lecture 11 and 12 ceramics and composites

8/2/2019 Lecture 11 and 12 Ceramics and Composites

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ISSUES TO ADDRESS...

Structures of ceramic materials:How do they differ from those of metals?

Point defects:How are they different from those in metals?

Impurities:How are they accommodated in the lattice and how

do they affect properties?

Mechanical Properties:What special provisions/tests are made for ceramic

materials?

Structures & Properties of

Ceramics


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Bonding:-- Mostly ionic, some covalent.

-- % ionic character increases with difference in

electronegativity.

Adapted from Fig. 2.7, Callister 7e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical

Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by

Cornell University.

Large vs small ionic bond character:

Ceramic Bonding

SiC: small

CaF2: large


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Ceramic Crystal Structures

Oxide structures

oxygen anions much larger than metal cations

close packed oxygen in a lattice (usually FCC)

cations in the holes of the oxygen lattice


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Coordination # increases with

Coordination # and Ionic Radii

Adapted from Table 12.2,

Callister 7e.

2

rcation

ranion

Coord

#< 0.155

0.155 - 0.225

0.225 - 0.414

0.414 - 0.732

0.732 - 1.0

3

4

6

8

linear

triangular

TD

OH

cubic

Adapted from Fig.

12.2, Callister 7e.

Adapted from Fig.

12.3, Callister 7e.

Adapted from Fig.

12.4, Callister 7e.

ZnS

(zincblende)

NaCl(sodiumchloride)

CsCl(cesiumchloride)

r

cationranionIssue: How many anions can you

arrange around a cation?


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Cation Site Size

Determine minimum rcation/ranion for OH site (C.N. = 6)

a 2ranion

2ranion 2rcation 2 2ranion

ranion rcation 2ranion rcation ( 2 1)ranion

2ranion 2rcation 2a

4140anion

cation.

r

r


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On the basis of ionic radii, what crystal structurewould you predict for FeO?

Answer:

5500

1400

0770

anion

cation

.

.

.

r

r

based on this ratio,

--coord # = 6--structure = NaCl

Data from Table 12.3,

Callister 7e.

Example: Predicting Structure of FeO

Ionic radius (nm)

0.053

0.077

0.069

0.100

0.140

0.181

0.133

Cation

Anion

Al3+

Fe2+

Fe3+

Ca2+

O2-

Cl-

F-


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AX Crystal Structures

AXType Crystal Structures include NaCl, CsCl, and zinc blende

939.0181.0

170.0

Cl

Cs

r

r

Adapted from Fig.

12.3, Callister 7e.

Cesium Chloride structure:

cubic sites preferred

So each Cs+ has 8 neighboring Cl-


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Mechanical Properties

We know that ceramics are more brittle than

metals. Why?

Consider method of deformation

slippage along slip planes in ionic solids this slippage is very difficult

too much energy needed to move one anion past

another anion


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Silicate Ceramics

Most common elements on earth are Si & O

SiO2 (silica) structures are quartz, crystobalite, &tridymite

The strong Si-O bond leads to a strong, high melting

material (1710C)

Si4+

O2-

Adapted from Figs.

12.9-10, Callister 7e.

crystobalite


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Amorphous Silica

Silica gels - amorphous SiO2

Si4+ and O2- not in well-ordered

lattice

Charge balanced by H+ (to form

OH-) at dangling bonds

very high surface area > 200 m2/g

SiO2 is quite stable, therefore

unreactive

makes good catalyst support

Adapted from Fig.

12.11, Callister 7e.


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Silica Glass

Dense form of amorphous silica

Charge imbalance corrected with counter

cations such as Na+

Borosilicate glass is the pyrex glass usedin labs better temperature stability & less brittle than sodium

glass


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Combine SiO44- tetrahedra by having them share

corners, edges, or faces

Cations such as Ca2+, Mg2+, & Al3+ act toneutralize & provide ionic bonding

Silicates

Mg2SiO4 Ca2MgSi2O7

Adapted from Fig.



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Layered Silicates

Layered silicates (clay silicates)

SiO4 tetrahedra connected

together to form 2-D plane

(Si2O5)2-

So need cations to balance charge =

Adapted from Fig.



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Kaolinite clay alternates (Si2O5)2- layer with Al2(OH)4

2+

layer

Layered Silicates

Note: these sheets loosely bound by van der Waals forces

Adapted from Fig.



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Layered Silicates

Can change the counterions

this changes layer spacing

the layers also allow absorption of water

Micas KAl3Si3O10(OH)2

Bentonite

used to seal wells

packaged dry

swells 2-3 fold in H2O

pump in to seal up well so no polluted groundwater seeps in to contaminate the water supply.


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Carbon Forms

Carbon black amorphous surface area ca. 1000 m2/g

Diamond

tetrahedral carbon

hard no good slip planes brittle can cut it

large diamonds jewelry

small diamonds

often man made - used for

cutting tools and polishing

diamond films

hard surface coat tools,

medical devices, etc.

Adapted from Fig.



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Carbon Forms - Graphite

layer structure aromatic layers

weak van der Waals forces between layers

planes slide easily, good lubricant

Adapted from Fig.



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Impurities must also satisfy charge balance = Electroneutrality

Ex: NaCl

Substitutional cation impurity

Impurities

Na+ Cl-

initial geometry Ca2+ impurity resulting geometry

Ca2+

Na+

Na+

Ca2+

cationvacancy

Substitutional anion impurity

initial geometry O2- impurity

O2-

Cl-

anion vacancy

Cl-

resulting geometry


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How do we classify ceramics?

What are some applications of ceramics?

How is processing different than for metals?

Applications and Processing of

Ceramics


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Properties:-- Tm for glass is moderate, but large for other ceramics.

-- Small toughness, ductility; large moduli & creep resist.

Applications:-- High T, wear resistant, novel uses from charge neutrality. Fabrication

-- some glasses can be easily formed

-- other ceramics can not be formed or cast.

Glasses Clay

products

Refractories Abrasives Cements Advanced

ceramics

-optical-compositereinforce

-containers/household

-whiteware-bricks

-bricks forhigh T(furnaces)

-sandpaper-cutting-polishing

-composites-structural

engine-rotors-valves

-bearings

-sensors

Adapted from Fig. 13.1 and discussion in

Section 13.2-6, Callister 7e.

Taxonomy of Ceramics


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Need a material to use in high temperature furnaces. Consider the Silica (SiO2) - Alumina (Al2O3) system.

Phase diagram shows:mullite, alumina, and crystobalite as candidate refractories.

Adapted from Fig. 12.27,

Callister 7e. (Fig. 12.27

is adapted from F.J. Klug

and R.H. Doremus,"Alumina Silica Phase

Diagram in the Mullite

Region", J. American

Ceramic Society70(10),

p. 758, 1987.)

Application: Refractories

Composition (wt% alumina)

T(C)

1400

1600

1800

2000

2200

20 40 60 80 1000

alumina+mullite

mullite

+ L

mulliteLiquid

(L)

mullite+ crystobalite

crystobalite+ L

alumina + L

3Al2O3-2SiO2


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tensileforce

Ao

Addie

die

Die blanks:-- Need wear resistant properties!

Die surface:-- 4 m polycrystalline diamond

particles that are sintered onto a

cemented tungsten carbidesubstrate.

-- polycrystalline diamond helps control

fracture and gives uniform hardness

in all directions.

Courtesy Martin Deakins, GE

Superabrasives, Worthington,

OH. Used with permission.

Adapted from Fig. 11.8 (d),

Callister 7e.Courtesy Martin Deakins, GE

Superabrasives, Worthington,OH. Used with permission.

Application: Die Blanks


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Tools:-- for grinding glass, tungsten,

carbide, ceramics

-- for cutting Si wafers

-- for oil drilling

bladesoil drill bits Solutions:

coated single

crystal diamonds

polycrystalline

diamonds in a resin

matrix.

Photos courtesy Martin Deakins,

GE Superabrasives, Worthington,

OH. Used with permission.

Application: Cutting Tools

-- manufactured single crystal

or polycrystalline diamonds

in a metal or resin matrix.

-- optional coatings (e.g., Ti to helpdiamonds bond to a Co matrix

via alloying)-- polycrystalline diamonds

resharpen by microfracturing

along crystalline planes.


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Example: Oxygen sensor ZrO2 Principle: Make diffusion of ions

fast for rapid response.

Application: Sensors

A Ca2+ impurity

removes a Zr4+

and aO2- ion.

Ca2+

Approach:Add Ca impurity to ZrO2:

-- increases O2-

vacancies-- increases O2- diffusion rate

referencegas at fixedoxygen content

O2-

diffusion

gas with anunknown, higheroxygen content

-+voltage difference produced!

sensor Operation:

-- voltage differenceproduced when

O2- ions diffuse

from the external

surface of the sensor

to the reference gas.


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Pressing:

GLASS

FORMING

Adapted from Fig. 13.8, Callister, 7e. (Fig. 13.8 is adapted from C.J. Phillips,

Glass: The Miracle Maker, Pittman Publishing Ltd., London.)

Ceramic Fabrication Methods-I

Gob

Parisonmold

Pressingoperation

Blowing:

suspendedParison

Finishingmold

Compressed

air

plates, dishes, cheap glasses

--mold is steel with

graphite lining

Fiber drawing:

wind up

PARTICULATE

FORMING

CEMENTATION


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Sheet Glass Forming

Sheet forming continuous draw

originally sheet glass was made by floating glass

on a pool of mercury

Adapted from Fig. 13.9, Callister 7e.


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Quartz is crystalline

SiO2:

Basic Unit: Glass is amorphous Amorphous structure

occurs by adding impurities

(Na+,Mg2+,Ca2+, Al3+)

Impurities:

interfere with formation ofcrystalline structure.

(soda glass)


Callister, 7e.

Glass Structure

Si04 tetrahedron4-

Si4+

O2-

Si4+

Na+

O2-


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Specific volume (1 ) vs Temperature (T):

Glasses:-- do not crystallize

-- change in slope in spec. vol. curve at

glass transition temperature, Tg-- transparent

- no crystals to scatter light

Crystalline materials:-- crystallize at melting temp, Tm-- have abrupt change in spec.

vol. at Tm

Adapted from Fig. 13.6, Callister, 7e.

Glass Properties

T

Specific volume

Supercooled

Liquid

solid

Tm

Liquid

(disordered)

Crystalline

(i.e., ordered)

Tg

Glass

(amorphous solid)


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Viscosity decreases with T Impurities lowerTdeform

Adapted from Fig. 13.7, Callister, 7e.

(Fig. 13.7 is from E.B. Shand, Engineering

Glass, Modern Materials, Vol. 6, Academic

Press, New York, 1968, p. 262.)

Glass Viscosity vs. T and Impurities

Visco

sity[Pa

s

]

1

102

106

1010

1014

200 600 1000 1400 1800 T(C)

Tdeform

: soft enough

to deform or work

annealing range

Tmelt

strain point

fused silica: > 99.5 wt% SiO2

soda-lime glass: 70% SiO2

balance Na2O (soda) & CaO (lime)

Vycor: 96% SiO2, 4% B2O3

borosilicate (Pyrex):

13% B2O3, 3.5% Na2O, 2.5% Al2O3


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Annealing:--removes internal stress caused by uneven cooling.

Tempering:--puts surface of glass part into compression

--suppresses growth of cracks from surface scratches.

--sequence:

Heat Treating Glass

further cooled

tension

compression

compression

before cooling

hot

surface cooling

hot

cooler

cooler

--Result: surface crack growth is suppressed.


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Milling and screening: desired particle size

Mixing particles & water: produces a "slip"

Form a "green" component

Dry and fire the component

ram billet

container

containerforce

die holder

die

Ao

Adextrusion--Hydroplastic forming:

extrude the slip (e.g., into a pipe)

Adapted from

Fig. 11.8 (c),

Callister 7e.

Ceramic Fabrication Methods-IIA

solid component

--Slip casting:

Adapted from Fig.


(Fig. 13.12 is fromW.D. Kingery,

Introduction to

Ceramics, John

Wiley and Sons,

Inc., 1960.)

hollow component

pour slipinto mold

drainmold

greenceramic

pour slipinto mold

absorb waterinto mold

green

ceramic

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION


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Clay Composition

A mixture of components used

(50%) 1. Clay

(25%) 2. Filler e.g. quartz (finely ground)

(25%) 3. Fluxing agent (Feldspar)

binds it together

aluminosilicates + K+, Na+, Ca+


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Clay is inexpensive

Adding water to clay-- allows material to shear easily

along weak van der Waals bonds

-- enables extrusion

-- enables slip casting

Structure of

Kaolinite Clay:Adapted from Fig. 12.14, Callister 7e.

(Fig. 12.14 is adapted from W.E. Hauth,

"Crystal Chemistry of Ceramics",American

Ceramic Society Bulletin, Vol. 30 (4), 1951,

p. 140.)

Features of a Slip

weak vander Waalsbonding

chargeneutral

chargeneutral

Si 4+

Al3+

-OH

O2-

Shear

Shear


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Drying: layer size and spacing decrease.Adapted from Fig.


(Fig. 13.13 is from

W.D. Kingery,

Introduction to

Ceramics, John

Wiley and Sons,

Inc., 1960.)

Drying and Firing

Drying too fast causes sample to warp or crack due to non-uniform shrinkage

wet slip partially dry green ceramic

Firing:--Traised to (900-1400 C)

--vitrification: liquid glass forms from clay and flows between

SiO2 particles. Flux melts at lowerT.Adapted from Fig. 13.14,

Callister 7e.(Fig. 13.14 is courtesy H.G.

Brinkies, Swinburne

University of Technology,

Hawthorn Campus,

Hawthorn, Victoria,

Australia.)

Si02

particle

(quartz)

glass formedaroundthe particle

micrograph ofporcelain

70 m


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Sintering: useful for both clay and non-clay compositions.

Procedure:

-- produce ceramic and/or glass particles by grinding-- place particles in mold

-- press at elevated Tto reduce pore size.

Aluminum oxide powder:-- sintered at 1700 C

for 6 minutes.


(Fig. 13.17 is from W.D. Kingery, H.K.

Bowen, and D.R. Uhlmann, Introduction

to Ceramics, 2nd ed., John Wiley and

Sons, Inc., 1976, p. 483.)

Ceramic Fabrication Methods-IIB

15m

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION


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Powder Pressing

Sintering - powder touches - forms neck & gradually neck thickens add processing aids to help form neck

little or no plastic deformation


Uniaxial compression - compacted in single direction

Isostatic (hydrostatic) compression - pressure applied byfluid - powder in rubber envelope

Hot pressing - pressure + heat


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Tape Casting

thin sheets of green ceramic cast as flexible tape

used for integrated circuits and capacitors

cast from liquid slip (ceramic + organic solvent)



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Produced in extremely large quantities.

Portland cement:

-- mix clay and lime bearing materials-- calcinate (heat to 1400C)

-- primary constituents:

tri-calcium silicate

di-calcium silicate

Adding water-- produces a paste which hardens-- hardening occurs due to hydration (chemical reactions

with the water).

Forming: done usually minutes after hydration begins.

Ceramic Fabrication Methods-III

GLASS

FORMING

PARTICULATE

FORMING

CEMENTATION


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Applications: Advanced Ceramics

Heat Engines

Advantages:

Run at higher

temperature

Excellent wear &

corrosion resistance

Low frictional losses

Ability to operate without

a cooling system

Low density

Disadvantages:

Brittle

Too easy to have voids-

weaken the engine

Difficult to machine

Possible parts engine block, piston coatings, jet engines

Ex: Si3N4, SiC, & ZrO2


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Ceramic Armor

Al2O3, B4C, SiC & TiB2

Extremely hard materials

shatter the incoming projectile

energy absorbent material underneath


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Electronic Packaging Chosen to securely hold microelectronics & provide

heat transfer

Must match the thermal expansion coefficient of themicroelectronic chip & the electronic packaging

material. Additional requirements include: good heat transfer coefficient

poor electrical conductivity

Materials currently used include: Boron nitride (BN)

Silicon Carbide (SiC)

Aluminum nitride (AlN)

thermal conductivity 10x that for Alumina

good expansion match with Si


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What are the classes and types of composites?

Why are composites used instead of metals,ceramics, or polymers?

How do we estimate composite stiffness & strength?

What are some typical applications?

Composite Materials


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Composites

Combine materials with the objective of getting amore desirable combination of properties

Ex: get flexibility & weight of a polymer plus the

strength of a ceramic

Principle of combined action

Mixture gives averaged properties


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Composites:-- Multiphase material w/significantproportions of each phase.

Dispersed phase:-- Purpose: enhance matrix properties.MMC: increase y, TS, creep resist.

CMC: increase Kc

PMC: increase E, y, TS, creep resist.

-- Classification: Particle, fiber, structural

Matrix:-- The continuous phase

-- Purpose is to:- transfer stress to other phases

- protect phases from environment

-- Classification: MMC, CMC, PMC

metal ceramic polymer

Terminology/Classification

wovenfibers

crosssectionview

0.5mm

0.5mm


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Composite Survey

Large-

particle

Dispersion-

strengthened

Particle-reinforced

Continuous

(aligned)

Aligned Randomly

oriented

Discontinuous

(short)

Fiber-reinforced

Laminates Sandwich

panels

Structural

Composites

Adapted from Fig.

16.2, Callister 7e.


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Composite Survey: Particle-I

Examples:Adapted from Fig.


(Fig. 10.19 is

copyright United

States Steel

Corporation, 1971.)

- Spheroiditesteel

matrix:ferrite ( )

(ductile)

particles:cementite(Fe3C)

(brittle)60 m

Adapted from Fig.

16.4, Callister 7e.

(Fig. 16.4 is courtesy

Carboloy Systems,

Department, General

Electric Company.)

- WC/Cocemented

carbide

matrix:cobalt(ductile)

particles:WC(brittle,hard)Vm:

10-15 vol%! 600 mAdapted from Fig.

16.5, Callister 7e.

(Fig. 16.5 is courtesy

Goodyear Tire and

Rubber Company.)

- Automobiletires

matrix:rubber(compliant)

particles:C(stiffer)

0.75 m

Particle-reinforced Fiber-reinforced Structural


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Composite Survey: Particle-II

Concrete gravel + sand + cement- Why sand andgravel? Sand packs into gravel voids

Reinforced concrete - Reinforce with steel rerod or remesh- increases strength - even if cement matrix is cracked

Prestressed concrete - remesh under tension during setting ofconcrete. Tension release puts concrete under compressive force

- Concrete much stronger under compression.

- Applied tension must exceed compressive force


threaded

rod

nut

Post tensioning tighten nuts to put under tension


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Composite Survey: Fiber-I

Fibers very strong

Provide significant strength improvement to

material

Ex: fiber-glass Continuous glass filaments in a polymer matrix

Strength due to fibers

Polymer simply holds them in place



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Composite Survey: Fiber-II

Fiber Materials Whiskers - Thin single crystals - large length to diameter ratio

graphite, SiN, SiC

high crystal perfection extremely strong, strongest known

very expensive


Fibers

polycrystalline or amorphous

generally polymers or ceramics

Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE

Wires Metal steel, Mo, W


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Fiber Alignment

aligned

continuous

aligned random

discontinuous

Adapted from Fig.

16.8, Callister 7e.


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Aligned Continuous fibers Examples:

From W. Funk and E. Blank, Creep

deformation of Ni3Al-Mo in-situ

composites", Metall. Trans. A Vol. 19(4), pp.

987-998, 1988. Used with permission.

-- Metal: '(Ni3Al)- (Mo)by eutectic solidification.

Composite Survey: Fiber-III


matrix: (Mo) (ductile)

fibers: (Ni3Al) (brittle)

2 m

-- Ceramic: Glass w/SiC fibersformed by glass slurry

Eglass = 76 GPa; ESiC = 400 GPa.

(a)

(b)

fracturesurface

From F.L. Matthews and R.L.

Rawlings, Composite Materials;

Engineering and Science, Reprint

ed., CRC Press, Boca Raton, FL,

2000. (a) Fig. 4.22, p. 145 (photo by

J. Davies); (b) Fig. 11.20, p. 349

(micrograph by H.S. Kim, P.S.

Rodgers, and R.D. Rawlings). Used

with permission of CRC

Press, Boca Raton, FL.


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Discontinuous, random 2D fibers Example: Carbon-Carbon

-- process: fiber/pitch, then

burn out at up to 2500C.

-- uses: disk brakes, gas

turbine exhaust flaps, nose

cones.

Other variations:-- Discontinuous, random 3D-- Discontinuous, 1D

Adapted from F.L. Matthews and R.L. Rawlings,

Composite Materials; Engineering and Science,

Reprint ed., CRC Press, Boca Raton, FL, 2000.

(a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151.

(Courtesy I.J. Davies) Reproduced with

permission of CRC Press, Boca Raton, FL.

Composite Survey: Fiber-IV


(b)

fibers liein plane

view onto plane

C fibers:very stiffvery strong

C matrix:less stiffless strong

(a)


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Critical fiber length for effective stiffening & strengthening:

Ex: For fiberglass, fiber length > 15 mm needed

Composite Survey: Fiber-V


c

fd

15lengthfiber

fiber diameter

shear strength of

fiber-matrix interface

fiber strength in tension

Why? Longer fibers carry stress more efficiently!Shorter, thicker fiber:

c

fd

15lengthfiber

Longer, thinner fiber:

Poorer fiber efficiency

Adapted from Fig.

16.7, Callister 7e.

c

fd

15lengthfiber

Better fiber efficiency

(x) (x)


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Composite Production Methods-I

Pultrusion Continuous fibers pulled through resin tank, then

preforming die & oven to cure

Adapted from Fig.



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Composite Production Methods-II

Filament Winding Ex: pressure tanks

Continuous filaments wound onto mandrel

Adapted from Fig. 16.15, Callister 7e. [Fig.

16.15 is from N. L. Hancox, (Editor), Fibre

Composite Hybrid Materials, The Macmillan

Company, New York, 1981.]


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Stacked and bonded fiber-reinforced sheets

-- stacking sequence: e.g., 0/90

-- benefit: balanced, in-plane stiffnessAdapted from

Fig. 16.16,

Callister 7e.

Composite Survey: Structural


Sandwich panels-- low density, honeycomb core

-- benefit: small weight, large bending stiffness

honeycombadhesive layer

face sheet


Callister 7e. (Fig. 16.18 is

from Engineered Materials

Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)


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CMCs: Increased toughness

Composite Benefits

fiber-reinf

un-reinf

particle-reinfForce

Bend displacement

PMCs: Increased E/

E(GPa)

G=3E/8K=E

Density, [mg/m3].1 .3 1 3 10 30

.01

.1

1

10

102

103

metal/metal alloys

polymers

PMCs

ceramics

Adapted from T.G. Nieh, "Creep rupture of a

silicon-carbide reinforced aluminum

composite", Metall. Trans. A Vol. 15(1), pp.

139-146, 1984. Used with permission.

MMCs:Increased

creep

resistance

20 30 50 100 20010

-10

10-8

10-6

10-4

6061 Al

6061 Alw/SiCwhiskers

(MPa)

ss (s-1)


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Composites are classified according to:-- the matrix material (CMC, MMC, PMC)-- the reinforcement geometry (particles, fibers, layers).

Composites enhance matrix properties:-- MMC: enhance y, TS, creep performance

-- CMC: enhance Kc-- PMC: enhance E, y, TS, creep performance

Particulate-reinforced:-- Elastic modulus can be estimated.

-- Properties are isotropic.

Fiber-reinforced:-- Elastic modulus and TS can be estimated along fiber dir.

-- Properties can be isotropic or anisotropic.

Structural:-- Based on build-up of sandwiches in layered form.

Summary

lecture 11 and 12 ceramics and composites

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