Introduction to Composite Materials
Steels Cast irons Al-alloys
Metals Cu-alloys Ni-alloys Ti-alloys PE, PP, PC PA (Nylon)
Alumina Si-Carbide
Ceramics, glasses o a-g ass Pyrex
Polymers, elastomers
GFRP CFRP
Butyl rubber eoprene
Composites KFRP Plywood
Polymer foams Metal foams
Foams Ceramic foams ass oams
Woods
Natural materials Natural fibres: Hemp, Flax, Cotton
Steels Cast irons Al-alloys
Metals Cu-alloys Ni-alloys Ti-alloys PE, PP, PC PA (Nylon)
Alumina Si-Carbide
Ceramics, glasses o a-g ass Pyrex
Polymers, elastomers
GFRP CFRP
Butyl rubber eoprene
Composites KFRP Plywood
Polymer foams Metal foams
Foams Ceramic foams ass oams
Woods
Natural materials Natural fibres: Hemp, Flax, Cotton
Composites are formed from two or more types . metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components. For example: polymer/ceramic composites have a , but aren't as brittle as ceramics.
• Definition: a material com osed of 2 or more constituents – Reinforcement phase (e.g., Fibers) – Binder phase (e.g., compliant matrix)
– High strength and stiffness – Low weight ratio – Material can be designed in addition to the structure
Interface Interface merupakan permukaan antara reinforcement dan matriks yang menentukan proses transfer tegangan dari matrikreinforcement-matrik, yang berpengaruh kepada : - spesific strength - spesific stiffnes - fracture toughness - ketahanan creep
• Molecule entanglement → adanya ikatan matrik. listrik secara atomik antara reinforce dan mengakibatkan tarik-menarik, bila ada gas, ikatan melemah.
• kump kumpul ulan an gu gugu gus s kimi kimia ay yan ang gs sal alin ing g . • Mechanical b bo onding → adanya sehingga semakin kasar permukaan .
• Rea Reaction ion & Interdiffusion bonding dima man na terja rjadi penjalinan rantai-ra -rantai - n er er us on on ng → er a interface log logam dan keramik dimana a an mem en u ap sa san permu aan yang berbeda
Two types of composites are: Fiber Reinforced Com osites
Particle Reinforced Com osites
Particle reinforced composites support higher tensile, compressive and shear stresses.
Figure 1. Examples for particle-reinforced composites. p ero ze s ee an au omo e
The followin are some of the reasons wh composites are selected for certain applications:
High strength to weight ratio (low density high tensile
High creep resistance
High tensile strength at elevated temperatures
High toughness
• – Wood •
– Bone •
• Artificial (man-made) –
,
Definitions • • Matrix phase – con nuous - surroun s o er p ase
• Dispersed phase – discontinuous phase Matrix (light) Dispersed phase (dark)
• – dispersed phase, matrix
• – particle-reinforced – fiber reinforced – structural composites
• Engineering applications often require unusual com nat ons o propert es – esp. aerospace, underwater, and transportation – ’ – e.g. - aerospace requires strong, stiff, light, and abrasion resistant material • most strong, stiff materials are dense and heavy • most light materials are not abrasion resistant
Classification of Artificial Composites Composites Particulate
Fiber
Large Dispersion Particle Strengthened Continuous
Structural Laminates
Discontinuous
Aligned
Random
Sandwich Panels
• constituent phases • re at ve amounts • geometry of dispersed phase – shape of particles – particle size – particle distribution – article orientation
ompos te arameters For a given matrix/dispersed phase system: • Concentration • Size • Shape • Distribution • Orientation
Shape
Size
Classification of Artificial Composites Composites Particulate
Fiber
Large Dispersion Particle Strengthened Continuous
Structural Laminates
Discontinuous
Aligned
Random
Sandwich Panels
Particle-Reinforced Composites Divided into two classes (based on strengthening mechanism)
• Large particle – interaction between articles and matrix are not on the atomic or molecular level – particle/matrix interface strength is critical
• Dispersion strengthened – . - . – inhibit dislocation motion
• Some polymers with added fillers are • Concrete (cement with sand or gravel) – cement is matrix, sand is particulate
Light phase - Matrix (Cobalt) Dark phase- Particulate (WC)
• Particles should be approximately • Particles should be small and evenly sr ue • Volume fraction dependent on desired properties
Large-Particle Composite Materials • – metals, ceramics, and polymers
•
– cemented carbide (WC, TiC embedded in Cu – cutting tools (ceramic hard particles to cut, but – large volume fractions are used (up to 90%!)
Large Particle Composites Concrete • – Concrete is the composite of cement and an
• Reinforced concrete –
matrix which is a composite – , , elastically while concrete dries to put system in m r i n
• Metals and metal alloys – hardened by uniform dispersion of fine particles of a very hard material (usually ceramic)
• of dislocations and the particulates • • Thoria in Ni • Al/Al2O3 sintered aluminum powder SAP
Composites Composites Particulate
Fiber
Large Dispersion Particle Strengthened Continuous
Structural Laminates
Discontinuous
Aligned
Random
Sandwich Panels
• Mempunyai diameter yang lebih kecil dari harus lebih kuat dari bulknya • arus mempunya ens e s reng tinggi
yang
• • •
•
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 stress yang ap as an e ompos t, ditransmisikan dan didistribusikan ke fiber.
• Ductility tinggi • em mo u us e ast s tans e ren a daripada fiber • Mempunyai ikatan yang bagus antara matriks dan fiber • Biasanya secara umum yang digunakan adalah olimer dan lo am
a.
or
scon nuous
Aligned
er re n orce compos es
Random
b. Continuous fiber (long fiber) reinforced composites
Fibers – Glass – Sangat umun digunakan, fiber yang murah adalah glass fiber yang sering digunakan untuk – Komposisi umum adalah 50 – 60 % SiO2 dan paduan lain yaitu Al, Ca, Mg, Na, dll. – Moisture dapat mengurangi kekuatan dari glass fiber – Biasan a di unakan untuk: i in tanks boats alat-alat olah raga
Sifat-Sifatn a • Densitasnya cukup rendah ( sekitar 2.55 g/cc) • Tensile stren th n a cuku tin i sekitar 1.8 GPa) • Biasanya stiffness nya rendah (70GPa) • Stabilitas dimensinya baik • Resisten terhadap panas • Resisten terhadap dingin • Tahan korosi
Keuntungan : • Biaya murah • Tahan korosi • Biayanya relative lebih rendah dari komposit lainnya • Kekuatannya relative rendah • • Keuatan dan beratnya sedang (moderate)
Jenis- enisn a antara lain : –
–
E-Glass - electrical, cheaper S-Glass - high strength
, Biasanya digunakan untuk : Armor, , , goods eun ungan : e u annya cu up ngg , an lebih ductile dari carbon
Carbon Fibers • Densitas karbon cukup ringan yaitu sekitar 2.3 g/cc • fiber berbentuk seperti kristal intan. • Karakteristik komposit dengan serat karbon : – ringan; – kekuatan yang sangat tinggi; – kekakuan modulus elastisitas tin
i.
• Diproduksi dari poliakrilonitril (PAN), melalui tiga tahap proses : • = • Karbonisasi= pemanasan untuk mengurangi O, H, N; • ra t sas = men ng at an mo u us e ast s tas.
•
, of composite or specific modulus = strength (or E) per – usually want to maximize specific strength
• Subclasses: – Short fiber and continuous fiber lengths
R ir m n f r h fi r • The small diameter fiber must be much stron er than the bulk material • High tensile strength • whiskers (single crystal - large aspect ratio) • • wires (large diameters - usually metal)
• Binds fibers together • externally applied stress is transmitted • Protects fiber from surface damage • from one fiber from propagating through
• Ductile • • Bonding forces between fiber and – otherwise fiber will just “pull-out” of matrix
•
enera y, on y po ymers an me a s are used as matrix material (they are uc e
• Mechanical ro erties de end on: • mechanical properties of the fiber • how much load the matrix can transmit to the – depends on the interfacial bond between the fiber and the matrix
• fiber diameter, fiber tensile strength • fiber/matrix bond strength
•
-
lc – “ ” 15 lc – “Short” fibers are anything c
= σf
c
τc
where d = fiber diameter τc = fiber-matrix bond stren th σf = fiber yield strength
No Reinforcement
• – arrangement with respect to each other – distribution – concentration
• – parallel to each other – totall random – some combination
• • •
Stage I - elastic deformation with intermediate Sta e II - matrix ields Failure - Non-catastrophic. When fibers fracture, you now have new fiber length and matrix is still present
• – properties of material are highly anisotropic – of the volume fraction of the E of the fiber and – modulus perpendicular to direction of ali nment is considerabl less the fibers do not contribute)
• – not dependent on direction
• aligned fibers • May be desirable to sacri ice strength or the isotropic nature of the composite
Fiberglass Reinforced Composites • • • •
it is easily drawn into fibers t s c eap an rea y ava a e it is easy to process into composites it can produce very strong, very light com osites hi h s ecific stren th • it is usually chemically inert (does not
Volume Fraction in Fiber Composites •
uu fraction of fibers
p
v u
• “ u e o m x ures equa on aga n – E - elastic modulus, V- volume fraction, m- matrix, f- fiber – u
er bound
(iso--strain) (iso
E c = E mV m + E f V f
–
(iso--stress) (iso
E m E f E f Vm + E mV f
(iso-strain) Upper bound
*
*
*
**
E c = E mV m + E V
*
Lower bound
c
(iso-stress) x i r t a m -
. Actual Values
r b i f E
=
E m E E f Vm + E mV f
• polyester reinforced with 60 vol% E-glass . • Epolyester = 6.9 x 103 MPa • E = 72.4 x 10 3 MPa
Ec = (0.4)(6.9x103 MPa) + (0.6)(72.4x103 MPa) = 46.2 x 103 MPa
•
In general, the rule of mixtures (for upper and lower bounds) can be used for any property Xc - thermal conductivity, density, electrical conductivity…etc. Xc = XmVm + XfVf Xc = XmX /(V f mXf + VfVm)
• 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) ma r x preven s crac s propaga ng rom one er o e nex w c cou cause catastrophic failure.
– ceramics-matrix: used to increase fracture oug ness o ceram c
• Essential that Fiber-Matrix bond be strong
• 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, res s an o mo s ure • polyimides - high temperature • , PEI, aerospace
,
Metal-Matrix Composites
Ceramic-Matrix Composites Example: Transformation toughened zirconia
Carbon-Carbon Composites carbon fiber in pyrolyzed carbon matrix hi h tensile stren th and modulus at hi h tem erature 2000ºC low coefficient of thermal expansion high thermal conductivities low thermal shock potential Applications include; rocket motors, friction materials in aircraft, advanced turbine engine components, ablative shields for reentry vehicles
Hybrid composites two or more different kinds of fibers.
Classification of Artificial Composites Composites Particulate
Structural
Fiber
Large Dispersion Particle Strengthened Continuous
Laminates Discontinuous
Aligned
Random
Sandwich Panels
• – composed of both homogeneous and – properties depend on constituent materials
• Types – – sandwich panels
•
wo mens ona s eets or panels with a preferred highstren th direction • 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 so that the high strength direction varies
• separated by a layer of less dense lower strength) – separates faces – res s s e orma on perpen cu ar o faces – o en oneycom s ruc ures
• Used in roofs, walls, wings
e