pkm-pengantar material komposit
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The world of materialsThe world of materialsSteels
Cast ironsAl-alloys
PE, PP, PC
y
MetalsCu-alloysNi-alloysTi-alloys
, ,PA (Nylon)
Polymers,elastomers
Butyl rubberN
GFRPCFRP
AluminaSi-Carbide
Ceramics,glasses
S d l NeopreneCompositesKFRP
Plywood
Soda-glassPyrex
Polymer foamsMetal foams
FoamsCeramic foams
Glass foams
Woods
Naturalmaterials
Natural fibres:Glass foams Hemp, Flax, Cotton
CompositesCompositesComposites are formed from two or more typesof materials Examples polymer/ceramic andof materials. Examples polymer/ceramic andmetal/ceramic composites.
Composites are used because overall propertiesof the composites are superior to those of theindividual components.For example: polymer/ceramic composites have agreater modulus than the polymer componentgreater modulus than the polymer component,but aren't as brittle as ceramics.
• Definition: a material composed of 2 or more pconstituents– Reinforcement phase (e.g., Fibers)
Bi d h ( li t t i )– Binder phase (e.g., compliant matrix)
• Advantages• Advantages– High strength and stiffness– Low weight ratio– Material can be designed in addition to the structure
InterfaceInterface merupakan permukaan antarareinforcement dan matriks yang menentukanproses transfer tegangan dari matrik-reinforcement-matrik, yang berpengaruhkepada :- spesific strength- spesific stiffnes- fracture toughness- ketahanan creep
Macam-macam interfacial bonding :Macam macam interfacial bonding :• Molecule entanglement → adanya ikatan
antar molekul di permukaan fiber danantar molekul di permukaan fiber dan matrik.
• Electrostatic → adanya perbedaan muatan• Electrostatic → adanya perbedaan muatanlistrik secara atomik antara reinforce danmatrik di permukaan interface yangmatrik di permukaan interface yang mengakibatkan tarik-menarik, bila adagas, ikatan melemah.g
• Reaksi kimia →pada interface terdapatReaksi kimia →pada interface terdapatkumpulan gugus kimia yang saling berikatan antara fiber dan matrikberikatan antara fiber dan matrik.
• Mechanical bonding → adanyamekanisme interlocking pada permukaanmekanisme interlocking pada permukaansehingga semakin kasar permukaan ikatan yang terjadi makin kuatikatan yang terjadi makin kuat.
• Reaction & Interdiffusion bonding- Reaction → terjadi pada material polimerReaction → terjadi pada material polimerdimana terjadi penjalinan rantai-rantaiI t diff i b di t j di di- Interdiffusion bonding → terjadi di interface logam dan keramik dimanak b t k l i di kakan membentuk lapisan di permukaan
yang berbeda
Particle reinforced composites support higher tensile, compressive and shear stresses.
Figure 1. Examples for particle-reinforced composites. (S h idi d t l d t bil(Spheroidized steel and automobile
The following are some of the reasons why g ycomposites are selected for certain applications:
High strength to weight ratio (low density high tensile strength)strength)
High creep resistance
High tensile strength at elevated temperatures
High toughness
Examples of CompositesExamples of Composites• NaturalNatural
– Wood• flexible cellulose fibers held together with stiff lignin• flexible cellulose fibers held together with stiff lignin
– Bone• strong protein collagen and hard brittle apatitestrong protein collagen and hard, brittle apatite
• Artificial (man-made)constituent phases are chemically distinct– constituent phases are chemically distinct
DefinitionsDefinitions
• Composites often have only two phasesComposites often have only two phases• Matrix phase
ti d th h– continuous - surrounds other phase• Dispersed phase
– discontinuous phase
Matrix (light)Dispersed phase (dark)
ObjectivesObjectives• Definitions in composite materialsDefinitions in composite materials
– dispersed phase, matrixStructure of composites• Structure of composites– particle-reinforced
f f– fiber reinforced– structural composites
• Engineering applications often require unusual bi ti f ticombinations of properties
– esp. aerospace, underwater, and transportationcan’t be achieved with a single material– can t be achieved with a single material
– e.g. - aerospace requires strong, stiff, light, and abrasion resistant materialabrasion resistant material• most strong, stiff materials are dense and
heavy• most light materials are not abrasion resistant
Classification of Artificial Composites
Composites
Particulate Fiber Structural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
Properties of CompositesProperties of CompositesDependent on:Dependent on:• constituent phases
l ti t• relative amounts• geometry of dispersed phase
– shape of particles– particle sizep– particle distribution– particle orientationp
C it P tComposite ParametersFor a given matrix/dispersed phase system:• Concentration• Size• Shape• Distribution• Orientation
ParametersParametersParametersParameters
ConcentrationDistribution OrientationConcentrationDistribution Orientation
SizeShape
Classification of Artificial Composites
Composites
Particulate Fiber Structural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
Particle-Reinforced Composites
Divided into two classes(based on strengthening mechanism)• Large particle
– interaction between particles and matrix pare not on the atomic or molecular level
– particle/matrix interface strength is criticalp g• Dispersion strengthened
– 0 01-0 1 μm particles0.01 0.1 μm particles– inhibit dislocation motion
Large Particle CompositesLarge Particle CompositesExamples:Examples:• Some polymers with added fillers are
really large particle compositesreally large particle composites• Concrete (cement with sand or gravel)
– cement is matrix, sand is particulate
CERMET Cutting Tool
Light phase - Matrix (Cobalt)
CERMET Cutting Tool
Dark phase- Particulate (WC)
Large Particle CompositesLarge Particle CompositesDesired CharacteristicsDesired Characteristics• Particles should be approximately
equiaxedequiaxed• Particles should be small and evenly
di t ib t ddistributed• Volume fraction dependent on desired
properties
Large-Particle Composite Materials
• All three material typesAll three material types– metals, ceramics, and polymers
CERMET (ceramic metal composite)• CERMET (ceramic-metal composite)– cemented carbide (WC, TiC embedded in Cu
or Ni)or Ni)– cutting tools (ceramic hard particles to cut, but
a ductile metal matrix to withstand stresses)a ductile metal matrix to withstand stresses)– large volume fractions are used (up to 90%!)
Large Particle CompositesConcrete
• Concrete is not cement)Concrete is not cement)– Concrete is the composite of cement and an
aggregate (fine sand or coarse gravel)aggregate (fine sand or coarse gravel)• Reinforced concrete
a composite (large particle composite) with a– a composite (large particle composite) - with a matrix which is a compositesteel rods wires bars (sometimes stretched– steel rods, wires, bars (sometimes stretched elastically while concrete dries to put system in compression)in compression)
Dispersion Strengthened CompositesDispersion Strengthened Composites• Metals and metal alloys
– hardened by uniform dispersion of fine particles of a very hard material (usually ceramic)
• Strengthening occurs through the interactions• Strengthening occurs through the interactions of dislocations and the particulates
• ExamplesExamples• Thoria in Ni• Al/Al2O3 sintered aluminum powder SAP
Classification of ArtificialClassification of Artificial Composites
Composites
Particulate Fiber Structural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
Fiber sebagai reinforcedFiber sebagai reinforced
Fiber yang digunakan harus:Fiber yang digunakan harus: • Mempunyai diameter yang lebih kecil dari
diameter bulknya (matriksnya) namundiameter bulknya (matriksnya) namun harus lebih kuat dari bulknyaH i t il t th• Harus mempunyai tensile strength yang tinggi
Matriks yang dipadukan dengan fiber berfungsi sebagai :
• Penjepit fiber• Melindungi fiber dari kerusakan permukaan• Pemisah antara fiber dan juga mencegah
timbulnya perambatan crack dari suatu fiber ke fiber lain
• Berfungsi sebagai medium dimana eksternal t di lik ik k k itstress yang diaplikasikan ke komposit,
ditransmisikan dan didistribusikan ke fiber.
Matriks yang digunakan harus :Matriks yang digunakan harus :• Ductility tinggi
M iliki d l l ti it l bih d h• Memiliki modulus elastisitans lebih rendah daripada fiber
• Mempunyai ikatan yang bagus antara matriks dan fiber
• Biasanya secara umum yang digunakan adalah polimer dan logamp g
Sh t(di ti ) fib i f d ita. Short(discontinuous) fiber reinforced composites
Aligned Random
b. Continuous fiber (long fiber) reinforced composites
Fiber yang biasa digunakan antara lain :Fiber yang biasa digunakan antara lain :
Fibers – Glass– Sangat umun digunakan, fiber yang murah adalah
glass fiber yang sering digunakan untuk reinforcement dalam matrik polimerreinforcement dalam matrik polimer
– Komposisi umum adalah 50 – 60 % SiO2 dan paduan lain yaitu Al, Ca, Mg, Na, dll.
– Moisture dapat mengurangi kekuatan dari glass fiber
– Biasanya digunakan untuk: piping, tanks, boats, y g p p g, , ,alat-alat olah raga
Sifat-Sifatnyay• Densitasnya cukup rendah ( sekitar 2.55 g/cc)• Tensile strengthnya cukup tinggi (sekitar 1.8 g y p gg (
GPa)• Biasanya stiffnessnya rendah (70GPa)• Stabilitas dimensinya baik• Resisten terhadap panas
R i h d di i• Resisten terhadap dingin• Tahan korosi
Keuntungan :• Biaya murah• Tahan korosi• Biayanya relative lebih rendah dari komposit
lainnyaKerugianKerugian
• Kekuatannya relative rendah • Elongasi tinggiElongasi tinggi• Keuatan dan beratnya sedang (moderate)
Jenis-jenisnya antara lain :j y– E-Glass - electrical, cheaper– S-Glass - high strength
Fibers - Aramid (kevlar Twaron)Fibers - Aramid (kevlar, Twaron)Biasanya digunakan untuk : Armor, protective clothing industrial sportingprotective clothing, industrial, sporting goodsK t k k t k ti i dKeuntungan :kekutannya cukup tinggi, dan lebih ductile dari carbon
Carbon Fibers• Densitas karbon cukup ringan yaitu sekitar 2.3
g/cc• Struktur grafit yang digunakan untuk membuatStruktur grafit yang digunakan untuk membuat
fiber berbentuk seperti kristal intan.• Karakteristik komposit dengan serat karbon :
– ringan;– kekuatan yang sangat tinggi;– kekakuan (modulus elastisitas) tinggi.( ) gg
• Diproduksi dari poliakrilonitril (PAN), melalui tiga tahap proses :
Stabilisasi = peregangan dan oksidasi;• Stabilisasi = peregangan dan oksidasi;• Karbonisasi= pemanasan untuk mengurangi O, H,
N;G fiti i i k tk d l l ti it• Grafitisasi = meningkatkan modulus elastisitas.
Flat flakes sebagai penguat (Flake composites)Flat flakes sebagai penguat (Flake composites)
Fillers sebagai penguat (Filler composites)Fillers sebagai penguat (Filler composites)
Fiber Reinforced CompositesFiber-Reinforced Composites• Technologically the most important typeTechnologically, the most important type
of composite• Characterized in terms of specific strength• Characterized in terms of specific strength
or specific modulus = strength (or E) per weightweight– usually want to maximize specific strength
and modulusand modulus• Subclasses:
– Short fiber and continuous fiber lengths
Fiber PhaseFiber PhaseRequirements for the fiberRequirements for the fiber• The small diameter fiber must be much
stronger than the bulk materialg• High tensile strengthDifferent classificationsDifferent classifications• whiskers (single crystal - large aspect ratio)• fibers (polycrystalline or amorphous)fibers (polycrystalline or amorphous)• wires (large diameters - usually metal)
Matrix PhaseMatrix PhaseFunctionFunction• Binds fibers together• Acts as a medium through which• Acts as a medium through which
externally applied stress is transmitted and distributed to the fibersand distributed to the fibers
• Protects fiber from surface damage• Separates fibers and prevents a crack• Separates fibers and prevents a crack
from one fiber from propagating through anotheranother
Matrix PhaseMatrix PhaseRequirementsRequirements• Ductile• Lower E than for fiber• Lower E than for fiber• Bonding forces between fiber and
matrix must be highmatrix must be high– otherwise fiber will just “pull-out” of matrix
G ll l l d t l• Generally, only polymers and metals are used as matrix material (they are d til )ductile)
Influence of Fiber LengthInfluence of Fiber Length• Mechanical properties depend on:p p p
• mechanical properties of the fiber• how much load the matrix can transmit to the
fiberfiber– depends on the interfacial bond between the fiber
and the matrix
• Critical fiber length depends on• Critical fiber length - depends on• fiber diameter, fiber tensile strength• fiber/matrix bond strength
Influence of Fiber LengthInfluence of Fiber Length
• Critical fiber length• Critical fiber length -lc– “Continuous” fibers l >>– Continuous fibers l >>
15 lc– “Short” fibers are anything
shorter 15 ll d/2shorter 15 lclc = σfd/2τc
where No Reinforcement
d = fiber diameterτc = fiber-matrix bond strengthstrengthσf = fiber yield strength
Influence of Fiber OrientationInfluence of Fiber Orientation• Fiber parametersFiber parameters
– arrangement with respect to each other– distributiondistribution– concentration
• Fiber orientationFiber orientation– parallel to each other– totally randomy– some combination
Influence of Fiber OrientationInfluence of Fiber Orientation
• Stage I - elastic deformation with intermediate • Stage II - matrix yieldsg y• Failure - Non-catastrophic. When fibers fracture, you now have new fiber
length and matrix is still present
Aligned FibersAligned Fibers• When fibers are alignedWhen fibers are aligned
– properties of material are highly anisotropicmodulus in direction of alignment is a function– modulus in direction of alignment is a function of the volume fraction of the E of the fiber and matrixmatrix
– modulus perpendicular to direction of alignment is considerably less (the fibers do g y (not contribute)
Randomly Oriented FibersRandomly Oriented Fibers• Properties are isotropicProperties are isotropic
– not dependent on directionUltimate tensile strength is less than for• Ultimate tensile strength is less than for aligned fibers
f f• May be desirable to sacrifice strength for the isotropic nature of the composite
Fiberglass Reinforced Composites
Glass is a common reinforcementGlass is a common reinforcement• it is easily drawn into fibers
it i h d dil il bl• it is cheap and readily available• it is easy to process into composites• it can produce very strong, very light
composites (high specific strength)p ( g p g )• it is usually chemically inert (does not
degrade in harsh environments)degrade in harsh environments)
Volume Fraction in Fiber Composites
Elastic modulus is dependent on the volume• Elastic modulus is dependent on the volume fraction of fibers“R l f i t ” ti ( i )• “Rule of mixtures” equation (again)– E - elastic modulus, V- volume fraction, m- matrix, f- fiber– upper boundpp
lower bound
Ec =EmVm +E fVf(iso(iso--strain)strain)
– lower bound
Ec =EmE f
(iso(iso--stress)stress) Ec = EfVm +EmVf
Rule of MixturesRule of Mixtures
*
Upper bound(iso-strain)
Ec =EmVm +E fVf
* **
***
* f f
EEmE f
conc of fibersx er
Lower bound(iso-stress)
Ecf
EfVm +EmVf=
Actual
conc. of fibers
E-m
atri
E -
fibe
ValuesE
ExampleExample• Calculate the composite modulus forCalculate the composite modulus for
polyester reinforced with 60 vol% E-glass under iso-strain conditionsunder iso strain conditions.
• Epolyester = 6.9 x 103 MPa• EE glass = 72.4 x 10 3 MPaEE-glass 72.4 x 10 MPa
Ec = (0.4)(6.9x103 MPa) + (0.6)(72.4x103 MPa) = 46.2 x 103 MPa
Other Composite PropertiesOther Composite Properties
• In general, the rule of mixtures (for upperand lower bounds) can be used for any property Xc - thermal conductivity,density, electrical conductivity…etc.
Xc = XmVm + XfVf
Xc = XmXf/(VmXf + VfVm)
Fiber and Matrix PhasesFiber and Matrix Phases • Fibers
• whiskers: flawless, large l/d ratio, very strong• fiber• wires
• Matrix– polymer or metal-matrix: used for their ductility
• bind fibers, transmits load to fibers• matrix should be more ductile, fiber should have higher E• matrix protects fibers from surface damage (cracks)
t i t k ti f fib t th t hi h ld• matrix prevents cracks propagating from one fiber to the next which could cause catastrophic failure.
– ceramics-matrix: used to increase fracture t h f itoughness of ceramic
• Essential that Fiber-Matrix bond be strong
Polymer Matrix CompositesPolymer-Matrix Composites • Fibers
• Glass Fiber - fiberglass• Carbon fiber - graphitic and amorphous C• Aramid fiber - Kevlar, highly linear polymer chain
• Matrix• polyester and vinyl esters - fiberglass• epoxies - aerospace applications, stronger,
resistant to moist reresistant to moisture• polyimides - high temperature• high temperature thermoplastics - PEEK PPShigh temperature thermoplastics PEEK, PPS,
PEI, aerospace
Metal-Matrix Composites
Ceramic-Matrix Composites
Employed to increase the fracture toughness of the ceramicEmployed to increase the fracture toughness of the ceramicExample: Transformation toughened zirconia
Other CompositesOther Composites
Carbon-Carbon Compositescarbon fiber in pyrolyzed carbon matrixhigh tensile strength and modulus at high temperature (2000ºC)g g g p ( )low coefficient of thermal expansionhigh thermal conductivitieslow thermal shock potentialApplications include; rocket motors, friction materials in aircraft,
advanced turbine engine components, ablative shields for reentry vehicles
Hybrid compositestwo or more different kinds of fibers.
Classification of Artificial Composites
Composites
Particulate Fiber Structural
Continuous Discontinuous
Laminates SandwichPanels
LargeParticle
DispersionStrengthened
Aligned Random
Structural CompositesStructural Composites• DefinitionDefinition
– composed of both homogeneous and composite materialscomposite materials
– properties depend on constituent materials and on geometrical design of the elementsand on geometrical design of the elements
• Typeslaminar composites– laminar composites
– sandwich panels
Laminar CompositesLaminar Composites
T di i l h t• Two dimensional sheets or panels with a preferred high-strength directiong
• Q. What is a natural example of this?
• A. Wood• Q. What is a man made example• A. Plywood - Layers are stacked
and subsequently bonded together h h hi h h di iso that the high strength direction
varies
Sandwich PanelsSandwich Panels• Two strong outer sheets (called faces)Two strong outer sheets (called faces)
separated by a layer of less dense material or core (which has lower E andmaterial or core (which has lower E and lower strength)
• Core• Core– separates faces
i t d f ti di l t th– resists deformation perpendicular to the facesoften hone comb str ct res– often honeycomb structures
• Used in roofs, walls, wings
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