Muravin physical principals of acoustic emission


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Physical principals of acoustic emission

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Muravin physical principals of acoustic emission

  1. 1. Seminar on Fundamentals of Acoustic Emission לשכת המהנדסים , האדריכלים והאקדמאים במקצועות הטכנולוגיים בישראל אגודת מהנדסי מכונות - ענף בדיקות לא הורסות Dr. Boris Muravin Chairman of Israeli Acoustic Emission Group Feb 24, 2011 יום עיון השנתי בנושא פליטה אקוסטית This presentation for acoustic emission education purposes only More in
  2. 2. סיכום פעילות התא לפליטה אקוסטית בשנת 2010. <ul><li>יום יעון בפליטה אקוסטית . </li></ul><ul><li>כנס מכונות 2010. </li></ul><ul><li>כנס בל &quot; ה 2011. </li></ul><ul><li>אירגון קורס בייסיק לפי ASNT ו EN 473. </li></ul><ul><li>אירגון מבחני הסמכה לרמה III לפי ASNT . </li></ul><ul><li>ליווי פרואקטים ויעוץ . </li></ul>More in
  3. 3. Seminar Outline <ul><li>9:15 – 10:30 History of AE, physical principals of acoustic emission, AE waves, AE source location </li></ul><ul><li>10:30-10:45 Break </li></ul><ul><li>10:45 – 12:30 Apparatus, data acquisition and analysis </li></ul><ul><li>12:30-13:15 Lunch break </li></ul><ul><li>13:15 – 14:30 Apparatus, data acquisition and analysis – Cont. </li></ul><ul><li>14:30-14:45 Break </li></ul><ul><li>14:45 – 16:00 Applications and standards. </li></ul><ul><li>16:00-16:15 Break </li></ul><ul><li>16:15 – 17:30 Applications and standards – Cont. </li></ul>More in
  4. 4. History of AE More in
  5. 5. Who was the First? <ul><li>They were the First who used AE as an alarm system </li></ul>He was the First who used AE as a forecasting tool More in
  6. 6. Early History of AE <ul><li>קול זעקה מבבל ושבר גדול מארץ כשדים ירמיהו נא , נד </li></ul><ul><li>“ The sound of a cry from Babylon and the sound of great fracture <comes> from the land of the Chaldeans.” Jeremiah 51:54 </li></ul><ul><li>One of the first sources that associates sound with fracture can be found in the Bible. </li></ul><ul><li>Probably the first practical use of AE was by pottery makers, thousands of years before recorded history, to asses the quality of there products. </li></ul><ul><li>Probably the first observation of AE in metal was during twinning of pure tin as early as 3700 B.C. </li></ul><ul><li>The first documented observation of AE in Middle Ages was made by an Arabian alchemist, Geber, in the eighth century. Geber described the “harsh sound or crashing noise” emitted from tin. He also describes iron as “sounding much” during forging. </li></ul>More in
  7. 7. History of First AE Experiments <ul><li>In 1920, Abram Joffe (Russia) observed the noise generated by deformation process of Salt and Zinc crystals. “ The Physics of Crystals” , 1928. </li></ul><ul><li>In 1936, Friedrich Forster and Erich Scheil (Germany) conducted experiments that measured small voltage and resistance variations caused by sudden strain movements caused by martensitic transformations. </li></ul><ul><li>In 1948, Warren P. Mason, Herbert J. McSkimin and William Shockley (United States) suggested measuring AE to observe the moving dislocations by means of the stress waves they generated. </li></ul><ul><li>In 1950, D.J Millard (United Kingdom) performed twinning experiments on single crystal wires of cadmium. The twinning was detected using a rochelle salt transducer. </li></ul>More in
  8. 8. History of First AE Experiments <ul><li>In 1950, Josef Kaiser (Germany) used tensile tests to determine the characteristics of AE in engineering materials. The result from his investigation was the observation of the irreversibility phenomenon that now bears his name, the Kaiser Effect. </li></ul><ul><li>The first extensive research after Kaiser was done in the United States by Bradford H. Schofield in 1954. Schofield investigated the application of AE in the field of materials engineering and the source of AE. He concluded that AE is mainly a volume effect and not a surface effect. </li></ul><ul><li>In 1957, Clement A. Tatro, after performing extensive laboratory studies, suggested to use AE as a method to study the problems of behavior of engineering metals. He also foresaw the use of AE as an NDT method. </li></ul>More in
  9. 9. Start of Industrial Application of AE <ul><li>The first AE test in USA was conducted in the Aerospace industry to verify the integrity of the Polaris rocket motor for the U.S Navy (1961). After noticing audible sounds during hydrostatic testing it was decided to test the rocket using contact microphones, a tape recorder and sound level analysis equipment. </li></ul><ul><li>In 1963, Dunegan suggested the use of AE for examination of high pressure vessels. </li></ul><ul><li>In early 1965, at the National Reactor Testing Station, researchers were looking for a NDT method for detecting the loss of coolant in a nuclear reactor. Acoustic Emission was applied successfully. </li></ul><ul><li>In 1969, Dunegan founded the first company that specializes in the production of AE equipment. </li></ul><ul><li>Today, AE Non-Destructive Testing used practically in all industries around the world for different types of structures and materials. </li></ul>More in
  10. 10. Physical Principals of Acoustic Emission More in
  11. 11. Definition of Acoustic Emission Phenomenon <ul><li>Acoustic Emission is a phenomenon of sound and ultrasound wave radiation in materials undergo deformation and fracture processes. </li></ul><ul><li>ASTM E1316-2010 definition: </li></ul><ul><li>Acoustic Emission (AE) —the class of phenomena whereby transient elastic waves are generated by the rapid release of energy from localized sources within a material, or the transient waves so generated. Acoustic emission is the recommended term for general use. Other terms that have been used in AE literature include (1) stress wave emission, (2) microseismic activity, and (3) emission or acoustic emission with other qualifying modifiers. </li></ul>More in
  12. 12. Classification of AE More in
  13. 13. Classes and Mechanisms of Acoustic Emission Mechanical acoustic emission - acoustic emission generated by a leakage, friction, impact or other sources of mechanical origin. Material acoustic emission - acoustic emission generated by a local dynamic change in a material structure due to fracture development and/or deformation processes. More in
  14. 14. Source Mechanisms of AE in Metals More then 80% of energy expended on fracture in common industrial metals goes to development of plastic deformation. More in
  15. 15. Source Mechanisms in Composites <ul><li>Matrix cracking. </li></ul><ul><li>Fiber fracture. </li></ul><ul><li>Delamination. </li></ul><ul><li>Fiber pullout. </li></ul><ul><li>Friction. </li></ul>More in
  16. 16. Primary vs. Secondary AE More in Secondary AE Primary AE Crack surface friction Crack jump Inclusion breakage in the process zones Plastic deformation Corrosion layer fracture in corrosion fatigue cases Crack growth
  17. 17. AE Types: Burst and Continuous AE Signals More in
  18. 18. Some Mechanisms of Burt and Cont. AE More in
  19. 19. Acoustic Emission is Flaw-Type-Material Specific Tree Falls Paper tear ICE CRACK Glass Ice Crack Brake Identification of distinctive flaw-type-material specific AE characteristics of different flaws in high energy equipment is a necessary condition for reliable diagnostics. Glass Brake More in
  20. 20. AE in Metals More in
  21. 21. Metals More in
  22. 22. Factors that Tend to Increase or Decrease the Amplitude of AE Nondestructive Testing Handbook, Volume 6 “Acoustic Emission Testing”, Third Edition, ASNT. More in
  23. 23. “ Friendly” Metals for Traditional AE Inspections <ul><li>“ Friendly” ( for newcomers ) metals can be considered those producing high amplitude (high Signal-to-Noise ratio) emissions. </li></ul><ul><li>Examples are various carbon steels, cast irons, low ductility steels, high inclusion content steels, large grain size steels. </li></ul>More in
  24. 24. Detectability by AE Depends on Failure Mechanism <ul><li>Flaws due to different failure mechanisms have different propagation characteristics: intergranular or transgranular, cleavage or ductile fracture, small scale or large yielding, etc. </li></ul><ul><li>For example high cycle and low cycle mechanical fatigue may different detectability (if we define detectability based on level of AE amplitudes). </li></ul>More in
  25. 25. Plastic Deformation as a Major Source of AE More in
  26. 26. Plastic Zone at the Crack Tip <ul><li>Flaws in metals can be revealed by detection of indications of plastic deformation development around them. </li></ul><ul><li>Cracks, inclusions, and other discontinuities in materials concentrate stresses. </li></ul><ul><li>At the crack tip stresses can exceed yield stress level causing plastic deformation development. </li></ul><ul><li>The size of a plastic zone can be evaluated using the stress intensity factor K, which is the measure of stress magnitude at the crack tip. The critical value of stress intensity factor, K IC is the material property called fracture toughness. </li></ul>Fracture Mechanics Fundamentals and Applications, Second Edition, T.L. Anderson. More in
  27. 27. Comparison of Plastic Deformation around Crack Tips Mode I and II 1 2 3 Mode II 0.5 mm 1 Mode I <ul><li>The size of plastic deformation around crack mode II is significantly larger (up to 3-5 times, see /1-3/) than the plastic deformation zone around crack mode I under the same load/max load ratio. </li></ul><ul><li>2. According to our experimental results, the estimated relation between plastic deformation zone for Mode II and Mode I crack is approximately 3. </li></ul>Our experimental results J. F. Kalthoff, Failure Methodology of Mode-II Loaded Cracks, Mechanics, Automatic Control and Robotics Vol.3, No 13, 2003, pp. 533 - 552 More in Plastic Strain Plastic Stress Mode I Mode II
  28. 28. Ellipses of Dispersion Energy vs. Average Frequency of Single Fatigue Crack under Mode I and Mode II Loading (1200kgf) 1– Plastic Deformation 2 – Micro Cracking More in Released Energy, r.u. Amount of Data Flaw Type 0.33 99 Plastic Deformation 0.5 16 Micro-Cracks Released Energy, r.u. Amount of Data Flaw Type 1 228 Plastic Deformation 1 23 Micro-Cracks
  29. 29. Models of AE in Metals <ul><li>Plastic Deformation Model </li></ul><ul><li>Plastic deformation model relates AE and the stress intensity factor ( ). </li></ul><ul><li>AE is proportional to the size of the plastic deformation zone. </li></ul><ul><li>Several assumptions are made in this model: (1) The material gives the highest rate of AE when it is loaded to the yield strain. (2) The size and shape of the plastic zone ahead of the crack are determined from linear elastic fracture mechanics concepts. </li></ul>(3) Strains at the crack tip vary at where r is the radial distance from the crack tip. (4) The assumptions lead to development of the following equations for the model ( ) More in
  30. 30. AE Effects <ul><li>Kaiser effect is the absence of detectable AE at a fixed sensitivity level, until previously applied stress levels are exceeded. </li></ul><ul><li>Dunegan corollary states that if AE is observed prior to a previous maximum load, some type of new damage has occurred. The dunegan corollary is used in proof testing of pressure vessels. </li></ul><ul><li>Felicity effect is the presence of AE, detectable at a fixed predetermined sensitivity level at stress levels below those previously applied. The felicity effect is used in the testing of fiberglass vessels and storage tanks. </li></ul>ASTM E1316: 2010 Kaiser effect —the absence of detectable acoustic emission at a fixed sensitivity level, until previously applied stress levels are exceeded. Discussion—Whether or not the effect is observed is material specific. The effect usually is not observed in materials containing developing flaws. Kaiser effect (BCB) Felicity effect (DEF) More in
  31. 31. Kaiser Effect <ul><li>The immediately irreversible characteristic of AE resulting from an applied </li></ul><ul><li>stress at a fixed sensitivity level. </li></ul><ul><li>If the effect is present, there is an absence of detectable AE until previously </li></ul><ul><li>applied stress levels are exceeded. </li></ul>Example of the Kaiser Effect in a cyclically loaded concrete specimen. Thick black lines represents AE activity, thin lines the loads and dashed lines the Kaiser Effect. More in
  32. 32. AE Waves More in
  33. 33. Types of Acoustic Emission Waves <ul><li>Type of AE waves generated depend on material properties, its mechanical behavior and level of stresses at the source. AE waves can be: </li></ul><ul><li>Elastic. </li></ul><ul><li>Non-linear elastic. </li></ul><ul><li>Elastic-plastic. </li></ul><ul><li>Elastic-viscoplastic and other. </li></ul><ul><li>Inelastic waves attenuate at short distances and therefore elastic waves are mostly detected and analyzed in acoustic emission testing. </li></ul>More in
  34. 34. Modes of Elastic Waves Propagation <ul><li>Longitudinal (dilatational, P-) wave is the wave in which the oscillations occurring in the direction of the wave propagation. </li></ul><ul><li>Shear (or transverse, or distortional, or equivolumal, or S-) wave is the wave in which the oscillations occurring perpendicular to the direction of the wave propagation. </li></ul><ul><li>Rayleigh (or surface) wave is the wave with elliptic particle motion in planes normal to the surface and parallel to the direction of the wave propagation. </li></ul><ul><li>Lamb (or plate) wave is the wave with particles motion in perpendicular to the plate. </li></ul><ul><li>Stoneley (or interfacial) wave is the wave at interface between two semi-infinite media. </li></ul><ul><li>Love wave is the wave in a layered media, parallel to the plane layer and perpendicular to the wave propagation direction. </li></ul><ul><li>Creeping wave is the wave that is diffracted around the shadowed surface of a smooth obstacle. </li></ul>More in
  35. 35. Longitudinal, Shear, Rayleigh and Love Waves Reference: More in
  36. 36. Wave Modes in Different Geometries <ul><li>In infinite media there are only two types of waves: dilatational (P) and distortional (S). </li></ul><ul><li>Semi-infinite media there are also Rayleigh and Lateral (Head) waves. Head waves produced by interaction of longitudinal wave with free surface. </li></ul><ul><li>In double bounded media like plates there are also Lamb waves. </li></ul>In thinnest plates only Lamb wave arrivals are visible. Symmetric Antisymmetric More in t = 10 mm t = 5 mm
  37. 37. Example of AE Signal More in
  38. 38. Wave Speed in Different Materials Wave speeds derivation: λ and μ – Lame constants ν – Poisson’s ratio ρ – material density More in
  39. 39. Properties of Elastic Waves in Semi-Infinite Media <ul><li>Rayleigh waves carry 67% of total energy (for ν =0.25). </li></ul><ul><li>Shear 26%. </li></ul><ul><li>Longitudinal 7%. </li></ul><ul><li>Longitudinal and shear waves decay at a rate 1/r in the region away of the free surfaces. </li></ul><ul><li>Along the surface they decay faster, at a rate 1/r 2 . </li></ul><ul><li>Rayleigh waves decays much slower, at a rate of 1/sqrt(r). </li></ul>Reference: “Dynamic Behavior of Materials” by M. Meyers More in
  40. 40. Wave Propagation Effects <ul><li>The following phenomena take place as AE waves propagate along the structure: </li></ul><ul><li>Attenuation : The gradual decrease in AE amplitude due to energy loss mechanisms, from dispersion, diffraction or scattering. </li></ul><ul><li>Dispersion : A phenomenon caused by the frequency dependence of speed for waves. Sound waves are composed of different frequencies hence the speed of the wave differs for different frequency spectrums. </li></ul><ul><li>Diffraction : The spreading or bending of waves passing through an aperture or around the edge of a barrier. </li></ul><ul><li>Scattering : The dispersion, deflection of waves encountering a discontinuity in the material such as holes, sharp edges, cracks inclusions etc…. </li></ul><ul><li>Attenuation tests have to be performed on actual structures during their inspection. </li></ul><ul><li>The attenuation curves allow to estimate amplitude or energy of a signal at a given distance from a sensor. </li></ul>More in
  41. 41. Group and Phase Velocity <ul><li>Lord Rayleigh: “It have often been remarked that when a group of waves advances into still water, the velocity of the group is less than that of the individual waves of which it is composed; the waves appear to advance through the group, dying away as they approach its interior limit” (1945, Vol. I, p. 475). </li></ul><ul><li>Group velocity is the velocity of propagation of a group of waves of similar frequency. </li></ul><ul><li>Phase velocity is the velocity at which the phase of the wave propagates in the media. </li></ul>Reference: More in
  42. 42. Dispersion Curves Example calculated for steel 347 plate (10mm thick) Triple point Non-dispersive part of A 0 mode More in
  43. 43. Use of Dispersion Curves <ul><li>Dispersion curves can be effectively used for accurate location and characterization of AE sources. Examples: </li></ul><ul><li>Filtering AE waveforms at frequency of the triple point (200 kHz), one can improve location accuracy. This is because all modes at this frequency have similar speed and the threshold will be triggered by the same wave mode at all sensors. </li></ul><ul><li>Filtering AE waveforms over non-dispersive range of A0 mode (80-180 kHz) can improve location accuracy even further. In this technique a wider frequency range of the original signal remain after filtration while the frequency content of the mode remain unchanged over the distance. </li></ul>More in
  44. 44. AE Source Location More in
  45. 45. Principals of Acoustic Emission Source Location <ul><li>Time difference based on Time of Arrival locations. </li></ul><ul><li>Cross-correlation time difference location. </li></ul><ul><li>Zone location. </li></ul><ul><li>Attenuation based locations. </li></ul><ul><li>Geodesic location. </li></ul>More in
  46. 46. Time of Arrival Evaluation <ul><li>Most of existing location procedures require evaluation of time of arrival (TOA) of AE waves to sensors. </li></ul><ul><li>TOA can detected as the first threshold crossing by AE signal, or as a time of peak of AE signal or as a time of first motion. TOA can be evaluated for each wave mode separately. </li></ul>More in
  47. 47. Effective Velocity <ul><li>Another parameter necessary for time difference location method is effective velocity. </li></ul><ul><li>Effective velocity can be established experimentally with or without considering different wave propagation modes. </li></ul><ul><li>When propagation modes are not separated, the error in evaluation of AE source location can be significant. For example, in linear location it can be about 10% of sensors spacing. </li></ul><ul><li>Detection of different wave modes arrival times separately and evaluation of their velocities can significantly improve location accuracy. Nevertheless, detection and separation of different wave modes is computationally expensive and inaccurate in case of complex geometries or under high background noise conditions. </li></ul><ul><li>Another parameter necessary for time difference location method is effective velocity. </li></ul><ul><li>Effective velocity can be established experimentally with or without considering different wave propagation modes. </li></ul><ul><li>When propagation modes are not separated, the error in evaluation of AE source location can be significant. For example, in linear location it can be about 10% of sensors spacing. </li></ul><ul><li>Detection of different wave modes arrival times separately and evaluation of their velocities can significantly improve location accuracy. Nevertheless, detection and separation of different wave modes is computationally expensive and inaccurate in case of complex geometries or under high and variable background noise conditions. </li></ul>More in
  48. 48. Linear Location <ul><li>Linear location is a time difference method commonly used to locate AE source on linear structures such as pipes, tubes or rods. It is based on evaluation of time difference between arrival of AE waves to at least two sensors. </li></ul><ul><li>Source location is calculated based on time difference and effective wave velocity in the examined structure. Wave velocity usually experimentally evaluated by generating artificially AE at know distances from sensors. </li></ul>More in
  49. 49. One Sensor Linear Location <ul><li>It is possible to use one sensor to evaluate the distance from AE source (but not direction). </li></ul><ul><li>The principal of this location is based on phenomenon of different velocity of propagation of different wave modes. </li></ul><ul><li>Such location method can be used on short rods, tubes or pipes, when mode detection and separation can be effectively performed. </li></ul>More in
  50. 50. Two Dimensional Source Location Sensor 1 Sensor 2 Sensor 1 Z D R2 R1 R1 R2 R3 Sensor 2 Sensor 3 For location of AE sources on a plane minimum three sensors are used. The source is situated on intersection of two hyperbolas calculated for the first and the second sensors detected AE signal and the first and the third sensor. More in R3
  51. 51. Over-determined Source Location <ul><li>Generally, it is necessary 2 sensors for linear, 3 sensors for 2D and 4 sensors for 3D locations. </li></ul><ul><li>When more sensors detect AE wave from a source than necessary it is possible to use this information to improve location accuracy by error minimization optimization methods. </li></ul>Chi Squared error function that minimized in over-determined source location. More in
  52. 52. 2D Location on Cylinder Minimization on χ 2 : (x o ,y o )– location of source (x i ,y i )– location of sensor i t i – arrival time to sensor i t 1 - arrival time to sensor 1 The time delay between the signal arrival to two sensors: <ul><li>At least 3 sensors are required for location. </li></ul><ul><li>However, more sensors increase the accuracy of the source location </li></ul>More in
  53. 53. X o – location of source X i – location of sensor i E o – energy at source E i – energy at sensor i β - the decay constant Energy attenuation in line: * 3 sensors are required for location for unknown β (for known β 2 sensors are required for location) Energy Attenuation Location More in Source ( ( ( ( * ) ) ) ) x I
  54. 54. Location in Anisotropic Materials <ul><li>In anisotropic materials, the velocity of wave propagation is different in different direction. </li></ul><ul><li>In order to achieve appropriate results in source location it is necessary to evaluate velocity profile as a function of propagation direction and incorporate this into the calculation of time differences as done in the example of the composite plate. </li></ul>More in
  55. 55. Cross-correlation based Location Ch 1 Ch 2 Cross-correlation method is typically applied for location of continuous AE signals. Cross-correlation is another method for location of AE sources based on estimation of time shifts between AE signals detected by different sensors. It is usually applied for continuous AE signals when it is impractical to estimate the time of wave arrival but possible to estimate time shifts between sensors. More in Δ t Normalized cross-correlation function Δ t Cross-correlation function
  56. 56. Zone Location <ul><li>Zone location is based on the principle that the sensor with the highest amplitude or energy output will be closest to the source. </li></ul><ul><li>Zone location aims to trace the waves to a specific zone or region around a sensor. </li></ul><ul><li>Zones can be lengths, areas or volumes depending on the dimensions of the array. </li></ul><ul><li>With additional sensors added, a sequence of signals can be detected providing a more accurate result. </li></ul>More in
  57. 57. Geodesic Location <ul><li>This time-difference location method is based on calculation of the shortest wave path over the mesh of the object by the principle of minimum energy. </li></ul><ul><li>The method allows to solve location problems in complex geometries but computationally expensive. </li></ul>Reference: G. PRASANNA, M. R. BHAT and C. R. L. MURTHY, “ACOUSTIC EMISSION SOURCE LOCATION ON AN ARBITRARY SURFACE BY GEODESIC CURVE EVOLUTION”, Advances in Acoustic Emission - 2007 More in
  58. 58. Other Location Methods <ul><li>FFT and wavelet transforms are be used to improve location by evaluation of modal arrival times. </li></ul><ul><li>Cross-correlation between signals envelopes. </li></ul><ul><li>There are works proposing use of neural network methods for location of continuous AE. </li></ul>More in
  59. 59. The End More in