3. HISTORY OF COMPOSITES
The earliest man-made composite materials
were straw and mud combined to
form bricks for building construction. Ancient brick-making was
documented by Egyptian tomb paintings.
Wattle and daub is one of the oldest man-made composite materials,
at over 6000 years old .Concrete is also a composite material, and is
used more than any other man-made material in the world. As of 2006,
about 7.5 billion cubic metres of concrete are made each year—
more than one cubic metre for every person on Earth.
Woody plants, both true wood from trees and such plants
as palms and bamboo, yield natural composites that were used
prehistorically by mankind and are still used widely in construction
and scaffolding.
Plywood 3400 BC by the Ancient Mesopotamians; gluing wood at
different angles gives better properties than natural wood.
Cartonnage layers of linen or papyrus soaked in plaster dates to
the First Intermediate Period of Egypt c. 2181–2055 BC and was used
for death masks.
4. HISTORY OF COMPOSITES
Papier-mache, a composite of paper and glue, has been used
for hundreds of years.
The first artificial fibre reinforced plastic was bakelite
(thermosetting phenol formaldehyde resin) which dates to 1907,
although natural polymers such as shellac predate it.
One of the most common and familiar composite
is fibreglass, in which small glass fibre are embedded within
a polymeric material (normally an epoxy or polyester). The
glass fibre is relatively strong and stiff (but also brittle),
whereas the polymer is ductile (but also weak and flexible).
Thus the resulting fibreglass is relatively stiff, strong, flexible,
and ductile.
5. ADVANTAGES OF COMPOSITE
Reason to use composite material:-
I. Higher specific strength than metals, non-metals
and even alloys.
II. Lower specific gravity in general.
III. Improved stiffness of material.
IV. Composite maintain their weight even at high
temperatures.
V. Toughness is improved.
VI. Fabrication or production is cheaper.
VII. Creep and fatigue strength is better.
VIII. Controlled Electrical conductivity is possible.
IX. Corrosion and oxidation resistance.
6. Composite Material Diagnosed
• A composite material is made by combining two or more materials –
often ones
that have very different properties.
• The two materials work together to give the composite unique
properties.
• However, within the composite you can easily tell the different materials
apart as they do not dissolve or blend into each other.
9. Definition:
They generally have two phases:-
1. Matrix Phase.
2. Dispersion Phase.
• Matrix Phase :-
It is the continuous material constituent
which encloses the composite and give it its bulk form.
Matrix phase may be metal , ceramic or polymer.
• Reinforcement Phase:-
It is the structure constituent , which
determines the internal structure of composite.
Reinforcement is connected to matrix phase by bonding
10. Matrix
• Made from metal, polymer or cferamic.
• Continues phase.
• Some ductility is desirable.
• Functions:
• Binds the reinforcement together.
• Mechanically support reinforcements.
• Load transfer to the reinforcements.
• Protect the reinforcement from surface damage
dye to abrasion or chemical cracks.
• High bonding strength between fiber and matrix is
important.
•Types:
•Thermo-set
•Thermo-plastic
11. Thermo-set Matrix
A Thermo-set matrix is formed by the irreversible chemical
transformation of a resin system into an amorphous cross-linked
polymer matrix.
The polymer is called resin system during processing and
matrix after the polymer has cured.
Resin: a solid or liquid synthetic organic polymer used as the
basis of plastics, adhesives, varnishes, or other products.
Thermosetting resins have low viscosity which allows for
excellent impregnation of the fiber reinforcement and high
processing speeds.
Shelf life: is the time the unmixed resin system can be stored
without degredation. (Refrigerated storage is usually
recommended)
Pot life or gel time: is the time the mixed resin can be handled
before the viscosity grows to a point where processing is no
longer possible.
12. Polyester Resins
unsaturated polyester
heat
free radical
initiator
* Cross linking can be accomplished at room temperature using suitable activators.
• Polyester resins can be used in many
outdoor applications. Superior durability,
color retention and resistance to fiber
erosion can be obtained when styrene-MMA
monomer blends are used.
• MMA-polyesters have refractive index
matched to that of glass fibers allowing to
prepare transparent building panels.
• Polyester resins are considered low cost
resins.
13. Vinyl Ester Resins
advantages over unsaturated polyesters :
•They don't absorb as much water,
•They don't shrink nearly as much when cured.
•They have very good chemical resistance.
•Because of the hydroxyl groups, it bonds well to glass.
It is a common resin in the marine industry due to its increased corrosion
resistance and ability to withstand water absorption.
14. Epoxy Resins
• Because of all those hydroxyl groups, epoxy resins can bond
well to glass fibers.
• Epoxies shrink less than other materials when they're cured
(1.2-4% by volume).
• Epoxy resins are widely used because of their high mechanical
properties and high corrosion resistances.
• Epoxy systems are used in applications like aerospace,
defense, marine, sports equipment. They are also used as
adhesives, body solders (lehim), sealant and casting
compounds. Besides, they have a wide range of uses in the
electrical business because of their excellent electrical
insulation.
15. Phenolic Resins
Used as molded disc brake
cylinders, saucepan handles,
electrical plugs and
switches, parts for electrical
irons and
interiorconstruction
materials of aircraft and
mass transit vehicles where
smoke production must be
extremely low.
• Phenolic resins have low flammability and low smoke production
compared with other low-cost resins.
• They have good dimensional stability under temperature
fluctuations and good adhesive properties.
• Cost of phenolic resins is competitive with polyesters. Disadvantages of
these resins include high curing temperatures and pressures, longer curing
times than polyesters, and limited color range.
16. • Unlike the curing process of thermosetting resins, the processing of
thermoplastics is reversible, and, by simply reheating to the process
temperature, the resin can be formed into another shape if desired.
• Thermoplastics have high viscosity at processing temperatures, which
makes them more difficult to process. The high shear stresses needed to
make thermoplastic flow cause damage to the fibers resulting in a
reduction of fiber length. Since, impregnation is impaired by high viscosity,
special care must be taken to assure contact between the fibers and the
polymer.
• Thermoplastics do not require refrigerated storage.
• Have unlimited shelf or pot life.
• Thermoplastics, although generally inferior to thermosets in high-
temperature strength and chemical stability, are more resistant to
cracking and impact damage. However, it should be noted that recently
developed high-performance thermoplastics or engineering
thermoplastics, such as PEEK, exhibit excellent high temperature
strength and solvent resistance.
Thermoplastic Matrices
17. Poly ether ether ketone (PEEK)
• The most common thermoplastic matrix for high performance
applications.
• Have a semi-crystalline microstructure with very low water absorption
(0.5% by weight) at room temperature, much lower than for most epoxies.
• PEEK has a glass transition temperature of around 143°C and melts around
343°C. The operating temperature is around 250°C (operating temperature
for brittle epoxies is ̴250°C and toughened epoxies between 75-185°C).
• CF/PEEK is shown to be more than 10 times tougher than CF/epoxy.
18. Polysulfones
• Amorphous thermoplastic.
• Excellent stability under hot and wet conditions.
• Their high hydrolysis stability allows their use in medical applications
requiring autoclave and steam sterilization.
• They rated as self-extinguishing, with low smoke and toxic fume
generation.
• PS has a glass transition temperature of around 185°C and the
operating temperature is around 165°C.
• Due to the high cost of raw materials and processing, polysulfones are
used in specialty applications.
• Not UV-stable .
19. Polyimides
• Amorphous thermoplastics
with high glass transition
temperatures.
•Polyamide-imides have
exceptional mechanical,
thermal and chemical resistant
properties. These properties put
polyamide-imides at the top of
the price and performance
pyramid.
•PAI has low processability .
20. Reinforcement
• A reinforcement is the strong and stiff intigral componrent which is incorporated into
matrix to achive desired properties.
• The term reinforcement implies some property enhancement.
• Reinforcement may be of any shape ranging from irregular to regular.
• these have low ductility.
• Types:
•Filament: a single thread like fiber
•Roving: a bundle of filaments wound to form a large strand
•Mesopotamians : assembled from chopped filaments bound with a binder
•Continuous filament random mat: assembled from continuous filaments bound
with a binder
•Many varieties of woven fabrics: woven from rovings.
27. Fiber reinforced composites provide improved strength, fatigue
resistance, Young’s modulus and strength to weight ratio over the
constituent materials.
This is achieved by incorporating strong, stiff, yet brittle fibers into
a more ductile matrix.
Generally speaking the fiber supplies the strength and stiffness
while the matrix binds the fibers together and provides a means of
transferring the load between fibers.
The matrix also provides protection for the fibers.
FIBER REINFORCED
COMPOSITES
28. Many factors must be considered when designing a fiber-reinforced
composite including the length, diameter, orientation, amount and
properties of the constituents, and the bonding between them.
The method used to produce the final product is also very important as it
dictates the type of properties just mentioned as well as the quality of the
product.
CHARACTERISTICS OF FIBER
REINFORCED COMPOSITES
29. Fiber length and diameter: Fiber dimensions are characterized
by their aspect ratio l/d where l is the fiber length and d is the
diameter.
The strength improves when the aspect ratio is large.
Typical fiber diameters are from 10 mm to 150 mm.
Fibers often fracture because of surface imperfections.
Making the diameter small reduces its surface area, which
has fewer flaws.
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.
CHARACTERISTICS OF FIBER
REINFORCED COMPOSITES
30. As can be seen
from this plot, the
strength of the
composite
increases as the
fiber length
increases .
(this is a chopped
E-glass-epoxy
composite)
CHARACTERISTICS OF FIBER
REINFORCED COMPOSITES
31. Maximum strength is
obtained when long fibers are
oriented parallel to the
applied load.
The effect of fiber
orientation and strength can
be seen in the plot.
FIBER ORIENTATION
32. The properties of fiber
composites can be tailored to
meet different loading
requirements.
By using combinations of
different fiber orientation
quasi-isotropic materials
may be produced.
FIBER ORIENTATION
Figure (a) shows a unidirectional arrangement
Figure (b) shows a quasi-isotropic arrangement
33. A three dimensional weave
is also possible.
This could be found when
fabrics are knitted or weaved
together .
FIBER ORIENTATION
34. In most fiber-reinforced composites, the fibers are strong, stiff and
lightweight.
If the composite is to used at elevated temperatures, the fiber should
also have a high melting temperature.
The specific strength and specific modulus of fibers are important
characteristics given by:
FIBER PROPERTIES
TS
StrengthSpecific
E
modulusSpecific
Where TS is the tensile strength, E is the elastic modulus and r is the
density.
35. On the left is a graph showing
specific strength vs. specific
modulus for different types of
fibers
FIBER PROPERTIES
36. Due to the relatively inexpensive cost glass fibers are the most
commonly used reinforcement
There are a variety of types of glass, they are all compounds of silica
with a variety of metallic oxides
GLASS FIBERS
Designation: Property or Characteristic:
E, electrical low electrical conductivity
S, strength high strength
C, chemical high chemical durability
M, modulus high stiffness
A, alkali high alkali or soda lime glass
D, dielectric low dielectric constant
• The most commonly used glass is E-glass, this is the most
popular because of it’s cost.
37. Carbon fibers have gained a lot of popularity in the last two decades
due to the price reduction.
“Carbon fiber composites are five times stronger than 1020 steel
yet five times lighter. In comparison to 6061 aluminum, carbon fiber
composites are seven times stronger and two times stiffer yet still 1.5
times lighter”.
Initially used exclusively by the aerospace industry they are becoming
more and more common in fields such as automotive, civil
infrastructure, and paper production.
CARBON FIBERS
53. Dispersion strengthened alloys can be considered as
composites because there is little or no interaction between the
two components and the reinforcement is not soluble in the
metal matrix.
The dispersoids are usually 10-250 nm diameter oxide particles
and are introduced by physical means rather than chemical
precipitation.
They are located within the grains and at grain boundaries but
are not coherent with the matrix as in precipitation hardening.
The dispersed particles are sufficiently small in size to impede
dislocation movement and thus improve yield strength as well as
stiffness.
Dispersion strengthened alloys are somewhat weaker than
precipitation hardened alloys at room temperature but since
overaging, tempering, grain growth or particle coarsening do
not occur on heating, they are stronger and more creep
resistant at high temperatures.
DISPERSION STRENGTHENED
MMC’S
54. Properties of SAP
compared to 2024-T8,
7075-T6 and a boron
fiber strengthened
1100 alloy.
SINTERED ALUMINUM POWDER (SAP)
COMPOSITES
55. An important group of dispersion-strengthened composites is thoria-
dispersed (TD) metals
Thorium is an element on the periodic table (atomic number 90)
THORIA-DISPERSED
COMPOSTIES
A common example is TD-nickel
TD-nickel composites produced by:
Powders of metallic Th and Ni are
ball milled, compacted at high pressure
and then sintered.
The compact is then heated in air and
oxygen diffuses in to react with Th metal
to form a fine dispersion of ThO2.
This method, internal oxidation is also
used for fabricating the W-ThO2
composites.
Electron micrograph of TD-Ni with 300
nm diameter ThO2 particles (X2000)
56. Cemented carbides are an example of regular particulate MMC’s (as
opposed to dispersion strengthened MMC’s).
Carbides such as WC (tungsten-carbide) are used for cutting tool inserts
but this hard ceramic is very brittle so it cracks or chips under impact loads,
to remedy this cobalt is used as a matrix.
Co-WC (cobalt tungsten-carbide) cermets are produced by pressing Co and
W powders into compacts, which are heated above the melting point of Co.
On cooling the carbide particles become embedded in the solidified Co, which
act as a tough matrix for the WC particles.
In addition to its strength and toughness, Co is also selected because it wets the
carbide particles to give a strong bond.
CEMENTED CARBIDES
(CERMETS)
57. -Cemented carbides are commonly used as inserts for
cutting tools
-I’m sure you’ve seen these in the machine shop
CEMENTED CARBIDES
(CERMETS)
Figure (from left to right):
Cutting tool inserts, a
milling tool and a lathe tool
58. Electrical contacts used in switches, relays and
motors must be quite wear resistant to stand up in
service .
Highly conductive metals such as Cu and Ag are
relatively soft and thus show excessive wear when used
as contacts resulting in arcing and poor electrical
conduction.
The goal is to produce a contact that is both a good
conductor and has excellent wear properties.
This is done by using silver reinforced with tungsten
particles, the Ag is a terrific conductor while the W
provides good wear properties.
PARTICULATE MMC’S FOR ELECTRICAL
CONTACTS
59. The composite is made in two stages:
First a low density compact with
interconnected pores is produced by pressing
and firing tungsten powders (figure a and b.)
Liquid silver is then infiltrated into the
connected voids under vacuum (figure c).
PARTICULATE MMC’S FOR ELECTRICAL
CONTACTS
The final product has a continuous Ag and W structure which provides
good electrical conductivity and wear resistance.
(c)(b)
60. Al alloys for automotive connecting rods and pistons can be
strengthened and hardened by the addition of SiC (silicon carbide)
particles.
The SiC particles are introduced at a temperature at which the alloy is
in the solid plus liquid state, ie., by “compocasting”.
CAST METAL PARTICULATE
MMC’S
61. Compocasting of Al-SiC:
Partially solidified alloy is stirred to break up dendrites (fig.
a)
Particles of SiC are added at this temperature (fig. b)
In a pressure die casting machine, the solid mixture
becomes thixotropic to form a high density casting (fig. c)
CAST METAL PARTICULATE
MMC’S
62. Microstructure of cast Al Alloy reinforced with particles of SiC
magnified X125
CAST METAL PARTICULATE
MMC’S
63. RULE OF MIXTURES
For particulate composites, the rule of mixtures predicts the
density of the composite as well as other properties
(although other properties may vary depending on how the
dispersed phase is arranged)
Density, , is given as a fraction, f, as:
ffmmc ff
Where the subscripts m and f refer to the matrix and fiber.
fm ff 1thatNote
64. RULE OF MIXTURES
• In a composite material with a metal matrix and ceramic
fibers, the bulk of the energy would be transferred through
the matrix.
• In a composite consisting of a polymer matrix containing
metallic fibers, the energy would be transferred through the
fibers.
• When the fibers are not continuous or unidirectional, the
simple rule of mixtures may not apply.
• For example, in a metal fiber-polymer matrix composite,
electrical conductivity would be low and would depend on
the length of the fibers, the volume fraction of fibers and
how often the fibers touch one another.
67. Composite products range from skateboards to components of the space
shuttle. The industry can be generally divided into two basic segments:
• industrial composites
• advanced composites
Industrial Composites. The industrial
composites industry has been in place for over
40 years in the world. This large industry
utilizes various resin systems including
polyester, epoxy, and other specialty resins.
These materials, along with a catalyst or curing
agent and some type of fiber reinforcement
(typically glass fibers) are used in the
production of a wide spectrum of industrial
components and consumer goods: boats,
piping, auto bodies, and a variety of other
parts and components.
Composite Products
The distinction is based on the level of mechanical properties. Materials
within these categories are often called "advanced" if they combine the
properties of high strength and high stiffness, low weight and corrosion
resistance.
68. Advanced Composites : Advanced composites industry is
characterized by the use of expensive, high-performance resin
systems and high-strength, high-stiffness fiber reinforcement.
The aerospace industry, including military and commercial
aircraft is the major customer for advanced composites. These
materials have also been adopted for use by the sporting goods
suppliers who sell high-performance equipment to the golf,
tennis, fishing, and archery markets.
While aerospace is the predominant market for advanced
composites today, the industrial and automotive markets will
increasingly see the use of advanced composites.
Surfboard with carbon nanotube
reinforced epoxies
69. BMW M6 with carbon fibre roof Glass/polyamide bumper beam for BMW M3
• Also BMW goes for composites. The BMW M6 has an overall
weight of only 1710 kg. The composite roof is 6 kg lighter than a
conventional steel roof.
• In the BMW M3 model, the aluminium bumper beam has been
replaced by a glass/polyamide bumper beam. A weight reduction
from 7 kg to 3.1 kg was realized, and its crash performance was
three to four times better than the metal beam.
70.
71. • CMCs: Increased toughness
Composite Benefits
fiber-reinf
un-reinf
particle-reinf
Force
Bend displacement
• PMCs: Increased E/
E(GPa)
G=3E/8
K=E
Density, [mg/m3]
.1 .3 1 3 10 30
.01
.1
1
10
102
103
metal/
metal alloys
polymers
PMCs
ceramics
Adapted from T.G. Nieh, "Creep rupture of a
silicon-carbide reinforced aluminum
composite", Metall. Tith permission.
• MMCs:
Increased
creep
resistance
20 30 50 100 200
10-10
10-8
10-6
10-4
6061 Al
6061 Al
w/SiC
whiskers
s(MPa)
ess(s-1)
72. Composite Survey: Particle-I
• Examples:
Adapted from Fig.
10.19, Callister 7e.
(Fig. 10.19 is
copyright United
States Steel
Corporation, 1971.)
- Spheroidite
steel
matrix:
ferrite (a)
(ductile)
particles:
cementite
(Fe3C)
(brittle)
60mm
Adapted from Fig.
16.4, Callister 7e.
(Fig. 16.4 is courtesy
Carboloy Systems,
Department, General
Electric Company.)
- WC/Co
cemented
carbide
matrix:
cobalt
(ductile)
particles:
WC
(brittle,
hard)Vm:
5-12 vol%! 600mm
Adapted from Fig.
16.5, Callister 7e.
(Fig. 16.5 is courtesy
Goodyear Tire and
Rubber Company.)
- Automobile
tires
matrix:
rubber
(compliant)
particles:
C
(stiffer)
0.75mm
Particle-reinforced Fiber-reinforced Structural
73. Composite Survey: Particle-II
Concrete – gravel + sand + cement
- Why sand and gravel? Sand packs into gravel voids
Reinforced concrete - Reinforce with steel rebar or remesh
- increases strength - even if cement matrix is cracked
Prestressed concrete - remesh under tension during setting of
concrete. Tension release puts concrete under compressive force
- Concrete much stronger under compression.
- Applied tension must exceed compressive force
Particle-reinforced Fiber-reinforced Structural
threaded
rodnut
Post tensioning – tighten nuts to put under rod under tension
but concrete under compression
74. • Elastic modulus, Ec, of composites:
-- two approaches.
• Application to other properties:
-- Electrical conductivity, se: Replace E in the above equations
with se.
-- Thermal conductivity, k: Replace E in above equations with k.
Adapted from Fig. 16.3,
Callister 7e. (Fig. 16.3 is
from R.H. Krock, ASTM
Proc, Vol. 63, 1963.)
Composite Survey: Particle-III
lower limit:
1
Ec
=
Vm
Em
+
Vp
Ep
c m m
upper limit:
E = V E + VpEp
“rule of mixtures”
Particle-reinforced Fiber-reinforced Structural
Data:
Cu matrix
w/tungsten
particles
0 20 40 60 80 100
150
200
250
300
350
vol% tungsten
E(GPa)
(Cu) (W)
75. Composite Survey: Fiber
• Fibers themselves are very strong
– Provide significant strength improvement to
material
– Ex: fiber-glass
• Continuous glass filaments in a polymer matrix
• Strength due to fibers
• Polymer simply holds them in place and
environmentally protects them
Particle-reinforced Fiber-reinforced Structural
77. • Critical fiber length (lC) for effective stiffening & strengthening:
• Ex: For fiberglass, a fiber length > 15 mm is needed since this length
provides a “Continuous fiber” based on usual glass fiber properties
Composite Survey: Fiber
Particle-reinforced Fiber-reinforced Structural
c
f d
s
15lengthfiber
fiber diameter
shear strength of
fiber-matrix interface
fiber strength in tension
• Why? Longer fibers carry stress more efficiently!
Shorter, thicker fiber:
c
f d
s
15lengthfiber
Longer, thinner fiber:
Poorer fiber efficiency
Adapted from Fig.
16.7, Callister 7e.
c
f d
s
15lengthfiber
Better fiber efficiency
s(x) s(x)
79. Composite Survey: Fiber
• Fiber Materials
– Whiskers - Thin single crystals - large length to diameter ratio
• graphite, SiN, SiC
• high crystal perfection – extremely strong, strongest known
• very expensive
Particle-reinforced Fiber-reinforced Structural
– Fibers
• polycrystalline or amorphous
• generally polymers or ceramics
• Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE
– Wires
• Metal – steel, Mo, W
82. Composite Strength: Longitudinal Loading
Continuous fibers - Estimate fiber-reinforced
composite strength for long continuous fibers in a
matrix
Longitudinal deformation
sc = smVm + sfVf but ec = em = ef
volume fraction isostrain
Ece = Em Vm + EfVf longitudinal (extensional)
modulus
mm
ff
m
f
VE
VE
F
F
f = fiber
m = matrix
Remembering: E = s/e
and note, this model
corresponds to the
“upper bound” for
particulate composites
83. Composite Strength: Transverse Loading
In transverse loading the fibers carry less of the
load and are in a state of ‘isostress’
sc = sm = sf = s ec= emVm + efVf
f
f
m
m
ct E
V
E
V
E
1
transverse modulus
Remembering: E = s/e
and note, this model
corresponds to the “lower
bound” for particulate
composites
84. An Example:
Note: (for ease of conversion)
6870 N/m2 per psi!
UTS, SI Modulus, SI
57.9 MPa 3.8 GPa
2.4 GPa 399.9 GPa
(241.5 GPa)
(9.34 GPa)
85. • Estimate of Ec and TS for discontinuous fibers:
-- valid when
-- Elastic modulus in fiber direction:
-- TS in fiber direction:
efficiency factor:
-- aligned 1D: K = 1 (aligned )
-- aligned 1D: K = 0 (aligned )
-- random 2D: K = 3/8 (2D isotropy)
-- random 3D: K = 1/5 (3D isotropy)
(aligned 1D)
Values from Table 16.3, Callister 7e.
(Source for Table 16.3 is H. Krenchel,
Fibre Reinforcement, Copenhagen:
Akademisk Forlag, 1964.)
Composite Strength
c
f d
s
15lengthfiber
Particle-reinforced Fiber-reinforced Structural
(TS)c = (TS)mVm + (TS)fVf
Ec = EmVm + KEfVf
86. • Aligned Continuous fibers
• Examples:
From W. Funk and E. Blank, “Creep
deformation of Ni3Al-Mo in-situ
composites", Metall. Trans. A Vol. 19(4), pp.
987-998, 1988. Used with permission.
-- Metal: g'(Ni3Al)-a(Mo)
by eutectic solidification.
Composite Survey: Fiber
Particle-reinforced Fiber-reinforced Structural
matrix: a (Mo) (ductile)
fibers: g’ (Ni3Al) (brittle)
2mm
-- Ceramic: Glass w/SiC fibers
formed by glass slurry
Eglass = 76 GPa; ESiC = 400 GPa.
(a)
(b)
fracture
surface
From F.L. Matthews and R.L.
Rawlings, Composite Materials;
Engineering and Science, Reprint
ed., CRC Press, Boca Raton, FL,
2000. (a) Fig. 4.22, p. 145 (photo by
J. Davies); (b) Fig. 11.20, p. 349
(micrograph by H.S. Kim, P.S.
Rodgers, and R.D. Rawlings). Used
with permission of CRC
Press, Boca Raton, FL.
87. • Discontinuous, random 2D fibers
• Example: Carbon-Carbon
-- process: fiber/pitch, then
burn out at up to 2500ºC.
-- uses: disk brakes, gas
turbine exhaust flaps, nose
cones.
• Other variations:
-- Discontinuous, random 3D
-- Discontinuous, 1D
Composite Survey: Fiber
Particle-reinforced Fiber-reinforced Structural
(b)
fibers lie
in plane
view onto plane
C fibers:
very stiff
very strong
C matrix:
less stiff
less strong
(a)
efficiency factor:
-- random 2D: K = 3/8 (2D isotropy)
-- random 3D: K = 1/5 (3D isotropy)
Ec = EmVm + KEfVf
88. Looking at strength:
'
'
'
'
where is fiber fracture strength
& is matrix stress when composite fails
where: d is fiber diameter &
is smaller of Matrix Fiber shea
1 1
2
1
f
m
C
C
C
cd f f m f
C
C
cd f m f
l l
l
V V
l
l l
l
V V
d
s
s
s s s
s s
r strength
or matrix shear yield strength
89. • Stacked and bonded fiber-reinforced sheets
-- stacking sequence: e.g., 0º/90º or 0/45/90º
-- benefit: balanced, in-plane stiffness
Adapted from Fig.
16.16, Callister 7e.
Composite Survey: Structural
Particle-reinforced Fiber-reinforced Structural
• Sandwich panels
-- low density, honeycomb core
-- benefit: light weight, large bending stiffness
honeycomb
adhesive layer
face sheet
Adapted from Fig. 16.18,
Callister 7e. (Fig. 16.18 is
from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)
90. The method of manufacturing composites is very important to the
design and outcome of the product.
With traditional materials one starts out with a blank piece of material
ie: rod, ingot, sheet, etc and works it to produce the desired part.
However, this is not the case with polymer-matrix composites.
With these composites the material and the component are being
produced at the same time, therefore we aim for the product to be a net or
near net shape with little to no post processing.
MANUFACTURING OF
COMPOSITES
91. MANUFACTURING OF
COMPOSITES
Description:
Resins are impregnated by hand into fibres which are in the form of woven,
knitted, stitched or bonded fabrics. This is usually accomplished by rollers or brushes,
with an increasing use of nip-roller type impregnators for forcing resin into the fabrics by
means of rotating rollers and a bath of resin. Laminates are left to cure under standard
atmospheric conditions.
Wet/Hand Lay-up
Materials Options:
• Resins: Any, e.g. epoxy, polyester,
• vinylester, phenolic
•Fibres: Any, although heavy aramid
•fabrics can be hard to wet-out by hand.
•Cores: Any.
Typical Applications:
Standard wind-turbine blades,
production
boats, architectural mouldings.
92. MANUFACTURING OF
COMPOSITESWet/Hand Lay-up
Advantages:
•Widely used for many years.
•Simple principles to teach.
•Low cost tooling, if room-temperature cure resins are used.
•Wide choice of suppliers and material types.
•Higher fibre contents and longer fibres than with spray lay-up.
Disadvantages:
•Resin mixing, laminate resin contents, and laminate quality are very dependent on
the skills of laminators. Low resin content laminates cannot usually be achieved
without the incorporation of excessive quantities of voids.
•Health and safety considerations of resins. The lower molecular weights of hand
lay-up resins generally mean that they have the potential to be more harmful than
higher molecular weight products. The lower viscosity of the resins also means that
they have an increased tendency to penetrate clothing.
•Limiting airborne styrene concentrations to legislated levels from polyesters and
vinylesters is becoming increasingly hard without expensive extraction systems.
•Resins need to be low in viscosity to be workable by hand. This generally
compromises their mechanical/thermal properties due to the need for high
diluent/styrene levels.
93. Spray Lay-Up
MANUFACTURING OF
COMPOSITES
Description:
Fibre is chopped in a hand-held gun and fed into a spray of catalyzed
resin directed at the mould. The deposited materials are left to cure under
standard atmospheric conditions.
Material Options:
•Resins: Primarily polyester
•Fibres: Glass roving only
•Cores: None. These have to be
• incorporated separately
94. MANUFACTURING OF
COMPOSITES
Typical Applications:
Simple enclosures, lightly loaded structural panels, e.g. caravan bodies,
truck fairings, bathtubs, shower trays, some small dinghies.
Advantages:
•Widely used for many years.
•Low cost way of quickly depositing fibre and resin.
•Low cost tooling.
Disadvantages:
•Laminates tend to be very resin-rich and therefore excessively heavy.
•Only short fibres are incorporated which severely limits the mechanical
properties of the laminate.
•Resins need to be low in viscosity to be sprayable. This generally compromises
their mechanical/thermal properties.
•The high styrene contents of spray lay-up resins generally mean that they have
the potential to be more harmful and their lower viscosity means that they have
an increased tendency to penetrate clothing.
•Limiting airborne styrene concentrations to legislated levels is becoming
increasingly difficult.
Spray Lay-Up
95.
96. Description:
This is basically an extension of
the wet lay-up process described above
where pressure is applied to the laminate
once laid-up in order to improve its
consolidation. This is achieved by
sealing a plastic film over the wet laid-up
laminate and onto the tool. The air under
the bag is extracted by a vacuum pump
and thus up to one atmosphere of
pressure can be applied to the laminate
to consolidate it.
MANUFACTURING OF
COMPOSITESVacuum Bagging
Materials Options:
•Resins: Primarily epoxy and phenolic. Polyesters and vinylesters may
have problems due to excessive extraction of styrene from the resin by the
vacuum pump.
•Fibres: The consolidation pressures mean that a variety of heavy fabrics
can be wet-out.
•Cores: Any.
97. Typical Applications:
Large, one-off cruising boats, racecar components, core-bonding in
production boats.
Advantages:
•Higher fibre content laminates can usually be achieved than with standard
wet lay-up techniques.
•Lower void contents are achieved than with wet lay-up.
•Better fibre wet-out due to pressure and resin flow throughout structural
fibres, with excess into bagging materials.
•Health and safety: The vacuum bag reduces the amount of volatiles
emitted during cure.
Disadvantages:
•The extra process adds cost both in labour and in disposable bagging
materials.
•A higher level of skill is required by the operators.
•Mixing and control of resin content still largely determined by operator skill.
MANUFACTURING OF
COMPOSITES
Vacuum Bagging
98.
99. MANUFACTURING OF
COMPOSITESFilament Winding
Materials Options:
•Resins: Any, e.g. epoxy, polyester, vinylester, phenolic
•Fibres: Any. The fibres are used straight from a creel and not woven or
stitched into a fabric form
•Cores: Any, although components are usually single skin
Typical Applications:
Chemical storage tanks and pipelines, gas cylinders, fire-fighters
breathing tanks
Description:
This process is primarily used for
hollow, generally circular or oval seoned
components, such as pipes and tanks.
Fibre tows are passed through a resin
bath before being wound onto a mandrel
in a variety of orientations, controlled by
the fibre feeding mechanism, and rate of
rotation of the mandrel.
100. Advantages:
•This can be a very fast and therefore economic method of laying material
down.
•Resin content can be controlled by metering the resin onto each fibre tow
through nips or dies.
•Fibre cost is minimised since there is no secondary process to convert
fibre into fabric prior to use.
•Structural properties of laminates can be very good since straight fibres
can be laid in a complex pattern to match the applied loads.
Disadvantages:
•The process is limited to convex shaped components.
•Fibre cannot easily be laid exactly along the length of a component.
•Mandrel costs for large components can be high.
•The external surface of the component is unmoulded, and therefore
cosmetically unattractive.
•Low viscosity resins usually need to be used with their attendant lower
mechanical and health and safety properties.
MANUFACTURING OF
COMPOSITESFilament Winding
101.
102. MANUFACTURING OF
COMPOSITES
Description:
Fibres are pulled from a creel through a resin bath and then on through a heated die.
The die completes the impregnation of the fibre, controls the resin content and cures the
material into its final shape as it passes through the die. This cured profile is then
automatically cut to length. Fabrics may also be introduced into the die to provide fibre
direction other than at 0°. Although pultrusion is a continuous process, producing a
profile of constant cross-section, a variant known as 'pulforming' allows for some
variation to be introduced into the cross-section. The process pulls the materials through
the die for impregnation, and then clamps them in a mould for curing. This makes the
process non-continuous, but accommodating of small changes in cross-section.
Material Options:
Resins: Generally epoxy, polyester,v
inylester and phenolic
Fibres: Any
Cores: Not generally used
Pultrusion
103. MANUFACTURING OF
COMPOSITES
Pultrusion
Typical Applications:
Beams and girders used in roof structures, bridges, ladders, frameworks
Advantages:
This can be a very fast, and therefore economic, way of impregnating and
curing materials.
Resin content can be accurately controlled.
Fibre cost is minimised since the majority is taken from a creel.
Structural properties of laminates can be very good since the profiles have
very straight fibres and high fibre volume fractions can be obtained.
Resin impregnation area can be enclosed thus limiting volatile emissions.
Disadvantages:
Limited to constant or near constant cross-section components.
Heated die costs can be high.
104.
105. Description:
Fabrics are laid up as a dry stack of materials. These fabrics are
sometimes pre-pressed to the mould shape, and held together by a binder.
These 'preforms' are then more easily laid into the mould tool. A second mould
tool is then clamped over the first, and resin is injected into the cavity. Vacuum
can also be applied to the mould cavity to assist resin in being drawn into the
fabrics. This is known as Vacuum Assisted Resin Injection (VARI). Once all the
fabric is wet out, the resin inlets are closed, and the laminate is allowed to cure.
Both injection and cure can take place at either ambient or elevated
temperature.
MANUFACTURING OF
COMPOSITES
Material Options:
Resins: Generally epoxy, polyester,
vinylester and phenolic, although high
temperature resins such as bismaleimides can be
used at elevated process temperatures.
Fibres: Any. Stitched materials work well in this
process since the gaps allow rapid resin
transport. Some specially developed fabrics can
assist with resin flow
Cores: Not honeycombs, since cells would fill
with resin, and pressures involved can crush
some foams
Resin Transfer Molding
107. Typical Applications:
Small complex aircraft and automotive components, train seats.
Main Advantages:
High fibre volume laminates can be obtained with very low void
contents.
Good health and safety, and environmental control due to enclosure of
resin.
Possible labour reductions.
Both sides of the component have a moulded surface.
Main Disadvantages:
Matched tooling is expensive and heavy in order to withstand pressures.
Generally limited to smaller components.
Unimpregnated areas can occur resulting in very expensive scrap parts.
MANUFACTURING OF
COMPOSITES
Resin Transfer Molding
108.
109. Prepregs
COMPOSITES
Description:
Fabrics and fibres are pre-impregnated by the materials manufacturer, under heat and
pressure or with solvent, with a pre-catalyzed resin. The catalyst is largely latent at
ambient temperatures giving the materials several weeks, or sometimes months, of
useful life when defrosted. However to prolong storage life the materials are stored
frozen. The resin is usually a near-solid at ambient temperatures, and so the pre-
impregnated materials (prepregs) have a light sticky feel to them, such as that of
adhesive tape. Unidirectional
materials take fibre direct from a
creel, and are held together by the
resin alone. The prepregs are laid
up by hand or machine onto a
mould surface, vacuum bagged
and then heated to typically 120-
180°C. This allows the resin to
initially reflow and eventually to
cure. Additional pressure for the
moulding is usually provided by an
autoclave (effectively a pressurized
oven) which can apply up to 5
110. MANUFACTURING OF
COMPOSITESPrepregs
Materials Options:
Resins: Generally epoxy, polyester, phenolic and high temperature resins
such as polyimides, cyanate esters and bismaleimides.
Fibres: Any. Used either direct from a creel or as any type of fabric.
Cores: Any, although special types of foam need to be used due to the
elevated temperatures involved in the process.
Typical Applications:
Aircraft structural components (e.g. wings and tail sections), F1 racing
cars, sporting goods such as tennis racquets and skis.
Advantages:
Resin/catalyst levels and the resin content in the fibre are accurately set
by the materials manufacturer. High fibre contents can be safely achieved.
The materials have excellent health and safety characteristics and are
clean to work with.
Fibre cost is minimized in unidirectional tapes since there is no secondary
process to convert fibre into fabric prior to use.
111. •Resin chemistry can be optimized for mechanical and thermal
performance, with the high viscosity resins being impregnable due to the
manufacturing process.
•The extended working times (of up to several months at room
temperatures) means that structurally optimized, complex lay-ups can be
readily achieved.
•Potential for automation and labour saving
Disadvantages:
•Materials cost is higher for preimpregnated fabrics.
•Autoclaves are usually required to cure the component. These are
expensive, slow to operate and limited in size.
•Tooling needs to be able to withstand the process temperatures involved.
•Core materials need to be able to withstand the process temperatures and
pressures.
MANUFACTURING OF
COMPOSITESPrepregs
112.
113. Description:
Dry fabrics are laid up interleaved with layers of semi-solid resin film supplied
on a release paper. The lay-up is vacuum bagged to remove air through the dry fabrics,
and then heated to allow the resin to first melt and flow into the air-free fabrics, and then
after a certain time, to cure.
Materials Options:
Resins: Generally epoxy only.
Fibres: Any
Cores: Most, although PVC foam
needs special procedures due to
the elevated temperatures involved
in the process
Typical Applications:
Aircraft radomes and submarine
sonar domes.
MANUFACTURING OF
COMPOSITES
Resin Film Infusion
114. Advantages:
High fibre volumes can be accurately achieved with low void contents.
Good health and safety and a clean lay-up, like prepreg.
High resin mechanical properties due to solid state of initial polymer
material and elevated temperature cure.
Potentially lower cost than prepreg, with most of the advantages.
Less likelihood of dry areas than SCRIMP process due to resin traveling
through fabric thickness only.
MANUFACTURING OF
COMPOSITES
Resin Film Infusion
115. Disadvantages:
Not widely proven outside the aerospace industry.
An oven and vacuum bagging system is required to cure the component
as for prepreg, although the autoclave systems used by the aerospace
industry are not always required.
Tooling needs to be able to withstand the process temperatures of the
resin film (which if using similar resin to those in low-temperature curing
prepregs, is typically 60-100°C).
Core materials need to be able to withstand the process temperatures and
pressures.
MANUFACTURING OF
COMPOSITES
Resin Film Infusion
116.
117. MANUFACTURING OF COMPOSITES
Description:
Fabrics are laid up as a dry
stack of materials as in RTM. The
fibre stack is then covered with peel
ply and a knitted type of non-structural
fabric. The whole dry stack is then
vacuum bagged, and once bag leaks
have been eliminated, resin is allowed
to flow into the laminate. The resin
distribution over the whole laminate is
aided by resin flowing easily through
the non-structural fabric, and wetting
the fabric out from above.
Materials Options:
Resins: Generally epoxy, polyester and vinylester.
Fibres: Any conventional fabrics. Stitched materials work well in this
process since the gaps allow rapid resin transport.
Cores: Any except honeycombs.
Other Infusion Processes
118. MANUFACTURING OF
COMPOSITES
Other Infusion Processes
Typical Applications:
Semi-production small yachts, train and truck body panels
Advantages:
As RTM above, except only one side of the component has a moulded
finish.
Much lower tooling cost due to one half of the tool being a vacuum bag,
and less strength being required in the main tool.
Large components can be fabricated.
Standard wet lay-up tools may be able to be modified for this process.
Cored structures can be produced in one operation.
Disadvantages:
Relatively complex process to perform well.
Resins must be very low in viscosity, thus comprising mechanical
properties.
Unimpregnated areas can occur resulting in very expensive scrap parts.
