5 Ande Course - Tofd
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Transcript of 5 Ande Course - Tofd
ANDE Course: TOFDANDE Course: TOFD
September 24, 2009
Time‐of‐Flight Diffraction (TOFD)
Typical A‐Scan
TOFD PrincipleTOFD Principle
Incident wave
DiffractedWave
Incident wave
Reflected wave
Defect
Specular – highly direction dependent
DiffractedWaveWave
Nonspecular ‐ independent of angle
L‐TOFD and S‐TOFD
Geometric Theory of Diffraction (GTD)
Bottom tip Top tip
Diffraction (GTD)
Optimum angles for P‐wave detection of symmetrically placed crack with negligible attenuation
Optimum angles for SV‐wave detection of symmetrically placed crack
Ray based (high frequency and far‐field)
Diffraction coefficients are derived to be used like reflection coefficients
Mode conversion considered
Top and bottom crack tips treated independently
Fails at shadow boundaries
TOFD: BasicsTOFD: Basics
• Wide beam widths for dtransmission and reception
• Short pulse widths (broad band)
• Cracks in thick samples (non‐overlapping signals) are simpler but for atten ationattenuation
• Cracks in thin samples (overlapping signals) need special signal processingspecial signal processing tools
• B‐scans are more useful than A scansthan A‐scans
TOFD: B‐Scan
B‐scan simulation using ray method for different relative positions of a vertical embedded crack in the (a) right half, (b) middle, and (c) left half of the probe, as well as the corresponding (d) B‐scan simulation.
Here 1, 2, 3, and 4 correspond to lateral, defect echo from the top, defect echo from the bottom, and backwall echo, respectively.
B‐Scan Examples
TOFD B‐scan image components for a 3.25 mm vertical defect in a 10 mm Al sample
TOFD is sensitive to all defectsincluding volumetric defects.
TOFD imaging of defects in weldTOFD imaging of defects in weld
TOFD B‐Scans at 5 MHz and 10 MHz5 MHz 10 MHz
Comparison of experimental and simulated B‐scan images . Figures (a), (b), (c), and (d) are experimental B scans over the defects of sizes 6.5, 3.25, 1.6, and 0.8 mm, respectively.
Figures (e), (f), (g), and (h) are simulated B scans over the same defects.
TOFD: B‐Scans of Inclined Cracks
Measuring the defect size (L) and the angle of inclination (θ) for an inclined defect
Comparison of experimental B scans with simulated B scans on a 10 mm thick aluminium sample, with 60° inclined defects of sizes (L), (a) 6.5 mm and (b) 3.25 mm
TOFD: B‐Scans of Inclinedof Inclined Cracks
Variation of defect curve shape for different angle of inclination (θ) ,from horizontal defect (a) to vertical defect (j), for a 6 mm defect
in a 10 mm thick aluminum plate
Baskaran et al., Journal of Pressure Vessel Technology, Vol. 127, pp 262‐268 (2005)
“TOFD” using PA Probes
βcos)( 12 UTUTHcrack −=
2UT
1UT
Relative arrival time technique (RATT) ‐ Crack height based on crack tip and corner trap signals
coscos ββ UTUTH =
Angle of arrival time technique (AATT) ‐ Crack height based on crack tip and corner trap signals
at distinct angles
Detection of inner surface‐breaking cracks using mode conversion
1122 coscos ββ UTUTHcrack −=
More inspection options with PA Probes
Detection of embedded cracks using mode conversion
ReferencesReferences
Baskaran G K Balasubramaniam C V Krishnamurthy and C L Rao (2005) A RayBaskaran, G, K. Balasubramaniam, C.V. Krishnamurthy and C.L. Rao (2005) A RayBased Model for the Ultrasonic Time of Flight Diffraction Simulation of Thin WalledStructure Inspection. ASME Trans. Journal of Pressure Vessel Technology, 127(3), 262-268.
Baskaran, G., K. Balasubramaniam and C.L. Rao (2006) Shear-wave time of flightdiffraction (S-TOFD) technique. NDT & E International, 39, 458-467diffraction (S TOFD) technique. NDT & E International, 39, 458 467
Mondal , S (2000) An overview TOFD method and its Mathematical Model, http://www.ndt.net/article/v05n04/mondal/mondal.htm, NDT.net. 5 ,No. 04.
Ogilvy J A and J A G Temple (1983) Diffraction of Elastic Waves by cracks: Ogilvy, J. A. and J. A. G. Temple (1983) Diffraction of Elastic Waves by cracks: Application to Time of Flight Inspection. Ultrasonics; 7,259-269.
Temple, J. A. G. (1983) Time-of-flight inspection: theory. Nucl. Energy, 22, No. 5, Oct., 335-348.