Electromagnetic testing emt chapter 18 - aerospace applications

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18.2 PART 2. Eddy Current Tests of Metal and Coating Thickness 18.2.1 Coating Thickness on Metals In the aerospace industry, numerous metal parts are coated or plated to obtain special surface properties such as corrosion resistance, wear resistance or improved appearance. These coatings are prepared by various means, including electro-deposition, hot dipping, cladding and spraying. For controlling the thickness of the deposit and also for testing purposes, reliable and rapid measurements of coatings are necessary. There are many methods available, including magnetic, mechanical, optical, radiographic, ultrasonic and electromagnetic testing. Each of these methods has applications and more than one method may be used for the same application. Charlie Chong/ Fion Zhang
■ Classification of Coatings and Base Materials Four general types of coatings and base materials lend themselves to eddy current testing. The operating procedure used with the test instrument is determined by the specific combination of materials. These material combinations are classified as follows: (1) metal foil and sheet or metal coating on a nonconductive base material, such as metallic film on glass, ceramics or plastics; (2) metal cladding with a higher conductivity than the base metal, such as copper, zinc or cadmium on steel or pure aluminum on aluminum alloy; (3) metal cladding with a lower conductivity than the base metal, such as nickel on aluminum; and (4) nonconductive coatings on a metallic base material, such as anodic film or paint on aluminum or such as other organic coatings on metals. Charlie Chong/ Fion Zhang
Page 1 and 2: Electromagnetic Testing MFLT/ ECT/
Page 3 and 4: Aerospace Applications Charlie Chon
Page 15 and 16: Vertical Take Off Plane ■ https:/
Page 17 and 18: Vertical Take Off Plane ■ https:/
Page 19 and 20: Charlie Chong/ Fion Zhang
Page 21 and 22: Greek letter Charlie Chong/ Fion Zh
Page 23 and 24: 18.1 PART 1. Introduction to Eddy C
Page 25 and 26: Aluminum Exfoliation Charlie Chong/
Page 27 and 28: Titanium - Brazing and Soldering Wh
Page 29 and 30: Titanium Aluminide - Through extens
Page 31 and 32: Titanium Aluminide Charlie Chong/ F
Page 33 and 34: Titanium Aluminide Charlie Chong/ F
Page 35 and 36: 18.1.2 Testing of Aluminum Alloys T
Page 37: Maintenance overhauls Charlie Chong
Page 41 and 42: 18.2.2 Metal Thickness Tests for me
Page 43 and 44: A technique called null balancing c
Page 45 and 46: FIGURE 2. Relative instrument readi
Page 47 and 48: The important fact illustrated in F
Page 49 and 50: FIGURE 3. Impedance graphs showing
Page 51 and 52: 18.2.4 Nonconductive Coating Thickn
Page 53 and 54: Vertical Liftoff Charlie Chong/ Fio
Page 55 and 56: FIGURE 5. Chart for determining sta
Page 57 and 58: 18.2.6 Metal Spacing There are time
Page 59 and 60: FIGURE 6. Probe coil impedance curv
Page 61 and 62: 18.3.1 Control of Tests Important c
Page 63 and 64: ■ Laboratory Evaluations Laborato
Page 65 and 66: The reference standards are identif
Page 67 and 68: Although the conductivity of copper
Page 69 and 70: ■ Laboratory Evaluation of Alumin
Page 71 and 72: ■ Curved Surfaces Eddy current te
Page 73 and 74: FIGURE 8. Influence of cylindrical
Page 75 and 76: FIGURE 9. Influence of edge effect
Page 77 and 78: The phase angle lag θ (radian) use
Page 79 and 80: FIGURE 10. Conductivity variations
Page 81 and 82: Whatever the test material is, it m
Page 83 and 84: FIGURE 11. Conductivity change as f
Page 85 and 86: Eddy current conductivity testing (
Page 87 and 88: ■ Test Material Temperatures Temp
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18.4 PART 4. Eddy Current Testing o
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Bolt Holes Charlie Chong/ Fion Zhan
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FIGURE 12. Eddy current hole probe.
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FIGURE 13. Normalized impedance gra
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18.4.1 Reference Standards for Bolt
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FIGURE 15. Calibration block for bo
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Calibration block for bolt hole and
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18.4.2 Procedure for Bolt Hole Test
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FIGURE 16. Strip chart indications
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Other rotating eddy current test sy
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FIGURE 17. Cathode ray tube display
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Eddy Current Bolt Hole Testing http
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Eddy Current Bolt Hole Testing http
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Charlie Chong/ Fion Zhang FIGURE 18
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Continuously changing the magnitude
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Examples of: • metal thinning are
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Penetration depth, however, is only
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This location for the material test
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The probe is placed on the taper ga
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FIGURE 19. Screen display calibrati
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FIGURE 20. Impedance plane screen d
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■ Metal Spacing During fabricatio
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FIGURE 21. Eddy current reference s
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FIGURE 21. Eddy current reference s
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FIGURE 22. Eddy current impedance p
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FIGURE 23. Eddy current impedance p
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Intergranular corrosion occurs alon
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The phase angle between the liftoff
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FIGURE 24. Eddy current cathode ray
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FIGURE 24. Eddy current cathode ray
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Figure 25b shows that for aluminum
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Airframe Structures- longerons Char
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FIGURE 25. Notches and cracks at 20
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FIGURE 26. Direction of surface cra
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FIGURE 27. Cracks in first layer in
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The liftoff locus is rotated about
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FIGURE 28. Improving test results a
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FIGURE 28. Improving test results a
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FIGURE 29. Direction of surface and
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18.6 PART 6. Low Frequency Eddy Cur
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The effective depth of penetration
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■ Applications for Low Frequency
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FIGURE 31. Typical applications for
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Intergranular Corrosion Charlie Cho
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Although the low frequency, 500 Hz
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FIGURE 32. Instrument response at 5
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FIGURE 33. Cracks in second layer i
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FIGURE 34. Detection of crack in se
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FIGURE 35. Detection of crack in se
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Fatigue cracks caused by pressuriza
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FIGURE 36. Window belt crack locati
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18.6.2 Automated Fastener Hole Test
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18.6.3 Conclusion Eddy current test
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18.7 PART 7. Eddy Current Testing o
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Jet Engine Charlie Chong/ Fion Zhan
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The aviation community recognizes t
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Therefore, a minimum of two or thre
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FIGURE 37. Probability of detection
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18.7.3 Standard versus Complex Geom
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FIGURE 39. Discontinuity locations
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FIGURE 39. Discontinuity locations
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Although bolt hole and scallop geom
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■ Signal Processing Signal proces
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18.7.4 Eddy Current Probes for Jet
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FIGURE 40. Axial alignment of probe
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FIGURE 41. Footprints of eddy curre
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Many standard techniques for aircra
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FIGURE 42. Eddy current probes: (a)
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■ Wide Field Probes The term wide
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The disadvantages of the wide field
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18.7.5 Conclusion The testing of cr
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Vertical Liftoff Charlie Chong/ Fio
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Vertical Liftoff Charlie Chong/ Fio
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Harrier Jump Jet Charlie Chong/ Fio
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Charlie Chong/ Fion Zhang
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Good Luck! Charlie Chong/ Fion Zhan
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