Understanding Acoustic Emission Testing- Reading 2015-2 NDTHB Vol5 Part 123A

1. Understanding Acoustic Emission Testing AET-R eading II NDTH B-Ed3 Vol.5 Part 1 My Pre-exam ASNT Self Study Notes 10th September 2015 Charlie Chong/ Fion Zhang

2. Petrol Chemical Applications Charlie Chong/ Fion Zhang

3. Petrol Chemical Applications Charlie Chong/ Fion Zhang

4. Petrol Chemical Applications Charlie Chong/ Fion Zhang

5. Petrol Chemical Applications Charlie Chong/ Fion Zhang

6. Petrol Chemical Applications Charlie Chong/ Fion Zhang

7. Petrol Chemical Applications Charlie Chong/ Fion Zhang

8. Charlie Chong/ Fion Zhang

9. The Magical Book of Acoustic Emission Charlie Chong/ Fion Zhang

10. 数字签名者：Fion Zhang DN：cn=Fion Zhang, o=Technical, ou=Academic, email=fion_zhang@ qq.com, c=CN 日期：2016.07.18 14:19:48 +08'00' Charlie Chong/ Fion Zhang

11. ASNT Certification Guide NDT Level III / PdM Level III AE - Acoustic Emission Testing Length: 4 hours Questions: 135 1 Principles and Theory • Characteristics of acoustic emission testing • Materials and deformation • Sources of acoustic emission • Wave propagation • Attenuation • Kaiser and Felicity effects, and Felicity ratio • Terminology (refer to acoustic emission glossary, ASTM 1316) Charlie Chong/ Fion Zhang

12. • Signal conditioning • Signal detection • Signal processing • Source location • Advanced signal processing • Acoustic emission test systems • Accessory materials • Factors affecting test equipment selection 2 Equipment and Materials • Transducing processes • Sensors • Sensor attachments • Sensor utilization • Simulated acoustic emission sources • Cables Charlie Chong/ Fion Zhang

13. 3 Techniques • Equipment calibration and set up for test • Establishing loading procedures • Precautions against noise • Special test procedures • Data displays 4 Interpretation and Evaluation • Data interpretation • Data evaluation • Reports 5 Procedures 6 Safety and Health 7 Applications • Laboratory studies (material- characterization) • Structural applications Charlie Chong/ Fion Zhang

14. R eference Catalog Number NDT Handbook, Second Edition: Volume 5, Acoustic Emission Testing 130 Acoustic Emission: Techniques and Applications 752 Charlie Chong/ Fion Zhang

15. Fion Zhang at Shanghai 11th September 2015 Charlie Chong/ Fion Zhang Charlie Chong/ Fion Zhang

16. Greek Alphabet Charlie Chong/ Fion Zhang

17. Charlie Chong/ Fion Zhang http://greekhouseoffonts.com/

18. Charlie Chong/ Fion Zhang

19. Study Note 1: Nondestructive H andbook Volume5-AET Charlie Chong/ Fion Zhang

20. SECTION 0 INTR ODUCTION TO ACOUSTIC EMISSION TECH NOLOGY Charlie Chong/ Fion Zhang

21. PAR T 1 H ISTOR Y OF ACOUSTIC EMISSION R ESEAR CH Early Uses of Acoustic Emission Acoustic emission and microseismic activity are naturally occurring phenomena. Although it is not known exactly when the first acoustic emissions were heard, fracture processes such as the snapping of twigs, the cracking of rocks and the breaking of bones were probably among the earliest. The first acoustic emission used by an artisan may well have been in making pottery (the oldest variety of hardfired pottery dates back to 6,500 BC) . In order to assess the quality of their products, potters t raditionally relied on the audible cracking sounds of clay vessels cooling in the kiln. These acoustic emissions were accurate indications that the ceramics were defective and did indeed structurally fail. Charlie Chong/ Fion Zhang

22. Acoustic Emission in Metalworking ■ Tin Cry It is reasonable to assume that the first observation of acoustic emission in metals was tin cry, the audible emission produced by mechanical twinning of pure tin during plastic deformation. This phenomenon could occur only after man learned to smelt pure tin, since tin is found in nature only in the oxide form. It has been established that smelting (of copper) began in Asia Minor as early as 3,700 BC. · The deliberate use of arsenic and then tin as alloying additions to copper heralde1 the beginning of the Bronze Age somewhere between the fourth and third millennium BC. The oldest piece of pure 'tin found to date is a bangle excavated at Thermi in Lesbos. The tin has been dated between 2,650 and 2,550 BC. It is 41 mm (1.6 in.) in diameter and . consists of two strands of pure tin , one wrapped around the other and hammered flat at the end. During the manufacture af this bangle, the craftsman could have heard considerable tin cry. Charlie Chong/ Fion Zhang

23. ■ Early Documented Observations of Tin Cry The first documented observations of acoustic emission may have been made by the eighth century Arabian alchemist Jabir ibn Hayyan (also known as Geber). His book Summa Perfectionis Magisterii (The Sum of Perfection or The Sum of Perfect Magistery) was published in English translation in 1678; the Latin edition was published in Berne in 1545. In it he writes that Jupiter (tin) gives off a "harsh sound" or "crashing noise." He also describes Mars (iron) as "sounding much" during forging. This sounding of iron was most likely produced by the fonnation of martensite during cooling. Since the time of the alchemists, audible emissions have become known and recognized properties of cadmium and zinc as well as tin. Tin cry is commonly found in books on chemistry published in the last half of the nineteenth century. For example, Worthington Hooker in 1882 describes "the cry of tin" as owing to the friction on minute crystals of the metal against each other." Charlie Chong/ Fion Zhang

24. In another text on chemistry published in 1883, Elroy M.Avery states that cadmium gives a crackling sound when bent, as tin does.“ He also describes an experiment with tin: "Hold a bar of Sn near the ear and bend the bar. Notice the peculiar crackling sound. Continue the bending and notice that the bar becomes heated. The phenomena noticed seems to be caused by the friction of the crystalline particles. Around the tum of the twentieth century, metals researchers started to break away from chemistry disciplines and began to develop metallurgy, their own specialized field . of science. A great deal of work was done on the study of twi.zming and martensitic phase transformation. Tin and zinc were historically well documented and two of the best metals for studying these phenomena. Dunng these studies, it was normal to hear the sounds emitted by metals such as tin, zinc, cadmium and some alloys of iron. In 1916, J.Czoch-Ralski was the first to report in the literature the association between "Zinn-und Zinkgeschrei'' (tin and zinc cry) and twinning.6 . He cited Gmelinraut's Handbuch der anorganisc!ten Chemie (1911 ), which in tum referenced an article by S. Kalischer (1882). Charlie Chong/ Fion Zhang

25. PAR T 2 DETECTING AND R ECOR DING ACOUSTIC EMISSION The transition from the incidental obsezvation of audible tin cry to the deliberate study of acoustic emission phenomena consisted of three separate and unrelated experiments in which instrumentation was used to detect, amplify and record acoustic emission events occurring in the test specimens. The first experiment instrumented specifically to detect acoustic emission was conducted in Germany and the results were published in 1936 by Friedrich Forster and Erich Scheil. They recorded the "Gerausche" (noises) caused by the formation of martensite in 29 percent nickel steel. Charlie Chong/ Fion Zhang

26. In the United States, Warren P. Mason, H.J. McSkimin and W. Shockley performed and published the second instrumented acoustic emission experiment in 1948. At the suggestion of Shockley, experiments were directed toward obsezvation of moving dislocations in pure tin specime by means of the stress waves they generated. The experiment's instrumentation was capable of measuring displacements of about 10-7mm occurring in times of 10-6seconds. The third instrumented experiment was performed in England by D.J. Millard in 1950 during research for his Ph.D. thesis at the University of Bristol. He conducted twinning experiments on single crystal wires of cadmium. Twinning was detected using a Rochelle salt transducer. Charlie Chong/ Fion Zhang

27. Kaiser's Study of Acoustic Emission Sources The early obsezvations of audible sounds and the three instrumented experiments were not directed at a study of the acoustic emission phenomenon itself, nor did the researchers carry on any further investigations in acoustic emission. The genesis of today's technology in acoustic e mission was the work of Joseph Kaiser at the Technische Hochschule Miinchen in Germany. In 1950 Kaiser published his Doktor-Ingenieur dissertation where he reported the first comprehensive investigation into the phenomena of acoustic emission. Kaiser used tensile tests of conventional engineering materials to determine: (1) what noises are generated from within the specimen; (2) the acoustic processes involved; (3) the frequency levels found; and (4) the relation between the stress-strain curve and the frequencies noted for the various stresses to which the specimens we re subjected. Charlie Chong/ Fion Zhang

28. His most significant discovery was the irreversibility phenomenon which now bears his name, the Kaiser effect. He also proposed a distinction between burst and continuous emission. Kaiser concluded that the occurrence of acoustic emission arises from frictional rubbing of grains against each other in the polycrystalline materials he tested and also from intergranular fracture. Kaiser continued his research at the Institut fiir Metallurgie und Metallkunde der Technischen Hochschule Mlinchen until his death in March 1958. His work provided the momentum for continued activities at the Institut by several of his coworkers, including Heinz Borchers and Hans Maria Tensi, and also furnished the impetus 动力 for further research elsewhere in the world. Charlie Chong/ Fion Zhang

29. Acoustic Emission Research in the United States Origins of US Research The first extensive research into acoustic emission phenomena following Kaiser's work was performed in the United States by Bradford H. Schofield at Lessells and Associates. His involvement came about as a result of a literature survey he and coworker A.A. Kyrala had conducted under another contract. They came across Kaiser's article in Archiv for das Eisenhuttenwesen. This precipitated a request for a copy of Kaiser's dissertation by John M. Lessells from his friend and the adjudicator of Kaiser's dissertation, Ludwig Foppl. Subsequently, Lessels and Schofield began a correspondence with Kaiser which continued until Kaiser's death. Charlie Chong/ Fion Zhang

30. Acoustic Emission studies for Materials Engineering In December 1954, Schofield initiated a research program directed toward the application of acoustic emission to the field of materials engineering. His initial research was to verify the findings of Kaiser and the primary purpose of this early work was to determine the source of acoustic emissions. This research work was published in 1958. Schofield performed an extensive investigation into how surface and volume effects related to acoustic emission behavior. Experimental data obtained from oriented single crystals of aluminum (both with and without an oxide layer.) and from oriented single crystals of gold, helped him conclude that surface condition does have a measurable influence on the acoustic emission spectrum. Charlie Chong/ Fion Zhang

31. However, Schofield's most important conclusion was that acoustic emission is mainly a volume effect and not a surface effect. In the fall of 1956, Lawrence E. Malvern at Michigan State University came across a one-page article entitled "Horbare Schwingungen beim Verformen“ ("Audible Vibrations from Deformation") in Fliessen und Kriechen der Metalle by Wilhelm Spath. The article references the observations of "Gerauschen" (noises) by Joffe and Ehrenfest, Klassen-Nekludowa, Becker and Orowan, and Kaiser. Interested in studying the asperity theory of friction, Malvern suggested to a new faculty member, Clement A. Tatro, that this acoustic technique would be interesting to investigate. Consequently, Tatro initiated laboratoty studies of acoustic emission phenomena. Charlie Chong/ Fion Zhang

32. Establishment and Expansion of Research Programs In 1957, Tatro became aware of the work of Schofield and the two began collaborating. Tatro thought that research programs in acoustic emission could follow one of two rather well-defined branches: (1) to pursue studies concerned with the physical mechanisms that give rise to acoustic emission to completely understand the phenomenon; or (2) using acoustic emission as a tool to study some of the vexing problems of behavior of engineering materials. He also foresaw the unique potential of acoustic emission as a nondestructive testing procedure. His enthusiasm for this new technology sparked the interests of a number of graduate students at Michigan State who chose acoustic emission as the subject of their research projects. The students included PaulS. Shoemaker (1961),33 Robert J. Kroll (1962),34 Robert G. Liptai (1963)35 and Robert B. Engle (1966).36 Tatro left Michigan State in 1962 for Tulane University where he continued research in acoustic emission, fostering two more graduate students, Benny B. McCullough (1965)37 and Davis M. Egle (1965).38 In 1966, Tatro joined the staff at Lawrence Radiation Laboratory (now Lawrence Livermore National Laboratory). Charlie Chong/ Fion Zhang

33. Schofield and Tatro encouraged others to become involved in research activity in the field of acoustic emission. That encouragement, combined with the impact of their published work (the first publications in the English language), helped establish acoustic emission research and application around the country. Julian R. Frederick at the University of Michigan had been engaged in research in ultrasonics since he was a graduate student under Floyd A.Firestone in 1939. His interest in acoustic emission, particularly for studying dislocation mechanisms, was excited. In 1948 after readirig Mason, McSkimin and Shockley's article "Ultrasonic Observation of Twinning in Tin" in Physical Review.” Frederick visited both Schofield and Tatro in the late 1950s. But it was not until 1960, when Frederick obtained a National Science Foundation grant for two of his graduate students, that he began his research in acoustic emission. A third student was funded several years later. These students were Jal N. Kerawalla (1965),39 Larry D. Mitchell (1965) and Anand B.L. Agarwal (1968). Charlie Chong/ Fion Zhang

34. PAR T 3 OR GANIZING TH E ACOUSTIC EMISSION COMMUNITY The Acoustic Emission Working Group Conception of the AEWG In the spring of 1967, Jack C. Spanner and Allen T. Green observed that a number of researchers were investigating the phenomena of acoustic emission and publishing reports of their work, but there seemed to be a lack of centralized communication. Spanner also observed that there were differences in terminology and experimental techniques, generally reflecting the researcher's educational background and field of expertise. Jointly Spanner and Green perceived the need to unite and organize these people for the purpose of compiling and exchanging information. Using the constitution and bylaws of the Western Regional Strain Gage Committee as a model {as suggested by Green), Spanner laid the groundwork for he formation of the Acoustic Emission Working Group (AEWG). Charlie Chong/ Fion Zhang

35. SECTION 1 FUNDAMENTALS OF ACOUSTICEMISSION TESTING Charlie Chong/ Fion Zhang

36. SECTION 1 PART 1 INTRODUCTION TO ACOUSTIC EMISSION TECHNOLOGY 1.1.1 The Acoustic Emission Phenomenon Acoustic emission is the elastic energy that is spontaneously released by materials when they undergo deformation. In the early 1960s, a new nondestructive testing technology was born when it was recognized that growing cracks and discontinuities in pressure vessels could be detected by monitoring their acoustic emission signals. Although acoustic emission is the most widely used term for this phenomenon, it has also been called stress wave emission, stresss waves, microseism, microseismic activity and rock noise. Formally defined, acoustic emission is "the class of phenomena where transient elastic waves are generated by the rapid release of energy from localized sources within a material, or the transient elastic waves so generated." This is a definition embracing both the process of wave generation and the wave itself. Charlie Chong/ Fion Zhang

37. Formally defined, acoustic emission is "the class of phenomena where transient elastic waves are generated by the rapid release of energy from localized sources within a material, or the transient elastic waves so generated." Charlie Chong/ Fion Zhang

38. Source Mechanisms Sources of acoustic emission include many different mechanisms of deformation and fracture. Earthquakes and rockbursts in mines are the largest naturally occurring emission sources. Sources that have been identified in metals include: - crack growth, - moving dislocations, - slip, - twinning, - grain boundary sliding and - the fracture and decohesion of inclusions. In composite materials, sources include matrix cracking and the debonding and fracture of fibers. These mechanisms typify the classical response of materials to applied load. Charlie Chong/ Fion Zhang

39. Secondary Sources Or Pseudo Sources Other mechanisms fall within the definition and are detectable with acoustic emission equipment. These include leaks and cavitation; friction (as in rotating bearings); The realignment or growth of magnetic domains (Barkhausen effect); liquefaction and solidification; And solid-solid phase transformations. Sometimes these sources are called secondary sources or pseudo sources to distinguish them from the classic acoustic emission due to mechanical deformation of stressed materials. A unified explanation of the sources of acoustic emission does not yet exist. Neither does a complete analytical description of the stress wave energy in the vicinity of an acoustic emission source. However, encouraging progress has been made in these two key research areas. Comments: Pseudo sources are not mechanical deformation induced. Charlie Chong/ Fion Zhang

40. 1.1.2 Acoustic Emission Nondestructive Testing Acoustic emission examination is a rapidly maturing nondestructive testing method with demonstrated capabilities for monitoring structural integrity, detecting leaks and incipient failures in mechanical equipment, and for characterizing materials behavior. The first documented application of acoustic emission to an engineering structure was published in 1964 and all of the available industrial application experience has been accumulated in the comparatively short time since then. Charlie Chong/ Fion Zhang

41. Comparison with Other Techniques Acoustic emission differs from most other nondestructive methods in two significant respects. First, the energy that is detected is released from within the test object rather than being supplied by the nondestructive method, as in ultrasonics or radiography. Second, the acoustic emission method is capable of detecting the dynamic processes associated with the degradation of structural integrity. Crack growth and plastic deformation are major sources of acoustic emission. Latent discontinuities that enlarge under load and are active sources of acoustic emission by virtue of their size, location or orientation are also the most likely to be significant in terms of structural integrity. Usually, certain areas within a structural system will develop local instabilities long before the structure fails. These instabilities result in minute dynamic movements such as plastic deformation, slip or crack initiation and propagation. Although the stresses in a metal part may be well below the elastic design limit; the region near a crack tip may undergo plastic deformation as a result of high local stresses. In this situation, the propagating discontinuity acts as a source of stress waves and becomes an active acoustic emission source. Charlie Chong/ Fion Zhang

42. Acoustic emission examination is non-directional. Most acoustic emission sources appear to function as point source emitters that radiate energy in spherical wavefronts. Often, a sensor located anywhere in the vicinity of an acoustic emission source can detect the resulting acoustic emission. This is in contrast to other methods of nondestructive testing, which depend on prior knowledge of the probable location and orientation of a discontinuity- in order to direct a beam of energy through the structure on a path that will properly intersect the area of interest. Keywords: Dynamic process Active process r1 r2 r3 Charlie Chong/ Fion Zhang

43. Spherical Wavefronts Charlie Chong/ Fion Zhang

44. Spherical Wavefronts Charlie Chong/ Fion Zhang https://figures.boundless.com/17178/full/spherical-wave.gif

45. Spherical Wavefronts- Planar Source Location r1 r2 r3 Charlie Chong/ Fion Zhang

46. Spherical Wavefronts Charlie Chong/ Fion Zhang https://figures.boundless.com/17178/full/spherical-wave.gif

47. Advantages of Acoustic Emission Tests The acoustic emission method offers the following advantages over other nondestructive testing methods: 1. Acoustic emission is a dynamic inspection method in that it provides a response to discontinuity growth under an imposed structural stress; Static discontinuities will not generate acoustic emission signals. 2. Acoustic emission can detect and evaluate the significance of discontinuities throughout an entire structure during a single test. 3. Since only limited access is required, discontinuities may be detected that are inaccessible to the more traditional nondestructive methods. 4. Vessels and other pressure systems can often be requalified during an in- service inspection that requires little or no downtime. 5. The acoustic emission method may be used to prevent catastrophic failure of systems with unknown discontinuities, and to limit the maximum pressure during containment system tests. Charlie Chong/ Fion Zhang

48. Acoustic emission is a wave phenomenon and acoustic emission testing uses the attributes of particular waves to help characterize the material in which the waves are traveling. Frequency and amplitude are examples of the waveform parameters that are regularly monitored in acoustic emission tests. Table 1 gives an overview of the manner by which various material properties and testing conditions influence acoustic emission response amplitudes. The factors should generally be considered as indicative, rather than as absolute. Charlie Chong/ Fion Zhang

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50. Factors That Tend to Increase Acoustic Emission Response Amplitude Factors That Tend to Decrease Acoustic Emission Response Amplitude High strength Low strength High strain rate low strain rate Low temperature High temperature Anisotropy Isotropy Non-homogeneity Homogeneity Thick sections Thin sections Brittle failure (cleavage) Ductile failure (shear) Material containing discontinuities Material without discontinuities Martensitic phase transformations Diffusion-controlled phase transformations Crack propagation Plastic deformation Cast materials Wrought materials Large grain size Small grain size Mechanically induced twinning Thermally induced twinning Charlie Chong/ Fion Zhang