1、,CHAPTER 15 FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,材料力學(xué),第十五章 實(shí)驗應(yīng)力分析基礎(chǔ),CHAPTER15 FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,151 SUMMARY 152 PRINCIPLE AND APPLICATION OF THE STRAINOMETER OF THE RESISTANCE 153 PRINCIPLE AND APPLICATION OF THE PHOTOELASTICITY,第十五章 實(shí)驗應(yīng)力分析基礎(chǔ),151 概 述 152

2、電阻應(yīng)變計法的原理及應(yīng)用 153 光彈性法的原理及應(yīng)用,15 Summary,一、Function of the stress analysis method in experiments ：,1. Determine the reasonable dimension and the structureal form of a memberaccording to the tested stress or strain of the model in designing.,2. Test the true stress or strain of a member in work and fin

3、d 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 ability for the equipment.,3. Analyze the destroyed or failed member and propose the measures of improvement in order to pr

4、event 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 stress analysis and the calculation method.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,15 概 述,一、實(shí)驗應(yīng)力分析方法的作用：,1.設(shè)計

5、時，測定模型的應(yīng)力或變形，依此來確定構(gòu)件的合理尺 寸和結(jié)構(gòu)形式。,2.工作中，測定構(gòu)件的真實(shí)應(yīng)力或變形，找出最大應(yīng)力的位置 和數(shù)值，以評價工程結(jié)構(gòu)的安全可靠性，并為提高設(shè)備的 工作能力提供依據(jù)。,3.對破壞或失效構(gòu)件進(jìn)行分析，提出改進(jìn)措施，防止再次破壞。,4.測定外載的大小、方向以及各種動響應(yīng)。,5.從試驗中探索新的規(guī)律，并對應(yīng)力分析理論和計算方法進(jìn)行 校核。,實(shí)驗應(yīng)力分析基礎(chǔ),二、Brief introduction of methods in the stress analysis of experiments,1.The machinery measuring method.,The f

6、igure of measuring deformations in the book annotated by Zheng Xuan(127-200)in the east Han dynasty.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,二、實(shí)驗應(yīng)力分析方法簡介：,1.機(jī)械量測法,東漢鄭玄(127200)注釋的考工記弓人中的測變形圖,實(shí)驗應(yīng)力分析基礎(chǔ),Leonardo Da Vinci( 1452-1519).This picture is considered to show the earliest test in Mecha

7、nics of Materials.,The tensile test of an iron wire designed by Leonardo Da Vinci.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,里奧納多達(dá)芬奇(14521519) 此圖被認(rèn)為是最早的材力試驗,實(shí)驗應(yīng)力分析基礎(chǔ),里奧納多達(dá)芬奇設(shè)計的鐵絲受拉試驗,tensile,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,Galileo (15641642),Fig.14 Sketch of the tensile tes

8、t of Galileo,Fig.15 Sketch of the bending test of Galileo,伽利略 (15641642),實(shí)驗應(yīng)力分析基礎(chǔ),FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,Fig.37 Tensile-test machine of Mushenbluic,Fig.38 Method to clamp two ends of a tensile specimen,Mushenbluic (16921761),穆申布洛依克 (16921761),實(shí)驗應(yīng)力分析基礎(chǔ),FOUNDATIONS OF THE ST

9、RESS ANALYSIS IN EXPERIMENTS,Hydraulic verstile testing machine controlled by the computer,實(shí)驗應(yīng)力分析基礎(chǔ),2. Other methods：,Since the early 20th century,the developments of electricity,optics acousics and materials science have provided conditions for the productionof other measurement methods of the stre

10、ss 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.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,2.其它方法：,20世紀(jì)初至今，電學(xué)、光學(xué)、聲學(xué)和材料科學(xué)的發(fā)展，為試驗應(yīng)力分析其它

11、測量方法的產(chǎn)生創(chuàng)造了條件。于是，電阻應(yīng)變法、普通光彈法、全息光彈法、散斑法、聲發(fā)射法等方法都有了快速發(fā)展和廣泛應(yīng)用。,實(shí)驗應(yīng)力分析基礎(chǔ),152 Principle and application of the strainometer of the resistance,1、Resistance law :Resisance of a conductor,2、Elastic law: Land A will change after the cinductor is subjected to forces or changes in temperatures.,3、Strain foil of

12、 resistance, Sensitive coefficient,Wire-coiled strain foil,1Overburden 2Fundus 3Drawn line 4Binder 5Sensitive bar,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,152 電阻應(yīng)變計法的原理及應(yīng)用,一、電阻定律：導(dǎo)體電阻,二、彈性定律：導(dǎo)體受力或變溫后，L、A都將發(fā)生改變。,三、電阻應(yīng)變片：, 靈敏系數(shù)：,實(shí)驗應(yīng)力分析基礎(chǔ),4、Balance principle of the electric bridge,After the re

13、sistance changes：,U,R1,R2,R4,I1,2,I3,4,A,B,C,D,Bridge with the output voltage,R3,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,四、電橋平衡原理,電阻變化后：,實(shí)驗應(yīng)力分析基礎(chǔ),U,R1,R2,R4,I1,2,I3,4,A,B,C,D,電壓輸出橋,R3,5、Strainometer of resistance,Transform to output voltage into the magnitude of strain.,FOUNDATIONS OF THE

14、STRESS ANALYSIS IN EXPERIMENTS,五、電阻應(yīng)變儀,將輸出電壓轉(zhuǎn)變?yōu)閼?yīng)變讀數(shù)。,實(shí)驗應(yīng)力分析基礎(chǔ),6、Arrange foils ：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 quant

15、ities.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,六、布片：,盡可能使片子的方向與主應(yīng)力方向一致。,主應(yīng)力方向未知時，必須由三個獨(dú)立量才能確定一點(diǎn)的應(yīng)力狀態(tài)。,實(shí)驗應(yīng)力分析基礎(chǔ),7、Relations between the principal strains and the measured strains.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,七、主應(yīng)變與測量應(yīng)變之間的關(guān)系：,實(shí)驗應(yīng)力分析基礎(chǔ),Example 1 Three linear strains of a

16、 point are tested by the strain foil 45.Try to determine the principal strain of this point.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,例1 用45應(yīng)變花測得一點(diǎn)的三個線應(yīng)變后，求該點(diǎn)的主應(yīng)變。,實(shí)驗應(yīng)力分析基礎(chǔ),45,x,y,u,Example 2 Try to determine the principal strain of a point after the three linear strains of this point are t

17、ested by the strain foil of 60。,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,例2 用60應(yīng)變花測得一點(diǎn)的三個線應(yīng)變后，求該點(diǎn)的主應(yīng)變。,實(shí)驗應(yīng)力分析基礎(chǔ),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 ofte

18、n used.,9、Temperature compensation：,It is better to realize the compensation by itself; otherwise we 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.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIME

19、NTS,八、接橋：,要使應(yīng)力正負(fù)相間；全橋精度高，半橋精度低。常用半橋雙臂式橋路。,九、溫度補(bǔ)償：,最好能在橋路中自補(bǔ)償；否則，要用絕對不受力的溫度補(bǔ)償片。,工作片與補(bǔ)償片要始終處于同一溫度場中。,實(shí)驗應(yīng)力分析基礎(chǔ),153 Principle and application of the photoelasticity,1、Principle of the photoelasticity:,. Permanent double refraction：,. Temporary(artificial)double refraction:,FOUNDATIONS OF THE STRESS ANAL

20、YSIS IN EXPERIMENTS,153 光彈性法的原理及應(yīng)用,一、光測原理：,1.永久雙折射：,2.暫時（人工）雙折射：,實(shí)驗應(yīng)力分析基礎(chǔ),2、Plane stress -optics law：,.Refractive index：,CStress optical coefficient of the model material,Plane polarized light,The plane polarized light passes through the model subjected to forces.,FOUNDATIONS OF THE STRESS ANALYSIS

21、IN EXPERIMENTS,So,二、平面應(yīng)力光學(xué)定律：,1.折射率：,C模型材料的應(yīng)力光學(xué)系數(shù)。,實(shí)驗應(yīng)力分析基礎(chǔ),平面偏振光,平面偏振光通過受力模型,. Optical path difference：,.The light intensity in the plane polarization field:,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,2.光程差：,3.平面偏振場中的光強(qiáng)：,實(shí)驗應(yīng)力分析基礎(chǔ),Equal inclination lines,FOUNDATIONS OF THE STRESS ANALYSIS IN

22、EXPERIMENTS,As,a black point occurs behind the 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

23、plane polarization field taken every 150.The position 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.,等傾線,引起的黑點(diǎn)的跡線形成的干涉條紋等傾線,等傾線上，主應(yīng)力方向相同且與偏振軸重合。,實(shí)驗應(yīng)力分析基礎(chǔ),Equal difference lines.,The formed in

24、terference fringes-equal difference lines.,The white light is 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.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,As N=0,they are called the No.0 eq

25、ual difference lines(black); as N=1,they are called the No.1 equal difference lines.,Simulating the plae part connected by screws and screw caps (method of pasting foils),等差線,形成的干涉條紋等差線,以白光為光源,等差線為彩色條紋,故等差線又稱等色線,實(shí)驗應(yīng)力分析基礎(chǔ),fThe value of the fringe of a material,a、Under the repeated loading, the equal

26、inclination lines are not changed, but the equal difference lines are changed,Distinguish equal inclination lines and equal difference lines,b、If we rotate synchronously the polarizer and the analyzer, the equal inclination lines are changed and the equal difference lines are not changed.,c、Accordin

27、g to experiences,the equal inclination lines are thick(all the black) and equal difference lines are thin(a line).,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,f材料的條紋值。,a、反復(fù)加載，等傾線不變，等差線改變。,區(qū)分等傾線與等差線,b、同步旋轉(zhuǎn)起偏鏡與檢偏鏡，等傾線改變，等差線不變。,c、憑經(jīng)驗，等傾線較粗（一片黑），等差線較細(xì)（一條線）。,實(shí)驗應(yīng)力分析基礎(chǔ),There are no equal inclination lines in the cross circular polarization field.So the equal difference lines are clear.,FOUNDATIONS OF THE STRESS ANALYSIS IN EXPERIMENTS,Light intensity:,as,B