Composite matierals lecture 2

18-Apr-16
1
Composite Matierals
Dimensionality of fillers
Factors effecting properties of composites
Composition of composites
Dr. Mohsin Ali Raza
Dimensionality of the nanofillers

18-Apr-16
2
Dimensionality of the nanofillers
Morphologies of the nanofillers

18-Apr-16
3
Carbon nanoparticles
Zero Dimensional Carbon black particles
Carbon Nanomaterials

18-Apr-16
4
Carbon nanofibres
1-D Carbon nanofibres
Carbon nanotubes
1-D Carbon nanotubes

18-Apr-16
5
Graphite nanoplatelets/Graphene
2-D Graphite nanoplatelets
2-D nanoclays in a polymer matrix
(Intercalated with polymer) (Exfoliated by polymer)

18-Apr-16
6
Cubic Fe2O3 nanoparticles

18-Apr-16
7
Two very important properties of the
fillers
• Surface area
Smaller particles have higher surface area per unit wt.
Interest in nanoparticles generate due to their high surface
area.
Offers much higher surface for polymer adsorption.
Small quantity of nanoparticles can occupy much more
volume in the matrix and improved properties can be achieved
at lower loading.

18-Apr-16
8
Surface to volume ratio
• Decreasing particle size increase the surface to volume ratio
Surface to volume ratio for a sphere =
𝐴
𝑉
=
3
𝑟

18-Apr-16
9
Ref. S.C. Tjong, H. Chen / Materials Science and Engineering R 45 (2004) 1–88
Ref. S.C. Tjong, H. Chen / Materials Science and Engineering R 45 (2004) 1–88
Effect of Particle size on the melting point of gold

18-Apr-16
10
Surface area
• Vol. of a particle (10 µm) = 5.23 x 1011 nm3
• Vol. of a particle (10 nm) = 523 nm3
• By diving 10 µm particle into 10 nm particle we get number
of particles
𝑎 =
𝑉(10 𝜇𝑚)
𝑉(10 𝑛𝑚)
=
5.23 ×1011
523
= 1 × 109 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
• Surface area of a particle (10 µm) = 3.14 x 108 nm2
• Surface area of a particle (10 nm) = 314 nm2
• Surface area of 1 billion particles = 3.14 x 1011 nm2
Surface area increased by a factor of 1000
Surface area
• Surface area of nanoparticles is in the range of 10-500
m2/g or higher
• More surface atoms are available for interaction
• Measured by N2 adsorption gas studies
• Average surface area is reported according to Brauner-
Emmer-Teller (BET) analysis

18-Apr-16
11
Aspect ratio
• Term used for 1 or 2- D fillers
• 𝐴 =
𝐿𝑒𝑛𝑔𝑡ℎ
𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟
• Fillers with higher aspect ratios lead to much stronger
reinforcement
• Carbon nanotubes have aspect ratios > 1000.
• Higher aspect ratios are required for developing interfiller
contacts
• Higher aspect ratio filler can serve the purpose at low wt.%
loading.
Factors on which properties of
composites depends
• Type of filler and matrix
• Concentration or wt.% of the constituents
• Size of the filler
• Dispersion of the filler
• Distribution of the filler
• Orientation of the filler
• Surface treatment of the filler

18-Apr-16
12
Factors on which properties of
composites depends
Dispersion of the
filler in polymer
matrix is always
a big challenge
Effect of concentration on properties of
composites

18-Apr-16
13
Effect of wt.% or vol.% of filler on the properties of PMC
Effect of addition of Vapour grown carbon nanofibres on thermal conductivity of
ABS and epoxy polymer
Effect of wt.% of filler on ductility of PMC

18-Apr-16
14
Effect of wt.% of filler on Flexural modulus of PMC
Effect of wt.% of filler on Notched Impact Strength of PMC

18-Apr-16
15
TEM images to judge dispersion of the nanoparticles
Does the strength keeps on increasing with the loading of fillers?

18-Apr-16
16
Does the strength keeps on increasing with the loading of fillers?
At high loading, Nanofillers tend to agglomerate more
Enhancement of modulus by the addition of nanoclays

18-Apr-16
17
Increase in electrical conductivity with increase of filler loading
C A R B O N 50 ( 2 01 2 ) 84 – 9 7
Electrical conductivity of VGCNF/epoxy composites
Size of fillers

18-Apr-16
18
Comparison of micro and nanosized filler
Distribution/Dispersion of fillers

18-Apr-16
19
Effect of distribution and dispersion on the electrical conductivity
of polymer composites
Distribution and dispersion of carbon
nanofibres in epoxy
Agglomerates
C A R B O N 50 ( 2 01 2 ) 84 – 9 7

18-Apr-16
20
Orientation of fillers
Effect of alignment of carbon nanotube on the thermal conductivity of
carbon nanotube/epoxy composites

18-Apr-16
21
Shape of the filler/dimensionality of
filler
Production of Nylon-Mica composites
Ref. http://www.imp.mtu.edu/jmmce/issue3-1/P31_3.pdf
Ball milling

18-Apr-16
22
Properties of Graphene and Carbon nanotube composites
Effect of Dimensionality of Filler on Barrier properties
Ref: C A R B O N 5 0 ( 2 0 1 2 ) 1 1 3 5 – 1 1 4 5

18-Apr-16
24
• Volume fraction of constituents
𝑉𝑐 = 𝑣𝑓 + 𝑣 𝑚
𝑉𝑜𝑙𝑢𝑚𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒 = 𝑉𝑓 =
𝑣𝑓
𝑉𝑐
𝑉𝑜𝑙𝑢𝑚𝑒 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑎𝑡𝑟𝑖𝑥 = 𝑉𝑚 =
𝑣 𝑚
𝑉𝑐
𝑉𝑓 + 𝑉𝑚 = 1
• Mass fraction of constituents
𝑊𝑐 = 𝑚 𝑓 + 𝑚 𝑚
𝑀𝑎𝑠𝑠 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒 = 𝑊𝑓 =
𝑚 𝑓
𝑊𝑐
𝑀𝑎𝑠𝑠 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑎𝑡𝑟𝑖𝑥 = 𝑊𝑚 =
𝑚 𝑚
𝑊𝑐
𝑊𝑓 + 𝑊𝑚 = 1

18-Apr-16
25
Relationship between volume fraction and mass
fraction
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝜌 𝑐 =
𝑊𝑐
𝑉𝑐
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 = 𝑊𝑐 = 𝜌 𝑐 𝑉𝑐 (1)
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑀𝑎𝑡𝑟𝑖𝑥 = 𝜌 𝑚 =
𝑚 𝑚
𝑣 𝑚
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑀𝑎𝑡𝑟𝑖𝑥 = 𝑚 𝑚 = 𝜌 𝑚 𝑣 𝑚 (2)
𝐷𝑒𝑛𝑠𝑖𝑡𝑦 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒 = 𝜌 𝑓 =
𝑚 𝑓
𝑣𝑓
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑓𝑖𝑏𝑟𝑒 = 𝑚 𝑓 = 𝜌 𝑓 𝑣𝑓 (3)
fraction
From Eq (1) and (2) (dividing 2 by 1)
𝑚 𝑚
𝑊𝑐
=
𝜌 𝑚 𝑣 𝑚
𝜌 𝑐 𝑉𝑐
(A)
𝑣 𝑚
𝑉𝑐
= 𝑣𝑜𝑙 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑎𝑡𝑟𝑖𝑥 = 𝑉𝑚
𝑚 𝑚
𝑊𝑐
= 𝑣𝑜𝑙 𝑓𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑚𝑎𝑡𝑟𝑖𝑥 = 𝑊𝑚
Eq. (A) becomes
𝑊𝑚 =
𝜌 𝑚
𝜌 𝑐
𝑉𝑚 (B)
Similarly from 1 and 3 we get,
𝑊𝑓 =
𝜌 𝑓
𝜌 𝑐
𝑉𝑓 (C)

18-Apr-16
26
Rule of mixture
The properties of composite material depend on the
relative quantities and properties of its constituents.
𝑃𝐶𝑀 = 𝑓𝑖 𝑝𝑖
PCM = Properties of composite material
fi= volume fraction of each 𝑖 , 𝑓𝑖=1
Density of composite in terms of volume fraction
𝑊𝑐 = 𝑊𝑚 + 𝑊𝑓
𝜌𝑐 𝑉𝑐 = 𝜌 𝑚 𝑣 𝑚 + 𝜌 𝑓 𝑣𝑓
𝜌𝑐 = 𝜌 𝑚
𝑣 𝑚
𝑉𝑐
+ 𝜌 𝑓
𝑣𝑓
𝑉𝑐
Density of composite
𝜌𝑐 = 𝜌 𝑚 𝑉𝑚 + 𝜌 𝑓 𝑉𝑓 (D)

18-Apr-16
27
fraction
Eq. (A) becomes
𝑊𝑚 =
𝜌 𝑚
𝜌 𝑐
𝑉𝑚 (B)
𝑊𝑚 =
𝜌 𝑚
𝜌 𝑚 𝑉𝑚 + 𝜌 𝑓 𝑉𝑓
𝑉𝑚
Similarly from 1 and 3 we get,
𝑊𝑓 =
𝜌 𝑓
𝜌 𝑐
𝑉𝑓 (C)
𝑊𝑓 =
𝜌 𝑚
𝑉𝑚
Relationship between volume fraction and mass fraction of
composite constituents
From Eq. (A)
𝑊𝑚 =
𝜌 𝑚
𝜌𝑐
𝑉𝑚
Putting value of ρc
𝑊𝑚 =
𝜌 𝑚
𝑉𝑚
Dividing and multiplying by ρm
𝑊𝑚 =
1
𝜌 𝑓
𝜌 𝑚
1−𝑉 𝑚 +𝑉𝑚
𝑉𝑚
Note 𝑉𝑓 = 1 − 𝑉𝑚
Also, 𝑊𝑓 =
𝜌 𝑓
𝜌 𝑚
𝜌 𝑓
𝜌 𝑚
𝑉 𝑓+𝑉 𝑚
𝑉𝑓

18-Apr-16
28
fraction of composite constituents
Prove the relation between volume fraction
of fibres to that of mass fraction and
densities of fibres and matrix.
i.e, Vm = ?
Actual volume of a Composite
𝑉𝑐 = 𝑉𝑓 + 𝑉𝑚 + 𝑉𝑣𝑜𝑖𝑑𝑠 (E)
Exp. Density of a composite
𝜌𝑐𝑒 =
𝑊𝑐
𝑉𝑐
(Actual density of a composite)
𝑉𝑐 =
𝑊𝑐
𝜌 𝑐𝑒
substitute in Eq (E)
𝑊𝑐
𝜌 𝑐𝑒
= 𝑉𝑚 + 𝑉𝑓 + 𝑉𝑣𝑜𝑖𝑑𝑠 (F)

18-Apr-16
29
Theoretical density of a composite
𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒
𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑣𝑜𝑙. 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒
𝜌 𝑐𝑡 =
𝑊𝑐
𝑉𝑐𝑡
Or 𝑉𝑐𝑡 =
𝑊𝑐
𝜌 𝑐𝑡
Since theoretical vol. of a composite = Vol. of matrix + Vol. of fibre
𝑉𝑐𝑡 = 𝑉𝑚 + 𝑉𝑓
𝑊𝑐
𝜌𝑐𝑡
= 𝑉𝑚 + 𝑉𝑓
Substituting value of "𝑉𝑚 + 𝑉𝑓”in Eq. (F)
Volume fraction of Voids
𝑊𝑐
𝜌 𝑐𝑒
=
𝑊𝑐
𝜌 𝑐𝑡
+ 𝑉𝑣𝑜𝑖𝑑𝑠
𝑉𝑣𝑜𝑖𝑑𝑠 =
𝑊𝑐
𝜌 𝑐𝑒
−
𝑊𝑐
𝜌 𝑐𝑡
𝑉𝑣𝑜𝑖𝑑𝑠 = 𝑊𝑐
1
𝜌 𝑐𝑒
−
1
𝜌 𝑐𝑡
𝑊𝑐
𝜌 𝑐𝑒
𝜌 𝑐𝑡 − 𝜌 𝑐𝑒
𝜌 𝑐𝑡
Since
𝑊𝑐
𝜌 𝑐𝑒
= 𝑉𝑐
𝜌 𝑐𝑡−𝜌 𝑐𝑒
𝜌 𝑐𝑡
This is fractional volume of voids present
in the composite.

18-Apr-16
30
Problem
Determine the density of glass fibre/epoxy composite with a
70% fibre vol. fraction. Also determine the mass fractions of
the fibre. The density of fibre and matrix is 2500 and 1200
kg/m3, respectively.
𝜌𝑐 = 𝜌 𝑚 𝑉𝑚 + 𝜌 𝑓 𝑉𝑓
𝜌𝑐 = 2110 𝑘𝑔/𝑚3
Using ,
𝑊𝑚 =
𝜌 𝑚
𝜌 𝑐
𝑉𝑚
and 𝑊𝑓 =
𝜌 𝑓
𝜌 𝑐
𝑉𝑓
𝑊𝑓 = 0.8294
𝑊𝑚 = 0.1706
Home work Problem
Calculate the amount of epoxy resin, curing agent and
carbon black to produce a 50 cm3 sample of carbon
black/epoxy composite at carbon black wt.% 10-90 (with
increments of 10 %). Also report volume fraction of resin
and carbon black. Make a table of data in excel and show
with the calculations. You are provided following data:
Density of curing agent = 0.991 g/cm3
Density of Epoxy resin = 1.16 g/cm3
Density of Carbon black = 2.26 g/cm3
Vol. of the composite to be fabricated = 50 cm3
The ratio of curing agent/Epoxy resin by weight = 75/25

18-Apr-16
31
Home work Problem
Calculate the amount of epoxy resin, curing agent, carbon black
and carbon fibres to produce a 50 cm3 sample of carbon
black/carbon fibre/epoxy composite at total content of carbon
black and carbon fibres wt.% 10-90 (with increments of 10 %).
Assume each composite composition has carbon black and
carbonf fibres in the ratio of 1:2. Also report volume fraction of
resin, carbon black and carbon fibre. Make a table of data in
excel and show with the calculations. You are provided following
data:
Density of curing agent = 0.991 g/cm3
Density of Epoxy resin = 1.16 g/cm3
Density of Carbon black = 2.26 g/cm3
Vol. of the composite to be fabricated = 50 cm3
The ratio of curing agent/Epoxy resin by weight = 75/25
Fibre reinforced Composites
• Fibres are reinforced in the matrix
Fibres can be micro or nanofibres
• Most important class of composites for structural
applications
• Important characteristics are specific strength
and modulus (offers high strength to weight
ratio)
• Utilises the low density of fibres and matrix to
produce high strength composites

18-Apr-16
32
Why fibres for reinforcement?
The most common geometrical shape used for reinforcement
Fibres have fewer flaws than bulk materials
 Real strength of materials is always lower than the theoretical
Strength
The strength of brittle materials is inversely proportional to the
square root of its max flaw size
𝜎 ∝
1
𝑎
Where a = max. crack length and σ is strength
Decreasing diameter increases strength of fibres
• As the area decreases, strength increases

18-Apr-16
33
Production of fibres result in orientation of
molecules
 Fibre strength can be increased by orienting the fibre
axis along the direction of the strong covalent bonds
Graphite planes oriented in graphite fibres
Graphite
Increasing the degree of
orientation increases
strength
Fibres offer higher fibre-matrix interface for
maximising strength and toughness
 Area of fibre-matrix interface is inversely proportional to
the diameter of the fibres.
Small fibre-matrix interface area large fibre-matrix interface area

18-Apr-16
34
Fibres offer higher fibre-matrix interface for
maximising strength and toughness
For fixed fibre volume in a given
volume of composite, the area of the
fibre-matrix interface is inversely
proportional to the diameter of the
fibres
Flexibility of fibres
• Smaller the diameter, higher will be flexibility of fibres
• Fibres made from brittle materials are highly flexible
• Bending stiffness of fibre is inversely
proportional to flexibility
Bending stiffness = EI
The minor decrease in fibre diameter can result in an
enormous decrease in bending stiffness or increase in
flexibility
Decreasing fibre
diameter, increases
modulus, strength and
flexibility

18-Apr-16
35
Problem
Flexible nylon fibres with E= 3 GPa and dia of 25 µm can
be easily wound on spools. What must be the diameter of
the following fibres (which have circular cross-section) to
show the same flexibility?
A. SiC
B. Pitch-based C fibres
C. Kevlar- 49
D. Boron
E for SiC = 430 Gpa
EI (nylon) = EI (SiC)
3 ×
𝜋 254
64
= 430 ×
𝜋𝑑4
64
d (SiC) = 7.2 µm
d(pitch based C fibre) = 9.5 µm
d(kevlar) = 9.7 µm
d (boron) = 7.3 µm
Flexural strength vs diameter of fibres

18-Apr-16
36
Mechanical Properties of reinforcing fibres
Typical fiber diameters are from 1 µm to 150 µm
Functions of fibres
• To carry load (ca. 70 to 90 % load is carried by fibres in a
composite)
• Fibres provide stiffness (rigidity), strength and structural
properties to the composite
• Fibres can also provide electrical conduction, thermal
conduction or insulation properties depending on the
requirement and type of the fibre used
 Attractive fibres for composite reinforcement must have
high strength and high elastic modulus.
 They must also be suitable for production in small
diameters.
 Popular fibres: glass fibres, carbon fibres, graphite fibres,
aramid fibres, SiC fibres, etc.

18-Apr-16
37
Influence of fibre length on the properties of composites
• Strong fibres are embedded in a softer matrix to produce products with
high strength-to-weight ratios
• The matrix transmits the load to the fibres
• Interfacial bond between the fibre and matrix determines how much load
will be transmitted to the fibres
Fibre-matrix bond ceases at the extremities of the fibre
All load transfers
to matrix
Fibre carrying
most of load
Critical length of fibre
• Critical length of fibre mandatory for maximum reinforcement
𝑙 𝑐 =
𝜎𝑓 𝑑
2𝜏 𝑐
𝑙 𝑐= critical length
d= diameter of fibre
𝜎𝑓= tensile strength of fibre
𝜏 𝑐= fibre-matrix bond strength (shear yield strength of the matrix)
Critical length of glass and carbon fibre-matrix combinations is ca. 1 mm , this is
20 to 150 x fibre diameter
Long fibers are preferred because the ends of the fiber carry less of
the load. Thus the longer the fiber, the fewer the ends and the
higher the load carrying capacity of the fibers

18-Apr-16
38
Strength of composite increases as length of
fibre increases
Strength of E-Glass/epoxy composite
Stress-position profiles for fibres
To achieve maximum reinforcement from fibres, continuous fibres
must be used

18-Apr-16
39
Classification of fibre reinforced composites
on the basis of length of fibres
Classification according to Length of fibres
l>>lc
(l>15lc)
l>>lc
(lc<l<15lc)

18-Apr-16
40
Influence of reinforcement type and quality on
composite performance
Mechanical Properties of fibre, matrix and
composite

18-Apr-16
41
Stress-strain behaviour of aligned fibre
reinforced composite
High potential to
be used as nanofiller
for producing high
strength, high
electrically and
thermally conducting
composites.

18-Apr-16
42
Continuous and aligned fibre reinforced
composites
• Lf> 15 Lc
• Usually fibres are very much long and present
in the matrix without any discontinuity
• Properties of these composite are highly anisotropic
• Excellent mechanical properties in the direction of
fibres but poor in transverse direction
Transverse direction
Longitudinal direction
Modulus of elasticity of continuous and
aligned composites
• Modulus of elasticity can be theoretically estimated for such
composites using rule of mixture
Assumptions
 Fibre-matrix interfacial bond is ideally good
 The deformation of the matrix and fibre in longitudinal
direction i.e, strain in Matrix and Fibre is same
(Iso-strain condition)

18-Apr-16
43
Modulus in longitudinal direction of aligned fibre
reinforced composites
• Iso-Strain condition
The total load sustained by the composite is
𝐹𝑐 = 𝐹 𝑚 + 𝐹𝑓 (i)
𝐹 = 𝜎𝐴
Eq (i) becomes
𝜎𝑐 𝐴 𝑐 = 𝜎 𝑚 𝐴 𝑚 + 𝜎𝑓 𝐴 𝑓
𝜎𝑐 = 𝜎 𝑚
𝐴 𝑚
𝐴 𝑐
+ 𝜎𝑓
𝐴 𝑓
𝐴 𝑐
(ii)
Assumption: Length of fibre and matrix are equal
𝑉𝑚 =
𝐴 𝑚
𝐴 𝑐
and 𝑉𝑓 =
𝐴 𝑓
𝐴 𝑐
Eq. (ii) becomes
𝜎𝑐 = 𝜎 𝑚 𝑉𝑚 + 𝜎𝑓 𝑉𝑓 (iii)
Modulus in longitudinal direction of aligned fibre reinforced composites
Under Iso-strain condition
𝜖 𝑐 = 𝜖 𝑚 = 𝜖 𝑓
Dividing Eq (iii) by respective strains
Furthermore,
𝜎 𝑐
𝜖 𝑐
= 𝐸𝑐 ,
𝜎 𝑚
𝜖 𝑚
= 𝐸 𝑚,
𝜎 𝑓
𝜖 𝑓
= 𝐸𝑓
Eq. (iv) becomes
𝐸𝑐𝐿 = 𝐸 𝑚 𝑉𝑚 + 𝐸𝑓 𝑉𝑓 (v)
or 𝐸𝑐𝐿 = 𝐸 𝑚(1 − 𝑉𝑓) + 𝐸𝑓 𝑉𝑓
𝜎 𝑐
𝜖 𝑐
=
𝜎 𝑚
𝜖 𝑚
𝑉𝑚 +
𝜎 𝑓
𝜖 𝑓
𝑉𝑓 (iv)
Modulus of Elasticity of aligned fibre
reinforced composite in longitudinal
direction is equal to volume fraction
weighted average of the modulii of
elasticity of the fibre and matrix phases

18-Apr-16
44
Tensile strength and coefficient of thermal expansion of aligned fibre
reinforced composite
Tensile strength in longitudinal direction
𝑈𝑇𝑆 𝑐𝐿 = 𝑈𝑇𝑆 𝑚 𝑉𝑚 + 𝑈𝑇𝑆𝑓 𝑉𝑓
Coefficient of thermal expansion
𝛼 𝑐𝐿 = 𝛼 𝑚 𝑉𝑚 + 𝛼 𝑓 𝑉𝑓
Modulus in Transverse direction of aligned fibre reinforced
composites
When load is applied perpendicular to the direction of the fibres; for
such case stress to which composite as well as both phases are
exposed is the same
Under Iso-stress condition
𝜎𝑐 = 𝜎 𝑚 = 𝜎𝑓
The strain of the entire composite would be
𝜖 𝑐 = 𝜖 𝑚 𝑉𝑚 + 𝜖 𝑓 𝑉𝑓 (vi)
since 𝜖 =
𝜎
𝐸
Eq. (vi) becomes
𝜎
𝐸𝑐
=
𝜎
𝐸 𝑚
𝑉𝑚 +
𝜎
𝐸𝑓
𝑉𝑓
or 𝐸𝑐𝑇 =
𝐸 𝑚 𝐸 𝑓
𝑉 𝑚 𝐸 𝑓+𝑉 𝑓 𝐸 𝑚
(vii)

18-Apr-16
45
Example Problem
A continuous and aligned fibre-reinforced composite is to be produced
consisting of 45 vol.% aramid fibres and 55 % vol. of a polycarbonate
matrix. Mechanical characteristics of these two are as follows:
phase M.E (psi) T.S (psi)
Aramid fibre 19 x 106 500,000
Poly carbonate 3.5 x 106 8000
For this composite compute (a) the longitudinal tensile strength (b)
longitudinal modulus of elasticity.
𝐸𝑐𝐿 = 𝐸 𝑚 𝑉𝑚 + 𝐸𝑓 𝑉𝑓
𝑈𝑇𝑆 𝑐𝐿 = 𝑈𝑇𝑆 𝑚 𝑉𝑚 + 𝑈𝑇𝑆𝑓 𝑉𝑓
Discontinuous fibre composites
• Lf < 15Lc
• Can be aligned or randomly oriented
• When fibre length is less than Lc, the matrix deforms around the fibre
such that there is virtually no stress transference and little
reinforcement by the fibres. Such composites come in the category of
particulate composites.
• Discontinuous and aligned fibre composite although have lower
reinforcement efficiency, they are becoming more important in
commercial market.
• Chopped glass fibres are extensively used to produce discontinuous
fibre reinforced composites. Their modulus and tensile strength
approach 90% and 50 % respectively of their continuous fibre
counterparts.

18-Apr-16
46
Fibre reinforcement efficiency parameter (η)
• The properties of discontinuous and aligned fibre
reinforced composites depend on η which itself depends
on the length of fibres.
𝜂 = 1 −
𝐿 𝑐
2𝐿
Tensile strength of discontinuous and aligned fibre
reinforced composites
• When L>Lc , tensile strength in longitudinal direction is given by
• When L<Lc, tensile strength is given by

18-Apr-16
47
Tensile strength of discontinuous and randomly
oriented fibre reinforced composites
• For these composites reinforcement efficiency parameter depends
on volume fraction of fibres and the ratio of Ef and Em.
• Elastic modulus of such composites according to rule of mixture can
be given as
𝐸𝑐𝑑 = 𝐾𝐸𝑓 𝑉𝑓 + 𝐸 𝑚 𝑉𝑚
Where K is reinforcement efficiency parameter
Practice problems
Solve the problems 17.10-17.22 of Chapter 17
from Book Materials Science and Engineering An
Introduction by W. D. Callister (5th edition)
Or problems 16.1 to 16.21 (8th Edition)

18-Apr-16
49
Read full
story at the
link
provided

18-Apr-16
51
Fibre reinforced polymer matrix composites
• Polymer is used as matrix and fibres can continuous, discontinuous
(aligned or randomly oriented)
• Matrix can be thermoplastic (nylon 6,6, polycarbonate, PET, etc are
used) or thermosetting (epoxy, polyester (unsaturated)
• Commonly used fibres are
 Glass fibres
 Aramid fibres (Kevlar)
 Carbon fibres

18-Apr-16
52
Glass fibre reinforced polymer composites
• Glass fibres can be continuous or discontinuous
• Most widely used composite and have wide range of
applications
Types of glass fibres
i. E-glass (Electrical glass): Lime-aluminium boro silicate glass with zero
or low sodium and potassium levels.
Composition of E-glass:
52-56% SiO2, 12-16% Al2O3, 16-25 % CaO and 8-13% B2O3
ii. S-glass (high strength): Have high strength to weight ratio. More
expensive than E-glass and is used primarily for military and
aerospace applications.
Composition of S-glass:
65% SiO2, 25%Al2O3, 10 % MgO
Diameter of glass fibre ranges from 3-20 µm
Comparison of strength of S- and E-glass fibres
Specific gravity of glass fibres is 2.5 which is very much higher than
carbon and aramid fibres (1.8 and 1.4 ,respectively)

18-Apr-16
53
Why glass fibres are most popular reinforcement
material?
• It can be easily drawn into fibres from molten state.
Continuous variation of glass viscosity with temperature and the high surface
tension favours the formation of fibres.
• It is readily available and low cost because its raw material is
relatively cheap.
• Available in the form of various fibre architectures or mats (like
woven cloth)
• Can be easily reinforced by different composite fabrication
techniques
• As a fibre, it is relatively very strong and when embedded in polymer
matrix, it produces a composite having very high specific strength
• When coupled with various polymers it possesses a chemical
inertness that make composite very useful for a variety of corrosive
environments.
Fiberizing/Production of glass fibres
Production of continuous filament of glass fibres
Batching
Melting (1700 ᵒC)
Fiberisation
Sizing/coating Drying and packaging
http://www.compositesworld.com/articles/the-making-of-glass-fiber
250 Platinum alloy nozzles of dia 10 µm
Drawing speed 25 m/s Strand has 200 filaments

18-Apr-16
54
Fiberizing/Production of glass fibres
Production of discontinuous filament of glass fibres
Chopped glass fibres Rovings
Woven fabric Emulsion mats
Needled mats
Size formulations

18-Apr-16
55
Surface characteristics of glass fibres
• Surface characteristics of glass fibres are extremely important
because even few surface flaws have deleterious effect on
mechanical properties.
• Surface flaws can be easily introduced by rubbing and
abrading the surface with another hard material.
• Newly drawn fibres are coated during drawing with a “size” a
thin layer of a substance that protects the fibre surface from
damage and undesirable environmental interactions.
• The size is usually removed before composite fabrication and
replaced with “coupling agent” or finish that provides better
bond between the fibre and matrix. Silane compounds are
most commonly used as coupling agents.
What is fibre glass?
It is technical term applied to products or composites made
from glass fibres
Disadvantages of fibre glass
 Lack rigidity which is required for example for structural members for
air planes and bridges.
 Limited service temperature (below 200 ºC).
Applications of fibre glass
Automotive and marine bodies, pipes, storage containers, industrial
flooring, roofing, lining for electroplating vats, sports goods, boats.

18-Apr-16
56
SEM images of fibreglass-reinforced
composites
Interfaces in glass fibre/polymer composites
• Stronger interfaces between the fibre and matrix ensures the
maximum reinforcement and enhanced mechanical
properties.
• Stability and durability of interfacial region is primary issue
because the environmental effects such as temperature,
moisture and stresses can degrade the interfacial bonding.
• Highly hygroscopic nature of unprotected glass fibres can
result in poor adhesion. (drying of fibres is essential)
• Unprotected and unbonded fibres can break at relatively low
loads and have enough stored elastic energy lost at the
ends of fibres which can propagate cracks in the matrix or
along the fibre/matrix interface (every end of fibres is source
of stress concentration)

18-Apr-16
57
• Strength/bonding of polymer adsorbed on glass fibre
depends on the intermolecular forces of attraction at the
interfaces.
• In the absence of primary chemical bonding then there
should be secondary bonding (Vander Waals forces or polar
bonding)
• The adsorption of polymer molecule on the surface (glass
fibre) decrease the mobility of the molecule but primary
modes of translational, rotational and vibration still remain
present.
• Foreign molecules like water can still penetrate at the
interface and replace the polymer chain segments
Glass fibre composites performance degrade under wet condition because
of loss of interfacial bonding and decrease in tensile strength of the
reinforcing fibres

18-Apr-16
58
Silane coupling agents for glass fibre/polymer composites
• Organofunctional silanes are the most widely used for
improvement of interfacial adhesion in glass fibre reinforced
composites
• The effectiveness of silane treatment depends on:
o Nature and pretreatment of the substrate
o Type of silane used
o Thickness of the silane layer
o Application process
o Nature of chemical bond between constituents
Reaction and bonding of alkoxysilane with substrate
Materials Science and Engineering
A302 (2001) 74–82

18-Apr-16
59
Reaction and bonding of alkoxysilane with substrate
M.M. Kabir et al. / Composites: Part B 43 (2012) 2883–2892
Changing matrix by
diffusion of siloxane
Polymer/siloxane/glass interface

18-Apr-16
60
Carbon fibre-reinforced polymer composites
What is a carbon fibre?
 Carbon fibres have a highly distorted and defective graphite-like
structure.
 Carbon fibres are produced so that the fibre axis lies in the basal plane,
along the direction of the strong covalent bonds.
 Elastic modulus along the fibre axis can be as high as 1000 GPa but in
transverse direction can be as low as 35 GPa.
 The mechanical, chemical, electrical and other physical properties
depends on the raw material and processing treatment.
• Carbon fibres are reinforced in polymer matrix
• Commonly used polymer matrix is thermosetting epoxy or PEEK
Precursor for carbon fibres
Carbon fibres can be fabricated from three precursors
(i) Polyacrylonitrile (PAN)
(ii) Pitch
(iii) Rayon, PVC

18-Apr-16
61
Types of carbon fibres
• On the basis of production techniques carbon fibres can
be divided into two major types
(i) High strength carbon fibres
(ii) High modulus carbon fibres
• Carbon fibres on commercial scale are made from Pitch
(pitch is converted into liquid crystalline material
(mesophase) and melt spun into fibres and then pyrolysed.
Produced from PAN
fibres
Production of Carbon fibres
Three stages of Production from PAN fibres
 Stabilisation
 Carbonisation
 Graphitisation

18-Apr-16
62
A carbonisation process then follows in huge
furnaces, where all non-carbon molecules are
removed while the chemical properties of the
remaining carbon molecules are changed to
help them bond better, thus making the
carbon strong.

18-Apr-16
63
800-1500 ᵒC
No air
Oxidisation
1500-2000 ᵒC
No air
High strength
carbon fibres
High modulus
carbon fibres
http://www.arrhenius.ucsd.edu/miakel/Miakel_B.html
Stretching
ensures
perfect
crystal
orientation
Modulus after
graphitisation
reaches 300-
600 GPa

18-Apr-16
64
SEM images of carbon fibres produced from PAN
and pitch
SEM micrographs of the transverse sections for carbon fibers: (a) PAN-13; (b) PAN-27;
(c) MPP-13; (d) Enlarged MPP-13;(e) MPP-27; (f) Enlarged MPP-27.
C A R B O N 5 0 ( 2 0 1 2 ) 4 4 5 9 – 4 4 6 9 4463
Formation of Carbon fibres
http://www.sciencedirect.com/science/article/pii/S0008622312004538

18-Apr-16
65
TEM images of Carbon fibres
TEM micrographs of the transverse sections: (a) PAN-13; (b) PAN-20; (c) PAN-25; (d)
PAN-27; (e) MPP-13; (f) MPP-20; (g)MPP-25; (h) MPP-27.
Effect of heat treatment on mechanical properties
of carbon fibres

18-Apr-16
66
Elemental analysis and diameters of carbon fibres
produced by heat treatment at various temperatures
C A R B O N 5 0 ( 2 0 1 2 ) 4 4 5 9 – 4 4 6 9 4463
Properties of Carbon fibres
• Advantages
– Low density (1.8-2.2 g/cm3)
– High tensile modulus and strength up to 2000 ºC (non-
oxidizing environment)
– Resistant to creep
– High fracture toughness
– Low coefficient of thermal expansion
– High thermal conductivity
• Thus, thermal shock is relatively unimportant
• Disadvantages
– High temperature oxidation
– Very expensive
– Complex and low volume processing/manufacturing

18-Apr-16
67
Carbon-Carbon composites
• Carbon fibres and carbon matrix
• These materials are relatively new and expensive and, therefore, are not
currently being utilized extensively.
• Their desirable properties include high-tensile moduli and tensile
strengths that are retained even at high temperatures, resistance to
creep, and relatively large fracture toughness values.
• Carbon–carbon composites have low coefficients of thermal expansion
and relatively high thermal conductivities; these characteristics, coupled
with high strengths, give rise to a relatively low susceptibility to thermal
shock. Their major drawback is a propensity to high temperature
oxidation.
Applications: For space structures , sports
equipment, biomedical application (body implants)
Carbon fibre architecture
Carbon fibres are used in 2-D or 3-D architecture to increase
the off-axis strength

18-Apr-16
68
Production of carbon matrix composites
• Carbonization, followed by impregnation of pitch or
resin, and repeating the carbonization-impregnation
process again and again until sufficient density has been
attained.
• Chemical vapor infiltration (CVI) using a
carbonaceous gas, i.e., CVD under a
temperature/pressure gradient so as to prevent crust
formation, thereby allowing complete infiltration; CVD
can be an extra step that follows carbonization-
impregnation for the purpose of filling the pores.

18-Apr-16
69
Flow sheet diagram for production of carbon matrix
composites
Carbon fibre preform
structure
Liquid impregnation
(phenol, furfural or pitch)
Chemical vapour deposition
(hydrocarbon gas)
1000-2000 ᵒC
Carbonisation
1000-1200 ᵒC
Heat treatment
2000-2800 ᵒC
C-C composite
1-5 times
1-3 times
Aramid Fibre reinforced Polymer Composites
 Aramid fibres are reinforced in polymer matrix
Aramid is generic name for aromatic polyamide fibres
The chemical repeating unit of aramid polymer chain is
that of a aromatic polyamide. This group of material is
known as poly paraphenylene terephthalamide.
Aramid structure

18-Apr-16
70
Production of Aramid Fibres
 Aramid fibres are produced by solution-
polycondensation of diamines and diacid halides at low
temperature.
Diacid chloride is rapidly added to a cool (5-10 °C)
amine solution while stirring.
The polymer formed is recovered from crumbs or gels
by pulverising, washing and drying.
To form filaments, the clean polymer, mixed with a
strong acid (H2SO4), is extruded from spinnerets at an
elevated temperature (50-100 °C) through a 0.5-1.9 cm
layer of air into cold water (0-4 °C).
The fibres are then washed thoroughly in water and
dried on bobbins.
Production of Aramid Fibres
Nomex
Kevlar

18-Apr-16
71
Structure of Aramid Fibres
Properties of Aramid fibres
 Good resistance to abrasion
 Non conductive
No melting point, high degradation temperature 500 ºC
Low flammability
Hydrophilicity due to amide linkage, high water absorption
(fibre structure plays an important role in moisture
absorption)
 Good fabric integrity at elevated temperature
 Sensitive to ultraviolet radiation
 Prone to static-build of charges
20 times higher specific strength than steel
 Very low density (1.4 g/cm3)
Poor under compression
Suffers corrosion in chlorine atmosphere
Strong acids attack at higher temperature
Difficult to dye due to their high Tg

18-Apr-16
72
Comparison of Properties of Aramid fibres with
other fibres
©2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.
Types of Aramid fibres
Kevlar 29
– Reinforcement for car and cycle tyres (reduces
puncture rates)
– Standard type is more expensive than that used in tyres
and this is used for body armour for light weight military
vehicles, bullet proof helmets and vests.
Kevlar 49
– Light weight and can withstand considerable force
(twisting, torque, tensile, impact)
– Used for boat hulls and in aerospace industry

18-Apr-16
73
Effect of addition of aramid on wear rates of
polyamide 6,6
Applications of Fibre reinforced Composites

18-Apr-16
74

18-Apr-16
75
Processing of Fibre-Reinforced Composites
 Open moulding processes
• Hand lay-up process
• Spray-up
• Vacuum bag autoclave moulding
• Pressure bag moulding
• Autoclave moulding
 Continuous/semi automatic processes
 Pultrusion
 Prepreg/Sheet moulding compound production
 Filament winding
 Close moulding
• Compression moulding
• Injection moulding
• Resin Transfer moulding or VARTM
Hand lay-up
• Commonly used for production of DCFRC
• Fibres in the form of mats (discontinues fibres) are used
• Parts of any shape or dimension and surface area of few square feet can
be produced by this method
• Easy method
• Resins used: epoxy, polyester, phenolic, vinylester
• Fibres used: any in the form of mats or stitched into a fabric form
• Applications: Aircraft component parts, boat hulls, bumpers, wind turbine
blades, tanks, etc.

18-Apr-16
76
Spray-up process
• Low cost method of quickly depositing fibre and matrix
• Glass fibre rovings are only used
• Parts of any shape or dimension and very large surface area can
be produced by this method
• Low tooling cost
• Resin need to be of high viscosity to be sprayed
• Only short fibres can be incorporated, this limits mechanical properties of
laminates.
• Simple enclosures, bath tubs, structural panels, shower trays, caravan
bodies, etc.
Vacuum bag moulding
• Pressure is applied by creating vacuum to improve the consolidation of
the laminate once laid up by hand lay-up or spray-up method.
• Even pressure on the component
• High pressure means heavy fibre mats can be wet-out.
• High fibre content can be achieved
• Fewer voids
• Better infiltration of resin into fibres network due to high pressures
• Cost increases
• Products manufactured: Cruising boats, race car components, space craft
Components, etc.

18-Apr-16
77
Pressure bag moulding
• Pressure is applied to improve the consolidation of the laminate once laid
up by hand lay-up or spray-up method.
• Extensively used in the production of composite helmets.
• Lower cost of unskilled labor
• Cycle times is 20 to 45 minutes
• Steam or hot air is used which can cure resin
• Finished heated shells require no further curing.
Autoclave pressure moulding
• Entire assembly is placed in an autoclave.
• Process generally performed at both elevated pressure and elevated
temperature
• High pressure allows much higher fibre loading and fewer voids
• Cycle times is 20 to 45 minutes
• Finished heated shells require no further curing.

18-Apr-16
78
Pultrusion
• Used for production of components having continuous
length and a constant cross-sections (rods-bars, tubes,
beams, etc)
• Fibre loading up to 70 % can be achieved
• High production rates
http://www.strongwell.com/pultrusion/
http://www.strongwell.com/pultrusion/

18-Apr-16
79
Prepreg Production Process
Prepreg
“Partially cured mixture of fibre and resin”
• Unidirectional fibre sheets ready to use
• Can be easily cured at certain pressure and temperature
• Stored at 0 ºC or below
• Have limited shelf life (six months)
• Plies of prepreg tape are laid up in the mould to acquire
desired thickness
Prepreg production process

18-Apr-16
80
Filament Winding
• Used for making hollow shapes
• Continuous fibres are positioned in a predetermined pattern
• Parts have very high strength-to-weight ratios
• Control over winding uniformity and orientation
• Can be fully automated, cost effective
• Products: rocket motor casings, storage tanks and pipes, and
pressure vessels
Closed Moulding
Resin transfer moulding
• Used when parts with two smooth surfaces are required
• Resins permeate through the material from the top displacing air
• Uses low viscosity catalyzed resins injected into the piece
• Cures with low temperature and low pressure

18-Apr-16
81
Closed Moulding
Compression moulding
• Sheet moulding compounds or prepregs are compression moulded
Manufacturing processes applications

18-Apr-16
82
Hybrid composites
• To improve properties of materials, composites
are produced
• Improving the properties of composites further
hybrid combination of fillers can be used
• A composite composed of two or more types of
fillers to combine benefits of both fillers.
Examples
Carbon black/graphite nanoplatelet/epoxy
composite, glass fibre/carbon nanofibre/epoxy
compsites, SiC/graphite/epoxy composite, Carbon
nanotube/boron nitride/epoxy composite
Carbon black prevents the settling of
Graphite nanoplatelets in epoxy matrix
J Mater Sci (2012) 47:1059–1070

18-Apr-16
83
Carbon black increase the electrical
conductivity of Graphite nanoplatelets/epoxy
J Mater Sci (2012) 47:1059–1070
Synergy between three types of Carbon
nanofillers
Materials Letters 64 (2010) 2376–2379

18-Apr-16
84
Synergy between three types of Carbon
nanofillers
Materials Letters 64 (2010) 2376–2379
The percolation threshold of the nanocomposites ﬁlled with GNP0.7CB0.1CNT0.2was only
0.2 wt.%, while those with GNP0.9CB0.1 and GNPs were 0.5 wt.% and 1 wt.%
respectively.
Natural fibre polymer composites
• Natural fibres are low cost, biodegradable and non-
abrasive in nature
• Incompatibility with hydrophobic polymer matrices,
tendency to form aggregates during processing and
poor resistance to moisture greatly reduce the
potential of natural fibres to be used as
reinforcement
• Natural fibres degrade at or above 200 ºC, so
processing temperatures should be below 200 ºC
• Thermal stability of fibres, surface adhesion
characteristics of the fibres and dispersion in
polymer matrices are key issues

18-Apr-16
85
Natural fibres
• Seed hairs (cotton)
• Bast fibres (ramie, jute, flax)
• Sisal and abaca (leaf fibres)
Properties of the natural fibres
Microstructure of Natural fibres
• Microstructure of natural fibres consists of
microfibrils in an amorphous matrix of lignin and
hemicellulose
• Fibrils consists of several fibres oriented along
the length of fibres
• Hydrogen bonding provides strength and
stiffness to these fibres.
• Chemical composition : fibres contain 60-80 %
cellulose, 5-20 % lignin, 20 % moisture

18-Apr-16
86
Chemical structure of Cellulose fibres
Structural organisation of Natural fibres
M.M. Kabir et al. / Composites: Part B 43 (2012) 2883–2892

18-Apr-16
87
Silane treatment of natural fibre to
improve bonding with matrix
Examples of Natural fibre/reinforced
composites
Advances in Polymer Technology, Vol. 18, No. 4, 351–363 (1999)

18-Apr-16
88
Metal Matrix Composites
What are metal matrix composites?
Metal matrix composites (MMCs), as the name implies, have a metal matrix.
Examples of matrices in such composites 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. For
example, the elastic stiffness and strength of metals can be increased, and large
coefficients of thermal expansion and thermal and electric conductivities of metals
can be reduced, by the addition of fibers such as silicon carbide.
What are the advantages of metal matrix composites?
Metal matrix composites are mainly used to provide advantages over monolithic
metals such as steel and aluminum. These advantages include higher specific
strength and modulus by reinforcing low-density metals, such as aluminum and
titanium; lower coefficients of thermal expansion by reinforcing with fibers with low
coefficients of thermal expansion, such as graphite; and maintaining properties such
as strength at high temperatures. MMCs have several advantages over polymer
matrix composites. These include higher elastic properties; higher service
temperature; insensitivity to moisture; higher electric and thermal conductivities;
and better wear, fatigue, and flaw resistances. The drawbacks of MMCs over PMCs
include higher processing temperatures and higher densities.
Do any properties degrade when metals are reinforced with fibers?
Yes, reinforcing metals with fibers may reduce ductility and fracture toughness.
Ductility of aluminum is 48% and it can decrease to below 10% with simple
reinforcements of silicon carbide whiskers. The fracture toughness of aluminum
alloys is 18.2 to 36.4 ksi 𝑖𝑛(20 to 40 ksi 𝑖𝑛 ) and it reduces by 50% or more when
reinforced with silicon fibers.
Show one process of how metal matrix composites are manufactured.
Fabrication methods for MMCs are varied. One method of manufacturing them is
diffusion bonding (Figure 1.28), which is used in manufacturing boron/aluminum
composite parts (Figure 1.29). A fiber mat of boron is placed between two thin
aluminum foils about 0.002 in. (0.05 mm) thick. A polymer binder or an acrylic
adhesive holds the fibers together in the mat. Layers of these metal foils are stacked at
angles as required by the design. The laminate is first heated in a vacuum bag to
remove the binder. The laminate is then hot pressed with a temperature of about
932°F (500°C) and pressure of about 5 ksi (35 MPa) in a die to form the required
machine element.

18-Apr-16
89
What are some of the applications of metal matrix composites?
Metal matrix composites applications are
• Space: The space shuttle uses boron/aluminum tubes to support its fuselage
frame. In addition to decreasing the mass of the space shuttle by more than 320
lb (145 kg), boron/aluminum also reduced the thermal insulation requirements
because of its low thermal conductivity. The mast of the Hubble Telescope uses
carbon-reinforced aluminum.
• Military: Precision components of missile guidance systems demand
dimensional stability — that is, the geometries of the components cannot
change during use. Metal matrix composites such as SiC/aluminum composites
satisfy this requirement because they have high micro yield strength. In
addition, the volume fraction of SiC can be varied to have a coefficient of
thermal expansion compatible with other parts of the system assembly.
• Transportation: Metal matrix composites are finding use now in automotive
engines that are lighter than their metal counterparts. Also, because of their
high strength and low weight, metal matrix composites are the material of
choice for gas turbine engines (Figure 1.30).

18-Apr-16
90
Ceramic Matrix Composites
What are metal matrix composites?
Ceramic matrix composites (CMCs) have a ceramic matrix such as alumina
calcium alumino silicate reinforced by fibers such as carbon or silicon carbide.
What are the advantages of ceramic matrix composites?
Advantages of CMCs include high strength, hardness, high service temperature
Limits for ceramics, chemical inertness, and low density. However, ceramics by themselves
have low fracture toughness. Under tensile or impact loading, they fail catastrophically.
Reinforcing ceramics with fibers, such as silicon carbide or carbon, increases their fracture
toughness because it causes gradual failure of the composite. This combination of a fiber
and ceramic matrix makes CMCs more attractive for applications in which high mechanical
properties and extreme service temperatures are desired.
Ceramic Matrix Composites
Show one process of how ceramic matrix composites are manufactured.
One of the most common methods to manufacture ceramic matrix composites is called the
hot pressing method.28 Glass fibers in continuous tow are passed through slurry consisting
of powdered matrix material, solvent such as alcohol, and an organic binder (Figure 1.31).
The tow is then wound on a drum and dried to form prepreg tapes. The prepreg tapes can
now be stacked to make a required laminate. Heating at about 932°F (500°C) burns
out the binder. Hot pressing at high temperatures in excess of 1832°F (1000°C) and
pressures of 1 to 2 ksi (7 to 14 MPa) follows this.

18-Apr-16
91
Please read out information on
Sandwich and Laminate
Composites

Composite matierals lecture 2

More Related Content

What's hot

Similar to Composite matierals lecture 2

More from University of the Punjab, Lahore, Pakistan

Recently uploaded

Composite matierals lecture 2