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MMF410803 Material
Komposit (2sks)
Prof. Dr. Ir. Anne Zulfia MSc
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Pengenalan
Komposit SecaraUmum
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The world of materials
PE, PP, PCPA (Nylon)
Polymers,elastomers
Butyl rubberNeoprene
Polymer foamsMetal foams
FoamsCeramic foams
Glass foams
Woods
Naturalmaterials
Natural fibres:Hemp, Flax,
Cotton
GFRPCFRP
CompositesKFRP
Plywood
Alumina
Si-Carbide
Ceramics,glasses
Soda-glassPyrex
SteelsCast ironsAl-alloys
MetalsCu-alloysNi-alloysTi-alloys
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Pengertian Komposit
Komposit merupakan kombinasi dari duamaterial atau lebih yang memiliki fasayang berbeda menjadi suatu material baru
yang memiliki properti lebih baik darikeduanya.
Jika kombinasi ini terjadi dalam skalamakroskopis maka disebut sebagai
komposit.
Jika kombinasi ini terjadi secaramikoroskopis (molekular level) maka
disebut sebagai alloy atau paduan.
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Two types of composites are:
Fiber Reinforced
Composites
Particle Reinforced
Composites
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Particle reinforced composites support higher tensile,
compressive and shear stresses.
Figure 1. Examples for particle-reinforced composites.
(Spheroidized steel and automobile
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The following are some of the reasonswhy composites are selected for certainapplications:
High strength to weight ratio (low density high tensile
strength)
High creep resistance
High tensile strength at elevated temperatures
High toughness
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Examples of Composites• Natural
–Wood
• flexible cellulose fibers held together with
stiff lignin
–Bone
• strong protein collagen and hard, brittleapatite
• Artificial (man-made)
– constituent phases are chemicallydistinct
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Definitions
• Composites often have only twophases
• Matrix phase
– continuous - surrounds other phase
• Dispersed phase
–discontinuous phase
Matrix (light)
Dispersed phase (dark)
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Introduction
• Engineering applications often require unusualcombinations of properties
– esp. aerospace, underwater, and
transportation– can’t be achieved with a single material
– e.g. - aerospace requires strong, stiff, light,and abrasion resistant material
• most strong, stiff materials are denseand heavy
• most light materials are not abrasionresistant
• Solution is in composite materials
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Examples of Composites• Natural
–Wood
• flexible cellulose fibers held together with
stiff lignin
–Bone
• strong protein collagen and hard, brittleapatite
• Artificial (man-made)
– constituent phases are chemicallydistinct
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Figure 16.1 Some examples of composite materials: (a)plywood is a laminar composite of layers of wood veneer, (b)fiberglass is a fiber-reinforced composite containing stiff,strong glass fibers in a softer polymer matrix ( 175), and(c) concrete is a particulate composite containing coarsesand or gravel in a cement matrix (reduced 50%).
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Properties of CompositesDependent on:
• constituent phases
• relative amounts• geometry of dispersed phase
– shape of particles
–particle size–particle distribution
–particle orientation
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Composite Parameters
For a given matrix/dispersedphase system:
• Concentration
• Size
• Shape
• Distribution
• Orientation
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Concentration
SizeShape
Distribution Orientation
Parameters
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Classification of ArtificialComposites
Composites
Particulate Fiber Structural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
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Particle-ReinforcedComposites
• Divided into two classes
– (based on strengthening mechanism)
• Large particle
– interaction between particles and matrix arenot on the atomic or molecular level
– particle/matrix interface strength is critical
• Dispersion strengthened
– 0.01-0.1 mm particles
– inhibit dislocation motion
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Large Particle CompositesExamples:
• Some polymers with added fillers arereally large particle composites
• Concrete (cement with sand orgravel)
– cement is matrix, sand is particulate
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Large Particle CompositesDesired Characteristics
• Particles should be approximatelyequiaxed
• Particles should be small and evenlydistributed
• Volume fraction dependent ondesired properties
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Large-Particle CompositeMaterials
• All three material types
–metals, ceramics, and polymers
• CERMET (ceramic-metal composite)
– cemented carbide (WC, TiC embeddedin Cu or Ni)
– cutting tools (ceramic hard particles to
cut, but a ductile metal matrix towithstand stresses)
– large volume fractions are used (up to
90%!)
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Large Particle CompositesConcrete
• Concrete is not cement)
–Concrete is the composite of cementand an aggregate (fine sand or coarse
gravel)• Reinforced concrete
–a composite (large particle composite) -
with a matrix which is a composite– steel rods, wires, bars (rebar,
sometimes stretched elastically whileconcrete dries to put system in
compression)
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Dispersion StrengthenedComposites
• Metals and metal alloys– hardened by uniform dispersion of fine particles of a
very hard material (usually ceramic)
• Strengthening occurs through theinteractions of dislocations and theparticulates
• Examples• Thoria in Ni
• Al/Al2O3 sintered aluminum powder SAP
• GP zones in Al
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CERMET Cutting Tool
Light phase - Matrix (Cobalt)
Dark phase- Particulate (WC)
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Figure 16.7 Microstructure of analuminum casting alloy reinforced with
silicon carbide particles. In this case, thereinforcing particles have segregated tointerdendritic regions of the casting( 125). (Courtesy of David Kennedy,Lester B. Knight Cost Metals Inc .)
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Klasifikasi Komposit
Komposit
Partikel Fiber Struktural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
Berdasarkan Bentuk dari Reinforcementnya
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Fiber sebagai reinforced
Fiber yang digunakan harus:
• Mempunyai diameter yang lebihkecil dari diameter bulknya(matriksnya) namun harus lebihkuat dari bulknya
• Harus mempunyai tensile strengthyang tinggi
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Figure 16.18 Photomicrographs of two fiber-reinforcedcomposites: (a) In Borsic fiber-reinforced aluminum, the fibersare composed of a thick layer of boron deposited on a small-
diameter tungsten filament ( 1000). (From Metals Handbook,
American Society for Metals, Vol. 9, 9th Ed., 1985 .) (b) In thismicrostructure of a ceramic-fiber–ceramic-matrix composite,silicon carbide fibers are used to reinforce a silicon nitridematrix. The SiC fiber is vapor-deposited on a small carbon
precursor filament (
125). (Courtesy of Dr. R.T. Bhatt, NASA
Lewis Research Center .)
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Matriks yang dipadukan dengan fiber
berfungsi sebagai :• Penjepit fiber
• Melindungi fiber dari kerusakanpermukaan
• Pemisah antara fiber dan juga mencegahtimbulnya perambatan crack dari suatufiber ke fiber lain
• Berfungsi sebagai medium dimanaeksternal stress yang diaplikasikan kekomposit, ditransmisikan dandidistribusikan ke fiber.
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Matriks yang digunakan harus :
• Ductility tinggi• Memiliki modulus elastisitans lebih
rendah daripada fiber
• Mempunyai ikatan yang bagusantara matriks dan fiber
• Biasanya secara umum yang
digunakan adalah polimer dan logam
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a. Short(discontinuous) fiber reinforced composites
Aligned Random
b. Continuous fiber (long fiber) reinforced composites
Fib bi
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Fiber yang biasadigunakan antara lain :
Fibers – Glass– Sangat umun digunakan, karena murah
sering digunakan untuk reinforcementdalam matrik polimer
– Komposisi umum adalah 50–
60 % SiO2dan paduan lain yaitu Al, Ca, Mg, Na, dll.– Moisture dapat mengurangi kekuatan dari
glass fiber– Glass fiber sangat rentan mengalami
static fatik– Biasanya digunakan untuk: piping, tanks,boats, alat-alat olah raga
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Sifat-Sifatnya• Densitynya cukup rendah ( sekitar 2.55g/cc)
• Tensile strengthnya cukup tinggi (sekitar1.8 GPa)
• Biasanya stiffnessnya rendah (70GPa)• Stabilitas dimensinya baik• Resisten terhadap panas
• Resisten terhadap dingin• Tahan korosi
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Keuntungan :
• Biaya murah
• Tahan korosi• Biayanya relative lebih rendah dari komposit
lainnya
Kerugian
• Kekuatannya relative rendah
• Elongasi tinggi
• Keuatan dan beratnya sedang(moderate)
Jenis-jenisnya antara lain :
– E-Glass - electrical, cheaper
– S-Glass - high strength
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Fibers - Aramid (kevlar, Twaron)
Biasanya digunakan untuk : Armor,protective clothing, industrial,sporting goods
Keuntungan :kekutannya cukuptinggi, dan lebih ductile dari carbon
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Carbon Fibers
• Densitaskarbon cukup ringan yaitu sekitar 2.3g/cc
• Struktur grafit yang digunakan untuk membuatfiber berbentuk seperti kristal intan.
• Karakteristik komposit dengan serat karbon :– ringan;
– kekuatan yang sangat tinggi;– kekakuan (modulus elastisitas) tinggi.
• Diproduksi dari poliakrilonitril (PAN), melalui tigatahap proses :
• Stabilisasi = peregangan dan oksidasi;
• Karbonisasi= pemanasan untuk mengurangi O, H, N;
• Grafitisasi = meningkatkan modulus elastisitas.
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Pengaruh Orientasi Fiber
• Parameter Fiber– arrangement with respect to each other
– distribution
– concentration
• Orientasi Fiber– parallel to each other
– totally random– some combination
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Flat flakes sebagai penguat (Flake
composites)
Fillers sebagai penguat (Filler composites)
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Specific Material Properties:Bila dibandingkan dengan engineering materials yang lain,
FRPs sangat competitive ditinjau dari beratnya
Tensile
Strength
s
(Mpa)
Stiffness
E
(Gpa)
Mild Steel
Aluminium
Nylon
ConcreteRandom Fibre FRP
Alligned Fibre FRP
(Load // Fibres)
(Load Fibres)
Specific
Stiffness
E/ r
Specific
Strength
s / r
Density
r
(kg/m3)
7800
2700
1100
24001800
1600
1600
208
70
2.5
4020
200
3
400
200
80
20300
1500
50
1
0.97
0.09
0.630.42
4.69
0.07
1
1.44
1.42
0.163.25
18.3
0.61
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Fiber Material Properties
Steel: density (Fe) = 7.87 g/cc; TS=0.380 GPa; Modulus=207 GPa
Al: density=2.71 g/cc; TS=0.035 GPa; Modulus=69 GPa
b S h
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Fiber Strength
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Structurtal Composite
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™
is a trademark used herein under license.
Figure 16.12 (a) Tapes containing aligned fibers can be joined to produce a multi-layered different orientations toproduce a quasi-isotropic composite. In this case, a0°/+45°/90° composite is formed.
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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™
is a trademark used herein under license.
Figure 16.13 A three-dimensional weave for fiber-reinforced composites.
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