Classification of-composites

various types of composites

1. UNIT 2: Classification of Composites
ME 434: Composite Materials
Course Instructor: SatadruKashyap
[email protected]
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
[email protected]
Department of Mechanical Engineering
TezpurUniversity

2. BASEDON THE TYPE OF MATRIX
•OrganicMatrix Composites(OMCs) –
•PolymerMatrix Composites (PMCs)
•Carbon matrix composites (carbon-carbon composites (carb on fibre in a graphite
matrix)
•MetalMatrixComposites(MMCs)
•CeramicMatrix Composites(CMCs)
BASEDON THE TYPE OF REINFORCEMENTFORM
•FibreReinforcedcomposites(FRP) – continuous ordiscontinuous
•considered to be a discontinuous fibre or short fibre compos ite if its properties
vary
with
fibre
length
.
Classifications of Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
vary
with
fibre
length
.
•On the other hand, when the length of the fibre is such that any further increase
in length does not further increase, the elastic modulus of t he composite, the
composite is considered to be continuous fibre reinforced.
•Fibres are small in diameter and when pushed axially, they be nd easily although
they have very good tensile properties. These fibres must be supported to keep
individual fibres from bending and buckling.
•LaminarComposites- layers of materials held togetherby matrix (Sandwich stru ctures)
•Particulate Composites- particles distributed or embedded in a matrix body. The par ticles
maybe flakes or in powder form (e.g. Concrete and wood partic le)

3. Classifications of Composites
Polymer Matrix Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

4. Classifications of Composites Metal Matrix Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

5. Classifications of Composites
Ceramic Matrix Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

6. OrganicMatrixComposites:PolymerMatrixComposites(PMC) Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

7. OrganicMatrixComposites:PolymerMatrixComposites(PMC) Twomain kinds of polymers arethermosetsandthermoplastics.
Classifications based on matrix SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

8. OrganicMatrixComposites:PolymerMatrixComposites(PMC) Polymers make ideal materials as they can be processed easil y, possess lightweight, and
desirable mechanical properties. Two main kinds of polymers arethermosetsand
thermoplastics.
Thermosets
have qualities such as a well-bonded three-dimensional mol ecular structure
aftercuring.
•They decompose instead of melting on hardening. Merely changing the basic
composition of the resin is enough to alter the conditions su itably for curing and
determine
its
other
characteristics
.
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
determine
its
other
characteristics
.
•They can be retained in a partially cured condition too over p rolonged periods of time,
rendering thermosets very flexible. Thus, they are most sui ted as matrix bases for
advanced fiberreinforced composites.
•Thermosets find wide ranging applications in the chopped fiber compositesform,
particularly, when a premixed compound with fibers happens to be the starting material
asin epoxy, polymer and phenolic polyamide resins.
•Thermosetresins are – epoxy,polyester, phenolic polyamid e resins
.

9. PolymerMatrixComposites(PMC):Thermosets •Epoxyresins
•widely used in filament-wound composites and electrical ci rcuit boards.
•reasonably stable to chemical attacks and are excellent adherentshaving slow
shrinkageduring curing and no emission of volatile gases.
•Theseadvantagesmake epoxies expensive.
•cannot be used above 140ºC (limiting their applications).
•Polyesterresins
•easilyaccessible, cheap and used widely.
•stored at room temperature for long periods and the mere addi tion of a catalyst can
cure
the
matrix
material
within
a
short
time
.
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
cure
the
matrix
material
within
a
short
time
.
•cured polyester is usually rigid or flexible and transparen t.
•usedin automobile and structural applications.
•withstand the variations of environment and stable against chemicals and can be
usedup to about 75ºC orhigher.
•compatibility with few glassfibers and can be used with vari ety of reinforced plastic.
•AromaticPolyamides
•most sought after as the matrices of advanced fiber composit es for structural
applications demanding long duration exposure for continu ous service at around 200-
250ºC .

10. PolymerMatrixComposites(PMC): Thermoplastics •have one- or two-dimensional molecular structure and they t end to show an exaggerated
melting point at an elevated temperature.
•soften at elevated temperatures can be reversed to regain it s properties during cooling,
facilitating applications of conventional techniques to m old the compounds.
•resins comprise an emerging group of composites and the main goal is to improve the
base
properties
of
the
resins
which
would
extract
the
greatest
functional
advantages
from
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
base
properties
of
the
resins
which
would
extract
the
greatest
functional
advantages
from
them.
•Whethercrystallineoramorphous, these resins possess the facility to alter their creep
overan extensiverange of temperature.
•Reinforcement in such systems can increase the failure load as well as creep resistance.
Moreover,addition of filler raisesthe heat resistance.

11. PolymerMatrixComposites(PMC): Thermoplastics •Thermoplastics are: polyethylene, polystyrene, polyamid es,nylons, and polypropylene
.
•Theadvantagesoverthermosets -
•there are no chemical reactions involved, which often resul t in the release of gases or
heat.
•Manufacturing is limited by the time required for heating, s haping and cooling the
structures.
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•Thermoplastics resins are sold as molding compounds. Fiberreinforcement is apt forthese
resins. Since the fibers are randomly dispersed, the reinfo rcement will be almostisotropic.
However, when subjected to moulding processes,they can be a ligned directionally.
•Tend to lose their strength at elevated temperatures. Howev er, theirredeeming qualities
likerigidity,toughnessand ability toavoid creep, place thermoplastics in the important
composite materials bracket.
•Usedin automotivecontrol panels, electronic products enc asementetc.

12. Metal Matrix Composites (MMC) Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

13. Metal Matrix Composites (MMC) •Though generating a wide interest in research, are not aswid ely in useas plastic.
•Highstrength,fracture toughnessandstiffnessare offered by metal matrices when
compared to their polymer counterparts.
•Withstand elevated temperature in corrosive environment t han polymer composites.
•Most metals and alloys - used as matrices. Hence, require rei nforcement materials - stable
overa range of temperatures and non-reactive too.
•Guiding aspect forthe choice depends on matrixmaterial.
•
Light
metals
(low
strength)
form
the
matrix
while
the
reinforcements
have
high
moduli
.
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
Light
metals
(low
strength)
form
the
matrix
while
the
reinforcements
have
high
moduli
.
•Ifmetalmatrix has high strength,they require even higher m odulus reinforcements.
•Hence, light metals (Al, Ti, and Mg) are the popular matrix me tals with their low density. e.g.
carbide in a metal matrix.
•The melting point, physical and mechanical properties of the composite at various
temperaturesdetermine the service temperature of composi tes.
•Most metals, ceramics and compounds can be used with matrice s of low melting point alloys.
As the melting points of matrix materials become high,the ch oice of reinforcements becomes
small.

14. CeramicMatrixComposites(CMC) •Ceramics-solid materials which exhibit strong ionic bondi ng (in some casescovalent bonding)
•High melting points, good corrosion resistance, stability at elevated temperatures and high
compressive strength - ceramic matrix materials used above 1500ºC (high temperature
applications). e.g.cermet, concrete.
•Most ceramic possess high modulus of elasticity and low tens ile strain and hence addition of
reinforcements to improve their strength have proved futil e. This is because at the stress
levels at which ceramics rupture, there is insufficient elo ngation of the matrix which keeps
composite
from
transferring
an
effective
quantum
of
load
to
the
reinforcement
and
the
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
composite
from
transferring
an
effective
quantum
of
load
to
the
reinforcement
and
the
composite may fail unless the percentage of fiber volume is h igh enough. However, addition
of any high-strength fiber (as reinforcing material) to a we aker ceramic has not always been
successfuland often the resultant composite has proved to b e weaker.
•When ceramics have a higher thermal expansion coefficient t han reinforcement materials,
the resultant composite is unlikely to have a superior level of strength. In that case, the
composite will develop stress within ceramic at the time of c ooling resulting in microcracks
extending from fiber to fiber within the matrix. Microcrack ing can result in a composite with
lowertensile strength than that of the matrix.

15. CeramicMatrixComposites(CMC) •motivation to develop CMCs - to overcome the problems associ ated with the conventional
technical ceramics like alumina, silicon carbide, alumini um nitride, silicon nitride or zirconia –
they fracture easily under mechanical or thermo-mechanica l loads because of cracks initiated
bysmall defects orscratches. The crack resistance is – like in glass – verylow.
•Multi-strand fibres has drastically increased the crack re sistance/ fracture toughness,
elongation and thermal shock resistance, and resulted in se veralnew applications.
•Carbon (C), silicon carbide (SiC), alumina (Al
2O
3) and mullite (Al
2O
3–SiO
2) fibres are most
widely used with the samematrix materials i.e. C, SiC, alumi na and mullite.
Classifications based on matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•CMC names include a combination oftype of fibre/type of matrix . For example,C/Cstands for
carbon-fibre-reinforced carbon (carbon/carbon), or C/SiCfor carbon-fibre-reinforced silicon
carbide (commercially available CMCs are C/C, C/SiC, SiC/S iC and Al
2O
3/Al
2O
3).
•Theydiffer fromconventional ceramics in the following pro perties:
•Elongation to rupture up to 1%
•Stronglyincreased fracture toughness
•Extremethermal shock resistance
•Improveddynamical load capability
•Anisotropicproperties following the orientation of fiber s

16. Classifications based on reinforcements
Reinforcements
Directionally
Solidified
Eutectics
Particulates
Flake
Whiskers
Filled
Fibres
Microspheres
Particle filled
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
Hollow
Solid
Microspheres
Particle filled

17. What are reinforcements?
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

18. What are reinforcements?
• A strong, inert, woven and nonwoven fibrous material incor porated into the matrix to
improve its mechanical and physical properties e.g. asbest os, boron, carbon, metal or glass
orceramic fibers, graphite, jute, sisal,whiskers, macera ted fabrics, and synthetic fibers.
• reinforcement and filler difference
• reinforcement markedly improves tensile and flexural str ength, whereas filler usually
doesnot To be effective, reinforcement must form a strong ad hesivebond with resin.
•
Role
of
the
reinforcement
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
Role
of
the
reinforcement
• increase the mechanical properties of the neat resin syste m. Different fibres have
differentproperties - affect the properties of the composi te in different ways.
• However, individual fibres or fibre bundles can only be use d on their own in a few processes
such asfilament winding.
• For most other applications, the fibres need to be arranged into some form of sheet,
known as a fabric, to make handling possible.

19. What are reinforcements?
• Different ways forassembling fibres into sheetsand the va riety of fibre orientations –
• Lead to different types of fabrics, each of which hasits own lead characteristics.
• Reinforcements forthe composites can be fibers, fabrics p articles orwhiskers.
• Fibers are essentially characterized by one very long axis with other two axes either
often circular or nearcircular.
• Particles haveno preferred orientation and so does their s hape.
•
Whiskers
have
a
preferred
shape
but
are
small
both
in
diameter
and
length
as
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
Whiskers
have
a
preferred
shape
but
are
small
both
in
diameter
and
length
as
compared to fibers.

20. Fibre Reinforced Polymer (FRP) Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

21. Fibre Reinforced Polymer (FRP) Composites
•Fibres - important class of reinforcements, as they effecti vely transfer strength to the
matrixinfluencing and enhancing composite properties asd esired.
•Glass fibers (earliest known reinforcing fibres)- Ceramic and metal fibers used
subsequentlyto make composites stifferand more heat resis tant.
•Theperformance of a fiber composite is judged by
•the length, shape, orientation, and composition of the fibe rs and the mechanical
propertiesof the matrix.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•orientation of the fiber in the matrix (strength greatest al ong the longitudinal
directional &slightest shift in the angle of loading drasti cally reduce the strength)
•Since unidirectional loading is found in very few structure s, a mix of fibre orientations is
given to withstand load from different angles (particularl y more fibres in the direction
where load is expected to be the heaviest).
•Monolayer tapesconsisting of continuous or discontinuous fibers can be ori ented
unidirectional stacked into plies containing layers of fil aments also oriented in the same
direction.

22. Fibre Reinforced Polymer (FRP) Composites
•Properties ofangle-plied compositeswhich are notquasi-isotropicmay vary with the
numberof plies and their orientations.
•Orientation of short fibers - random orientations by sprink ling on to given plane, addition
ofmatrix in liquid or solid state before orafter the fiberde position.
•Experience has shown thatcontinuous fibers(or filaments) exhibit better orientation,
although it does not reflect in their performance.
•
Mass
production
of
filaments
in
different
ways
like
winding,
twisting,
weaving
and
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
Mass
production
of
filaments
in
different
ways
like
winding,
twisting,
weaving
and
knitting,which exhibit the characteristics of a fabric.
•Organicandinorganicfibersare used to reinforce composites.
•Almostall organic fibers havelow density, flexibility, an d elasticity.
•Inorganic fibers (glass fibers, silicon carbide fibers, hi gh silica and quartz fibers,
aluminina fibers, metal fibers and wires, graphite fibers, boron fibers, aramid fibers
and multiphase fibers) are of high modulus, high thermal sta bility and possess
greaterrigidity than organic fibers.

23. Whisker Reinforced Composites •Whiskers- Single crystals grown with nearly zero defects (usually di scontinuous and short
fibers of different cross sections made from materials like graphite, silicon carbide, copper,
iron etc). Typical lengths are range from 3 - 55 nm.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
Tin whiskers on Cu substrate
Whiskers are usually thin, metal films, 0.5 μm to 50 μm, that have been deposited onto a substrate mate rial.
They often grow from nodules (a). A typical whisker is 1 to 5 μm in diameter and between 1 μm and 500 μm
long, as seen in this cross-section (b). They can c ome in different shapes, including kinked (c) or wi th rings (d).

24. Whisker Reinforced Composites •Whiskers- Single crystals grown with nearly zero defects (usually di scontinuous and short
fibers of different cross sections made from materials like graphite, silicon carbide, copper,
iron etc). Typical lengths are range from 3 - 55 nm.
•Whiskers differ from particles in that, whiskers have a defi nite length to width ratio (> 1)
with extraordinary strengthsup to 7000 MPa.
•Whiskers (laboratory produced) Metal-whisker combinatio n, strengthening the system at
high temperatures,has been demonstrated at the laboratory level.
•Since whiskers are fine, small sized materials and not easy t o handle, it becomes a
hindrance
in
composite
fabrication
.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
hindrance
in
composite
fabrication
.
•Early research has shown that whisker strength varies inver sely with effective diameter.
When whiskers were embedded in matrices, whiskers of diamet er up to 2 - 10μm yielded
fairly good composites.
•Ceramicwhiskers have high moduli, usefulstrengths and low densities. Specificstrength and
specific modulus are very high and this makes them suitable f or low weight structure
composites. They also resist temperature, mechanical dama ge and oxidation more than
metallic whiskers (which are denser than ceramic whiskers) . However, they are not
commercially viable because they are damaged while handlin g.

25. Flakes Reinforced Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)

26. Flakes Reinforced Composites
•Flakesare often used in place of fibers as they can be densely packed.
•Metal flakes that are in close contact with each other in poly mer matrices can conduct
electricity or heat, while mica flakes and glasscan resist b oth.
•Flakesare not expensiveto produce and usually cost less tha n fibers.
•Butlimitations are - control of size,shape of flakes and def ects in the end product.
•Glass flakes tend to have notches or cracks around the edges, which weaken the final
product. (also resistant to be lined up parallel to each othe r in a matrix, causing uneven
strength)
.
They
are
usually
set
in
matrices,
or
held
together
by
a
matrix
with
a
glue
-
type
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
strength)
.
They
are
usually
set
in
matrices,
or
held
together
by
a
matrix
with
a
glue
-
type
binder.
•Advantagesof flakes overfibers –
•Parallel flakes filled composites provide uniform mechani cal properties in the same
plane as the flakes.
•While angle-plying is difficult in continuous fibers which need to approach isotropic
properties,it is not so in flakes.
•Flake composites have a higher theoretical modulus of elast icity than fiber reinforced
composites.
•Theyare relatively cheaper to produce and be handled in smal lquantities.

27. Filled Composites
•Addition of filer materials to plastic matrices to replace a portionof the matrix which would
enhance or change the properties of the composites. The fill ers also enhance strength and
reduce weight in somecases.
•Fillers may be themain ingredient or an additional one in a composite. The filler particles
may be irregular structures, or have precise geometrical sh apes like polyhedrons, short
fibers or spheres.They also occasionallyimpart colour or opacityto the composite which
theyfill.
•
As
inert
additives,
fillers
can
change
almost
any
basic
resin
characteristic
in
all
directions
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
As
inert
additives,
fillers
can
change
almost
any
basic
resin
characteristic
in
all
directions
required, to surpass many limitations of basic resins. The f inal composite properties can be
affected by the shape, surface treatment, blend of particle types, size of the particle in the
fillermaterial and the size distribution.
•Filled plastics tend to behave like two different constituen ts. They do not alloy and accept
the bonding (they desist from interacting chemically with e ach other).
•Although the matrix forms the bulk of the composite, the fill er material is also used in such
greatquantities relatively that it becomes the rudimentar y constituent.

28. Filled Composites •The benefits of fillers - increase stiffness, thermal
resistance, stability, strength and abrasion resistance,
porosity and a favorable coefficient of thermal
expansion.
•Disadvantages - methods of fabrication are very limited
and the curing of some resins is greatly inhibited, shorten
the life span of some resins,weaken a few composites.
•
Fillers
produced
from
powders
are
also
considered
as
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
Fillers
produced
from
powders
are
also
considered
as
particulate composite.
•In a porous or spongy composite, metal impregnates are
used to improve strength or tolerance of the matrix.
Metal casting, graphite, powder metallurgy parts and
ceramics belong to this class of filled composites.
•In the honeycomb structure, sheet materials in the
hexagonal shapes are impregnated with resin or foam
and are used as a core material in sandwich composites.

29. Microsphere Composites
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
Glass Microspheres
Hollow carbon microspheres (HCM) in epoxy matrix
– EPOXY SYNTATIC FOAMS

30. Microsphere Composites •Microspheres- useful fillers due to specific gravity, stable particle si ze, strength and
controlled density - modify products without compromising profitsor physical properties.
•Solidglassmicrospheresare most suitable for plastics.
•Microspheres coated with a binding agent - bonds btween sphe re’s surface and resin.
This increases the bonding strength and basically removes absorption of
contaminants/moisture (reduce attraction between partic les).
•Solid Microsphereshave relatively low density, and therefore, influence the c ommercial
valueand weight of the finished product.
•
Hollow
microspheres
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
Hollow
microspheres
•essentiallysilicate based,made at controlled specific gr avity.
•largerthan solid glassspheres,used in polymers and havewi der range of particle sizes.
•Commercially, silicate-based hollow microspheres with di fferent compositions using
organic compounds are also available. Due to this modificat ion, they are less sensitive
to moisture (reduce attraction between particles) - vital i n highly filled polymer
compositesas viscosity increase constraints limit filler loading.

31. Microsphere Composites
•Earlier used in thermosetting resin. Now, several new stron g spheres are available and they
are at least 5 times stronger than hollow microspheres in static crush strengthand 4 times
long lasting in shear.
•Recently,ceramicalumino-silicatemicrosphereshavebeen used in thermoplastic systems
•greater strength and higher density of this system in relati on to siliceous microspheres
and their abrasion resistance makethem suitable forhigh pr essureapplications.
•Hollowmicrosphereshavea lowerspecificgravitythanthepureresin.
•
find
wide
applications
in
aerospace
and
automotive
industries
where
weight
reduction
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
•
find
wide
applications
in
aerospace
and
automotive
industries
where
weight
reduction
forenergy conservation is one of the main considerations.
•Microspheres, whether solid or hollow, due to their spherical shape behave like minute ball
bearing,and hence, they give better flow properties.
•Theyalso distribute stressuniformly throughout resin mat rices.
•Inspherical particles, the ratio of surface area to volume i s minimal (smallest).
•In resin-rich surfaces of reinforced systems, the microsph eres which are free of
orientation and sharp edgesare capable of producing smooth surfaces.

32. Particulate reinforced Composites •Microstructures of metal and ceramics composites, which sh ow particles of one phase
scatteredin the matrix, are known as particlereinforcedcomposites.
•Square, triangular, irregular and round shapes of reinforc ement are known, but the
particle dimensions are observed to be more orless equal.
•The size and volume concentration of thedispersantdistinguishes particle reinforced
compositesfrom dispersion strengthened composites.
•The dispersed size in particulate composites is of the order of a few microns and volume
concentration is greaterthan 28%.
•
Particle
reinforced
composite
-
particle
-
matrix
interaction
do
not
occur
at
atomic
or
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
Particle
reinforced
composite
-
particle
-
matrix
interaction
do
not
occur
at
atomic
or
molecular level. Particles harder and stiffer than matrix – hence, tend to bear the load.
Degree of reinforcement depends on strongmatrix particle b onding. e.g..Concrete.
•Dispersion strengthened composites
–particles smaller (diameter 0.01 - 0.1 x 10
-6
m). Particle
matrix interactions that lead to strengthening occur on ato mic level. The matrix bears the
major portion of load. While dispersed particles hinder mot ion of dislocations. Thus plastic
deformation is restricted such that yield and tensile stren gth as well as hardness improve. e.g..
thoria dispersed nickel.
•The composite’s strength depends on - diameter of the partic les, the inter-particle spacing,
and the volume fraction of the reinforcement.

33. Cermets/Ceramal: •Cermet– ‘ceramic’and‘metal’composite.
•designed to have the optimal properties of both ceramic (hig h temperature resistance
and hardness) and metal (the ability to undergo plastic defo rmation). The metal (Ni, Mo,
Co etc.) used as a binder foran oxide, boride, carbide, or alu mina.
•Cermetsare usually lessthan 20% metalby volume – usedin
•manufacture of resistors (potentiometers), capacitors et c - experience high temperatures.
•spacecraft shielding (as they resist the high velocity impa cts of micrometeoroids and
orbital
debris
better
than
Al
and
other
metals
.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
orbital
debris
better
than
Al
and
other
metals
.
•vacuumtube coatings of solarhot water systems.
•materialforfillings and prostheses.
•machining of cutting tools. Titanium nitride (TiN), titani um carbonitride (TiCN), titanium
carbide (TiC)
•Cermet are usually produced by -
•usingpowermetallurgytechniques (ceramic and metal powder mixed and sintered).
•Impregnationof a porous ceramic structure with a metallic matrix binder.
•coatingin powder form which is sprayed through a gas flame and fused t o a base
material.

34. Directionally solidified eutectics: •Directional solidification of alloys is adopted to produce in-situ fibers. They are really a part of
the alloy being precipitated from the melt, while the alloy i s solidifying.
•This compriseseutectic alloys(Mixture of two or more components in such proportion that
their combined melting point is the lowest attainable) wherein the molten material
degeneratesto form many phasesat a steady temperature.
•When the reaction is carried out after ensuring the solidify ing phases, directionally solidified
eutectics result.
•
During
the
solidification
of
alloy,
crystals
nucleate
from
the
mold
or
some
relatively
cooler
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
During
the
solidification
of
alloy,
crystals
nucleate
from
the
mold
or
some
relatively
cooler
region. A structure with many crystalline particles or grai ns results from this and grows into
each other. When composites are unidirectionally solidifi ed, randomcoalescingis not allowed
tooccur.
•E.g. Al
2O
3-YSZ (Aluminium oxide – Yttria stabilized Zirconia), Al2O3 -GdAlO3 (GAP)) - dental
porcelain.
•Gd- gadolinium

35. Role and Selection of Reinforcements: •Compatibilitywith matrixmaterial, thermalstability, density, melting temperature etc.
•Efficiency of discontinuously reinforced composites - dep endent on tensile strength and
densityof reinforcing phases.
•difference between thecoefficients of thermal expansion of the matrix and reinforcement -
compositesused in thermal cycling application.
•Themanufacturingprocessselected and thereinforcementaffectsthe crystalstructure.
•In particulate/whisker reinforced composites
, the matrix (major load bearing constituent).
Role
of
the
reinforcement
-
strengthen
and
stiffen
the
composite
through
prevention
of
matrix
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
Role
of
the
reinforcement
-
strengthen
and
stiffen
the
composite
through
prevention
of
matrix
deformation by mechanical restraint. This restraint is gen erally a function of the ratio of inter-
particlespacingtoparticlediameter.
•In continuous fiber reinforced composites, the reinforcement (principal load-bearing
constituent). The matrix serves to hold the reinforcing fib ers together and transfer as well as
distribute the load.
•Discontinuous fiber reinforced composites - properties be tween continuous fiber and
particulate reinforced composites.
•Addition of reinforcement increases the strength, stiffne ssand temperature capability.
•Reduce density of composite if the matrixmaterial has high d ensity.

36. Role and Selection of Matrix: •The matrix provides support for the fibres and assists them i n carrying the loads. It also
provides stability to the composite material. Resin matrix system acts as a binding agent in a
structuralcomponent in which the fibres are embedded.
•When too much resin is used, the part is classified as resin rich. On the other hand, if there is
toolittle resin,the part is called resinstarved.
•A resin rich part is more susceptible to cracking due to lack o f fibre support, whereas a
resin starved part is weaker because of void areas and the fac t that fibres are not held
togetherand they are not well supported.
•
In
case
of
MMCs,
thermodynamically
stable
dispersoids
(particles)
are
essential
for
high
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
In
case
of
MMCs,
thermodynamically
stable
dispersoids
(particles)
are
essential
for
high
temperatureapplications.
•done using an alloy-matrix (alloy particles in a metal matri x) system in whichsolid state
diffusivity,interfacial energiesandelemental solubilityare minimized, in turn reducing
interfacial reactions.
•Aland Mg alloys matrices widely used due to low density and hi gh thermalconductivity.
•Additionally, composites with low alloying additions to th e matrix result in attractive
combinations of ductility, toughnessand strength.
•alloying elements (usually used as grain refiners)may formcoarse inter-metallic
compounds during consolidation, thus, reducing the tensil e properties of the composite.

37. Role and Selection of Matrix: •Thechoice of a matrix is dictated by - continuously ordiscon tinuously reinforced fibres
.
•Continuous fibers- transfer of load to the reinforcing fibres (hence composit e strength will be
governedby the fiber strength.
•The role of matrix - provide efficient transfer of load to the fibers and blunt cracks in the
event that fiber failure occurs (matrix used for toughness t han strength). Hence, lower
strength,ductile, and tough matrix may be utilized in conti nuous reinforced composites.
•Discontinuousreinforcedcomposites-the matrix may govern composite strength.
•Then, the choice of matrix will be influenced by considerati on of the required composite
strength
and
higher
strength
matrix
may
be
required
.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
strength
and
higher
strength
matrix
may
be
required
.
•Choice of the matrix also include - potentialreinforcement/matrix reactions(during
processing or in service - degraded composite), thermal stresses(thermal mismatch between
reinforcementsand matrix), andmatrixfatiguebehaviorunder cyclic conditions.
•Thermal mismatch- a large melting temperature difference may result in matri x creep while
the reinforcements remain elastic, even at temperatures ap proaching the matrix melting
point.
•However,creep in both the matrix and reinforcementmust be considered when there is a
smallmelting point difference in the composite.

38. Functions of Matrix: •Holds the fibres together.
•Protects the fibres from environment.
•Distributes the loads evenly between fibres so that all fibr es are subjected to the same
amountof strain.
•Enhances transverseproperties of a laminate.
•Improvesimpact and fracture resistance of a component.
•Avoid propagation of crack growth through the fibres by prov iding alternate failure path along
the
interface
between
the
fibres
and
the
matrix
.
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials)
the
interface
between
the
fibres
and
the
matrix
.
•Carry inter-laminar shear
(design consideration for structures under bending loads) ; in-plane
shearstrength
(under torsion loads)
•Minorrole - in the tensile load-carrying capacity of a compo site structure.
•Provide lateral support against the possibility of fibre bu ckling under compression loading.
•Finally, the processing ability and defects in a composite m aterial depend strongly on the
physical and thermal characteristics, such as viscosity, m elting point, and curing temperature
ofthe matrix.

39. Desired Functions of Matrix: •Reduced moisture absorption.
•Low shrinkage.
•Low coefficient of thermal expansion.
•Good flow characteristics so that it penetrates the fibre bundles completely and eliminates
voids during the compacting/curing process.
•Reasonable strength, modulus and elongation (elonga tion should be greater than fibre).
•Must be elastic to transfer load to fibres.
•
Strength at elevated temperature (depending on appl ication).
SATADRU KASHYAP ME
434
(Mechanical Engineering, Tezpur University) (Composite Materials) •
Strength at elevated temperature (depending on appl ication).
•Low temperature capability (depending on applicatio n).
•Excellent chemical resistance (depending on applica tion).
•Should be easily fabricated into the final composit e shape.
•Dimensional stability(maintains its shape).