断裂力学——1绪论

ShanghaiUniversity断裂力学FractureMechanics郭战胜我的联系方式E-mail：[e-mail]办公地点：延长校区力学所317室断裂力学第一讲我的希望希望大家喜欢希望大家参与——勇于回答问题勇于提出问题勇于参与讨论希望大家能够有所收获——收获一点新意断裂力学第一讲课堂讲授课堂讨论课外学习研究课外个别学习指导与互动断裂力学第一讲考试、考核方法1.期末考试：考试内容——课外作业考试方式——笔试，闭卷成绩认定——70分。2.课外作业：成绩认定——20分3.平时分：1)课堂表现：5分；2)出勤：5分。断裂力学第一讲解决问题的四个步骤问题陈述-StatetheProblem计划求解（数学化、模型化)-PlantheSolution求解-CarryOuttheSolution结果判断、评价-ReviewtheSolution1.)Developbasicfundamentalunderstandingoftheeffectsofcrack-likedefectsontheperformanceofaerospace,civil,andmechanicalengineeringstructures.2.)Learntoselectappropriatematerialsforengineeringstructurestoinsuredamagetolerance.3.)Learntoemploymodernnumericalmethodstodeterminecriticalcracksizesandfatiguecrackpropagationratesinengineeringstructures.4.)Gainanappreciationofthestatusofacademicresearchinfieldoffracturemechanics.CourseObjectives教材及参考书目•程靳，赵树刚编.断裂力学.北京：科学出版社，2006•王铎，杜善义编.断裂力学.哈尔滨：哈尔滨工业大学出版社，1989•范天佑.断裂理论基础.北京：科学出版社，2003•王自强，陈少华.高等断裂力学.北京：科学出版社，2009•杨卫.宏微观断裂力学.北京：国防工业出版社，1995断裂力学第一讲绪论结构失效的类型TypesofstructuralfailureHistoryoffracturemechanicsIntheearlydaysofWorldWarII.theUnitedStateswassupplyingshipsandplanestoGreatBritainundertheLend-LeaseAct.Britain'sgreatestneedatthetimewasforcargoshipstocarrysupplies.TheGermanNavywassinkingcargoshipsatthreetimestheratealwhichtheycouldbereplacedwithexistingship-buildingprocedures.LibertyshipsArthurM.HuddelloneofthelastWorldWarIILibertyshipsUndertheguidanceofHenryKaiser,afamousconstructionengineerwhosepreviousprojectsincludedtheHooverDam,theUnitedStatesdevelopedarevolutionaryprocedureforfabricatingshipsquickly.Thesenewvessels,whichbecameknownastheLibertyships,hadanall-weldedhull,asopposedtotherivetedconstructionoftraditionalshipdesigns.TheLibertyshipprogramwasaresoundingsuccess,untilonedayin1943,whenoneofthevesselsbrokecompletelyintwowhilesailingbetweenSiberiaandAlaska.SubsequentfracturesoccurredinotherLibertyships.Oftheroughly2700libertyshipsbuildduringWorldWarII,approximately400sustainedfractures,ofwhich90wereconsideredserious.In20shipsthefailurewasessentiallytotal,andabouthalfofthesebrokecompletelyintwo.S.S.SchenectadyOn16January1943,Withoutwarning,andwithanoiseaudibleforatleastamile,thehullcrackedalmostinhalf.Onlythebottomplatesoftheshipheld.Thiswasnotthefirstofthewar-builtmerchantfleettofractureinthisway–therehadbeentenothermajorincidents,andseveralmorewouldfollowbutitwasperhapsthemostprominent;itoccurredinfullviewofthecityofPortland,andwaswidelyreportedinthenewspapersevenunderwartimeconditions.AlanArnoldGriffithAlanArnoldGriffith(13June1893–13Oct1963)wasanEnglishengineer,who,amongmanyothercontributions,isbestknownforhisworkonstressandfractureinmetalsthatisnowknownasmetalfatigue,aswellasbeingoneofthefirsttodevelopastrongtheoreticalbasisforthejetengine.Hetookafirstinmechanicalengineering,followedbyaMaster’sDegreeandaDoctoratefromLiverpoolUniversity.AlanArnoldGriffith格氏1893年出生于伦敦，1911年毕业于曼岛的一所中学，获得奖学金进入利物浦大学读机械工程，1914年以一等成绩获得学士学位，并获得最高奖章。1915年，格氏到皇家航空研究中心工作，并与G.I.Taylor一起发表了用肥皂膜研究应力分布的开创性论文，该文获得机械工程协会的金奖。同年，格氏获得利物浦大学工程硕士学位。1921年，格氏以他的断裂力学成名作获得利物浦大学工程博士学位。其后，格氏历任空军实验室首席科学家，航空研究中心工程部主管等职，在航空发动机设计方面做出了同样卓越的贡献，与他在断裂方面的名望相比，这些成就就少为人知了。格氏于1939年加盟劳斯莱思公司，1941年当选皇家学会院士，1960年退休，1963年辞世，享年70岁AlanArnoldGriffithIn1915hewasacceptedbytheRoyalAircraftFactoryasatrainee,beforejoiningthePhysicsandInstrumentDepartmentthefollowingyearinwhatwasnowbeenrenamedastheRoyalAircraftEstablishment(RAE).SomeofGriffith'searlierworksremaininwidespreadusetoday.In1917heandG.I.Taylorsuggestedtheuseofsoapfilmsasawayofstudyingstressproblems.Usingthismethodasoapbubbleisstretchedoutbetweenseveralstringsrepresentingtheedgesoftheobjectunderstudy,andthecolorationofthefilmshowsthepatternsofstress.Thismethod,andsimilarones,wereusedwellintothe1990swhencomputerpowerbecamegenerallyavailablethatcoulddothesameexperimentnumerically.AlanArnoldGriffithThework,publishedin1920(Thephenomenonofruptureandflowinsolids),resultedinsweepingchangesinmanyindustries.Suddenlythehardeningofmaterialsduetoprocessessuchascoldrollingwerenolongermysterious.Aircraftdesignersimmediatelyunderstoodwhytheirdesignshadfailedeventhoughtheywerebuiltmuchstrongerthanwasthoughtnecessaryatthetime,andsoonturnedtopolishingtheirmetalsinordertoremovecracks.Theresultwasaseriesofparticularlybeautifuldesignsinthe1930s,suchastheBoeing247.ThisworkwaslatergeneralizedbyG.R.Irwin,inthe1950s,applyingittoalmostallmaterials,notjustrigidones.AlanArnoldGriffith•Thetheorywasconsideredtoapplyonlytoalimitedclassofextremely,suchasglassesorceramicsGriffiththeory-1920Inabodyofaglasscrackspre-exist.Thetipofsuchacrackconcentratesstress.Theintensestressbreaksatomicbondsonebyone,likeopeningazipper.Asthecrackadvances,freshsurfacesarecreated.Thesurfaceenergyincreases,buttheelasticenergydecreases.Thecrackadvancesiftheadvancereducesthesumofthesurfaceenergyandelasticenergy.AlanArnoldGriffithFromthisworkGriffithformulatedhisowntheoryofbrittlefracture,usingelasticstrainenergyconcepts.Histheorydescribedthebehaviorofcrackpropagationofanellipticalnaturebyconsideringtheenergyinvolved.Theequati