断裂力学Griffith理论VIP免费

1ShanghaiUniversity断裂力学FractureMechanics断裂力学第二讲断裂力学第二讲郭战胜davidzsguo@shu.edu.cn办公地点：延长校区力学所317室平时答疑：每周一：5-6节晚修答疑:每周一：18：00-20：30地点：HE108或HE104b2能量原理3线弹性断裂力学认为，材料和构件在断裂以前基本上处于弹性范围内，可以把物体视为带有裂纹的弹性体。研究裂纹扩展有两种观点：一种是能量平衡的观点，裂纹扩展的动力是构件在裂纹扩展中所释放出的弹性应变能，它补偿了产生新裂纹表面所消耗的能量，如Griffith理论；一种是应力场强度的观点，认为裂纹扩展的临界状态是裂纹尖端的应力场强度达到材料的临界值，如Irwin理论。4线弹性断裂力学的基本理论线弹性断裂力学的基本理论包括：Griffith理论，即能量释放率理论；Irwin理论，即应力强度因子理论。断裂力学作为一门崭新的学科是在上个世纪50年代才建立和发展起来的。但是Griffith在1920年建立的针对玻璃、陶瓷等脆性材料的脆性断裂准则，成功地解释了这类材料的实际断裂强度远小于理论强度这一客观事实。该理论仅适用于完全脆性材料，对于绝大多数金属材料，在断裂前和断裂过程中裂纹尖端总存在塑性区，裂纹尖端也因塑性变形而钝化。不能使用Griffith理论，这就是该理论长期得不到重视和发展的主要原因。后来Irwin修正了Griffith的理论，使得断裂力学成为一门学科。Griffith理论5Griffith理论Inglis的论文1913年，Inglis研究了无限大板中含有一个穿透板厚的椭圆孔的问题，得到了弹性力学精确分析解，称之为Inglis解。1920年，Griffith研究玻璃与陶瓷材料脆性断裂问题时，将Inglis解中的短半轴趋于0，得到Griffith裂纹。TransactionsoftheInstitutionofNavalArchitects,55(1913),pp.219–230.6C.E.InglisSirCharlesEdwardInglis(31July1875-19April1952)wasaBritishcivilengineer.InglisspentmuchofhislifeasalecturerandacademicatKing'sCollegeCambridgeandmadeseveralimportantstudiesintotheeffectsofvibrationanddefectsonthestrengthofplatesteel.Hismotherdiedwhenheonlyiselevendays,hewasbroughtupbyhisfather’sunmarriedsister.InglisservedintheRoyalEngineersduringtheFirstWorldWarandinventedalightweight,reusablesteelbridge-theprecursorandinspirationfortheBaileybridgeoftheSecondWorldWar.HismilitaryservicewasrewardedwithanappointmentasanOfficeroftheOrderoftheBritishEmpire7DepartmentofEngineeringHeadofDepartment1919-43Hecarriedthelargestteachingload,coveringthesubjects:statics,dynamics,theoryofstructures,materialsanddrawing,balancingengines,girderdesignandreinforcedconcrete."Hispersonalitywassuchthathenotonlytaughtthesubjectmostdelightfullybutinspiredthemembersoftheaudiencewithrespectandaffection."C.E.Inglis8C.E.InglisAMathematicalTreatiseonVibrationsinRailwayBridges.ByC.E.Inglis.Cambridge,UniversityPress,andNewYork,Macmillan,1934.203pp.and65figures.Griffith理论RoyalEngineersconstructinganInglisBridgeMkIIIattheSchoolofMilitaryEngineering,18June19439Griffith理论TheInternationalUnionofTheoreticalandAppliedMechanicswasfoundedin1946,duringtheSixthCongressinParis.Eachofthefirstsixcongresseshadbeenorganizedbyanationalcommitteeofscientistsfromthecountrywherethecongresswastobeheld.FourthC.E.InglisCongressPresident1934CambridgeUKInternationalCongressesonTheoreticalandAppliedMechanics(ICTAM)Beijing，BaiYilong23rd10Griffith理论ThemaximumstressoccursattheendsoftheThemaximumstressoccursattheendsofthemajoraxisofthecavityandisgivenbymajoraxisofthecavityandisgivenbyInglis’sformulaInglis’sformulamax12abthinplateofglasswithanellipticalholeinthemiddleHefoundthatpointA,attheendoftheellipse,wasfeelingthemostpressure.Healsofoundthatastheratioofa/bgetsbigger(theellipsegetslongerandthinner)thatthes...