Materi ke-9

03/11/2015
KLASIFIKASI KOMPOSIT BERDASARKAN MATRIKSNYA
PERTEMUAN KE-9
Composite
materials
POLYMER MATRIX
COMPOSITES (PMC)
Matrices
Polymer Matrix
Composites (PMC)
Thermoset
Metal Matrix
Composites MMC)
Thermoplastic
Ceramic Matrix
Composites (CMC)
Rubber
Material Komposit
What is a polymer?
Poly
many
mer
repeat unit
A polymer is a large molecule (macromolecule) composed of repeating
structural units typically connected by covalent chemical bonds
Examples of polymers:
repeat
unit
repeat
unit
H H H H H H
C C C C C C
H H H H H H
H H H H H H
C C C C C C
H Cl H Cl H Cl
Polyethylene (PE)
Polyvinyl chloride (PVC)
Polymer Matrix Composites are very popular due to their low cost
and simple fabrication methods.
repeat
unit
H
C
H
H H
C C
CH3 H
H H
C C
CH3 H
Polymer Matrix Composite (PMC) is the material consisting of a
polymer (resin) matrix combined with a fibrous reinforcing dispersed
phase.
H
C
CH3
Polypropylene (PP)
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Classification of Polymers
Polimer Linear - Semua polimer yang molekulnya dalam
bentuk rantai.
Polimer Termoplastik - Polimer linear atau bercabang di
mana rantai molekul tidak saling berhubungan satu sama
lain.
Polimer Thermosetting - Polimer yang saling menyilang
untuk menghasilkan struktur jaringan dimensi tiga yang
kuat.
Elastomer - Ini adalah polimer (termoplastik atau
termoset ringan) yang memiliki deformasi elastis > 200%.
Polymer(Matrix)
Composite (Matrix + Reinforcement)
Konfigurasi rantai
Molekul:
a. Linear
b. Branched
c. Crossed linked
d. Ladder
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Resin thermoset adalah polimer yang paling banyak digunakan
pada PMC.
Polymerisation:
This is the process of joining monomers into gaint chain like molecules.
Epoxy dan polyester biasanya dicampur dengan penguat fiber.
Methods of Polymerisation:
• Condensation polymerisation
• Addition polymerisation
Bentuk yang paling banyak digunakan adalah struktur laminar,
dibuat dengan menumpuk dan ikatan lapisan tipis pada fiber dan
polimer sampai ketebalan yang diinginkan diperoleh.
Fibers in PMCs
•
•
•
•
Bentuknya bermacam-macam : discontinuous, continuous atau
woven/tenun seperti pada pembuatan kain .
Bahan utama fiber pada FRPs adalah gelas, karbon, dan Kevlar 49.
Fiber yang tidak umum, seperti boron, SiC, Al2O3 dan baja.
Glass (in particular E-glass) adalah bahan fiber yang paling umum
pada FRPs saat ini; penggunaannya untuk memperkuat plastik dari
sekitar tahun 1920.
Degree of polymerization = No of monomer units in a chain
≈ 103 to 105
Thermosets
•
•
Bahan termoset biasanya cair atau lunak sebelum pendinginan,
dan dirancang untuk dicetak menjadi bentuk akhirnya.
•
Memiliki sifat mengalami reaksi kimia melalui aksi panas, katalis,
sinar ultraviolet, dll, menjadi zat yang relatif tidak larut dan dapat
dicairkan.
•
Mereka mengembangkan struktur ikatan tiga dimensi yang baik
pada pendinginan. Setelah mengeras atau terikat silang, mereka
akan terurai dari pada mencair.
•
•
•
Thermoset dibuat dengan mencampurkan dua komponen (resin dan
hardener) yang bereaksi dan mengeras, baik pada temperatur ruang
atau panas.
Hasil polimernya biasanya berupa ikat silang yang besar, sehingga
thermoset ini disebut juga dengan polimer jaringan.
Bentuk ikat silang terjadi selama polimerisasi pada resin cair dan
hardener, sehingga strukturnya hampir selalu amorphous.
Bahan termoset umumnya lebih kuat dari pada bahan termoplastik
karena jaringan ikatan 3-D nya, dan juga lebih cocok untuk
aplikasi suhu tinggi hingga mencapai suhu dekomposisi bahan.
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Types of Thermosetting plastics
Thermosets
• Extensive cross-linking formed by covalent
bonds.
• Bonds prevent chains moving relative to
each other.
Epoxy:
Polyester:
Epoxy is a polymer that contain an epoxide group in its chemical structure.
Example: DGEBA (Diglcidyl Ether of Bisphenol A )
A condensation reaction between a glycol and an unsaturated dibasic
acid results in polyster. This contains a double bond C=C between its
carbon atoms.
Example: poly ethylene terephthalate (PET).
Charecteristics of Polyester:
Charecteristics of Epoxy:
• Better Moisture Resistence
• Low shrinkage
• Good adhersion with Reinforcement
• Cheap
• Resistance to variety of chemicals
• Adequate moisture resistance
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Thermoplastics
•
•
•
In thermoplastic polymer, individual molecules are linear in structure with
no chemical linking between them.
Some thermoplastics normally do not crystallize, they are termed
as"amorphous" plastics and are useful at temperatures below the Tg.
Mereka berada di tempat karena ikatan sekunder yang jelek
(intermolecular force), seperti ikatan van der Walls dan hydrogen.
•
Generally, amorphous thermoplastics are less chemically resistant.
Reasons for the use of thermoplastic matrix composites
Thermoplastics (80%)
•
Refrigeration is not necessary with a thermoplastic matrix.
•
Parts can be made and joined by heating.
•
Parts can be remolded, and any scrap can be recycled.
•
Thermoplastics have better toughness and impact resistance than
thermosets.
• No cross links between chains.
• Weak attractive forces between chains broken by
warming.
• Change shape - can be remoulded.
• Weak forces reform in new shape when cold.
•
Shorter fabrication time.
•
Can be recycled.
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UNIQUE CHARACTERISTIC OF
THERMOPLASTIC
•
•
•
•
Near to glass transition temperature
Tg, polymeric materials changes a
hard solid to soft, tough ( leather like)
solid. Over a temperature range
around Tg.Near this temperature, the
materials is also highly viscoelastic.
When load is applied it exhibit Elastic
deformation.
With increasing temperature polymer
changes
into
rubberlike
solid
undergoing deformation on external
load.
Further increasing the temp both
amorphous
and
semicrystallline
thermoplastic achieve highly viscous
state and attain the melting temp Tm.
•
•
Thermoplastic polymer have higher strain-to-failure.
Variation of Tensile modulus with temperature for
Amorphous and Semi crytaline thermoplastic.
Types of Thermoplastics
COMPARISON OF THE THREE POLYMER CATEGORIES
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Thermoplastics Vs Thermosets
Functions of Matrix
•
Menopang fiber secara bersama-sama.
•
Melindungi fiber dari lingkungan.
•
Mendistribusikan beban secara merata di antara fiber sehingga semua
fiber terdistribusi sejumlah regangan yang sama.
•
Meningkatkan sifat sebuah lapisan tranversal.
•
Meningkatkan resisytansi impak dan kerusakan komponen.
•
Membantu menghindari rambatan retak yang tumbuh melalui fiber dengan
memberikan alternatif kegagalan sepanjang permukaan antara fiber dan
matriks.
•
Reasonable strength, modulus and elongation (elongationshould be
greater than fibre).
•
Strength at elevated temperature (depending on application).
Desired Properties of a Matrix
•
Reduced moisture absorption.
•
Low shrinkage.
•
Low coefficient of thermal expansion.
•
Low temperature capability (depending on application).
•
Good flow characteristics so that it penetrates the fibre bundles
completely and eliminates voids during the compacting/curing
process.
•
Excellent chemical resistance (depending on application).
Must be elastic to transfer load to fibres.
•
Should be easily processable into the final composite shape.
•
Dimensional stability (maintains its shape).
•
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Effect of Temperature on Thermoplastics
Thermoplastic polymers
Thermosetting polymers
80
90
Polysulfon
70
80
70
60
50
40
Polyamid
Polyethylene
30
20
Stress (Mpa)
Degradation
temperature - The
temperature above
which a polymer
burns,
chars,
or
decomposes.
Glass temperature The
temperature
range below which
the
amorphous
polymer assumes a
rigid
glassy
structure.
Stress (Mpa)
Stress-strain behavior of different polymer
matrices
Polyester
Epoxy
60
Phenolic
50
40
30
20
10
10
0
0
0
100
The effect of temperature on the modulus of
elasticity for an amorphous thermoplastic.
200
300
Strian(% )
400
500
0
1
2
3
Strian(%)
4
5
Notice to the range of ultimate strains of different polymers
Comparision of various polymers as matrix materials
Limitations of PMC (Termoplastis)
–
Low maximum working temperature.
–
High coefficient of thermal expansion- dimensional instability
–
Sensitivity to radiation and moisture.
–
Processing temperature are generally higher than those with
thermosets.
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Pultrusion -characteristics
Pultrusion
Advantages:
Minimal kinking of
fibres/fabrics
•
Potential Problems:
Improper fibre wet-out
Fibre breakage
Rapid processing
Inadequate cure
Low material scrap rate
Die jamming
Good quality control
Complex die design
•
•
•
•
•
•
•
seek uniform thickness in order to achieve uniform cooling and hence minimise
residual stress.
hollow profiles require a cantilevered mandrel to enter the die from the fibre-feed
end.
continuous constant cross-section profile
normally thermoset (thermoplastic possible)
– impregnate with resin
– pull through a heated die
• resin shrinkage reduces friction in the die
• polyester easier to process than epoxy
tension control as in filament winding
post-die, profile air-cooled before gripped
– hand-over-hand hydraulic clamps
– conveyor belt/caterpillar track systems.
moving cut-off machine ("flying cutter"). The solid laminate will be cut to the
desired length
Inside the metal die, precise temperature control activates the curing of the
thermoset resin.
The Interface
Interfacial bonding
•
Good bonding (adhesion) between matrix phase and dispersed
phase provides transfer of load, applied to the material to the
dispersed phase via the interface. Adhesion is necessary for
•
•
There is always an interface between constituent phases in a
composite material.
For the composite to operate effectively, the phases must bond
where they join at the interface.
achieving high level of mechanical properties of the composite.
•
There are three forms of interface between the two phases:
•
Direct bonding with no intermediate layer. In this case adhesion
(”wetting”) is provided by either covalent bonding or van der
Waals force.
•
Intermediate layer (inter-phase) is in form of solid solution of the
•
Intermediate layer is in form of a third bonding phase
matrix and dispersed phases constituents.
(adhesive).
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Reinforcement-Matrix Interface
• The load acting on the matrix has to be transferred to the reinforcement
via. Interface.
• The reinforcement must be strongly bonded to the matrix if high stiffness
and strength are desired in the composite materials
• A weak interface results in low stiffness and strength but high resistance
to fracture.
• A strong interface produces high stiffness and strength but often low
resistance to fracture, i.e. brittle behavior
Interfacial bonding
• Setelah matriks memiliki kebasahan (wetability) terhadap penguat,
ikatan akan terjadi.
• Untuk sistem tertentu, lebih dari satu mekanisme ikatan mungkin
terjadi pada waktu yang sama.
2 types of failure at interface
• Ikatan dapat berubah selama tahap produksi atau selama perbaikan.
1) Adhesive failure - failure occur at interface
2) Cohesive failure – failure occur close to the interface (either at the fiber or
matrix)
Types of interfacial bonding at interface
• Mechanical bonding
• Physical bonding
• Chemical bonding
Mechanical Bonding
• It is a simple mechanical keying or
interlocking effect between the
fiber-matrix phases.
Physical Bonding
• These kind of bonding involves weak secondary
waals forces, dipolar interactions and hydrogen bonds.
or
vander
• These type of bonding mechanism is of low significance because of its
low magnitude.
• The bond energy lies in the range of 8-16 kJ/mol.
• When the matrix shrinks radially on
cooling over the
reinforcement leads to a griping
action of the matrix on the fiber.
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Chemical bonding
Interphase
• Dissolution Bonding: This bonding is of short range and occurs at an
electronic scale. This type of bonding is hindered by the presence of
impurities on the fiber surface and also gas or air bubbles at the
interface.
•
•
In some cases, a third ingredient must be added to achieve
bonding of primary and secondary phases
Called an interphase, this third ingredient can be thought of as
an adhesive
• Reaction Bonding: This bonding is due to the transport of the molecules,
atoms or ions which diffuse to the interface.
APPLICATIONS OF PMCs
Another Interphase
•
Polymer composites are used to make very light bicycles that are
faster and easier to handle than standard ones, fishing boats that
are resistant to corrosive seawater and lightweight turbine blades
that generate wind power efficiently. New commercial aircraft also
contain more composites than their predecessors. A 555-passenger
plane recently built by Airbus, for example, consists of 25 percent
composite material, while Boeing is designing a new jumbo aircraft
that is planned to be more than half polymer composites.
•
Polymer Matrix Composites (PMCs) are used for manufacturing:
secondary load-bearing aerospace structures, boat bodies, canoes,
kayaks, automotive parts, radio controlled vehicles, sport goods (golf
clubs, skis, tennis racquets), fishing rods, bullet-proof vests and
other armor parts, brake and clutch linings.
Interphase consisting of a solution of primary and
secondary phases
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