Engineering materials for students lecture

Engineering materials for students lecture

1. ENGINEERING
MATERIALS
By
Ch.V.Sushma
Assistant Professor
Mechanical Engineering Department
Chaitanya Bharathi Institute of Technology
Hyderabad

2. CLASSIFICATION OF ENGINEERING
MATERIALS

3. METALS AND NON-FERROUS METALS
Common engineering materials are normally classified as metals
and nonmetals.
Metalsmay conveniently be divided into ferrous and non-ferrous
metals. Important ferrous metals for the present purpose are:
(i) cast iron
(ii) wrought iron
(iii) steel.
Some of the important non-ferrous metals used in engineering
design are:
(a)Light metal group such as aluminum and its alloys,
magnesium and manganese alloys.
(b) Copper based alloys .
(c) White metal group such as nickel, silver, white
bearing metals.

4. FERROUS MATERIALS
Cast iron-
It is an alloy of iron, carbon and silicon and it is hard and
brittle. Carbon content may be within 1.7% to 3% and
carbon may be present as free carbon (graphite) or iron
carbide Fe
3C.
In general the types of cast iron are
(a) Grey cast iron
(b) White cast iron
(c) Malleable cast iron
(d) Spheroidal or nodular cast iron
(e) Austenitic cast iron
(f) Abrasion resistant cast iron.

5. GREY CAST IRON
GreycastironCarboncontentis3to3.5%.
Carbonhereismainlyintheformofgraphite.This
typeofcastironisinexpensiveandhashigh
compressivestrength.Ithaslowtensilestrength
andlowductility.Graphiteisanexcellentsolid
lubricantandthismakesiteasilymachinablebut
brittle.Someexamplesofthistypeofcastironare
FG20,FG35orFG35Si15.Thenumbersindicate
ultimatetensilestrengthinMPaand15indicates
0.15%silicon.

6. GREY CAST IRON
Applications:
Duetolubricatingactionit
isverysuitableforparts
whereslidingactionis
desired.They are
machinetoolbodies,
automotive cylinder
blocks,heads,housings,
fly-wheels,pipesandpipe
fittingsandagricultural
implements.

7. AUSTENITIC CAST IRON
Dependingontheformofgraphitepresentthiscast
ironcanbeclassifiedbroadlyundertwoheadings:
Austeniticflakegraphiteiron,Austeniticspheroidalor
nodulargraphiteiron.Thesearealloycastironsand
theycontainsmallpercentagesofsilicon,
manganese,sulphur,phosphorusetc.Theymaybe
producedbyaddingalloyingelementsviz.nickel,
chromium,molybdenum,copperandmanganesein
sufficientquantities.Theseelementsgivemore
strengthandimprovedproperties.Theyareusedfor
makingautomobilepartssuchascylinders,pistons,
pistonrings,brakedrumsetc.

8. WHITE CAST IRON
Whitecastiron-Carboncontentis1.75to
2.3%.Inthesecastironscarbonispresent
intheformofironcarbide(Fe
3C)whichis
hardandbrittle.Whitecastironhashigh
tensilestrengthandlowcompressive
strength.Thepresenceofironcarbide
increaseshardnessandmakesitdifficultto
machine.Consequentlythesecastirons
areabrasionresistant.

9. WHITE CAST IRON
Applications:
Duetowearresisting
characteristicsitisused
forcarwheels,rollsfor
crushinggrainsandjaw
crusherplates.

10. ABRASION RESISTANT CAST IRON
Thesearealloycastironandthealloying
elementsrenderabrasionresistance.A
typicaldesignationisABR33Ni4Cr2which
indicatesatensilestrengthinkg/mm
2
with
4%nickeland2%chromium.

11. MALLEABLE CAST IRON
Malleablecastiron-Thesearewhitecastirons
renderedmalleablebyannealing.Theseare
tougherthangreycastironandtheycanbetwisted
orbentwithoutfracture.Theyhaveexcellent
machiningpropertiesandareinexpensive.
Dependingonthemethodofprocessingtheymay
bedesignatedasblackheartBM32,BM30orwhite
heartWM42,WM35etc.

12. MALLEABLE CAST IRON
Applications:
Malleablecastironis
usedformakingparts
where forgingis
expensivesuchashubs
forwagonwheels,brake
supports.

13. SPHEROIDAL OR NODULAR GRAPHITE
CAST IRON
Inthesecastironsgraphiteispresentintheformof
spheresornodules.Thistypeofcastironisformed
byaddingsmallamountsofmagnesium(0.1to0.8%)
tothemoltengreyiron.Theadditionofmagnesium
causesthegraphitetotakeformofnodulesor
spheroidsinsteadofnormalangularflakes.They
havehightensilestrengthandgoodelongation
properties.Theyaredesignatedas,forexample,
SG50/7,SG80/2etcwherethefirstnumbergivesthe
tensilestrengthinMPaandthesecondnumber
indicatespercentageelongation.

14. SPHEROIDAL OR NODULAR GRAPHITE
CAST IRON
Applications:
Nodularcastironis
generallyusedforcasting
requiresshockandimpact
resistancealongwith
goodmachinability,such
ashydrauliccylinders,
cylinderheadsrollsfor
rollingmills and
centrifugally cast
products.

15. WROUGHT IRON
Thisisaverypureironwheretheironcontentis
oftheorderof99.5%.Itisproducedbyre-
meltingpigironandsomesmallamountof
silicon,sulphur,orphosphorusmaybepresent.
Itistough,malleableandductileandcaneasily
beforgedorwelded.Itcannothowevertake
suddenshock.
Applications-Chains,cranehooks,railway
couplingsandsuchothercomponentsmaybe
madeofthisiron.

16. STEEL
Thisisbyfarthemostimportantengineering
materialandthereisanenormousvarietyofsteel
tomeetthewidevarietyofengineering
requirements.Steelisbasicallyanalloyofironand
carboninwhichthecarboncontentcanbeless
than1.7%andcarbonispresentintheformofiron
carbidetoimparthardnessandstrength.Twomain
categoriesofsteelare
(a) Plain carbon steel
(b) Alloy steel.

17. PLAIN CARBON STEEL
Thepropertiesofplaincarbonsteeldependmainlyon
thecarbonpercentagesandotheralloyingelements
arenotusuallypresentinmorethan0.5to1%such
as0.5%Sior1%Mnetc.Thereisalargevarietyof
planecarbonsteelandtheyaredesignatedasC01,
C14,C45andC70andsoonwherethenumber
indicatesthecarbonpercentage.
Following categorization of these steels is sometimes
made for convenience:
Dead mild steel-up to 0.15% C
Low carbon steel or mild steel-0.15 to 0.46% C
Medium carbon steel-0.45 to 0.8% C.
High carbon steel-0.8 to 1.5% C

18. LOW CARBON STEEL -(MILD STEELS (OR)
SOFT STEELS)-
Noalloyingelementotherthancarbonispresentinlowcarbonsteel.
Ithascarboncontentof0.15%to0.45%.Howevertheremaysmall
magnitudeofP,S,SiandMn.Theyarepresentasimpuritiesasitis
difficulttoremovethemintheprocessofsmelting.Becauseoflow
carbonpercentageitcannotundergoheattreatmentprocess.Its
hardnesscannotbeincreasedbyconventionalheattreatment
method.Thehardnessnumberisabout150BHN.Ithaslowertensile
strengthandmalleable.
Applications-
Screws,bolts,nuts,washers,wirefences,automobilebodysheet,
plates,wires,buildingbars,grills,beams,angles,channelsetc.

19. MEDIUM CARBON STEEL -(MACHINERY STEELS)
Thecarboncontentofmediumcarbonsteelis0.45%to
0.8%.Mediumcarbonsteelshashighertensilestrengthand
hardnessthanlowcarbonsteels.Thehardnessnumberisabout
300BHN.Mediumcarbonsteelsrespondsslightlytoheat
treatmentprocessandhenceitshardnesscanbefurther
increasedifrequiredforaparticularapplication.Theyalsohave
bettermachiningqualities.Generallytheyarehotworked.
Applications-
Hooks,wireropes,shafts,connectingrods,spindles,railaxles,
gears,turbinebucketwheels,steeringarmsandothermachine
componentswhichrequiremediumstrength.

20. HIGH CARBON STEEL
Ithascarboncontentof0.8%to1.7%.Highcarbon
steelshashighertensilestrengthandhardness
thanmediumcarbonsteels.Thehardnessnumber
isabout500BHN.Highcarbonsteelsresponds
readilytoheattreatmentprocessandhenceits
hardnesscanbefurtherincreasedtodesired
values.Theyhavegoodwearresistance.Generally
theyarehotworked.
Applications-
Theyareusedformakinghandtoolssuchas
wrenches,chisels,punchesandrailwheels,files,
cuttingtoolslikedrills,woodworkingtoolsandrails,
rodsforreinforcedconcrete,forgingdies,knives,
drawingdies,sawsetc.

21. ALLOY STEEL
Thesearesteelsinwhichelementsotherthancarbonare
addedinsufficientquantitiestoimpartdesiredproperties,
suchaswearresistance,corrosionresistance,electricor
magneticproperties.
Chief alloying elements added are usually
•Nickel for strength and toughness
•Chromium for hardness and strength
•tungsten for hardness at elevated temperature
•vanadium for tensile strength
•manganese for high strength in hot rolled and heat treated
condition
•silicon for high elastic limit
•cobalt for hardness
•molybdenum for extra tensile strength

22. Stainless steel
isonesuchalloysteelthatgivesgoodcorrosionresistance.
Oneimportanttypeofstainlesssteelisoftendescribedas
18/8steelwherechromiumandnickelpercentagesare
18and8respectively.Atypicaldesignationofastainless
steelis15Si2Mn2Cr18Ni8wherecarbonpercentageis
0.15.
High speed steel:
Thissteelcontains18%tungsten,4%chromiumand1%
vanadium.Itisconsideredasoneofbestofallpurposetool
steels.Itisusedwidelyfordrills,lathe,planerandshaper
tools,millingcutters,reamers,broaches,threadingdies,
punchesetc.

23. Non-ferrousmetals-Metalscontainingelementsother
thanironastheirchiefconstituentsareusuallyreferredto
asnon-ferrousmetals.Thereisawidevarietyofnon-
metalsinpractice.
Aluminum-Thisisthewhitemetalproducedfrom
Alumina.Initspurestateitisweakandsoftbutaddition
ofsmallamountsofCu,Mn,SiandMagnesiummakesit
hardandstrong.Itisalsocorrosionresistant,lowweight
andnon-toxic.

24. Duralumin-Thisisanalloyof4%Cu,0.5%Mn,0.5%Mg
andaluminum.Itiswidelyusedinautomobileandaircraft
components.
Y-alloy-Thisisanalloyof4%Cu,1.5%Mn,2%Ni,6%
Si,Mg,FeandtherestisAl.Itgiveslargestrengthathigh
temperature.Itisusedforaircraftenginepartssuchas
cylinderheads,pistonetc.
Magnalium-Thisisanaluminumalloywith2to10%
magnesium.Italsocontains1.75%Cu.Duetoitslight
weightandgoodstrengthitisusedforaircraftand
automobilecomponents.

25. Copper alloys
Copper-isoneofthemostwidelyusednon-ferrousmetalsin
industry.Itissoft,malleableandductileandisagood
conductorofheatandelectricity.
Brass(Cu-Znalloy)-Itisfundamentallyabinaryalloywith
Znupto50%.AsZnpercentageincreases,ductilityincreases
upto~37%ofZnbeyondwhichtheductilityfalls.Small
amountofotherelementsviz.leadortinimpartsother
propertiestobrass.Leadgivesgoodmachiningquality
ductilityZn(%)37andtinimpartsstrength.Brassishighly
corrosionresistant,easilymachinableandthereforeagood
bearingmaterial

26. Bronze(Cu-Snalloy)-Thisismainlyacopper-tinalloy
wheretinpercentagemayvarybetween5to25.It
provideshardnessbuttincontentalsooxidizesresulting
inbrittleness.DeoxidizerssuchasZnmaybeadded.
Gunmetal-isonesuchalloywhere2%Znisaddedas
deoxidizingagentandtypicalcompositionsare88%Cu,
10%Sn,2%Zn.Thisissuitableforworkingincold
state.Itwasoriginallymadeforcastinggunsbutused
nowforboilerfittings,bushes,glandsandothersuch
uses.

27. Non-metals-Non-metallicmaterialsarealsousedinengineering
practiceduetoprincipallytheirlowcost,flexibilityandresistanceto
heatandelectricity.Thoughtherearemanysuitablenon-metals,the
followingareimportantfewfromdesignpointofview:
Timber-Thisisarelativelylowcostmaterialandabadconductorof
heatandelectricity.Ithasalsogoodelasticandfrictionalproperties
andiswidelyusedinfoundrypatternsandaswaterlubricated
bearings.
Leather-Thisiswidelyusedinengineeringforitsflexibilityand
wearresistance.Itiswidelyusedforbeltdrives,washersandsuch
otherapplications.
Rubber-Ithashighbulkmodulusandisusedfordriveelements,
sealing,vibrationisolationandsimilarapplications.Plasticsare
syntheticmaterialswhichcanbemouldedintodesiredshapes
underpressurewithorwithoutapplicationofheat.Thesearenow
extensivelyusedinvariousindustrialapplicationsfortheircorrosion
resistance,dimensionalstabilityandrelativelylowcost.

28. Thermosettingplastics-Thermosettingplasticsareformedunder
heatandpressure.Itinitiallysoftensandwithincreasingheatand
pressure,polymerizationtakesplace.Thisresultsinhardeningofthe
material.Theseplasticscannotbedeformedorremoldedagain
underheatandpressure.Someexamplesofthermosettingplastics
arephenolformaldehyde(Bakelite),phenol-furfural(Durite),epoxy
resins,phenolicresinsetc.
Thermoplastics-Thermoplasticsdonotbecomehardwiththe
applicationofheatandpressureandnochemicalchangetakes
place.Theyremainsoftatelevatedtemperaturesuntiltheyare
hardenedbycooling.Thesecanbere-meltedandremoldedby
applicationofheatandpressure.Someexamplesofthermoplastics
arecellulosenitrate(celluloid),polythene,polyvinylacetate,polyvinyl
chloride(PVC)etc.

29. POLYMERS
Polymers –Chain of H-C molecules. Each repeat unit of H-C is
a monomer e.g. ethylene (C2H4), Polyethylene –(–CH2 –
CH2)n
Polymers:
Thermo plasts–Soften when heated and harden on cooling –
totally reversible.
Thermosets –Do not soften on heating
oPlastics –moldable into many shape and have sufficient
structural rigidity. Are one of the most commonly used class
of materials.
oAre used in clothing, housing, automobiles, aircraft,
packaging, electronics, signs, recreation items, and medical
implants.
oNatural plastics –hellac, rubber, asphalt, and cellulose.

30. APPLICATIONS OF SOME COMMON THERMOPLASTICS
Material Characteristics Applications
Polyethylene Chemically resistant, tough, low friction
coefficient, low strength
Flexible bottles, toys, battery
parts, ice trays, film wrapping
materials
Polyamide (Nylon) Good strength and toughness,
abrasion resistant, liquid absorber, low
friction coeff.
Bearings, gears, cams,
bushings and jacketing for
wires and cables
Fluorocarbon (Teflon)Chemically inert, excellent electrical
properties, relatively weak
Anticorrosive seals, chemical
pipes and valves, bearings,
anti-adhesive coatings, high
temp electronic parts
Polyester (PET) Tough plastic film, excellent fatigue and
tear strength, corrosion resistant
Recording tapes, clothing,
automotive tyre cords,
beverage containers
Vinyl Low-cost general purpose material,
rigid, can be made flexible
Floor coverings, pipe, electric al
wire insulation, garden hose,
phonograph records
Polystyrene Excellent electrical prop and optical
clarity, good thermal and dimensional
stability
Wall tile, battery cases, toys,
lighting panels, housing
appliances

31. APPLICATIONS OF SOME COMMON THERMOSETS
Material Characteristics Applications
Epoxy (Araldite)Excellent mechanical properties and
corrosion resistance, good electrical
prop., good adhesion and dimensional
stability
Electricalmoldings,sinks,
adhesives, protective
coatings,fiberreinforced
plastic(FRP),laminates
Phenolic
(Bakelite)
Excellent thermal stability (>150 C),
inexpensive, can be compounded with
many resins
Motorhousings,telephones,
autodistributors,electrical
fixtures
Polyester
(Aropol)
Excellent electrical properties, low cost,
can formulated for room or high
temperature, often fiber reinforced
Helmets,fiberglassboats,
autobodycomponents,chair
fans

32. CERAMICS
Ceramics Materials
•Refractory Materials
•Advanced Ceramics
•Abrasives
•Glass Ceramics

33. REFRACTORY MATERIALS
Zirconia -extremely high temperatures.
Sic and Carbon –also used in some very severe
temperature conditions, but cannot be used in oxygen
environment, as they will oxidize and burn.

34. ABRASIVE CERAMICS
oAbrasives are used in cutting and grinding tools.
oDiamonds -natural and synthetic, are used as
abrasives, though relatively expensive. Industrial
diamonds are hard and thermally conductive.
Diamonds unsuitable as gemstone are used as
industrial diamond
oCommon abrasives –SiC, WC, Al2O3 (corundum)
and silica sand.
oEither bonded to a grinding wheel or made into a
powder and used with a cloth or paper.

35. ADVANCED CERAMICS
Automobile Engine parts Advantages:
Operate at high temperatures –high efficiencies; Low
frictional losses; Operate without a cooling system; Lower
weights than current engines Disadvantages: Ceramic
materials are brittle; Difficult to remove internal voids (that
weaken structures);
Ceramic parts are difficult to form and machine Potential
materials: Si 3 N4 (engine valves, ball bearings), SiC
(MESFETS), & ZrO2 (sensors), Possible engine parts:
engine block & piston coatings

36. REFRACTORY MATERIALS
Refractory -retains its strength at high temperatures > 500°C.
Must be chemically and physically stable at high
temperatures. Need to be resistant to thermal shock, should
be chemically inert, and have specific ranges of thermal
conductivity and thermal expansion.
Are used in linings for furnaces, kilns, incinerators, crucibles
and reactors.
Aluminum oxide (alumina), silicon oxide (silica), calcium oxide
(lime) magnesium oxide (magnesia) and fireclays are used to
manufacture refractory materials.

37. COMPOSITES
Amaterialssystemcomposedoftwoormorephysically
distinctphaseswhosecombinationproducesaggregate
propertiesthataredifferentfromthoseofits
constituents
Examples:
Cementedcarbides(WCwithCobinder)
Plasticmoldingcompoundscontainingfillers
Rubbermixedwithcarbonblack
Wood(anaturalcompositeasdistinguishedfroma
synthesizedcomposite)

38. WHY COMPOSITES ARE IMPORTANT
Compositescanbeverystrongandstiff,yetvery
lightinweight,soratiosofstrength-to-weightand
stiffness-to-weightareseveraltimesgreaterthan
steeloraluminum
Fatiguepropertiesaregenerallybetterthanfor
commonengineeringmetals
Toughnessisoftengreatertoo
Compositescanbedesignedthatdonotcorrode
likesteel
Possibletoachievecombinationsofpropertiesnot
attainablewithmetals,ceramics,orpolymersalone

39. DISADVANTAGES ANDLIMITATIONSOFCOMPOSITE
MATERIALS
Properties of many important composites are
anisotropic -the properties differ depending on the
direction in which they are measured –this may be an
advantage or a disadvantage
Many of the polymer-based composites are subject to
attack by chemicals or solvents, just as the polymers
themselves are susceptible to attack
Composite materials are generally expensive
Manufacturing methods for shaping composite materials
are often slow and costly

40. ONE POSSIBLE CLASSIFICATION OF COMPOSITE
MATERIALS
Traditionalcomposites–compositematerialsthat
occurinnatureorhavebeenproducedby
civilizationsformanyyears
Examples:wood,concrete,asphalt
Syntheticcomposites-modernmaterialsystems
normallyassociatedwiththemanufacturing
industries,inwhichthecomponentsarefirst
producedseparatelyandthencombinedina
controlledwaytoachievethedesiredstructure,
properties,andpartgeometry

41. CLASSIFICATION

42. DISPERSION-STRENGTHENED COMPOSITES
In dispersion-strengthened composites, particles are
comparatively smaller, and are of 0.01-0.1μm in size.
Here the strengthening occurs at atomic/molecular
level i.e. mechanism of strengthening is similar to that
for precipitation hardening in metals where matrix
bears the major portion of an applied load, while
dispersoids hinder/impede the motion of dislocations.
Examples: thoria (ThO2) dispersed Ni-alloys (TD Ni-
alloys) with high-temperature strength; SAP (sintered
aluminium powder) –where aluminium matrix is
dispersed with extremely small flakes of alumina
(Al2O3).

43. PARTICULATECOMPOSITES
Particulatecompositesareotherclassofparticle-reinforced
composites.Thesecontainlargeamountsofcomparatively
coarseparticles.Thesecompositesaredesignedtoproduce
unusualcombinationsofpropertiesratherthantoimprove
thestrength.Mechanicalproperties,suchaselasticmodulus,
ofparticulatecompositesachievableareintherangedefined
byruleofmixtures.
Particulatecompositesareusedwithallthreematerialtypes
–metals,polymersandceramics.Cermetscontainhard
ceramicparticlesdispersedinametallicmatrix.Eg.:tungsten
carbide(WC)ortitaniumcarbide(TiC)embeddedcobaltor
nickelusedtomakecuttingtools.Polymersarefrequently
reinforcedwithvariousparticulatematerialssuchascarbon
black.Whenaddedtovulcanizedrubber,carbonblack
enhancestoughnessandabrasionresistanceoftherubber.

44. PARTICULATECOMPOSITES
Particulate composites are used with all three material types –
metals, polymers and ceramics. Cermets contain hard ceramic
particles dispersed in a metallic matrix. Eg.: tungsten carbide (WC)
or titanium carbide (TiC) embedded cobalt or nickel used to make
cutting tools. Polymers are frequently reinforced with various
particulate materials such as carbon black. When added to
vulcanized rubber, carbon black enhances toughness and abrasion
resistance of the rubber. Aluminium alloy castings containing
dispersed SiC particles are widely used for automotive applications
including pistons and brake applications. Concrete is most
commonly used particulate composite. It consists of cement as
binding medium and finely dispersed particulates of gravel in
addition to fine aggregate (sand) and water. It is also known as
Portland cement concrete. Its strength can be increased by
additional reinforcement such as steel rods/mesh.

45. FIBER-REINFORCED COMPOSITES
Most fiber-reinforced composites provide improved strength
and other mechanical properties and strength-to-weight ratio
by incorporating strong, stiff but brittle fibers into a softer,
more ductile matrix. The matrix material acts as a medium to
transfer the load to the fibers, which carry most off the applied
load. The matrix also provides protection to fibers from
external loads and atmosphere. These composites are
classified as either continuous or discontinuous. Generally,
the highest strength and stiffness are obtained with
continuous reinforcement.

46. FIBER-REINFORCED COMPOSITES
Discontinuous fibers are used only when
manufacturing economics dictate the use of a
process where the fibers must be in this form. The
mechanical properties of fiber-reinforced composites
depend not only on the properties of the fiber but also
on the degree of which an applied load is transmitted
to the fibers by the matrix phase. Length of fibers,
their orientation and volume fraction in addition to
direction of external load application affects the
mechanical properties of these composites.

47. Effectoffiberorientationandconcentration:with
respecttoorientation,twoextremespossibilitiesare–
parallelalignmentandrandomalignment.Continuous
fibersarenormallyaligned,whereasdiscontinuous
fibersarerandomlyorpartiallyorientated.Two
instantsofloadingare:longitudinalloadingand
transverseloading.

48. STRUCTURALCOMPOSITES
These are special class of composites, usually consists of
both homogeneous and composite materials. Properties of
these composites depend not only on the properties of the
constituents but also on geometrical design of various
structural elements.
Two classes of these composites widely used are: laminar
composites and sandwich structures.

49. LAMINARCOMPOSITES
Laminar composites: there are composed of two-
dimensional sheets/layers that have a preferred
strength direction. These layers are stacked and
cemented together according to the requirement.
Materials used in their fabrication include: metal
sheets, cotton, paper, woven glass fibers embedded
in plastic matrix, etc. Examples: thin coatings, thicker
protective coatings, claddings, bimetallics, laminates.
Many laminar composites are designed to increase
corrosion resistance while retaining low cost, high
strength or light weight.

50. SANDWICHSTRUCTURES
these consist of thin layers of a facing material joined to a
light weight filler material. Neither the filler material nor the
facing material is strong or rigid, but the composite
possesses both properties. Example: corrugated cardboard.
The faces bear most of the in-plane loading and also any
transverse bending stresses. Typical face materials include
Al-alloys, fiber-reinforced plastics, titanium, steel and
plywood. The core serves two functions –it separates the
faces and resists deformations perpendicular to the face
plane; provides a certain degree of shear rigidity along
planes that are perpendicular to the faces. Typical materials
for core are: foamed polymers, synthetic rubbers, inorganic
cements, balsa wood. Sandwich structures are found in
many applications like roofs, floors, walls of buildings, and in
aircraft for wings, fuselage and tailplane skins.