Selection of Materials for Engineering Applications

8/18/2019 Selection of Materials for Engineering Applications

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Selection of Materials for

Engineering Applications


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Selection of a suitable material for a particular engineeringapplication is an important responsibility of an engineering

designer .

Materialization of a design is a process;

prototype final detailed construction

Selection of materials is a-continues and iterative process ,

which should proceed throughout the development ofengineering products,

by an effective teamwork realized by Designer/MaterialsEngineer combination .


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In the process of material selection the following aspectshave to be considered;

Properties of the material

Every useful material must possess a combination ofproperties.

Exact combination required will depend upon the givenapplication (Table 1.1).

Certain types of materials can be broadly generali ed as possessing certain combinations of properties (Table 1.!).

"roperty characteristics of various #ind of materials(Table 1.$).


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Failure in ServiceManufacturer should ensure that failure does notoccur in service.Failure occurs either mechanically or by corrosiveattack.

hree main failure mechanisms!(a) Ductile failure : "f the applied static stress is higher thanthe yield stress of a ductile material ,this failure can beoccurred.

(b) Brittle failure : "f the crack propagation in an unstable andrapid manner, this type of failure can proceed.


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(c) Fatigue failure : "f the components are under dynamic stressconditions then the materials are failing under particular type ofcracks #crack initiation, crack propagation and brittle failure$.

Typical corrosion mechanisms, hich influence the failure!

% &itting corrosion in chemical plants- 'ownward propagation

of small pits ( holes.

% Stress-corrosion in forgings - Stress ( corrosion work together at cracktips.

% Fuel ash corrosion in gas turbines )*oiler damage in high-temperature areas. he corrosion is caused

principally by comple+ o+ide-slag sodium vanadyl vanadate, a /.0 / 1- 20 / 2$3with low melting points. hese li4uid melted salts are strongly corrosive forstainless steel and other alloys. progresses rapidly between 5566 and 57268F.


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Surface durability

he resistance to corrosion, surface wear andpenetration.

can be gained by the composite materialsi.e. a bulk material can be coated with a corrosionresistant or abrasion resistant layer.

"hemically treated in such a way the surfacestability is enhanced .


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Special physical properties

"n applications such as electrical, electronic andnuclear engineering special physical propertieshave to be taken into account.

electrical conductors and components formeasuring instrumentation special properties like resistivity , thermal e+pansion coefficients etc. have to be considered.


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"ost and availabilityhe total cost of the materials is depending upon; - basic

material cost

- machining cost - cost for storage

basic material cost has to be calculated according to the

ratio ;

P m 9 &rice per unit mass

"f the price is given in price per unit volume, P v then;

% imber and concrete are sold in terms of volume% /ther materials are sold in units of weight


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#ecycling and environmental aspects

Selected materials should have following properties;- on to+ic

- :asier to recycle

- ighter - ess energy intensive in e+traction

his should be achieved optimizing the product4uality and cost.


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$ecision ma%ing process for the selectionof materials


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"n the points #b$ and #c$ the risk level is fairly lowbut

the responsibility of a materials engineeris high.herefore thoroughly analyze the;

- :+isting function of the product compared to the newre4uirements.

- he reasons for the failure.


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'ecision making in selection of materials iscategorized in four principal attributes.

FunctionManufacturing method

>ppearance


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Criteria for the Selection of Materials#a$


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Service Temperature% =oom emperature% :levated emperature% *elow =oom emperature% Fluctuating temperatures

or%ing Atmosphere% ormal atmosphere% >ggressive atmosphere

ther Special #e*uirements% Special physical properties

' Electrical, magnetic, Thermal etc+% Special chemical properties

' uclear, Environmental etc+


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-eometrical $imensions of the component

% Shape of the raw product#s$' Plate+ #od, ire etc+

% Shape of the finish product.

eight

% *etter strength weight ratio

Appearance


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#b$


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Processing of the Material% &rocessing of raw material% Manufacturing method of the semi-finished and finished

product

#ecycling Possibilities

Total "ost

%


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Strength of materialsStatic Strength

Static strength of metals#"$ ow strength ! low carbon steels, >" and " and


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#iii$ Cigh strength! medium and high carbon steels, i alloys,high alloy steels.- Ceat treatable- ow workability- ow ductility- :+pensive

- D26 B Ays B5266 M&a

#iv$ Eltra-high strength! high alloyed steels with i,


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Static strength of thermoplastics

) Strength is time dependant ) Strength is very sensitive for the service temperature ) he failure is depend on the type of plastic

) *etter strength G weight ratio


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Static strength of structural ceramic (Al . / , 0r . , Si",Si / 1 + etc+)

- high at elevated temperature- measured by using H or 1 point bending- very low ductility

- very poor workability- high creep resistance- special design concepts are needed #not advisable tostressed in tensile direction$


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Static strength of fibre'reinforced composites

% "mportance is high strength-to-weight ratio ) aero space

applications, bicycles, sail'boats+% he strength is depends on

- relative properties of the matri+ and fibre.- relative proportion of the fibre and matri+ in the composite.- length of the individual fibre particles.- geometrical arrangement of fibre within the composite#higher strength in unidirectional fibre in polyester-glassfibre composite$

% Strength is depend on the direction of the stress applied on it.

% ype of fibre #carbon, glass, boron. ceramic$ influence the

mechanical properties.


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% Cybrid composites - combination of two types of fibres#carbon fibre in glass fibre body- Ford @ 16 racing car$

- Stiffness of glass fibre will be combined with the impactresistance of carbon fibre #>ero spatial S> H76Celicopter, rotor blades$

glass and carbon fibre frame work as honey-comb corecovered with a carbon fibre skin$

> honeycomb shaped structureprovides an obIect with a highstiffness relative to its weight.

Coney-comb core

Sandwich layers


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Static strength of cement and concrete

% ?eak in tension and bending and particularly strong inimpact loads.

% 'epends upon ater'cement ratio .% Strength increase with the curing duration .% =einforced by steel bars #better tensile properties$

- Steel and concrete having similar coefficient ofthermal e2pansion

- Passivating effect of concrete inhibits the corrosionof steel

% More strength by pre-pressing the concrete.% @ood strength-weigh ratio.


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Static strength of ood

% Ma+imum strength of wood is developed parallel to the grains .% ow compression strength% Cigh toughness% imitations in engineering applications because of its e+treme

3anisotropy4 , #direction dependence of the properties$% @ood workability% Sensitive to water, fungal attack and swelling ( warping.


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Fatigue strength

close-up view of the fracture surface.

% he blue arrow points to the fracture origin at a brittleintergranular zone.%Fatigue arrest marks and o+idation are noted in fatiguezone .

% Final torsional fracture .


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% Fatigue fracture can occur at load much lower than failureby static loading.

% For ultimate fracture, it takes long duration and failureoccurs without any e+ternal indications.

% >ssessment of fatigue resistance can be done by;- Stress- ife relationship #S- curve$- =ate of fatigue crack propagation #F


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Fatigue strength of polymers dependence on;% Molecular weight%

'egree of cross linking%


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"reep strength

Following factors influence the creep strength of metals;

% Melting point #metals with lower melting point also used as thebasis for creep resistant alloys$.' for metals, T56+1T m , crac% propagation occurs+

% Solid solution strengthening .%


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"ost basis for selection

&rocess of selecting a list of materials for a given application

will be carried out initially in terms of re4uired properties. *ut final decision will be taken on cost factor.

&lacing a product on the market involves risk because the

aim is earning profit within a certain period ."ncrease in costs from superior materials has to be offset byimprovement in performance.

"nteraction between performance and cost;&erformance oriented products ' Advanced armaments (e+g+ atomic submarines) ' Space vehicles+


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-


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"ost'effectiveness and value analysis

7alue ' e+tent to which the appropriate performance criteria

are satisfied."ost' what has to be paid to achieve a particular level of value."ost effective 8 the e+tent of dispensing with in the interests of

reducing costs.


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Materials engineer should have the ability to distinguishbetween material'sensitive and design'sensitive properties.

material'sensitive' tough material is one that is resistant tothe initiation and propagation of cracks.

design'sensitive' tough design is one that is free fromnotches and stress-raisers.

"t may be e+pensive to obtain tough material for a criticalapplication .

*ut relatively cheap to free a design from stress-raisers .


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Analysis of "ostFig /+9


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$esign and Evolution of the 7acuum "leaner

eed 8 $evice to remove dust from a carpets in the home

"onceptsto suc% the dust from the carpet ith a vacuumto blo it out ith compressed air to dra it out electrostaticallyto trap it ith an adhesive beltto brush it out

All have been tried at one time+After a revie , vacuum method is selected and a functionstructure is devised+


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it consist- po er source,- vacuum pump,- filter to catch the dust,' tube to direct the action of the pump to the carpet+

Embodiment Stage' detailed calculations of flo rates' pump design' form of the filter ' diameter and length of the tube' :o they all fit together


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;ayout diagram ith appro2imate dimensions

Estimates of po er, eight and performance+

$ecide the shape, te2ture and color 8 &ndustrialdesigner+


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Reciprocating EngineReciprocating Engine Rotary EngineRotary Engine


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Source of EnergySource of Energy Method ofMethod of

energy releaseenergy release

Out put machineryOut put machinery

ReciprocatingReciprocating RotaryRotary

#i$ Fossil fuel#i$ Fossil fuel "nternal"nternalcombustioncombustion

:+ternal:+ternalcombustioncombustion

&etrol engine&etrol engine/il engine #diesel$/il engine #diesel$Steam engineSteam engine

@as turbine@as turbine?ankel engine?ankel engineSteam turbineSteam turbine

#ii$ uclear fuel#ii$ uclear fuel uclear fusionuclear fusion Steam turbineSteam turbine

#iii$ Cydraulic power #iii$ Cydraulic power


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15

Factors influenced by application

MachineryMachinery "ritical parts are"ritical parts aresub=ected tosub=ected to

"ondition"ondition

of theof theor%ingor%ing

atmosphereatmosphere

Si>e of theSi>e of thepart arepart are

"nternal"nternalcombustioncombustiontype gas turbinetype gas turbine

0ery high0ery hightemperaturetemperature#D66-5666#D66-5666 oo


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Thermal efficiency of a engine is proportional to?here 5- :ntry temperature

- :+haust temperature9 :fficiency K if 5 K and L

Si>e of the components #power unit for small modernaircrafts, lawn movers, compressors, power tools, cargo ships$Size K - Manufacturing and treatment difficulties?eight K -


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#eciprocating &nternal "ombustion Engine

"ylinder bloc% is bolted to the cylinder head - oint issealed by gasket.

Most engines operate on the four'stro%e auto'cycle#i$ "nduction stroke #fuel-air mi+ture will be sucked into the

cylinder-piston closed volume$#ii$


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Materials for #eciprocating &nternal "ombustion Engine

"ylinder bloc%

Factors determined by the application% Strength% #igidity% -ood thermal conductivity (cooling is necessary)

% ;o density% -ood resistance to abrasion, ear and corrosion% ;o thermal e2pansion


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Material selection for the cylinder bloc%

>ll re4uirements #e+cept density$ satisfied with flakegra hite cast iron.

Al - as a replacement since the cylinder block is lightlystressed and increase the po er' eight ratio+

Al has advantages.- ow density- 'ie casting ability

'isadvantages are- ow abrasion resistance.- =elatively high thermal e+pansion coefficient.- :+pensive.


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Ma+imizing the difference in hardness between piston andbore ) minimize wear.

- either bore must be harder than the piston or vice-versa.Esing pre'finished cylinder'liners can solve the problemwith low abrasion resistance.

?ear is at worst ) similar materials rub together.-*ut flake gra hite cast iron can be used for Piston andCylinder ! lubricating effect .

>nother cheaper and easier method is to hard chromium

plating of the piston .


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Alloy "u? Si? Mg? Al?

M 6.D- .2 N.6-55.2 - rem

M 1 H.6-1.6 D.2-N.2 - rem

MN 56.6-5H.6 6. -6.7 rem

MH6 1.6-2.6 57.6-5O.6 6.1-6.D rem

M 2 - 7.2-D.2 6. -6.12 rem

&ossible >l alloys for the engine block


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"ylinder head

his part is in fairly lo stress condition+

special re4uirements;' matching thermal e+pansion coefficient withcylinder block.

' lo heat resistance.Material may be cast iron " Al#alloy or Mg#alloy.

&roduced by sand casting

" %


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"ran% case

Structural support for the crankshaft.

Mechanical re4uirements are;

- strength and rigidity+


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Piston #e*uirements from the application@

% Cigh temperature strength.% ow thermal e+pansion coefficient,

>l piston , 5N- 2+56 -7 8l posses high thermal conductivity , lightness.


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% Multi metallic # >l piston with steel inserts to limit thermale+pansion$.

% >l , . 2P


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%


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"onnecting #odCighly stressed and other re4uirements as crankshaft.

Materials for connecting rod% S&heroidal gra&hite cast iron #for motor cars$% 'on heat treatable Al alloy #>l; H.2P


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Selection of Materials for AircraftStructures ("ase Study)

Principal "haracteristics of aircraft structures


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ings )


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ings ) subIected to the highest levels and most comple+ variationof stresses.

?hen plain is on the ground , wings hang down due to;- self eight- eight of fuel stored- eight of engines (if ing mounted)

- upper wing surfaces ) tension- lower surfaces )


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"ritical re*uirments are@- #esistance to fatigue' #esistance to stress corrosion

plates must be thick, and heat treated to make free fromresidual stresses.

' need stiffness to resist bending and buc%ling+

Stress corrosion crac%ing of an aircraft component

F l


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Fuselage


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;anding gears

Functions once per flight as the eight of the holeaircraft hits the ground+


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Materials for ings


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ield Stress(Mpa) E (-Pa ) $ensity(tonnesBm / )

Stainless steel,F0 2 6

56O5 52 D.OH 6.D72

itanium alloy,i-7>l-10

OH6 556 1.1H 5.6O

>luminium alloyD6D2- 7

1D6 D .O6 5.1O

Materials used for an aeroplane ings


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Materials for landing gears

Cltra'high'strength steels are most appropriate.Al alloys largely abandoned in large civil craft .

Ti alloys for military crafts , because cost is less important factor - >merican*5 bomber.

able

"ontrol surfaces ! #udder and Elevator


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ontrol surfaces ! #udder and Elevator

#udder is attached to the back of the vertical stabilizer. 'uring flight, it is used to move the nose left and right+

Elevator attached to the back of the horizontal stabilizer.

used to move the nose up and do n+

Materials for "ontrol surfaces


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Materials for ontrol surfaces

=esistance to large deflections ) Ade*uate stiffness

Materials

% "' fibre reinforced plastics ("F#P) 8' Multi-directional lay-up allows control of anisotropy' Significant weight savings +

% -lass'carbon reinforced epo2y 8 give the stiffnessre4uired at any particular point in a structure.


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#e*uirements for high'speed flight

"n flight aircraft skin is heated due to stagnant layer of air

contiguous with the surface.Surfaces on the ing and at the nose heating effect isgreater - successive pockets of air become sharplycompressed.

Thermal stresses are developed ) outside skin of theaircraft heats up whilst the internal structure stays cool.

"andidate materials for Aircraft structures


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andidate materials for Aircraft structures

Magnesium

ow weight #two thirds that of aluminium$Cigh strength to weight ratio:+cellent corrosion resistanceCigh temperature mechanical properties

Mg N1.62, Qn 2.7 , Qr 6.5N,


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Mg'91;i'9+.DAl ) for outer space shuttles.

Alloy containing eodymium and Praseodymium (Pr)used as castings for aircraft components.

Mg casting alloy MS#'nglo-French aguar

Aluminium Alloys


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Aluminium AlloysMaIor Material for airframe construction .Strength Bdensity ratio is superior to steel. hough not to i.Stiffness is better than both Steel and Ti ./ther properties:igh toughnessfatigue resistance"orrosion resistance ) stress corrosion

e+foliation corrosion

able

&recipitation hardening alloys ) duralumin, .6.1+Al'0n'Mg'"u alloys , strongest >l alloys ) 6 D idely used .

The concorde alloy


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The concorde alloy"oncorde , urboIet-powered supersonic passengerairliner.

ose temp. - 5 O 6


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== 27 >l- NH.DP


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:igh strength to eight ratio.

capable of operating at temperatures from sub >ero to H66I"+

For aero'engines ' blades, shafts and casings from the frontfan to the last stage of the high pressurecompressor.

Air'frames 8Ti >lloys with strength up to 5 66M&a. - landing gears and large wing beams.

able

"omposites


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omposites@enerally consist of a matri+ of epo+y-resin reinforced byfibers of ;-


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For cabin floors, lightly loaded parts- plastic'glass honey comb core between glass'fibre

facing sheets+

he most advanced use of composites so far is to befound in the Mc'onnell 'ouglas >0O* >dvanced Carrier .

- ing is manufactured entirely from carbon'fibre' epo2y .- 9D6 %g eight savings+

&mpact properties of carbon fibre composites, improved byglass fibers .

Stiffness of @F=& may be increased by the addition ofcarbon fibers .


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biomaterial is defined as any systemically,

&harmacologically inert substance or combination ofsubstances utili+ed for im&lantation ithin or incor&oration itha li ing system to su&&lement or re&lace functions of li ingtissues or organs.


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#e*uirements of biomaterial must be!%"nert or specifically interactive

%*iocompatible

%Mechanically and chemically stable

%*iodegradable

%&rocessable #for manufacturability$

%Sterilizable #ability of material to make it completely

clean and free from bacteria$

Biocom atibility is the ability of material to &erform


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ithin an a&&ro&riate host res&onse in a s&ecifica&&lication.

in other words is the 4uality of not having to2ic or in=uriouseffects on biological systems+

&nternal Medicine


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Metal (originally stainless steel) femoral component.


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( g y ) p

Teflon (polytetrafluoroethylene (PTFE) acetabularcomponent.

bone cement and screws - Poly(methyl methacrylate)(PMMA)! transparent thermoplastic

>crylic bone cement is the only material currently used to

fill the irregular space between artificial Ioint #prosthesis$and bone during total hip replacements # C=$. "ts mainfunction is to transfer body weight and service loads fromthe metal prosthesis to the bone andGor increase the load

carrying capacity of the prosthesis- bone cement- bonesystem


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Plate for fracture fi2ation )


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% Stainless steel% cobalt-chromium alloy


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pp y

> dental implant is essentially a substitute for a natural rootmade from medical and dental grade titanium . he amazingthing with a titanium dental implant is that the body does notrecognise it as a foreign obIect and so completely integrates .

$ental &mplant


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dental cro ns Some common materials used for are;nic%el, chromium, -old, "eramic and porcelain

abutments are connected to the dental implants via ascrew. his screw needs to be tightened to a predetermined

tor4ue, in order to avoid screw loosening during chewing,which can often create a counter-clockwise tor4ue on theimplant-abutment interface, encouraging the abutmentscrew to come loose. his can largely be prevented withproper screw design and tor4uing of the abutment.

nic%el, stainless steel, -old, 0irconia

"ardiovascular system


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y

Ceart valve - Stainless steel, carbon

*lood vessel - eflon, 'acron, &olyurethane


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membrane is a thin, film-like structure that

separates two fluids.

rtificial Ceart - &olyurethane


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y

Ceart ung Machine - Silicone rubber

Materials selection for ship structures


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pShape ( characteristics are determined by;

- i4uid and solid cargo- &assengers- emperature

Ship surface operate at the interface between two media ofdiffering density #water (air$.- determination of suitable shape is complicated.

wo main parts! - Cull - SuperstructureCull - watertight body of a shipSu&erstructure - structure consisting of the part of a shi& above the main deck.


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- &rovide re4uired buoyancy .

- Shape ensure good stability and handling .- oists are attached to plates, which conferstiffness and resistance to buckling.


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?hen ship in e4uilibrium, two sorts of forces!- do n ard'acting forces due to total mass.

- upthrusts from the ater due to the buoyancy ofthe immersed parts.

"n total, these two forces are e4ual.

*ut their distribution along the length of the hull are not.- floating hull bends longitudinally like a beam .- bending stresses are resisted by the deck and bottom

structures.

:ogging is the stress a shipRs hull e+periences that causes


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the center of the hull bends upward.

Sagging is the stress , when the hull is in the trough of twowaves -hull bends downward.

:ogging

Sagging

Materials for ship hulls


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/ne of the parameters used in ship design is the ratio ;B$ +' ; , length of the ship' $ , depth! distance between top and bottom

structures.

-reater the ;B$ ratio, larger the deflections (K)+

"f G' ratio is larger, top and bottom sections need to beprovide stiffness.

able 57.5

Al alloy

Al alloy hulls e+hibit deflections than steel.


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Al, use for smaller vessels and special-purpose craft such as hydrofoils ) lo density

Sailing spars

hydrofoil

Esed in sheet for all-metal hulls , andl b ili


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structural members - sailing spars

>l is difficult to weld- re4uires heat treatments such asprecipitation strengthening.

Mild Steel


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rdinary'strength A


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cycles will not cause cracksGfailures.

Ship design criteria generally assume that all normal loadson the ship should be belo the fatigue limit+

assume that the ship will regularly operate fully loaded , inheavy weather and strong waves .

"u' i Alloys


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:+tensively used alloys are% "u i DFe% "u i 96 Fe 9Mn % "u i .6 Fe

@ood resistance to corrosion and macro fouling

- savings in fuel ; friction due to developed rough layers- savings in hull maintenance time and cost


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higher stiffness and strengthGweight ratio.

lighter weight keeps fuel costs down.


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- =e4uired to increase material thic%ness .

-F#P is not used for large cargo vessels.- used for fishing boats up to H6 m.

"n longitudinal structures, low elastic modulus of -F#P causes panel type buckling.

countered by; ' enlarging longitudinal stiffeners' decreasing the spacing between panels

Materials selection for


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("ase study)

Friction is caused by two surfaces resisting movementbetween them ) sliding


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between them ) sliding .

"f however two surfaces can contact each other by rolling

then friction problems are significantly reduced.*earings reduce friction either by using hard smooth balls orrollers.

*alls or rollers TbearT any loads , allowing the bearing torotate smoothly .

-ood bearing design involves three fundamentalelements!


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elements!% understanding the service environment.

% designing for proper lubrication.% selecting the best bearing material for the Iob.

Service conditions ! Ma=or areas of consideration are!

% ;oad ' steady and impact% Speed at design load% "orrosive environments% $irty environments andBor lubricants

% Temperature,

*all bearings are dealing with two kinds of loadingcondition;


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radial load and thrust load

'epending on the type of application the bearing is usedradial load only,thrust load only orcombination of both.

apered roller bearings connected to car wheel.


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most common type

hey are found in from washing machines to &< hard

drives .usually found in applications where the load is light to

medium and is constant in nature - not shock loading .

capable of taking both radial and thrust loads.

#oller


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used in heavy duty applications such as conveyer belt rollers- must hold heavy radial loads.

contact between the inner and outer race is not a point #likethe ball bearing above$ but a line .

spreads the load out over a larger area, allowing to handle

much greater loads than a ball bearing .cannot handle thrust loads

Taper roller bearing


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apered roller bearings are designed to support large radialand large thrust loads .

hese loads can take the form of constant loads or shockloads.

used in many car hubs , mounted in pairs facing opposite

directions ) his gives them the ability to take thrust loads inboth directions.

Materials for


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in Bronzes:

>lloy os.


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>lloy os.


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>lloy os.


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% he lead addition makes these alloys easy to machine .

Alloys " / 66 and " 1/66%low strength , superior lubricity - containing 52- 2 P &b.%should not be specified for use under high loads or in

applications where impacts can be anticipated.


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Manganese Bronzesll O7H66 O7166


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>lloy os.


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OOP Sn , rest of composition is Sb,


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6P of Sn added to >l to improve seizure resistance .dvantages;- corrosion resistance- high thermal conductivity

- high fatigue strength .'isadvantages

- Moderate embedding properties- Cigh coefficient of thermal e+pansion

>l based engine bearings have bi-metal structure consisting oftwo layers!


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a steel back and an >l-tin alloy of about 6.65U #6. 2 mm$thick.

Materials selection for Armor Systems


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("ase study)

LIGH -WEIGH E!AMI A!M"!


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Military vehicles have traditionally been manufactured fromhigh strength armor plate steel .Modern ceramic composites have largely replaced steel dueto;

its significantly lower areal weight which allows weightsavings of more than 26P over conventional steel.

lumina #>l . / H$- Silicon carbide #Si


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- silicon and boron carbide

/ther ceramic materials used for ballistic protection% Silicon nitride #S $% itanium boride # i* $% >luminium nitride #>l $% S"> / #Silicon aluminium o+ynitride$% Fibre-reinforced ceramic #e.g.


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% Spall foil%


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the composite backing .

"omposite bac%ing is formed by polyaramide ,polyethylene or polypropylene fibers.

% he stiffening and structural enhancement of theindividual polymer layers is achieved by impregnation and

subse4uent curing of the adhesive! rubber, polyurethane or epo+ies

his chemical bond between

- ceramic and composite substrate- individual polymer layersis the key significance for the performance of theentire system .

A;CM& A A#M # MATE#&A;S


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A; TE" H S<

h >l / t t i N7P


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he >l . / H content is N7P.@lass forming silicates are used as sintering additives whichcause a lowering of the sintering temperature and regulatethe grain growth.

A; TE" S / :< N7 S*.

A; TE" S<

ack of glass-forming substances


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ack of glass-forming substances.

l . / H enhances the mechanicalproperties - increase in ballistic efficiency.

A; " # 966

>l / H content of above NN N2P


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>l . / H content of above NN.N2P.

>n ultrafine-grained microstructure with grain sizes B 5Vmcan be generated by applying a two-step sintering process .

:+tremely high mechanical properties and increasedballistic efficiency .

A!BI%E A!M"! MA E!IALS


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S&"A$C#N F (SSi")produced by solid-state-sintering .


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Sintering additives, boron carbide and carbon, lie at 5P.

nearly nonporous ; hardness lies in the range of 2 @&a,though the fracture toughness is slightly lower than that of&SSil . / H , . / H in 4uantities of appro+.56P .

he material has high fracture toughness and fracturestrength.

< "A$C#N Cot-pressed boron carbide is the lightest, hardest , but also


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most e+pensive material being used today in series ofballistic protection.

he emphasis of its application is on personal protection asinserts for armor vests.

Penetration mechanism'well effect


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well effect ?hen the proIectile impacts the surface of the ceramic, its

kinetic energy is greatly reduced without penetrating theceramic.

his is caused by the d ell effect . "n that phase theproIectile e+periences a highly ductile deformation .

X:J due to dwell is to appro+imately H2P.

:rosion >fter appro+.52 to 6 Vs, the proIectile actually penetratesthe ceramic body.kinetic energy of the proIectile is reduced further by erosion.

X:J by erosion is appro+imately 26P.

*acking Shattered fragments of the proIectile completely penetrateth i ft + H6 V


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the ceramic after appro+.H6 Vs.

he residual energy of these fragments can be fully absorbedby the backing.

X:J by backing is appro+imately 52P.


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#e*uired properties of ceramics used in armorsystems


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defined microstructure with high grain size stability combinedwith high homogeneity .

high hardness and high sonic velocity are necessary forballistic efficiency.

Cigh modulus of elasticity and high relative density arethe prere4uisites for high sonic velocity .

mechanical strength #pressure, bend and shear strength$and fracture resistance.

Bod& Armorshelps absorb the impact from fired proIectiles and from


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e+plosions .

Metal or ceramic plates can be used for soft vest, providingadditional protection from rifle attacks .

Jevlar - high tensile strength-to-weight ratio .- ! times stronger than steel on an e ual eight basis

Jevlar is the registered trademark for a para-aramidsynthetic fiber.

fiber has ! tensile strength of about H,7 6 Mpa

! relative density of 5.11.high strength gained by inter-molecular hydrogen bondsform between the carbonyl groups and / centers .


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Molecular structure of Jevlar!

' bold represents a monomer unit,' dashed lines indicate hydrogen bonds.

>t higher temperatures the tensile strength is immediatelyreduced.% >t 5768< #H 68F$ about 56P reduction% >t 768< #2668F$ about 26P reduction

Safety glass


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)uench hardening (*hermal tem ering$

%made from annealed glass via a thermal tempering process.

%heat it up to softening pt. then rapidly cooled by inIecting airwhile the inner portion remains free to flow for a short time.

%"nitially the rapid cooling tends to induce tensile stress on thesurface. his is reversed in the latter stages of coolingresulting in compressive stresses on the surface.

% his compressive stress tends to close surface flaws .

%surface compressive stress should e+ceed 566 Mpa, forsafety glass+

7iscosity (poise) $escription

Melting Point #make the glass melt


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56 5-56 g g

homogeneous$

56 H-56 1 or%ing Point #pressing, blowing, gob forming$

56 D-56 OSoftening Point #glass retains its own shape $

56 55-56 5 -lass Transition Temperature, T g#become high viscous, no rearrangement ofatoms below g $

56 5 -56 5H Annealing Point #Stress is relieved within aseveral minutes$

56 5H.2-56 51.2 Strain Point #Stress is relieved within severalhours, below this, glass can be cooled rapidly.$

emperature dependence of !iscosity


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%greater the surface stress , the smaller the glass particleswhich are shattered into small fragments instead of sharpi


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pieces.

%Applications - 0ehicle windows- glass doors and tables- refrigerator trays- as a component of bulletproof glass- for diving masks

%Schematic representation of the stress profile in toughenedglass


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glass

&on E2change?hen a large ion is e+change for smaller ion at


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?hen a large ion is e+change for smaller ion , attemperature below g a compressive stresses build up in

the e+change region #by immersing soda lime silica glassin molten J / H at 166 Y


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addition of second phase particles increase the strength

due to pinning #making obstacles$ of the propagationcracks.

hese constituents re4uired higher energy for fracture :g! "omposites of glass and alumina

Documents

Selection of Materials for Engineering Applications