working in high temperature
environment
X However they are quite brittle compared to
PMCs
B. Classification Based on Reinforcement Materials:
Fibers/Particulates/Flakes/Whiskers
1. Fiber Reinforcement
• Fibers made from various materials are placed within the matrix
phase to form a composite of desired strength/properties
• Fibers form the major load carrying element and are most common
reinforcement

9. 3.B Classification/By Reinforcement/Fibers …. Contd.
8
3.B.1 Fiber Reinforcement:
 Types of Fiber Reinforcement
A. Continuous/Long Fiber
• Long, continuous and unbroken fibers are used with L/D > 100
• Most common type of composite materials
• Fibers may be oriented unidirectional or bidirectional
 Better ‘impact resistance and rigidity at elevated, sub zero
temperatures
 Modulus retention at elevated temperature
 Creep resistance
 Dimensional stability during solidification (thermoplastics used
as matrix phase)
B. Short/Chopped Fibers
• Chopped or small pieces of fibers are used instead of long,
continuous fibers
• L/D ratio is within 100
Common Fiber Materials
A. Carbon/Graphite B.
Glass
C. Aramid D. Boron
Fig-2: Fiber
Composite

10. 3.B.1 Classification/Based on Reinforcement/Fibers/ Common Fiber
Materials……. Contd.
9
A. Carbon/Graphite Fibers
• Fibers are made from carbon/graphite material, commonly derived from
Polyacrylonitrile
 Excellent fatigue resistance and do not undergo stress rupture like glass
fibers
 High electrical conductivity, due to conductive nature of Carbon, thus used
for applications requiring good electrical properties
B. Glass Fiber
• Glass is the most common reinforcement material for PMC
• Common variants are E-glass, R-glass, S-glass, D-glass, ECR-glass etc.
• Configuration may be Roving, Sheet Moulding, Woven Roving, Chopped
Strand Mat etc.
 High Tensile Strength
X Lower Modulus compared to other
fibers
C. Aramid Fiber
• Kevlar is a common aramid fiber
composite
 Highest strength to weight ratio among all commercial composites
 Similar tensile strength but at least twice modulus compared to glass
fibers
 High Toughness
X Lower compression strength, poor adhesion to matrix

11. 1
0
3.B.1 Classification/By Reinforcement/Fiber/Fiber Materials …..
Contd.
D. Boron Fibers
• Has been in use much before the use of Carbon fibers began
• High cost led to gradual reduction in their except for specific
purposes
 Similar tensile strength to glass fibers but very high modulus, up to
5 times higher
 Composite has higher stiffness
3.B.2 Particulate Reinforcement
• Reinforcement in form of particles which are of order of few microns in
diameter
• Use of particles increases modulus and decreases ductility of matrix
material
• Load is shared by both particle and matrix, majority by particles
 E.g. Automobile type Carbon Black (particulate)+Rubber
(matrix)
Fig – 3: Particulate

12. 11
3.B. Classification/By Reinforcement ….Contd.
3.B.3 Flakes
Fig – 4: Flake Composite
• Flakes refer to small, flat (i.e. 2D geometry)
layer or chips
• Very effective reinforcement as they impart
almost equal strength in all the directions
• They can be packed very densely when laid
parallel, that is denser than the longitudinal
fibers
 Aluminum flakes are used in paints, they align themselves parallel to
surface of the coating and impart good properties
3.B.4 Whiskers
• Single crystal fibers; short,
discontinuous and with
polygonal section Fig – 5: Microscopic view
of Whiskers
Fig – 6: Whisker
Composite

13. 12
4. Mechanical Characterization :
Composites
4.1 Introduction
• Estimation of mechanical properties of composite is a bit complex compared
to metals as they are anisotropic and the properties vary with directions
• Structural analysis involves more parameters (like Stiffness/Strength
Constants) than the analysis of metals.
• Mechanical characterization of composites is still under development, with
many existing methods under debate.
4.2 Loading Orientation and Rule of Mixture
A. Loading Orientation
• Load may be
• Iso Strain : Load aligned with
fibers
OR
• Iso Stress : Load transverse to
the fibers Fig – 7: (a) Iso Strain Load (b) Iso

14. 13
4.2 Mechanical Characterization …. Contd.
B. Rule of Mixture
• It’s an approach to estimate the mechanical properties of composite
materials
• Property of composite is the volume weighed average of the properties
of the constituents matrix and the dispersed phases
• Some of the properties may depend on loading direction and vary for Iso
Strain and Iso Stress conditions, while other properties are same for both
the loading conditions
4.3 Estimation of various Mechanical Properties of the Composites
1. Density
dc = dm . Vm + df . Vf
dc ,dm,df – densities of the composite, matrix and dispersed phase
respectively;
Vm ,Vf – volume fraction of the matrix and dispersed phase

15. 14
4.3 Mechanical Characterization/Mechanical Properties ……
Contd.
2. Coefficient of Thermal
Expansion
A. Iso-Strain/Parallel to fibers
αc =( αm . Em .Vm + αf . Ef . Vf ) / (Em . Vm + Ef Vf )
αc , αm , αf – Coefficient of thermal expansion of composite in longitudinal
direction, matrix and dispersed phase (fiber) respectively;
Em , Ef – Modulus of elasticity of matrix and dispersed phase (fiber) respectively.
B. Iso-Stress/Transverse to Fibers
αct = (1+μm) αm . Vm + αf . Vf
μm - Poisson’s ratio of matrix
αct – Coefficient of thermal expansion in transverse
direction

16. 15
4.3 Mechanical Properties …. Contd.
3. Modulus of Elasticity
A. Iso Strain Condition
Ec = Em . Vm + Ef . Vf
B. Iso Stress Condition
1/Ect = Vm/Em + Vf/Ef
C. Short Fibers
Ecl = ηo . ηl . Vf . Ef + Vm . Em
ηl = 1 – 2 / (βL) . tan h(βL / 2 )
β =[ 8Gm / ( Ef . D2 . ln ( 2 R/ D))]1/2
Ef - Modulus of elasticity of matrix materials ηo - 0.0 align in transverse
direction
Gm - Shear modulus of matrix material ηo - 1/5 random orientation in
any direction ( 3D )
ηl - Length correction factor ηo - 3/8 random orientation in
any direction (2D)
L - Fibers length η - ½ bi- axial parallel to the fibers

17. 16
4.3 Mechanical Properties …… Cont.
4. Sheer Modulus
Gc = Gf . Gm / ( Vf . Gm + Vm . Gf )
Gf - shear modulus of elasticity of fiber material
Gm - shear modulus of elasticity of matrix
material
Gc - shear modulus of elasticity of composite
5. Poisson’s Ratio
µ = Vf . µf + Vm . µm
µf - Poisson’s ratio of fiber materials
µm - Poisson’s ratio of matrix materials
µ - Poisson’s ratio of composite

18. 17
4.3. Mechanical Properties ……. Contd.
6. Tensile Strength
A. Long Fiber
σc = σm . Vm + σf . Vf
σc , σm, σf - tensile strength of the composite ,matrix and
dispersed phase (fiber) respectively
B. Short Fiber
 σc = σm . Vm + σf . Vf . ( 1 – Lc/ 2L ) for length less then
critical length, Lc
 σc = σm*Vm + L* τc*Vf/d for length more than
critical length
L c = σf * d / Tc
d - diameter of fiber
Tc - shear strength of the bond between the matrix and dispersed
phase
L - length of the fiber

19. 18
5. Advantages of Composite Materials
 High Strength to Weight Ratio
 Light Weight
 Design Flexibility, to achieve desired stiffness, strength
and manufacturing requirements
 Complex shapes are easily accomplished
 Fire Resistance
 Chemical and weathering Resistance
 Resistance to fatigue damage with good damping properties
 Low thermal conductivity

20. 19
5. Disadvantages
 High Manufacturing Cost. A typical finished composite may cost
in between 10-15 times (or even more) the cost of material
being used.
 Synthetic fibers have low melting point and thus high
temperature operation is not feasible for those type of
composite
 Repairs of composites is very difficult and complicated, unlike
metal based components
 Sometimes, critical flaws and cracks in the composite structure
may go unnoticed
6. Conclusion
• A field of heave research and development
• Development of new types and obtaining the desired properties
is the main focus
• Attempts are being made to reduce the manufacturing cost

21. THANK YOU !!!