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1、Mechanics of Materials12CHAPTER15 FOUNDATIONS OF THE STRESS CHAPTER15 FOUNDATIONS OF THE STRESS CHAPTER15 FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS ANALYSIS IN EXPERIMENTS ANALYSIS IN EXPERIMENTS 151 SUMMARY152 PRINCIPLE AND APPLICATION OF THE STRAINOMETER OF THE RESISTANCE153 PRINCIPLE AND
2、APPLICATION OF THE PHOTOELASTICITY3 第十五章第十五章第十五章第十五章 实验应力分析基础实验应力分析基础实验应力分析基础实验应力分析基础151 概概 述述152 电阻应变计法的原理及应用电阻应变计法的原理及应用153 光弹性法的原理及应用光弹性法的原理及应用4 15 SummarySummary一、一、Function of the stress analysis method in experiments：1.Determine the reasonable dimension and the structureal form of a memberacco
3、rding to the tested stress or strain of the model in designing.2.Test the true stress or strain of a member in work and find out the position and the value of the maximum stress in order to evaluate the safty and reliability of the engineering structure and to provide the basis of improving working
4、ability for the equipment.3.Analyze the destroyed or failed member and propose the measures of improvement in order to prevent it from destroying again.4.Test the magnitude,derection and all kinds of dynamic responses of the external load.5.Explore the new rule from tests and check the theory of str
5、ess analysis and the calculation method.515 概概 述述一、实验应力分析方法的作用：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。6二、二、Brief introduction of methods in the
6、stress analysis of experiments 1.The machinery measuring method.The figure of measuring deformations in the book annotated by Zheng Xuan(127-200)in the east Han dynasty.7二、实验应力分析方法简介：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8Leonardo Da Vinci(1452-1519).This picture is considered to show the ea
7、rliest test in Mechanics of Materials.The tensile test of an iron wire designed by Leonardo Da Vinci.9里奥纳多达芬奇(14521519)此图被认为是最早的材力试验里奥纳多达芬奇设计的铁丝受拉试验10tensileGalileo(15641642)Fig.14 Sketch of the tensile test of GalileoFig.15 Sketch of the bending test of Galileo11伽利略伽利略(15641642)12Fig.37 Tensile-tes
8、t machine of MushenbluicFig.38 Method to clamp two ends of a tensile specimenMushenbluic(16921761)13穆申布洛依克穆申布洛依克(16921761)14Hydraulic verstile testing machine controlled by the computer15162.Other methods：Since the early 20th century,the developments of electricity,optics acousics and materials scie
9、nce have provided conditions for the productionof other measurement methods of the stress analysis in experiments.Then the resistance-strain method,ordinary photoelasticity method,hologram photoelasticity method,sound launching method and so on are made fast developments and wide applications.172.其它
10、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。18152 Principle and application of the strainometer of the resistance 1 1、Resistance law:Resisance of a conductor 2、Elastic law:Land A will change after the cinductor is subjected to forces or changes in t
11、emperatures.3、Strain foil of resistance Sensitive coefficient 12345Wire-coiled strain foil1Overburden 2Fundus3Drawn line 4Binder 5Sensitive bar 19152 电阻应变计法的原理及应用电阻应变计法的原理及应用 一、电阻定律一、电阻定律：导体电阻 二、弹性定律：二、弹性定律：导体受力或变温后，L、A都将发生改变。三、三、电阻应变片：电阻应变片：灵敏系数：12345丝绕式应变片1覆盖层 2基底 3引出线4粘结剂 5敏感栅20 4、Balance princip
12、le of the electric bridgeAfter the resistance changes：UR1R2R4I1,2I3,4ABCDBridge with the output voltageR321 四、电桥平衡原理四、电桥平衡原理电阻变化后：UR1R2R4I1,2I3,4ABCD电压输出桥R322 5、Strainometer of resistanceTransform to output voltage into the magnitude of strain.23 五、电阻应变仪五、电阻应变仪将输出电压转变为应变读数。将输出电压转变为应变读数。246、Arrange f
13、oils：Make the directions of foils coincide with those of principal stresses as much as possible.When the directions of principal stresses are un-known,the stress state of a point must be determined by three independent quantities.Three strain foils of 4504590Three strain foils of 60 06012025六、布片：六、布
14、片：尽可能使片子的方向与主应力方向一致。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。三片45应变花04590三片60应变花060120267、Relations between the principal strains and the measured strains.27七、主应变与测量应变之间的关系：七、主应变与测量应变之间的关系：28Example 1 Three linear strains of a point are tested by the strain foil 45.Try to determine the princip
15、al strain of this point.0max45xyu29 例例1 1 用用4545应变花测得一点的三个线应变后，求该点的主应应变花测得一点的三个线应变后，求该点的主应变。变。0max45xyu30Example 2 Try to determine the principal strain of a point after the three linear strains of this point are tested by the strain foil of 60。Three strain foils of 60 06012031 例例2 用60应变花测得一点的三个线应变后
16、，求该点的主应变。三片60应变花060120328 8、Connect the bridge：Make the stress distribute alternately;make the total bridge have a high precision and the half bridge a low precision.The half bridhe with two arms is often used.9、Temperature compensation：It is better to realize the compensation by itself;otherwise we
17、 should use the temperature compensator that is without any forces.We must make the working foil and the compensation foil in the same temperature field.33八、接桥：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：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。34153 Principle and application of the phot
18、oelasticity 1、Principle of the photoelasticity:.Permanent double refraction：.Temporary(artificial)double refraction:Double refraction in the anisotropic body due to the entering of light eo35153 光弹性法的原理及应用光弹性法的原理及应用 一、光测原理：一、光测原理：1.永久双折射：2.暂时（人工）双折射：光射入各向异性体产生的双折射eo36 2、Plane stress-optics law：.Refr
19、active index：CStress optical coefficient of the model material D Ds s1 1s s1 1s s2 2s s2 2Plane polarized lightThe plane polarized light passes through the model subjected to forces.So37 二、平面应力二、平面应力光学定律：光学定律：1.折射率：C模型材料的应力光学系数。D Ds s1 1s s1 1s s2 2s s2 2平面偏振光平面偏振光通过受力模型38.Optical path difference：.T
20、he light intensity in the plane polarization field:The model subjected to forces is in the cross plane polarization field.Ps s1 1s s2 2AOfLight sourceModelAnalyzerPolarizer392.光程差：3.平面偏振场中的光强：受力模型在正交平面偏振布置中Ps s1 1s s2 2AOf光源光源模型模型检偏镜检偏镜起偏镜起偏镜40Equal inclination linesAsa black point occurs behind the
21、 analyzer.The interference fringes formed in the locus of the black points are called equal inclination lines.On the equal inclination lines,the directions of the pricipal stresses are same and they coincide with the polarization axle.Pictures of the plane polarization field taken every 150.The posi
22、tion of the colored equal color lines is not changed,but the position of the black equal inclinnation lines is changed when the polaroid rotates synchronously.41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。42Equal difference lines.The formed interference fringes-equal difference lines.The white light is
23、 considered to be the light source and the equal difference lines aare coloured fringes,so the equal difference lines are also called equal colour lines.As N=0,they are called the No.0 equal difference lines(black);as N=1,they are called the No.1 equal difference lines.Simulating the plae part conne
24、cted by screws and screw caps(method of pasting foils)43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44 fThe value of the fringe of a material a、Under the repeated loading,the equal inclination lines are not changed,but the equal difference lines are changedDistinguish equal inclination lines and equal dif
25、ference linesb、If we rotate synchronously the polarizer and the analyzer,the equal inclination lines are changed and the equal difference lines are not changed.c、According to experiences,the equal inclination lines are thick(all the black)and equal difference lines are thin(a line).45 f材料的条纹值。a、反复加载
26、，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）。46There are no equal inclination lines in the cross circular polarization field.So the equal difference lines are clear.Light intensity:asBlack points occur behind the analyzer.(N=0,1,2,)AsAsThey are called the No.0.5 equal
27、difference lines.They are called the No.1.5 equal difference lines.47正交圆偏振场中，无等倾线。故等差线比较清晰。正交圆偏振场中，无等倾线。故等差线比较清晰。(N=0,1,2,)48.Light intensity in the cross circular polarization field.Cross circular polarization field45 45Fast axleSlow axle45 45Fast axleSlow axlePASz494.正交圆偏振场中的光强：正交圆偏振场正交圆偏振场45 45快轴
28、慢轴45 45快轴慢轴PASz50Figure of the equal difference lines of a disc subjected to radial pressures5152Equal-colour lines of the spinning disc5354Interference fringes of the ring subjected to radial pressures in the plane polarization field.There are only equal-different interference fringes in the circular polarization field when the ring is subjected to radial pressures.55565758