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Evaluation of Load Damage in Steel Using The LCR Ultrasonic Technique

Don E. Bray, Ph. D., P. E.

Don E. Bray, Inc.

P. O. Box 10315

College Station, Texas USA 77842-0315

Voice/Cellular 979-492-9534

Email debray1@brayengr.com

http://brayengr.com

PVP2007/CREEP8 Conference July 22-26, 2007, San Antonio, Texas USA

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Schematic of LCR Probe

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Beam Profile for LCR Wave

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Interrogation Area for LCR (from

Bray and Tang, 2001)

Wd

EnergyDistribution

Figure 3. Illustration of the penetration energy distribution for LCR wave.

w - distance between two half power points on energy distribution curve

d - distance between outer surface and the peak energy point

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Tensile Specimen Used for Ultrasonic Studies

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Relationships of the LCR travel time (t) versus stress (From Tang and Bray, 1996).

7.576

7.58

7.584

7.588

7.592

7.596

0 200 400 600 800

Applied Stress (MPa)

Travel Time (us)

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Relationship of the LCR travel time (t) versus residual strain. (From Tang and

Bray, 1996).

7.578

7.58

7.582

7.584

7.586

7.588

7.59

7.592

7.594

7.596

0 0.025 0.05 0.075 0.1 0.125 0.15

Residual Strain (in./in.)

LCR Travel Time (us)

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fp = peak frequency fc = central frequency

fa = low half power point fb = upper half power point

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Frequency Analysis Definitions

fc = 0.5 (fb + fa)

fsk = (fp - fa)/(fb - fp)

Bandwidth = B = fb - fa

ICPIIT Houston, Texas USA 18-22 June 2001 Don E. Bray, Inc., College Station, Texas 77842-0315

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Fb and KIC (McGrath and Bray 2001)

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Setup for Present Experiments

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Table 1 Velocities (m/s) for locations on the steel bar

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Mean 3.530333333 3.630925Known Variance 0.004356 0.001024Observations 39 40Hypothesized Mean Difference 0z -8.58497236P(Z<=z) one-tail 0z Critical one-tail 1.644853476P(Z<=z) two-tail 0z Critical two-tail 1.959962787

Table 2a z-Test Comparing End and Center Data Two Sample Means for Fa

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Table 2b z-Test Comparing End and Center Data Two Sample Means for Fc

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Hydrogen Attack

• Imanaka and Suetsugu (1995) - showed just less than 10% increase in travel time for samples exposed to hydrogen.

• Kot (2001) - compares NDE methods for evaluating H2 attack. Dismisses creeping wave technique because it does not provide information about the opposite surface.

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Propagation on Inner Surface

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Arrival Time Equations

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Typical LCR Arrivals

150

75

R2-R1 mm

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Latest LCR Probe

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Using the Probe

QuickTime™ and aMotion JPEG OpenDML decompressor

are needed to see this picture.

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Conclusions

• Velocity data and frequency analysis can be used to evaluate load damage in steel parts.

• Suggests that LCR could be used to interrogate the inside wall of structures for hydrogen damage.