空客A380疲勞裂縫-今天的飛機(jī)換代太快了 每種新飛機(jī)本身都是試驗(yàn)品

1、空客空客A380出現(xiàn)裂縫？出現(xiàn)裂縫？當(dāng)今天上的飛機(jī)都在拿自己做實(shí)驗(yàn)當(dāng)今天上的飛機(jī)都在拿自己做實(shí)驗(yàn).Cracks in Airbus380? Every plane now in the air is an experiment by itself. TheAirbus A380isadouble-deck,wide-body,four-enginejetairlinermanufacturedbytheEuropeancorporationAirbus,asubsidiaryofEADS.Itistheworldslargestpassengerairlinerandduetoitssize.

2、MajorstructuralsectionsoftheA380arebuiltinFrance, Germany, Spain, and the United Kingdom.Duetotheirsize,theyarebroughttotheassemblyhall(theJean-Luc Lagardre Plant)inToulouseinFrancebysurfacetransportation,thoughsomepartsaremovedbytheA300-600STBelugaaircraftusedintheconstructionofotherAirbusmodels.A3

3、80componentsareprovidedbysuppliersfromaroundtheworld;thefivelargestcontributors,byvalue,areRolls-Royce,Safran,UnitedTechnologies,GeneralElectricandGoodrich.thesizeoftheturbinesandwingsalsoincrease,whichinturnincreasesweightandfuelconsumption.Ontheotherhand,theEuropeanmegalinerwas also required to be

4、 20 percent more efficientthanthecompetingBoeing747.TomWilliams,theexecutivevicepresidentofprogramsatToulouse-basedAirbus,andhiscreativeengineersweretoldtosubjecttheA380toaradical diet.Innovativecompositematerialandextremelylightweightaluminumalloys,evenforimportantpartsofthewings.Weveusedthisalloyi

5、nmanyotheraircraftinthepastsaysA380designerWilliams.issue12/2012(Mar.19,2012)ofDERSPIEGELOn4November2010,aRollsRoyceTrent972poweredAirbusA380-842(RegistrationVH-OQA)ofQantasFlightQF32sufferedanuncontainedenginefailureinenginenumber2enroutefromSingaporetoSydneyandreturnedtoSingaporeChangiAirportwhere

6、itlandedsafely.QantasgroundeditsfleetofsixA380sforoverthreeweeksaftertheaccidentpendingtheinvestigationandsaiditmayreplaceupto16enginesafteridentifyingpotentialproblems.FollowinganunscheduledinternalinspectionofanA380wing,someribfeethavebeenfoundwithcracksSo EASA called for a general inspection on a

7、ll A380 in EuropeEASAsaysthattheremaybeariskAirbusNO!RepairHow?An Update by Doric Asset Finance & Verwaltungs GmbHAccordingtoAirbus,thedamagetothewingsisnotverydangerous,becausethereare4,000ofthebracketsinquestion.Nevertheless,thehairlinecrackshavetoberepaired,andthelargenumberofdefectivebracket

8、smakesitacostlyandcomplexprocedure.Butsimplyreplacingthebracketsisnotapermanentsolutiontotheproblembecausehairlinecrackscanalsooccurinthenewbrackets.BecausethesameAlloyisstillbeingusedinproduction,therepairremainsapatchworksolution.Atfirst,Airbusofficialssaidthatitwouldhavetosellabout250aircrafttore

9、coupitscosts.ButaccordingtotheLatestestimatesbyaviationexperts,thecompanywillhavetosellatleast600unitsoftheworldslargestaircrafttomakeaprofit.Butwithatotalof253ordersonitsbookssofar,Airbusisstillalongwayfromthattarget.350 MORE A380 FOR BREAK EVEN POINT, i.e. US$ 100Bn!issue12/2012(Mar.19,2012)ofDERS

10、PIEGELOnSeptember1st2005theA380-800FullScaleFatigueTestinDresdenstartedconductedbyteamsofIABGandIMA.It is the worlds largest Full Scale Fatigue Test on a civilian aircraft.ThespecimenconsistsoftheA380fuselageandtwowings.Itismountedinatestrigmadeof1800tonsofsteelwith190hydraulicjacks.Thewingswillmove

11、4,2metersupwardsand1,3metersdownwards.http:/ 26 months 47.500 flights will be simulated in Dresden. This corresponds to a life span of appr. 25 years.One important milestone are the first 5000 flights which are expected to be completed at the beginning of 2006. Progress as scheduled is a pre-conditi

12、on for the certification of the Airbus double-decker.Informationdisclosedbyhttp:/www.ima-dresden.de/Plausiblehypothesisisthatthesecomponentswerenotconsideredstructurallysignificant.andthereforenostudiesconductedonitsfatiguebehavior.EASA Certification Specifications for Large Aeroplanes CS25EASA Cert

13、ification Specifications for Large Aeroplanes CS25 Book 2Are the rib fits are PRINCIPAL STRUCTURAL ELEMENTS OR NOT?1.Currentdesignmethodologieshavebeenobservedagainunreliable!2.Thesedefectswereonlydiscoveredthrougharandom(notplanned)inspection!3.EASA&Airbusdisagreeoncriticallyoftheseparts.Thisre

14、mindsmeofafamoussentence,intheearlytraindays.There is not a single rail now down in England or elsewhere which in not an experiment in itselfTheEngineer(1867)TwodeHavillandCometpassengerjetsbrokeupinmid-airandcrashedwithinafewmonthsofeachotherin1954.Asaresultsystematictestswereconductedonafuselageim

15、mersedandpressurisedinawatertank.Aftertheequivalentof3,000flightsinvestigatorsattheRoyalAircraftstablishment(RAE)wereabletoconcludethatthecrashhadbeenduetofailureofthepressurecabinattheforwardAutomaticDirectionFinderwindowintheroof.Thiswindowwasinfactoneoftwoaperturesfortheaerialsofanelectronicnavig

16、ationsysteminwhichopaquefibreglasspanelstooktheplaceofthewindowglass.Thefailurewasaresultofmetalfatiguecausedbytherepeatedpressurisationandde-pressurisationoftheaircraftcabin.Failsafety(redundancy) Structuresuponwhichhumanlifedependshavelongbeenrecognizedasneedinganelementoffail-safety.Whendescribin

17、ghisflyingmachine,LeonardoDaVincinotedthatIn constructing wings one should make one chord to bear the strain and a looser one in the same position so that if one breaks under the strain, the other is in the position to serve the same function.1 REDUNDANCYCONCEPT.AlsoinhumanbodyforcriticalcomponentsA

18、irForceAircraftStructuralIntegrityProgramASIP(1958) InthefinalapprovalletterestablishingtheAirForceAircraftStructuralIntegrityProgramwhichstillholdstruetoday: The successful accomplishment of this program is vital to the Air Forces capability to perform its assigned mission, and requires complete an

19、d active support and cooperation of all staff and command levels of the Air Force organization.GeneralCurtisE.LeMay,U.S.AirForceViceChiefofStaff,19November1958ASIP(USAF,1958)TheobjectivesofASIPareto:a)Establish,evaluate,andsubstantiatethestructuralintegrity(airframestrength,rigidity,damagetolerance,

20、anddurability)oftheairplane.b)Acquire,evaluate,andutilizeoperationalusagedatatoprovideacontinualassessmentofthein-serviceintegrityofindividualairplanes.c)Provideabasisfordetermininglogisticsandforceplanningrequirements(maintenance,inspections,supplies,rotationofairplanes,systemphase-out,andfuturefor

21、cestructure).d)Provideabasistoimprovestructuralcriteriaandmethodsofdesign,evaluation,andsubstantiationoffuturesystems.http:/ Notallstructureneedbedamagetolerantoffatigueloadingtoensuresafetyofoperation.Somestructuresoperateunderthesafe-lifedesignprinciple,whereanextremelylowlevelofriskisacceptedthro

22、ughacombinationoftestingandanalysisthatthepartwilleverformadetectablecrackduetofatigueduringtheservicelifeofthepart.Thisisachievedthroughasignificantreductionofstressesbelowthetypicalfatiguecapabilityofthepart. Safe-lifestructuresareemployedwhenthecostorinfeasibilityofinspectionsoutweighstheweightpe

23、naltyanddevelopmentcostsassociatedwithsafe-lifestructures.3Anexampleofasafe-lifecomponentisthehelicopterrotorblade.Duetotheextremelylargenumbersofcyclesenduredbytherotatingcomponent,anundetectablecrackmaygrowtoacriticallengthinasingleflightandbeforetheaircraftlands,resultinacatastrophicfailurethatre

24、gularmaintenancecouldnothaveprevented.SafelifeWohlerorBasquinslawCNNNkkkR00NNN0 ANOTHER EMPIRICAL LAW! There is no strong reason why the law should hold at all, despite some attempts to justify power-laws coming from critical phenomena (also of Coffin-Manson)Crack growth Paris law 1963Parislaw1963ma

25、KCNavddKthKKIc(1-R) DamagetoleranceApproachtoengineeringdesignbasedontheassumptionthatflawscanexistinanystructureandsuchflawspropagatewithusage.Thisapproachiscommonlyusedinaerospaceengineeringtomanagetheextensionofcracksinstructuresthroughtheapplicationoftheprinciplesoffracturemechanics.Amaintenance

26、programisimplementedthatwillresultinthedetectionandrepairofaccidentaldamage,corrosionandfatiguecrackingbefore such damage reduces the residual strength of the structure below an acceptable limit.multiple-sitedamage manysmallcracksgrowslowlybythemselves,tojoinoneanotherovertime,creatingamuchlargercra

27、ck,andsignificantlyreducingtheexpectedtimeuntilfailure2Non-Destructive InspectionsManufacturersandoperatorsofaircrafthaveafinancialinterestinensuringthattheinspectionscheduleisascost-efficientaspossible.Becauseaircraftareoftenrevenueproducing,thereisanopportunitycostassociatedwiththemaintenanceofthe

28、aircraft(lostticketrevenue),inadditiontothecostofmaintenanceitself.Thus, this maintenance is desired to be performed infrequently, even when such increased intervals cause increased complexity and cost to the overhaul. Theexponentialgrowthofcracksinstructurehasledtothedevelopmentofnon-destructivetes

29、tingmethodswhichallowinspectorstolookforverytinycrackswhichareofteninvisibletothenakedeye.Examplesofthistechnologyincludeeddycurrent,ultrasonic,dyepenetrant,andX-rayinspections.Bycatchingstructuralcrackswhentheyareverysmall,andgrowingslowly,thesenon-destructiveinspectionscanreducetheamountofmaintena

30、ncechecks,andallowdamagetobecaughtwhenitissmall,andstillinexpensivetorepair.HowmanyParislaws? ButhowsolidisDamageToleranceifeverythingisbasedonfracturemechanics,andParislaw,howreliableisParislaw?HowmanyParislaws Howrobustisitwithrespecttorandomloading?Howmanyassumptionsinpredictingeffectofloadsequen

31、ce Howrobustisthecalculationofloadinginservicetoreproduceintesting HowimportantareextremeeventsBarenblatt & Botvina demonstrated that Paris law would be a true strong power-law (complete scaling), only if the power came directly from dimensional analysis, implying m=2). WE HAVE A STRONG SIZE EFF

32、ECT!Z = 52CRITICISM TO DAMAGE TOLERANCE AND PARIS “LAW” Incomplete self-similarity in 1, 5, 6 and 7 gives:Therefore, the experimentally observed deviations from the simplest power-law regime suggested by Paris is the result of incomplete self-similarity in the various dimensionless numbers:where the

33、 exponents i can be functions of i.Completesimilarity,m=2Correspondstoearlymodels,butishardlyeverobservedincomplete self-similarity in 1, 5, 6 and 7 gives:Therefore, the experimentally observed deviations from the simplest power-law regime suggested by Paris is the result of incomplete self-similari

34、ty in the various dimensionless numbers, for example Z. We found in particular a correlation between C and m based on the dimensionless number Z (size of the specimen). M. Ciavarella, M. Paggi and A. Carpinteri, (2008), One, no one, and one hundred thousand crack propagation laws: a generalized Bare

35、nblatt and Botvina dimensional analysis approach to fatigue crack growth, Journal of the Mechanics and Physics of Solids, Volume 56, Issue 12, 3416-3432Parismforallmaterials -(size) dependence of m: ductile materialsAl alloys4340 steelASTM steelLow carbon steelAl alloys4340 steelHigh strength concre

36、teNormal strength concrete -dependence of m: quasi-brittle materialsExponential vs. power-law Z-dependence of C4340 steel4340 steelASTM steelASTM steelHigh strength concreteHigh strength concreteNormal strength concreteNormal strength concreteExponential vs. power-law Z-dependence of CCorrelation be

37、tween C and m4340 steelASTM steelHigh strength concreteNormal strength concreteTanakaPaggi & CarpinteriTanakaPaggi & CarpinteriPaggi & CarpinteriPaggi & Carpinteri45yParisErdoganlaw(1963)yNASGROlaw(Newman Forman)yPREFFASDavy,1985yStripYieldmodel(NASGRO)Dugdale&Barenblatt,1960Kthd

38、dmaCKNmax1d1d11pthmqcKafKCKNRKK ddmaCKNKcLog(da/dN)Log(K)RegionIRegionIIRegionIII10-10R:stressratiomax1KKR1dfiamaRNaCKLawformacrocracksPart of this uncertainty is reflected in poor predictions using Paris law-based methodsMergingofsafelifewithdamagetolerance-variousattempts20032012(ElHaddadequationt

39、ofinitelife)M.CiavarellaLog a oKtMateriali Fragilia0a* MAXMateriali Duttilioa*Sa0 SVITAVITAATERMINEINFINITA=Rm mKtRMAX=thLogg“finite”lifediagramAtzori B, Lazzarin P, (2000) Analisi delle problematiche connesse con la valutazione numerica della resistenza a fatica, convegno AIAS, Lucca, e Quaderno AI

40、AS n.7, p.33-50. “safe life”“damage tolerance”?“safe life notches”TheKitagawadiagram&EHeqt213MaterialStressunitsUTSYield StrengthFatigue Strength CoeffFatigue Strength ExponentCrack Growth Coeff (CGC)CGC Units/ cycleCrack Growth ExponentThresh SIF R=0Fracture Toughness1045MPa621382948-0,098,20E-

41、13m 3,57,1801 from Multiaxial Fatigue, Analysis & Experiments, Eds. G.E. Leese, D.Socie, SAE Pub. AE-14, 1989. Also, in Fatigue Database of the Lifest software database of Somat http:/ Region above the threshold but below fat limit 2. Region above fat limit but below fat threshold3. Region above

42、 both, fat limit and fat thresholdEH beatifully expresses the condition for non propagation of cracks or crack self-arrest“safe life”“damage tolerance”?“short cracks”ShortcracksbreakParislawPugno,Ciavarellaetal-1AmodifiedParislawaddinganintrinsiccrackintheIrwinSIFN.Pugno,M.Ciavarella,P.CornettiandA.

43、Carpinteri,(2006)AgeneralizedParislawforfatiguecrackgrowth,JournaloftheMechanicsandPhysicsofSolids,Volume54,Issue7,Pages1333-1349CiavarellaMonno-2006transition Nttransition Nt to EH fat limitOriginal fat limitmthmmimitKCmaaaN22/2/021,M. Ciavarella, F. Monno, (2006) On the possible generalizations of

44、 the Kitagawa-Takahashi diagram and of the El Haddad equation to finite life, International Journal of Fatigue 28 18261837Resultofpreviousapproach(2)Curious lack of continuity with the El Haddad equation. AsaSNcurveAnewcontribution2012 Fatigue & Fracture of Engineering Materials & Structures

45、Volume35,Issue3,pages247256,March2012 A simple approximate expression for finite life fatigue behaviour in the presence of crack-like or blunt notches M.CiavarellaA simple approximate expression.r= 3, k=10 (a metal) r=10 , k=10 (a ceramic)ResultsinKitagawadiagramCrack Propagation Laws Corresponding

46、to a Generalized El Haddad EquationInternational Journal of Aerospace and Lightweight Structures (IJALS) Volume 1 Number 1 (2011)doi: 10.3850/S2010428611000109M. Ciavarella Politecnico di Bari, 70125 Bari, Italy ABSTRACTTheElHaddadequationpermitstodealsimplywithbothshortandlongcracks,andwehaverecent

47、lysuggestedageneralizationforfinitelife,defininga“finitelifeintrinsiccracksize”,asapowerlawofnumberofcyclestofailure.Here,wederivethecorrespondingcrackpropagationlaw,findingthatitshowsfeaturessimilartoParislawinthelimitoflongcracks,butshowssomedependenceofthe“equivalent”$C,m$Parismaterial“constants”

48、withappliedstressrange.Theincreaseofcrackpropagationspeedisobtainedforshortcracks,butadditionalsizeeffectsarederived,whichmayrequirequantitativevalidation,andcorrespondtotheintrinsicdifferencewithrespecttothestandardParislaw.DerivationofcrackproplawSpecialcaser=kApproximatelawr=3,k=10r=10,k=10Damage

49、 tolerance & safe life with notches are two different worlds? On fatigue limit in the presence of notches: classical vs. recent unified formulations Ciavarella,MicheleandMeneghetti,Giovanni(2004)Onfatiguelimitinthepresenceofnotches:classicalvs.recentunifiedformulations.International Journal of F

50、atigue,26,(3),289-298.0.010.11100.010.11101001000a/a01/KfKtgEl HaddadKtg=3Ktg=10Ktg=50Ktg= (crack)from eq. (3), cH=a00.010.11100.010.11101001000a/a01/KfKtgEl HaddadKtg=3Ktg=10Ktg=50Ktg= (crack)from eq. (2), cN=4a00.010.11100.010.11101001000a/a01/KfEl HaddadKtg=3Ktg=10Ktg=50Ktg= (crack)from eq. (1), cp=a0KtgPrediction of