IN-PLANTTRAININGREPORT

Submittedto:Mr.Kuppuraj,AGM,FuselageGroup,ARDC

Undertheguidanceof:

Mr.ParvathamR,FuselageGroup,ARDC

Submittedby:MANASAMALKAKARAN

NIKITHANARAYANAPRASADKARAKKADAmritaVishwaVidyapeetham(University),Coimbatore

Periodoftraining:

From:22/06/2015To:11/07/2015

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TABLEOFCONTENTS

SNO TITLE PAGENO

1 Acknowledgements 32 IntroductiontoHAL 43 Fuselage 84 LandingGear 135 Aerodynamics 186 ArmamentandEscapeSystem 197 Avionics 218 Composites 249 DesignandManufacturingProcesses 2610 ECSandLSS 2911 FCS 3012 Hydraulics 3113 Materials 3214 PowerPlantandFuelSystems 3415 StressAnalysis 36

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ACKNOWLEDGEMENTS

WewouldliketothanktheAircraftResearchandDevelopmentCenter,HindustanAeronauticsLimitedforgrantingustheopportunitytointernforaperiodof threeweeks.Wewould liketothankMr.Kuppuraj(AGM,FuselageGroup,ARDC,Bangalore)forallowingustobeapartoftheFuselagegroup.WewouldpersonallythankMr.ParvathamR(FuselageGroup,ARDC,Bangalore)forguidingusthroughoutourinternshipandofferingusvaluableadvice.

Secondly, we would like to thank the following officers at ARDC for theirvaluabletimeandknowledge

• Mr.AshwinKP,Miss.Shraddha–Landinggeargroup

• Mr.Mukesh,Mr.Arun–WingandEmpennagegroup

• Mr.Srinivas,Mr.Rajath–Fuelsystemsgroup

• Mr.Venkatesh,Mr.Kiran,Mr.Prashanth,Mr.Krishnakumar,Mrs.DivyaMadhuri–Fuselagegroup

• Mr. Diwahar, Mr. Palani Rajan, Mr. Suresh, Mr. Guruswamy – Stressanalysisgroup

• Mr.Hitesh–FlightControlSystemsgroup

• Miss.Monica,Mr.Arjun,Mr.Kannan–Aerodynamicsgroup

• Mrs.RajashreePillai–Materialsgroup

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INTRODUCTIONTOHAL

Hindustan Aeronautics Limited is one of the major aircraftmanufacturingcompaniesinAsiawitharichheritagespanningover75years.Itwasfoundedin1940byMr.SethHirachandWalchandwiththeobjectiveofmeetingtheneedsoftheIndianAirForcealongwithdevelopingtheaerospaceindustryinIndia.DuringWorldWarII,itservedasanMROunittotheUnitedStates ArmyAir Force and produced railway coaches in the interim period,post-war. HF -24 Marut was one of the first indigenous fighter aircraftsproducedbyHAL.Over the spanofyears, theyproducedmany trainersandfighters like Kiran, Chetan and some utility aircrafts like Basant. They alsomanufactured licensed aircrafts like Dornier, Sukhoi Su-30 MKI, Jaguar andHawk.

HAL currently comprises of 19 Production Units, 1 FacilityManagementDivisionand10R&DcentersspreadacrossIndiain locationslikeBangalore,Hyderabad,Koraput,Nasik,Barrackpore,Kanpur,KorwaandLucknow.

TheBangalorecomplexofHALincludesthefollowingdivisions:

• Aircraft• Overhaul• Aerospace• Engine• Helicopter• FoundryandForge• AirportServices• FacilitiesManagement• IJTLimitedSeriesProduction• LCALimitedSeriesProduction• CentralMaterialsandProcessLaboratoryCentre• IMGT

TheongoingprojectsinHALBangalorearethefollowing:

Ø LCA–Tejas

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Ø HTT40Ø HJT36–SitaraØ ALH–Dhruv

TYPESOFAIRCRAFTS

1. Trainera. Pistonengineb. Turboprop-BasicTrainer(HTT40)

c. ClubTrainerd. JetTrainer

i. IntermediateJetTrainer(HJT36)

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ii. AdvancedJetTrainer(Hawk)

2. Militaryaircraftsa. Fighter(LCA-TejasAirForce/Navy)

b. Bomber

3. Transportaircraftsa. Passengerb. Executivec. Cargo

TYPESOFJOINTS

Thejointsinastructurearebroadlyclassifiedasfollows:

• PermanentJoints–Rivets,Welds

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• TemporaryJoints–BoltandNut

Someimportantjointsinanaircraftarethefollowing:

Ø EngineMountØ LandingGearAttachmentØ FinAttachmentØ CanopyandWindShieldØ Wingattachment

Ø AirBrakeattachment

Anaircraftstructurecomprisesoffuselage,wing,empennageandlandinggear.

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FUSELAGE

Fuselageisthebodyoftheaircraftwhichholdstheliftproducingandthecontrolsurfacesandthelandinggeartogether.Itcontainsvarioussystemslikeavionics,ECSandLSS,fuelandengine,hydraulicsystemsandcarriespayload(passengers /cargo in transport aircrafts and pilot/trainer in militaryaircrafts).

Therearethreetypesoffuselagestructurebasedonitsconstruction:

Ø TrusstypeØ MonocoqueØ Semimonocoque

Earlylighterthanairvehicleslikehotairballoonhadamonocoquestructureandthefirstseriesofaircraftshadatrusstypeoffuselage.Inthemonocoquetype,athickhollowsinglestructuretakestheentireloadonthefuselageandhasadisadvantageofpropagationofcrackandreadyfailureinthepresenceofany defect. With the advancement in aircraft design, the semi monocoquestructurewasadoptedasitovercomesthislimitation.Inthistypeoffuselagestructure the thin skin is stiffened and prevented from buckling by usingstringers,bulkheads,frames andlongeronswhichmakesthestructurestrongenoughtoendurevariousshear forcesandbendingmomentsactingon it. Italsohastheaddedadvantagesofreductioninweightoftheaircraftandeaseofmanufacturing and repair. This structure is presently used by almost allmodernaircrafts.

Longeronsare longitudinalmemberswhichrunthroughthe lengthof thefuselage and take axial and bending loads. Bulkheads and frames enhancebuckling strength of the skin and provide shape to the fuselage. Bulkheadsenable transfer of loads fromwing to fuselage and vice versa. Stringers areshortermembersthatactasstiffenersandfunctionsimilartolongerons.Shearwalls are present between top and bottom longerons on either side of thebulkhead and as the name suggests, distribute the shear load between thelongeronsandthebulkhead.Apartfromthesebasicstructuralmembers,side

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walls and floors divide the internal structure into cells to allocate space forothersystems.

Therearethreetypesofframestypicallyfoundinafuselagestructure:

Ø Openring–itisfoundatlocationswheresystemslikelandinggearareattached

Ø CloseringØ Full web – it is found at locations where there is a requirement towithstand high pressure, say at the front and rear of thecockpit(internallypressurized)

For the ease ofmanufacturing and assembly the fuselage is divided intofront,centreandrearfuselage.

FRONTFUSELAGE:

Thefrontfuselageconsistsofanose(radomeinthecaseofafighterandIJTandapropellerincaseofabasictrainer),windscreenandcanopy.Radomeisthecoverfortheradarwhichisfittedinthefrontpartofthefuselage.Itismade up of Kevlar which has a large impact resistance and capable oftransmittingradarsignalswithoutattenuatingthesignals.Boththewindscreenand the canopyare transparent innature.This isdone forproperand clearvision.Thewindscreenandthecanopyneedtowithstandvariousforceslikepressure difference, aerodynamic pressure, bird impact, airframe torsion,thermal expansion and contraction and fatigue. In order towithstand theseforces,thematerialusedtomanufacturethesepartsneedtohavehighstrengthtoweightratio,thermalproperties,abrasionandimpactresistance.Stretchedacrylicsheetsarebestsuitedtomanufacturetheseparts.Sincethewindscreenis subjected to higher risks of a bird impact, it is made sufficiently thickcomparedtothecanopy.Thecanopyishingedatthesidesandsupportedbyaspringmechanismenablingthepilottoliftthecanopyandenterthecockpiteffortlessly.Oncethepilotisseatedinthecockpit,hecanlockthecanopy,asealwhichisattachedtotherimgetsinflatedautomaticallythuspreventinganypressure leakage. There is a provision of oxygen intake for the pilot’s

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sustenance. Varioussensorsareattachedtoindicatewhetherthecockpit isshutornot.Thisisforthepilot’ssafety.Incaseofanemergency,thepilotcanpull a trigger which initiates an explosion of the RDX which is pasted in abeading attached to the edgesof the canopy.Once the canopy, thepilot canescapewithhisejectionseatwhich is fittedwithboostersandasurvivalkit.For fighters,astubwing isattachedforthesmoothtransformationfromthefuselagetothedeltawing.

CENTERFUSELAGE:

Thecentrefuselagecarriesshearandbendingtypewingattachmentstotransfertheloadfromthewingtothebulkhead.Thenumberandpositionoftheseattachmentsdependonloadonwing.IncaseofLCA,therearethreeshearattachments and two bending attachments. In HTT-40, there are two shearattachmentsandonebendingattachment.

Betweentwostations,thereisaprovisionforDCdistributionbox,groundmaintenancepanelandfuelfillingpanel.

Infighteraircraftsandincertainintermediateandadvancedjettrainers,apylonisprovided,towhichadroptankormissilecanbeattached.InLCA,thepylon attachment is provided is at the rear andmid stations. Gun bays arepresentatLHof themiddle stationswhereasRHofoneof the stationhasafacility to fit an ammunition box. LDP (laser designator pod) fitting is alsoprovided.

Air ducts for atmospheric air intake is present at either sides ofbulkheads.Atrouserductisalsopresentforthesamepurposebelowthespine.Air duct converges to a circular shape towards the rear from the last fewstations.

Landing gear is attached to the fuselage to two stations using a RRJK(RadiusRodJackFitting).

ThecenterfuselagecontainstheF1fueltankrunningthroughthecenterofthebulkheadsandF2fueltankbetweenthetrouserductandthespine. It

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alsocontainsasecondarypowersystemwhichusesbatteriesandgearboxestoignitetheengine.Itmaybeusedasabackupincaseofenginefailure.

REARFUSELAGE:

Airbrakesareusedinaircraftsduringlandingtoproducedrag.TherearfuselageoftheLCAhasanairbrakehingeandairbrakejack.Theverticalfinattachmentsarealsoprovidedatthesestations.Thetrailingedgeofthewingrootisattachedattheaftstation

Basedonthetypeofenginethattheaircraftusestopropel,thelocationoftheengineinthefuselagevaries.Incaseofaturboproptype,theengineislocatedatthefrontfuselage(asinHTT-40)whereaswhenaturbojetengineisemployed,itismountedintherearsection(asinLCA).

The top and bottom floor assembly runs through the length of the rearfuselage to provide extra support and also to create space to place avionicsequipmentsandiscoveredbyskinonthesides.

IntheLCA,theengineisattachedtothetopfloorassemblyonthesides(usingguidepins)andheldupbythebulkheads.Atiebeamwhichisamovablemember attached to the engine bay door, is provided at a station for thepurpose of mounting the engine. The engine is covered by a shroud whichprotectsthesurroundingstructuresfromtheheatandvibrationintheengineand is insulated with polyamide foams. Engine cooling is done using a precooler attached in the dorsal spine at the junction of the center and rearfuselage.

Topskinseparatesthebulkheadfromthespine.Betweenthespineandtheengineshroud,ECSunitsareplacedwhichareaccessedthroughcoversonthesidewalls.

TEX(TrailingEdgeExtension)assemblyislocatedatthelastfewstationsand it contains equipments like data recorder, cockpit voice recorder, andlightning box, SSCDR (Solid State Crash Data Recorder and firing controller(CMD)CutoutsareprovidedonthecoverofSSCDRforthepurposeofcooling.

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Theendconeassembly,afttheairbrake,consistsofformationlightsandtheparachutebay.Theendcapisopenedduringlandingejectingtheparachutethusprovidingadditionaldrag.

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LANDINGGEAR

Thelandinggearisacrucialentityinaircraftdesign,especiallyinsupersonicaircraftslikeLCA,andisuniquetoeachaircraft.

Inthenosewheellayout,theNLGisplacedforwardandfarfromtheCGoftheaircraftandtheMLG,aftandclosetoCG.Inthetailwheellayout,thetailwheelisplacedaftandfarfromtheCGandtheMLG,forwardandclosetoCG.

Mostaircraftshaveanosewheellayoutasitismorestable,tailwheellayoutisgenerallyfoundinhelicopters.

Thelandinggearconsistsofthefollowingparts:Wheel,Axle,PistonandBarrel.

ConfigurationsofLanding

Gear

Bicycle Tricycle

Nosewheellayout

Tailwheellayout

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Thedesignof the landinggeardependson thevertical sinkvelocityand thetowagearea.Basedonthedesign,landinggearsareclassifiedasfollows:

1. ArticulatedlandinggearTheaxleisattachedtotheshockabsorberthroughaleverwhich

takesapartoftheloadonthelandinggear,thusfacilitatingtheuseofashortershockabsorberunit.LCA–Fighter,HTT-40andIJThavethistypeoflandinggear.

2. TelescopiclandinggearThe axle is directly attached to the shock absorber and is thus

largerinsize;itprovidestheadvantageofmoregroundclearanceand,therefore, finds applications in naval aircrafts (LCA – NAVAL) whichemployanarrestorhooktolandoverashorterdistance.NLGisgenerallytelescopicinnatureasitisdesignedtotakelesserload.

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Locationof landinggear:TheMLGcanbeplaced in thewingor the fuselagedependingonspaceavailability.InHTT-40,theMLGismountedonthewingswhereasinLCA,itismountedonthefuselageduetolackofadequateretractionspaceinitscompositewings.

LandingGearSystem

RetractionSystem

BreakingSystem

SteeringSystem

ShockAbsober

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1. ThebreakingsystemisplacedinthewheeloftheMLG.Discbrakes,usedinaircrafts,consistsasetofrotorsthatrotatewiththewheelandstators.When force is appliedon the rudderpedal, thepistonmovesapplyinghydraulic pressure on the stator. The stator hits the rotating rotors,providing breaking action. In order to prevent skidding, hydraulicpressureisappliedandreleasedalternatively.

2. After takeoff, brakes are applied and cams are engaged to make thewheels straight. The landing gear is then retracted using hydraulicactuators;retractionisdonetoreduceadditionaldragduringcruise.Thedirectionofretractioninsomeaircraftsisgivenbelow.

Aircraft MLG NLGLCA Aft ForwardIJT Inwards ForwardHTT-40 Inwards Backward

3. Thesteeringsystemisrequiredfordirectionalcontrolonthegroundsaywhiletaxiing.Anaircraftcanperformthisactionevenwithoutasteeringsystem,as inthecaseof IJTandHTT-40. Intheseaircrafts,differentialbreakingisemployedforthepurposeofsteering.

4. Shock absorbers are primarily used with the purpose of preventingdamagetothelandinggearonimpactwiththeground.Inaircrafts,oliopneumatic shock absorbers are employed, where the compressed gasandhydraulic fluidareequivalent to thespringanddampenerseen inmechanical shock absorbers. A separator separates the oil and gaschambers. The toggle has different functions in theMLG andNLG – itprevents the wheel from rotating independently in the former androtatesthewheelbytransferringtorqueinthelatter.Aspringisprovidedbetween the toggles, which is removed during towing, allowing 360degreerotationofthewheels.Ahardlandingindicatorislocatedabovetheoilchamberwhichindicateswhetherhardlandinghasoccurredornotbasedontheoilpressure.Thepoppingoutofthespringinbetweenthetogglesisalsoanindicationofhardlanding.

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LRUslikeuplocksanddownlocksarepresentinthelandinggearsystem.Uplocks are hydraulically released, prior to extension of landing gear andmechanicallyengaged,postretractionoflandinggear.Downlocksareengagedoncompleteextensionandreleasedpriortoretractionoflandinggear.Threeindicationlightsatthecockpitoftheaircraft,oneeachfortheNLG,LHMLGandRHMLG,displaythestatusofthelandinggearretraction/extensionandlockingsystems.

For the purpose of redundancy, the following emergency systems are alsopresentinaircrafts:

1. LCA:Emergencyleverisprovided,apartfromtheregularlevertooperatetheabovesystems.

2. Su30:Pneumaticsystemsarepresentinadditiontohydraulicsystems.3. HTT-40:Anaccumulatorsystemisusedinsteadofhydraulicsystem.4. PilatusPC7:Facilityisprovidedformanuallanding.

Burstingoftiresduringtakeofforlandingisfatalasitcancausetheaircrafttolosedirectionalcontrol.Topreventthis,afuse-ableplugisprovidedbetweenthe metallic wheel and the tire, which melts on overheating, allowing thecompressedairinthetiretoescape,hencepreventingthetirefrombursting.

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AERODYNAMICS

Based on the ASR (air staff requirements), and the NMG, the aerodynamicsgroupgenerateasuitableaerodynamicbody.Aprototypeismadeandistestedinthewindtunnelforstaticmotionandtherotarytesttocheckforthedynamicmotion. SimilarconditionsaresimulatedintheCFDandvariousparametersarecheckedandverified.Theflighttestcentreinteractswiththepilotduringtheflighttestandnotesthedataandcheckswiththeotherresultsproduced.Fromthenonwardscontinuoustestsaredoneandthevariousparametersanddataismonitored.

CFD is used for its low cost and speed and various properties likemasstransfer,flowofheat,phasechange,chemicalreaction,mechanicalmovementandstressesenduredbythebodywillbedepicted.ItworksonthebasisoftheNavier-Stokesequation.

StepsfollowedinusingCFD:

1) Identifytheproblem2) Chooseanairfoilsectionthatsuitstheproblem,modelthegeometryandtheflowdomain

3) Gridandmeshiscreated4) Specifytheboundaryconditionandtheinitialcondition5) Solutionisgenerated6) Visualizevariousparameterdistributions7) Each point on the grid gives the required parameter at that point, onintegratingtheloadatallpointswecanfindthetotalloadactingonthatbody.

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ARMAMENTANDESCAPESYSTEM

Duringacombatvariousweaponsfittedtotheaircraftarereleasedandused.Themaintypesofammunitionusedare:

1) Bombs2) Rockets3) Missiles4) Guns

Bombs follow the ejection system. It is dropped from air to the groundwhereasrocketsareusedduringcombats, released inairandattacks thetargetintheair.Missilesaregenerallylaunchedfromairandtargetedtothegroundandsea.Therearetwotypesofamissilelaunch:

1) Closecombatmissilewhichfollowsraillaunch–suitableforlightweightmissiles

2) Beyondvisualrangewhichfollowsejectionsystem–suitableforheavymissilesTotherightssideofthefuselage,thegunisattachedandtotheleftthelaserdesignatorpod(LDP)whichroutesthemissilestothetargetisfixed.The laser on hitting the target is captured by sensors fitted on to themissiles,bombsetcandisthenreleased.BombsarealsofittedwithaGPStohitthetarget.Onthelarboardwithinthefuselage,theammunitionboxis fixed which feeds the gun through a mechanism built within thefuselage.Theattachmentsaremade toa structure called thepylonwhich isindeedattachedtothewingandthefuselagebody.Accordingtothetypeof the weapon used different types of pylon attachments are made.BombsareattachedusinghooksandareejectedusinganERU(ejectorreleaseunit).Thewingcancarrythreeattachmentsnamelytheinboard,midboardandtheoutboardattachment.Sincetheinboardisclosesttothefuselageandhasthemaximumloadcarryingcapacityheavymissilesarefittedhere.

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Moderndayaircraftshaveamechanismofstoringtheweaponswithinthefuselageandcanbereleasedoncommand.Themainadvantageofthisisthattheweaponsareconcealed.In case of an emergency, the pilot can eject himself by pulling atriggerattached tohisseat.Thecanopybreaksand therocketboosterattached to the seat get ignited. To reducemajor impacts on the pilotstabilizersareused,aparachuteisreleasedandthepilotisboughtonthegroundsafely.Apersonalsurvivalpackwhichcontainsbasicamenitiesrequired for survival is fitted to the seat. Thusmaking armament andescapesystemasignificantpartofafighteraircraft.

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AVIONICS

TheavionicsinLCAmainlyconsistsofthefollowing:

1. AUSMS(UtilitySystemsManagementSystem)whichrelaysinformationfromthesystemstotheOpenArchitectureComputer(OAC).

2. AnOAC (OpenArchitectureComputer) thatprocesses the informationfromtheUSMSandsendsittothedisplayinfrontofthepilot.

3. Abus(1553BSerial incaseofLCA)withmultiplechannelredundancythatrelaystheinformationfromtheUSMSandtransfersittotheOAC.

4. A Multi Functional Display (MFD) which collectively displays theinformationgatheredfromthevarioussensorsandmicroswitchesinthesystems,tothepilot.

InearlierversionsofLCA,theUSMSconsistedoffourelectronicunits–DHEU,EEMS,DFMandECM.Inmorerecentaircrafts,theDHEUandEEMSunitswerecombinedtoformtheBHEEM–EUandDFMandECM,toformECFM–EU.TheBHEEM–EUcontrolsthefollowingsystemsinanaircraft:

BHEEM-EU

Hydraulics

Undercarriage

Electronics

Engine

BrakeMechanismSystem

NoseWingSteering

FireDetectionWarningSystem

VibrationSystem

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1. Thehydraulicsystemsareduplexredundantandconsistsoftwosystems.Onfailureonone,theothertakesoverandonfailureofboth,signalsaretransmittedbyEMDD.

2. The undercarriage has micro switches which relay information toBHEEM-EUastowhethertheundercarriageisretractedanduplockedorextendedanddownlocked.Signal SignificanceGreen ExtendedandDownlockedRed IntransitNosignal Retractedanduplocked

3. The avionics in an engine consists of a Jet Fuel Starter (JFS) and anIntegrated Drive Generator (IDG) connected to the Aircraft MountedAccessoryGearBox(AMAGB).TheJFSunithasaGroundRelayUnit(GRU)andabatterywhichprovided initialpower to theaircraft through thePower Take-Off (PTO) shaft and is cut off, once the engine rotationreachesitsselfsustainedrpm.TheIDGperformsthedualfunctionofanengine drive until the engine is self sustained and then acts as agenerator.ThislogiciscontrolledbyBHEEM–EU.

4. Therearedifferentbreakingmechanismsforanaircraft:a. DirectBreakingb. RetractionBreakingc. AntiSkidBreakingd. EnginerunwayBreaking

Accordingtotheinputfromthepilotandthesensorsonthewheels,theBHEEM–EUoperatestheShut-OffValve(SOV),controllingtheamountofhydraulicfluidthatflowsintothebreakingsystem.

5. TheBHEEM–EUoperatestheSteeringValve(SV)similartotheSOVinthebreakingsystem.

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6. Information from temperature sensors placed along the shroudof theengineisprocessedandawarningissignalediftheenginetemperatureexceedstheallowablelimit,thusindicatingafire.

7. Piezo-crystalsplacedontheshroudoftheenginesensestheamountofvibrationandaccordingtoAWDstandardssignalsthepilotifitexceedsanacceptablevalue.

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COMPOSITES

Acompositematerial isacombinationof twoormorematerialsofdifferentphysicalandchemicalpropertieswhencombinedtogethergivesaproductofcompletely different properties. These materials are stronger and lightercomparedtothetraditionallyusedAlalloys.Commonlyusedcompositesintheaerospace domain are the carbon reinforced and the fiber reinforcedcomposites. LCA which is of indigenous make consists 90% of compositematerials.Theskin,wings,elevonsandthesparsandribsofthefinandrudderarepurelymadeofcomposite.

Composites are isotropic in nature. Every 2 degree shift changes thestrengthofthecompositeby20%.Theyareoftwotypes:monolithicstructureandsandwichedstructurewhereacoreisused.

Thepre-impregnatedfiberwhichishalfcurediscutusingaspecialSianddiamond cutter into the desired shape and placed on the template in anautoclavewhichhasatemperatureof175degreeCelsius.Onemustbecarefultocheckthatthefiberisnotmoist.Ithastobestoredunder-18degreesCelsiusandshouldbeusedwithinamonthif leftout fora longtime.Onceit is fullycuredintheautoclave,itissenttotheovenandheatedupto125degreeCelsiustoremoveanyuncuredparts.Co–curingprocessistheprocesswherethepartstobeassembledareplacedinthedesiredmannerandcured.Thisreducestheextracostonusingfasteners.

Thesecompositeswhenexposedtoametalpartundergogalvaniccorrosion.Inordertoavoidthisglasslayerorasealantisusedintheinterface.Phenolicresinsresistsmokeandbismalimidehaveahightemperatureresistance,soitisusedinpartsneartheengineshroudwherethetemperatureisnormallyhigh.

Compression strength in composites can be improved by using thesandwichedstructure.Acoremadeupofpaperandnameisplacedbetweentwomonolithiclayersandisthencured.Suchstructuresareusedintheelevonsandtherudderwhicharesubjectedtohighcompressiveforces

Someofthedisadvantagesofusingacompositeareasfollows:

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1) Itisbrittleinnatureandsocannotenduretensionforces2) Ifthereisnoproperstoragethentherawmaterialwilldeteriorate3) Itdoesn’thaveahightemperatureandmoistureresistant, ifmoist thelayerswilldelaminateleadingtofailureofthestructure

4) Ithasapoorimpactresistance5) Internalcracksformedwillnotbevisibleandcannotbedetected.

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DESIGNANDMANUFACTURINGPROCESS

ThedesignprocessisinitiatedonreceivingthecustomerrequirementsintheformofASR(AirStaffRequirements).InthecaseofHAL,theserequirementsareobtainedfromtheirprimarycustomers-AirForce,NavyandArmy.TheASRusuallycontainsdetails likevelocityoftheaircraft,thealtitudeatwhichit isrequiredtofly,themaneuversthatitisexpectedtoperform,thev-ndiagramregioninwhichitistoflyandsoon.Thedesignercaterstotheserequirementswhileconformingtocertainsetstandards:

• MIL-STD,DEF-STDincaseofmilitaryaircrafts• FAAincaseofcommercialaircrafts

Based on experience, numerical calculations and wind tunnel testing, theaerodynamicsgrouparrivesatashapefortheaircraft.Thisisfurthervalidatedusing software and CFD and the NMG (Numerical Master Geometry) of theaircraftisdefined.

ThisNMGisusedasthebasetodesigntheinternalstructureoftheaircraftandspaceisallocatedforallsystemswithintheshapeoftheNMG.Theinboardandstationdiagramsaregeneratedforagivenaircraft–theformercontainsdetailsoftheLRUsandstructuralarrangementsinanaircraftandthelatterdividesthestructureof say the fuselage intovariousstations for thepurposeofeaseofidentificationandassembly.

Duringandafterthedesignofeachpart,thefollowingfactorsareanalyzedanddesignmodificationsaremadeaccordingly:

Ø WeightDistributionØ MaterialØ StaticAnalysisØ DynamicAnalysisØ Fatigue

On approval from all the above groups, the design is sent for DQ (DesignQuality) approval to check if it meets the requirements specified by thecustomerandthestandards.

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Onceapproved,thedesigndrawingissenttotheMethodsdepartmentwhichdecides theprocessesnecessary tomanufacture thepart and issues a routecard accordingly. The part is then manufactured using various machiningprocesses.

The conventional machine shop has machines like radial drilling machine,milling machine (universal, vertical and horizontal), lathe, surface andcylindrical grindingmachine and so on.Basic operations like cutting of rawblocks and surface rough finishing of parts that do not require the highprecisionofCNCmachinesareperformedhere.ThecutblocksofrawmaterialarethensuppliedtotheCNCshopsforfurthermachiningoperations.

IncaseofCNCmachines,theCADdrawingisconvertedintoaprogrammedcodeandfedintoacomputer,whichaccordinglyperformstherequiredmachiningoperation. The machines available in this shop include a variety of millingmachines (5 axes and3 axes)withdifferentbeddimensions, also jigboringmachinesfordrillingandboringminuteholes.Thetoolsusedformachiningaremade of carbide. Any desired surface finish can be obtained using CNCmachines and in inaccessible locations in a part, hand working is done toremoveburrsandfinishthesurfaceofthepart.

Inthecasewhereaprototypeofanaircraftisbeingmade,usingmetaltoolstoformthesheetmetalpartswillbeanexpensiveandlaboriousprocess.Sincesuchhighprecisionformingisnotrequiredinsuchcases,toolsmadefromjobrock wood are used for the purpose of forming sheet metal parts. Thewoodworksdepartmentmakes tools toserve thispurpose. Jobrockwood isbasicallylayersofwoodjoinedtogetherandprovidesmoreresistanceandfitstocontourwhileformingthesheetmetal.Smallersheetmetalpartsarehandformed using a mallet and other forming tools while bigger parts requireformingmachines like brake press, rubber press and punch press. Prior toforming, the raw aluminium sheets are subjected to heat treatment andannealedtoT0state.Thisprocessisnecessaryasthesheetispronetocrackformationifformedinitsnaturaltemperedstate.Afterforming,thealuminiumsheetisartificiallyagedtoT3orT4stateandthensubjectedtoanodizingandprimerapplication.

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The product undergoes a quality check between subsequentmanufacturingprocesses where the dimensions are checked either using metrologicalinstrumentsorusingaCMCmachineforpartswithcontours.Themanufacturedproductoninspectionandapprovalissentforassembly.

Intheassemblyshop,thepartsareassembledusingjigs.Priortoassembling,thejigsarecalibratedeitherusingamasterjigorusinglaserbeam.ThebasestructureisfirstassembledfollowingwhichvariousLRUsarefittedandtested.Finally,theouterskinandcoversarefitted.

Tosummarize,theworkflowisasfollows:

Tomanage and document the entire process of creation of a product fromdesign to assembly, PLM (Process Life Cycle Management) software likeInnoviaisused.ThePLMcontainsthedesign/productionstatusofeachpart,sub-assemblyandassembly.Itcontainsallissuesofadesignalongwithdetailsof the changes implemented from theprevious issues in the formofChangeNotice. Generally, design changes can be implemented in retro (in currentlyproducedaircrafts)orinlinecompliance(inthenextproductionseries).ThesedetailsareintegratedinthePLMsoftware.ItalsostoresnecessaryinformationliketheMAsheet(BillofMaterial)andorganizestheworkflowbymandatingapprovalfromeachdepartmentbeforeforwardingtothenext.

Skeletondefinition

Preliminarylayout

definition

Detaileddesignofparts Manufacturing Assembly

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ENVIROMENTCONTROLSYSTEMANDLIFESUPPORTSYSTEMS(ECSandLSS)

TheobjectiveofECSisforthecabinpressurizationandairconditioningof the cockpit. It is also used to demist the wind shield and to provide anambienttemperatureinsidethecockpit.Compressedairfromthe7thstageoftheengineistakenandisusedtoachievethispurpose.

Aminimumof30%ofhumidityisrequiredinthecockpit.Aninflatablesealisusedalloverthecanopytoavoidanyleakageofairandpressure.Atemperaturesensorisusedtocheckthetemperatureofairbeforeitleavesforthecockpit,if thetemperature is toohighortoo lowit issent toasystemwheretheairexpandsandcompressesandisthencheckedbythetemperaturesensoragain.Thiscycleensuresthemaintenanceofacomfortabletemperaturewithinthecock pit. An IRV (inward relief valve) is used as a back up tomaintain thepressureiftheprimarysystemfails.

Rightamountsofoxygenisrequiredforhumansustenance.Iftheleveloftheoxygendecreasesaconditioncalledanoxiaprevailswhichisdangerousas the pilot will not be able to make the right decision. Oxygen cylinderwrappedwithKevlarissuppliedtothepilotviaAlpipelines.AlpipelinesarepreferredoverCulinesasAlwillhavelesserhoopstress.Pneumaticsystemsareusedassecondarysystemsincaseofafailureofoxygensupply.

TheECSisplacedbelowthespineoftheaircraftandtheoxygencylinderisplacedbehindthepilot’sseat.Iftheseatisjettisoned,thepilotwillstillhaveanoxygensupplyasasmallcylinderisattachedtohisseat.

Acousticpaddingmadefromsiliconfoamgelisusedtoreducethenoise.Thenoise should not be higher than 113 dB as higher decibels would result inhearingimpairment.

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HYDRAULICSYSTEMS

Hydraulicsystemsareanintegralpartoftheaircraft.Alotofmechanismslikepressurization, landing gear and power generation use hydraulic system.Hydraulicjacksareusedtomaintainthepressureinthecockpit.

The main units for power generation are the pump, reservoir and theaccumulator.TheHMDG,HMDFPandtheEMDPareexclusivelyusedintheLCA.Anisolationvalveisusedinthelinestoblocktheutilitycircuittopreventanyleakages.LCAisfittedwithtwopumps;ifpump1failsthenthesecondpumpcanbeused.IfboththepumpfailsthenEDPwhichisanenginebasedmotorisusedasabackup.IfEDPalsofailsthenEMDPwillbeautomated.Theactuatorsusepneumaticsystemsforitsworking.Thereservoirsareplacedinthelandinggearbay.

The under carriage and the wheel brakes have a primary and secondarysystemwhereastheairbrakesandtheparkingbrakeshavejustonesystem.TiandAlpipelinesareusedforitsstrengthastheworkingfluidusedishighlyviscous. The working fluid used should be fire resistant and the viscosityshouldnotchangebyahighfactorasthetemperaturechanges.

Each component andpipes are tested. Validation in hydraulic system is tocheckifeverycomponentworksinthegivenspecifictimes.Testsaredonetocheckifitisleakageproof,slushingisdonetoremovedustandforeignparticles.Functionaltestsarecarriedout.Wheelbrakesarecheckedinthenormalandstandby mode. Nose wheel steering systems are checked using the rudderpedal.Finally,workingofallFCSischecked.Aftercompletingallthevalidationsareportwillbemade.

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FCS

Basic trainer aircrafts operate their control surfaces using kinematic linkmechanismswhere thepilot is required toprovideanequivalentamountofforcetodeflectthecontrolsurfacestotherequiredangle.Thiscallsforalotofeffort from the pilot. Advanced aircrafts use fly bywire systems to performthesemaneuvers,significantlyreducingtheloadfeltbythepilot.Thesesystemsaredesignedbasedonafeedbackloopsystemwhichmonitorsthedeflectionofthe control surface and automatically moves it until it has deflected to thedesiredangleanddoesnotmandatemanualcorrectionsbythepilot,asinthecase of mechanical systems. A Digital Flight Control Computer (DFCC)processesdatafromthesensorsandperformsthistaskforthepilot.

LCA has 13 control surfaces – LH and RH elevons (elevators and ailerons),rudder,3LHslats,3RHslatsandapairofairbrakes.

An aircraft has six degrees of freedom along three translational axes –longitudinal,lateralanddirectionalandthreerotationalaxes–pitch,rollandyaw. The control surfaces on an aircraft are designed to perform motionslimited to these six degrees of freedom. The control surfaces can thusmathematicallybemodeledasdifferentialequationswith6degreesoffreedom(calledthe6DoFmodel).

Inthe6DoFmodel,variableslikevelocity,attitude,ratesandthrottlearefedintothedifferentialequations.Thecoefficientsinthedifferentialequationsaregivenbytheaerodynamicsdepartmentbasedonnumericalcalculations,windtunneltestingandCFD.Environmentalconditionsarealsofedintothemodeltovisualizehowthecontrolsurfacesareexpectedtoperforminflight.

The data from flight testing is then compared to the model to check howeffectivelythemodelreplicatestheactualperformanceofthecontrolsurfacesinflight.Deviationsarerecordedandusedtofurtherimprovethemodel.

Therefore,thefunctionoftheFCSgroupistodesignthecontrolsurfaces,modelthemonanaircraftandvalidatethemodelusingrealtimedata.

MATERIALS

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Therearetwomainfactorstobeconsideredwhileselectingamaterialforanaircraft:

Ø SpecificStrength=Ultimatetensilestrength/DensityØ SpecificModulus=Young’sModulus/Density

Thefirstaircraftsusedwoodbecauseofitseaseofformingandcapabilitytogeneratehighlift.ButitlaggedintermsofstrengthtoweightratiocomparedtoAluminiumandwasthusreplaced.

Of themetallicmaterialsused inmodernaircrafts, the followingAluminiumalloysarethemostpredominantlyused:

o Al-Cuo Al–Zn(mostcommonlyused)o Al-Mg(highcorrosionresistance)o Al-Li

Theothermetallicmaterialsusedinaircraftsare:

Ø Titanium/Titanium alloys – It has high corrosion resistance and highspecific strength and toughness at low temperatures (applications incryogenic containers in space vehicles) but has the disadvantage ofdifficultyinmachiningandhighcost.

o PureTitaniumo α–alloy:ithasahighmeltingpointofaround1700degCelsiuso β–alloyo α+βalloy

Ø Steel–OnmanufacturinganAluminiumpartofthesamestrengthasthatofSteel,thesizeofthepartconsiderablyincreases.Steelismainlyusedwheresuchvolumerequirementsarecrucial.

o StainlessSteel§ Austenite–usedinapplicationswheretemperaturerangesfrom350-400degCelsius

§ Ferrous§ Magnetic

o PHSteel

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o CMSteelo NCMSteel–Itisusedinthelandinggearo Maraging Steel – it is one of the strongest and toughest yetmalleable materials known to man. It is predominantly used inlandinggear.InLCA,itisusedintheslattracksinthewing.

Ø Ni based super alloys – high temperature applications where thetemperatureliesintherangeof850-900degCelsius

Allmetallicmaterialsarepronetocorrosionandrequirespecialprocessestoprotectthematerial.IncaseofAluminium,theprocessofcreatinganon-corrosive Aluminium oxide layer is called Anodizing. It is basically theprocess of creating a thin layer (inmicrons) of AluminiumOxide on thesurfacesothattheanodizedlayergetsoxidizedfirst,protectingthemetalsurfacebeneathit.AsimilarprocessisfollowedforTitaniumandSteelandiscalledBlueAnodizingandPassivationrespectively.

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POWERPLANTANDFUELSYSTEM

Toruntheaircraftfuelisthemostintegralpartandishencewidelystoredinthefuselageandthetwowings.Theprimeobjectiveofthissystemistoprovidetherightamountoffueltotheengineatanycondition.Additionalamountoffuelisstoredindroptanksattachedtothepylonattachmentwhichisattachedtothewings.Oncethedroptanksfittednearthefuselageareemptieditcanbedispatchedfromthewing,reducingtheoverallweightoftheaircraft.Pipelinesfromthedroptanksandthewingsareconnectedtothe fuselagetanksfromwherethemainsupplytotheenginetakesplace.Fuselageconsistsoftwotanks-one being the space inside the bulk heads and the other being the spacebetweenthespineandthetopofthebulkhead.Thedroptanksaremaintainedathighpressureasthefuelhastobepumpedagainstgravitytothefuselagetanks.Thewingsarealsomaintainedatahighpressure(lowerthanthedroptank)forthesamereasonandthefuselagetankshavesmallopeningsinorderto maintain atmospheric pressure. The pressurization is done by the ECSsystem.Reliefvalvesandsurgevalvesarefittedtoreleaseanyexcesspressure;if thepressurizationistoohighthentherewillbeasignificantpressure losswhiletransportingthefuel.Whenthedroptanksarecompletelydrainedandreleased, fuel from the wing and fuselage are taken simultaneously in aproportionandfedtotheenginetomaintainthecentreofgravityofthebody.

Thefuelisrefilledusingpressurizationmethodsandgravityflowmethod.Afuelflowtransistorvalveisfittedtocheckandindicatethatthetankisfull.Thefuselagetankisnotfilledcompletelyfortheatmosphericpressurization.Thereisagroundrefuelingpanelwhichisusedtofillanddrainthetankatthegroundlevel.Areversetankisfittedwithinthisfueltank.Foraninvertedflightthistankgetsfilledandcansustaintheflightfor30seconds.Only90%ofthefilledfuelisusable.Fuelslashinghasaffectsonthegaugingsystembutitcanbeignoredastheflightvelocityismuchhigher.Theinward/outwardventvalveenablesthesmoothflowofthefuelduringclimbingupordown.FuelpipesarefittedwithfilterstoremoveanyforeignparticlesandaLPshutupcorkisusedtopreventthereverseflowofthefuel.Fuelindicatorsarefittedandawarningsignalwillbedisplayedatthecockpitdisplaytoshowthelevelsoffuelandalsoto indicateanyproblems in the fuel line. A fueldumpsystemisrequiredto

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removeexcessfuelbeforelandingonadeck;ifthefuelisnotremoveditwilllead to explosions. The maximum temperature of the fuel should be 80-90degreeCelsius.Ifthedestinationisacoldregionthenantifreezingagentsaremixedwiththefueltodefreezethefuel.

Thefuelisalsousedtocoolthegearboxandthehydraulicsystems.Jetfuelsystem(JFS)isusedtostarttheengineandisthenfedbytheincomingfuelfromthetanks.

Researchisdonetouseanalternativetypeoffueltankisabladdertypewhichcanbeeasilyremovedandcleanedandcanbeinstalledback.

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STRESSANALYSIS

ThecustomerrequirementsintheformofASRcontaindetailsofthespeedoftheaircraftandthev-ndiagramrangeinwhichitisexpectedtofly.Basedonwind tunnel testing, the aerodynamic loads on the aircraft are given by theaerodynamicsdepartment.Thisdataisusedbythestressgrouptoanalyzeifthe given structure is designed towithstand the static, dynamic and fatigueloadsthatitwillbesubjectedtoinflight.

STATICANALYSIS:

Thev-ndiagramisarrivedatusingtheequation,

LiftL=CL*0.5*ρV2*S

andusingtheformula,

LoadFactorn=L/W

Onmanipulatingtheabovetwoequations,weget

VelocityV=(2W/ρSCL)1/2

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FromtheV-Ndiagram,weobservethatVB>VAandthoughnB=nA,bothpointsA andB are analyzed to see if the design lieswithin this range as CL variesgreatly at these two points on the diagram. Similarly, all critical points areanalyzedtocheckifthedesignisstructurallysafefromfailure.

Themainpurposeofstaticanalysisistofindthereservefactorforthegivenstructureandverifyifitliesintheacceptablerange.ReserveFactorisdefinedas!"#$%&#')#*'++

,-#$./)#*'++.

Ideally,reservefactorshouldbegreaterthan1butitisnotadvisabletodesignforaveryhigh reserve factor.To sight anexample, ifR.F.=1000andUTS=100MPa,ActingStress=0.1MPawhichimpliesthatweareineffectivelyusingthematerial.ToreduceR.F.,either

i. Theactingstressshouldbeincreasedi.e.,themomentofinertiahastobedecreasedsince

𝜎 =𝑀𝐼 𝑦

ii. TheUTSshouldbedecreasedbychangingthematerial.

Inaircrafts,theuniversallyacceptedR.F.usedis1.5allowinga50%marginforerror.

𝐷𝑒𝑠𝑖𝑔𝑛 𝑜𝑟 𝑈𝑙𝑡𝑖𝑚𝑎𝑡𝑒𝐿𝑜𝑎𝑑 = 𝐿𝑖𝑚𝑖𝑡𝐿𝑜𝑎𝑑 ∗ 1.5

Where,limitloadisdefinedasthemaximumloadthatanaircraftissubjectedto,initslifetime.

The static stress analysis report generated is compared to the datafromgroundtestingandifthedifferenceinvalueliesintheacceptablerange asperASRandMIL-STD, the analysis is accepted to comply towiththerequirementsandthedesignisaccepted.

FATIGUEANALYSIS:

Fatigue failure is defined as the tendency of amaterial to fracture bymeansofprogressivecrackingunderrepeatedalternatingorcyclicstressesofintensity considerably below the normal strength. Fatigue analysis is done

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basedontheamountofdamagecausedduetovariousfactors.Thethreedesignphilosophiesaresafe-life, fail-safeanddamagetolerance.Safelifemeansthatthecomponentorsystemisdesignedtonotfailinacertainperiodoftime.Fail-safe type of design philosophy considers the effects of failures andcombinationsoffailuresindefiningasafedesign.Thisdependsonthealternateloadpaths.Damagetoleranceisthetimeperioduntilwhichasystemcanresistafailureduetosomepreexistentdamagewithoutriskingthesafeoperationoftheothercomponentsorsystemsanduntilthedamagecanberepaired.

Fracturestrength,alsoknownasbreakingstrength,isthestressatwhichaspecimenfailsviafracture.Failureoccurswhenthefreeenergyattainsapeakvalue at a Critical Crack Length beyond which free energy decreases byincreasingthecracklength.

Thesafelifeperiodofanaircraftismeasuredinhours.Itis3000hrsforLCA, 7500 hrs for IJT and 10,000 hrs for HTT-40. One landing is the timedurationofaflightfromtakeofftilllanding.ThisisbasedonASRorNSR.ForLCA,1landingisapproximately45minutes;ithasasafelifeof4000landings.

Tocalculatesafelifeofasystem,weuseSNorENmethod.Tocalculatefail-safe,weusefracturemethod.InSNmethod,wedrawthestressvs.numberofcyclestofailuregraphofthematerial.Fromthiswefindoutthesafelifeofamaterial.Thenweapplytheloadspectrumtofindthesafelifeofasystem.Thisloadspectrumisderivedfromsimilaraircraftmodelsusingfatiguemeter.InENmethod,insteadofstressweusestrainvs.numberofcyclestofailure.

An important factor in calculating safe life and fail-safe of a system isStress Concentration Factor (Kt), which is defined as the ratio of MaximumStresstoNominalStress.

UnfactoredLife𝐿 = 1 ÷ 𝐷

Where,D=cumulativedamageundergonebythesystem.

FactoredLife=!.I&-#J*'KL$I')-&##'*M&-#J*

ScatterFactorisdefinedforeachaircraftusinganalysis.

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Onceanalysis isdone, it is send for testingwherea schedule isgivenwhichcontainsdataonhowtheloadshouldbeapplied,whereshoulditbeappliedandhowmanytimesitshouldbeappliedforfatiguetesting.

DYNAMICANALYSIS:

Dynamics dealswith stiffness andmass distribution of a system. It isassociatedwithloadsonabodywhileinmotion.Fordoingdynamicanalysis,thesystemisdividedintomanyfiniteelementsusuallyquadortriangleshapein3D,2Dor1Dwithrespecttocrosssectionunderanalysis.

Fromtheequation,

𝐹 = 𝐾×𝜕

We can get displacementwithwhichwe can find strain and then using therelation

𝑠𝑡𝑟𝑒𝑠𝑠 = 𝑦𝑜𝑢𝑛𝑔𝑠𝑚𝑜𝑑𝑢𝑙𝑢𝑠×𝑠𝑡𝑟𝑎𝑖𝑛

Wecangetstress.

Here,Kisthestiffnesswhichisloadperunitdisplacement.

ReserveFactorisdefinedasratioofallowablestresstoworkingstress.Thisshouldalwaysbegreaterthan1.Ifitislessthanonethecomponentwillfail.Thepermittedrangeis1.1to1.25.

Normal modal analysis deals with different modes of vibration in acomponent.Whenthenaturalfrequencyofthecomponentissameasfrequencyexertedthenresonanceoccursandtheamplitudeofvibrationincreasesveryrapidly and leads to failure of that part. For first mode of vibration, thedisplacementisverylargeandhencefailsfaster,onceresonancetakesplace.Weknowtherelation

𝑓 = (1/2𝑝𝑖)×√(𝑘/𝑚)

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Therefore, frequency depends on the ratio k/m where k depends ondisplacement.

Forcantilever,𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 = (𝑝×𝑙\) ÷ (3×𝐸×𝐼)

Sodisplacementinturndependsonloadapplied,length,young'smodulusandmomentofinertia.Momentofinertiadependsonthecrosssection.

The other methods of analysis are Transient Response, RandomResponse,andSinusoidalResponseetc.

Theusualanalysisprocedureconsistsof3parts-preprocessing,solvingandpostprocessing.Preprocessingconsistsofcleaningofmodel,discretizingthemodel, applying boundary conditions, assigningmaterial properties andcrosssection,applyingload.Solvingincludesanalysis.Postprocessingincludesviewingoftheresultgotafteranalysis.