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POLYMER MATRIX COMPOSITES (PMC)

PERTEMUAN KE-9

Material Komposit

KLASIFIKASI KOMPOSIT BERDASARKAN MATRIKSNYA

Composite materials

Matrices

Polymer Matrix Composites (PMC)

Metal Matrix Composites MMC)

Ceramic Matrix Composites (CMC)

Thermoset Thermoplastic Rubber

What is a polymer?

Poly mer

many repeat unit

C C C C C C

HHHHHH

HHHHHH

Polyethylene (PE)

ClCl Cl

C C C C C C

HHH

HHHHHH

Polyvinyl chloride (PVC)

HH

HHH H

Polypropylene (PP)

C C C C C C

CH3

HH

CH3CH3H

repeat

unit

repeat

unit

repeat

unit

Examples of polymers:

A polymer is a large molecule (macromolecule) composed of repeating

structural units typically connected by covalent chemical bonds

Polymer Matrix Composite (PMC) is the material consisting of a

polymer (resin) matrix combined with a fibrous reinforcing dispersed

phase.

Polymer Matrix Composites are very popular due to their low cost

and simple fabrication methods.

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Polymer(Matrix) Composite (Matrix + Reinforcement)

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%.

Konfigurasi rantai Molekul:

a. Linearb. Branchedc. Crossed linkedd. Ladder

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• 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.

Resin thermoset adalah polimer yang paling banyak digunakan

pada PMC.

Epoxy dan polyester biasanya dicampur dengan penguat fiber.

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

Polymerisation:This is the process of joining monomers into gaint chain like molecules.

Methods of Polymerisation:• Condensation polymerisation• Addition polymerisation

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.

• 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.

• 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.

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Thermosets

• Extensive cross-linking formed by covalent bonds.

• Bonds prevent chains moving relative to each other.

Types of Thermosetting plastics

Epoxy:

Epoxy is a polymer that contain an epoxide group in its chemical structure.Example: DGEBA (Diglcidyl Ether of Bisphenol A )

Charecteristics of Epoxy:

• Better Moisture Resistence• Low shrinkage• Good adhersion with Reinforcement

Polyester:

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:

• 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.

• Mereka berada di tempat karena ikatan sekunder yang jelek

(intermolecular force), seperti ikatan van der Walls dan hydrogen.

• Some thermoplastics normally do not crystallize, they are termed

as"amorphous" plastics and are useful at temperatures below the Tg.

• Generally, amorphous thermoplastics are less chemically resistant.

Thermoplastics (80%)

• 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.

Reasons for the use of thermoplastic matrix composites

• 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.

• 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.

• Variation of Tensile modulus with temperature for

Amorphous and Semi crytaline thermoplastic.

• Thermoplastic polymer have higher strain-to-failure.

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 semuafiber terdistribusi sejumlah regangan yang sama.

• Meningkatkan sifat sebuah lapisan tranversal.

• Meningkatkan resisytansi impak dan kerusakan komponen.

• Membantu menghindari rambatan retak yang tumbuh melalui fiber denganmemberikan alternatif kegagalan sepanjang permukaan antara fiber danmatriks.

Desired Properties of a Matrix

• Reduced moisture absorption.

• Low shrinkage.

• Low coefficient of thermal expansion.

• Good flow characteristics so that it penetrates the fibre bundlescompletely and eliminates voids during the compacting/curingprocess.

• Must be elastic to transfer load to fibres.

• Reasonable strength, modulus and elongation (elongationshould be

greater than fibre).

• Strength at elevated temperature (depending on application).

• Low temperature capability (depending on application).

• Excellent chemical resistance (depending on application).

• Should be easily processable into the final composite shape.

• Dimensional stability (maintains its shape).

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Effect of Temperature on Thermoplastics

� Degradationtemperature - Thetemperature abovewhich a polymerburns, chars, ordecomposes.

� Glass temperature -The temperaturerange below whichthe amorphouspolymer assumes arigid glassystructure.

The effect of temperature on the modulus of

elasticity for an amorphous thermoplastic.

Stress-strain behavior of different polymer

matrices

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5

Strian(%)

Str

ess (M

pa)

Phenolic

Polyester Epoxy

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500

Strian(%)S

tress (M

pa)

Polysulfon

PolyamidPolyethylene

Thermoplastic polymers Thermosetting polymers

Notice to the range of ultimate strains of different polymers

Comparision of various polymers as matrix materialsLimitations 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

Advantages:

� Minimal kinking of

fibres/fabrics

� Rapid processing

� Low material scrap rate

� Good quality control

Potential Problems:

� Improper fibre wet-out

� Fibre breakage

� Inadequate cure

� Die jamming

� Complex die design

Pultrusion -characteristics

• 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.

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

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

matrix and dispersed phases constituents.

• Intermediate layer is in form of a third bonding phase

(adhesive).

The Interface

• There is always an interface between constituent phases in acomposite material.

• For the composite to operate effectively, the phases must bondwhere they join at the interface.

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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

2 types of failure at interface

1) Adhesive failure - failure occur at interface2) Cohesive failure – failure occur close to the interface (either at the fiber or

matrix)

• Setelah matriks memiliki kebasahan (wetability) terhadap penguat,

ikatan akan terjadi.

• Untuk sistem tertentu, lebih dari satu mekanisme ikatan mungkin

terjadi pada waktu yang sama.

• Ikatan dapat berubah selama tahap produksi atau selama perbaikan.

Interfacial bonding

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.

• When the matrix shrinks radially on cooling over the reinforcement leads to a griping action of the matrix on the fiber.

Physical Bonding

• These kind of bonding involves weak secondary or vanderwaals forces, dipolar interactions and hydrogen bonds.

• These type of bonding mechanism is of low significance because of itslow magnitude.

• The bond energy lies in the range of 8-16 kJ/mol.

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Chemical bonding

• Dissolution Bonding: This bonding is of short range and occurs at anelectronic scale. This type of bonding is hindered by the presence ofimpurities on the fiber surface and also gas or air bubbles at theinterface.

• Reaction Bonding: This bonding is due to the transport of the molecules,atoms or ions which diffuse to the interface.

Interphase• 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

Another Interphase

Interphase consisting of a solution of primary and

secondary phases

APPLICATIONS OF PMCs

• Polymer composites are used to make very light bicycles that arefaster and easier to handle than standard ones, fishing boats thatare resistant to corrosive seawater and lightweight turbine bladesthat generate wind power efficiently. New commercial aircraft alsocontain more composites than their predecessors. A 555-passengerplane recently built by Airbus, for example, consists of 25 percentcomposite material, while Boeing is designing a new jumbo aircraftthat 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 (golfclubs, skis, tennis racquets), fishing rods, bullet-proof vests andother armor parts, brake and clutch linings.