英汉双语材料力学15ppt课件.ppt

,CHAPTER15FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,材料力学,第十五章实验应力分析基础,CHAPTER15FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,151SUMMARY152PRINCIPLEANDAPPLICATIONOFTHESTRAINOMETEROFTHERESISTANCE153PRINCIPLEANDAPPLICATIONOFTHEPHOTOELASTICITY,第十五章实验应力分析基础,151概述152电阻应变计法的原理及应用153光弹性法的原理及应用,15Summary,一、Functionofthestressanalysismethodinexperiments：,1.Determinethereasonabledimensionandthestructurealformofamemberaccordingtothetestedstressorstrainofthemodelindesigning.,2.Testthetruestressorstrainofamemberinworkandfindoutthepositionandthevalueofthemaximumstressinordertoevaluatethesaftyandreliabilityoftheengineeringstructureandtoprovidethebasisofimprovingworkingabilityfortheequipment.,3.Analyzethedestroyedorfailedmemberandproposethemeasuresofimprovementinordertopreventitfromdestroyingagain.,4.Testthemagnitude,derectionandallkindsofdynamicresponsesoftheexternalload.,5.Explorethenewrulefromtestsandcheckthetheoryofstressanalysisandthecalculationmethod.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,15概述,一、实验应力分析方法的作用：,1.设计时，测定模型的应力或变形，依此来确定构件的合理尺寸和结构形式。,2.工作中，测定构件的真实应力或变形，找出最大应力的位置和数值，以评价工程结构的安全可靠性，并为提高设备的工作能力提供依据。,3.对破坏或失效构件进行分析，提出改进措施，防止再次破坏。,4.测定外载的大小、方向以及各种动响应。,5.从试验中探索新的规律，并对应力分析理论和计算方法进行校核。,实验应力分析基础,二、Briefintroductionofmethodsinthestressanalysisofexperiments,1.Themachinerymeasuringmethod.,ThefigureofmeasuringdeformationsinthebookannotatedbyZhengXuan(127-200)intheeastHandynasty.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,二、实验应力分析方法简介：,1.机械量测法,东汉郑玄(127200)注释的考工记弓人中的测变形图,实验应力分析基础,LeonardoDaVinci(1452-1519).ThispictureisconsideredtoshowtheearliesttestinMechanicsofMaterials.,ThetensiletestofanironwiredesignedbyLeonardoDaVinci.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,里奥纳多达芬奇(14521519)此图被认为是最早的材力试验,实验应力分析基础,里奥纳多达芬奇设计的铁丝受拉试验,tensile,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,Galileo(15641642),Fig.14SketchofthetensiletestofGalileo,Fig.15SketchofthebendingtestofGalileo,伽利略(15641642),实验应力分析基础,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,Fig.37Tensile-testmachineofMushenbluic,Fig.38Methodtoclamptwoendsofatensilespecimen,Mushenbluic(16921761),穆申布洛依克(16921761),实验应力分析基础,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,Hydraulicverstiletestingmachinecontrolledbythecomputer,实验应力分析基础,2.Othermethods：,Sincetheearly20thcentury,thedevelopmentsofelectricity,opticsacousicsandmaterialssciencehaveprovidedconditionsfortheproductionofothermeasurementmethodsofthestressanalysisinexperiments.Thentheresistance-strainmethod,ordinaryphotoelasticitymethod,hologramphotoelasticitymethod,soundlaunchingmethodandsoonaremadefastdevelopmentsandwideapplications.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,2.其它方法：,20世纪初至今，电学、光学、声学和材料科学的发展，为试验应力分析其它测量方法的产生创造了条件。于是，电阻应变法、普通光弹法、全息光弹法、散斑法、声发射法等方法都有了快速发展和广泛应用。,实验应力分析基础,152Principleandapplicationofthestrainometeroftheresistance,1、Resistancelaw:Resisanceofaconductor,2、Elasticlaw:LandAwillchangeafterthecinductorissubjectedtoforcesorchangesintemperatures.,3、Strainfoilofresistance,Sensitivecoefficient,Wire-coiledstrainfoil,1Overburden2Fundus3Drawnline4Binder5Sensitivebar,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,152电阻应变计法的原理及应用,一、电阻定律：导体电阻,二、弹性定律：导体受力或变温后，L、A都将发生改变。,三、电阻应变片：,灵敏系数：,实验应力分析基础,4、Balanceprincipleoftheelectricbridge,Aftertheresistancechanges：,U,R1,R2,R4,I1,2,I3,4,A,B,C,D,Bridgewiththeoutputvoltage,R3,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,四、电桥平衡原理,电阻变化后：,实验应力分析基础,U,R1,R2,R4,I1,2,I3,4,A,B,C,D,电压输出桥,R3,5、Strainometerofresistance,Transformtooutputvoltageintothemagnitudeofstrain.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,五、电阻应变仪,将输出电压转变为应变读数。,实验应力分析基础,6、Arrangefoils：Makethedirectionsoffoilscoincidewiththoseofprincipalstressesasmuchaspossible.,Whenthedirectionsofprincipalstressesareun-known,thestressstateofapointmustbedeterminedbythreeindependentquantities.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,六、布片：,尽可能使片子的方向与主应力方向一致。,主应力方向未知时，必须由三个独立量才能确定一点的应力状态。,实验应力分析基础,7、Relationsbetweentheprincipalstrainsandthemeasuredstrains.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,七、主应变与测量应变之间的关系：,实验应力分析基础,Example1Threelinearstrainsofapointaretestedbythestrainfoil45.Trytodeterminetheprincipalstrainofthispoint.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,例1用45应变花测得一点的三个线应变后，求该点的主应变。,实验应力分析基础,45,x,y,u,Example2Trytodeterminetheprincipalstrainofapointafterthethreelinearstrainsofthispointaretestedbythestrainfoilof60。,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,例2用60应变花测得一点的三个线应变后，求该点的主应变。,实验应力分析基础,8、Connectthebridge：,Makethestressdistributealternately;makethetotalbridgehaveahighprecisionandthehalfbridgealowprecision.Thehalfbridhewithtwoarmsisoftenused.,9、Temperaturecompensation：,Itisbettertorealizethecompensationbyitself;otherwiseweshouldusethetemperaturecompensatorthatiswithoutanyforces.Wemustmaketheworkingfoilandthecompensationfoilinthesametemperaturefield.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,八、接桥：,要使应力正负相间；全桥精度高，半桥精度低。常用半桥双臂式桥路。,九、温度补偿：,最好能在桥路中自补偿；否则，要用绝对不受力的温度补偿片。,工作片与补偿片要始终处于同一温度场中。,实验应力分析基础,153Principleandapplicationofthephotoelasticity,1、Principleofthephotoelasticity:,.Permanentdoublerefraction：,.Temporary(artificial)doublerefraction:,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,153光弹性法的原理及应用,一、光测原理：,1.永久双折射：,2.暂时（人工）双折射：,实验应力分析基础,2、Planestress-opticslaw：,.Refractiveindex：,CStressopticalcoefficientofthemodelmaterial,Planepolarizedlight,Theplanepolarizedlightpassesthroughthemodelsubjectedtoforces.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,So,二、平面应力光学定律：,1.折射率：,C模型材料的应力光学系数。,实验应力分析基础,平面偏振光,平面偏振光通过受力模型,.Opticalpathdifference：,.Thelightintensityintheplanepolarizationfield:,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,2.光程差：,3.平面偏振场中的光强：,实验应力分析基础,Equalinclinationlines,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,As,ablackpointoccursbehindtheanalyzer.,Theinterferencefringesformedinthelocusoftheblackpointsarecalledequalinclinationlines.,Ontheequalinclinationlines,thedirectionsofthepricipalstressesaresameandtheycoincidewiththepolarizationaxle.,Picturesoftheplanepolarizationfieldtakenevery150.Thepositionofthecoloredequalcolorlinesisnotchanged,butthepositionoftheblackequalinclinnationlinesischangedwhenthepolaroidrotatessynchronously.,等倾线,引起的黑点的迹线形成的干涉条纹等倾线,等倾线上，主应力方向相同且与偏振轴重合。,实验应力分析基础,Equaldifferencelines.,Theformedinterferencefringes-equaldifferencelines.,Thewhitelightisconsideredtobethelightsourceandtheequaldifferencelinesaarecolouredfringes,sotheequaldifferencelinesarealsocalledequalcolourlines.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,AsN=0,theyarecalledtheNo.0equaldifferencelines(black);asN=1,theyarecalledtheNo.1equaldifferencelines.,Simulatingtheplaepartconnectedbyscrewsandscrewcaps(methodofpastingfoils),等差线,形成的干涉条纹等差线,以白光为光源,等差线为彩色条纹,故等差线又称等色线,实验应力分析基础,fThevalueofthefringeofamaterial,a、Undertherepeatedloading,theequalinclinationlinesarenotchanged,buttheequaldifferencelinesarechanged,Distinguishequalinclinationlinesandequaldifferencelines,b、Ifwerotatesynchronouslythepolarizerandtheanalyzer,theequalinclinationlinesarechangedandtheequaldifferencelinesarenotchanged.,c、Accordingtoexperiences,theequalinclinationlinesarethick(alltheblack)andequaldifferencelinesarethin(aline).,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,f材料的条纹值。,a、反复加载，等倾线不变，等差线改变。,区分等倾线与等差线,b、同步旋转起偏镜与检偏镜，等倾线改变，等差线不变。,c、凭经验，等倾线较粗（一片黑），等差线较细（一条线）。,实验应力分析基础,Therearenoequalinclinationlinesinthecrosscircularpolarizationfield.Sotheequaldifferencelinesareclear.,FOUNDATIONSOFTHESTRESSANALYSISINEXPERIMENTS,Lightintensity:,as,Blac