UT - FBH: DGS curves

Global overview:

 

Contact Probes 1.0 MHz 20x22 mm 2.0 MHz 20x22 mm >4.0 MHz 8x9 mm
SV45° Done Done  
SV60° Done Done Done

 

Specific cases 2.0 MHz, Ø24mm 2.0 MHz, Ø24mm
P0°

Contact

very large FBH

Immersion

FBH in water

 

CONFIGURATION

DGS (Distance Gain Size) or AVG (Abstand Verstaerkung Gröesse – in german) curves from manufacturer (Krautkrämer) are compared to simulation data for some probes. For each FBH diameter, this steel specimen with 11 FBH at different depths has been modeled:

 

 

For each hole, the maximum amplitude of the specular echoes of the FBH is measured relatively to a calibration hole. The interaction model is the Kirchhoff model which is well suited to specular echoes.

The measurements have been made with the following contact probes:

 

Frequency Crystal Mode Calibration flaw Calibration depth
1.0 MHz 20x22 mm SV45° Ø1.5 mm FBH 100 mm
20x22 mm SV60° Ø1.5 mm FBH 100 mm
2.0 MHz 20x22 mm SV45° Ø3 mm FBH 100 mm
20x22 mm SV60° Ø1.5 mm FBH 200 mm
4.0 MHz 8x9 mm SV60° Ø0.5 mm FBH 30 mm

 

A specific experiment has been performed with a Ø24 mm probe in P0° mode. It is first used with great diameter reflectors, then with FBH of different diameters at different depths in water:

 

Frequency Crystal Mode Calibration flaw Calibration depth
2 MHz Ø24 mm P0° Ø » 1 mm FBH 100 mm
Ø24 mm Ø2.4 mm FBH 590 mm

 

RESULTS

 

sincle ElEment contact probe 1.0 MHz, 20 x 22 mm, SV45°

For the 20 x 22 mm contact probe at 1 MHz, the SV45° mode is used for inspection. The input signal frequency is 1.0 MHz, with 55% bandwidth and 0° phase.

The acoustic focusing depth is 25 mm, deduced from the simulated beam as illustrated below, which corresponds to a 35 mm distance.

 

 

The results are calibrated versus the Ø1.5 mm FBH at 100 mm depth.

 

 

There is good agreement between simulation and measurement. Discrepancies higher than 2 dB only appear for small FBH located above the focal spot.

 

single ElEment Contact probe 1.0 MHz, 20 x 22 mm, SV60°

For the 20 x 22 mm contact probe at 1 MHz, the SV60° mode is used for inspection. The input signal frequency is 1.0 MHz, with 55% bandwidth and 0° phase.

The acoustic focusing depth is 15 mm, deduced from the simulated beam as illustrated below, which corresponds to a 25 mm distance.

 

 

The results are calibrated relatively to the Ø1.5 mm FBH at 100 mm distance.

 

 

The curves show a good agreement between simulated and experimental data with often less than 2 dB discrepancies.

 

single ElEment contact probe 2.0 MHz, 20 x 22 mm, SV45°

For the 20 x 22 mm contact probe at 2 MHz, the SV45° mode is used for inspection. The input signal frequency is 2.0 MHz, with 41% bandwidth and 75° phase.

The acoustic focusing depth is 53 mm, deduced from the simulated beam as illustrated below.

 

 

The results are calibrated versus the Ø3 mm FBH at 100 mm depth.

 

 

There is an overall good agreement with often less than a 2 dB discrepancies. For small FBH above the focal spot the difference is up to 6 dB.

 

single ElEment contact probe 2.0 MHz, 20 x 22 mm, SV60°

For the 20 x 22 mm contact probe at 2 MHz, the SV60° mode is used for inspection. The input signal frequency is 2.0 MHz, with 40% bandwidth and 0° phase.

The acoustic focusing depth is 36 mm, deduced from the simulated beam as illustrated below, which corresponds to a 63 mm distance.

 

 

The results are calibrated relatively to the Ø1.5 mm FBH at 200 mm distance.

 

 

The curves show a good agreement between simulated and experimental data for FBH deeper than the focal depth. For FBH which depth is smaller than the acoustic focusing depth, CIVA over-estimates the echo: for example, for Ø6 mm, Ø8 mm or Ø12 mm FBH, the discrepancy is around 5 dB.

 

siNgle ElEment contact probe 4.0 MHz, 8 x 9 mm, SV60°

For the 8 x 9 mm contact probe at 4 MHz, the SV60° mode is used for inspection. The input signal frequency is 4.0 MHz, with 42% bandwidth and 151° phase.

The acoustic focusing depth is 12 mm, which corresponds to a 21 mm distance. It has been deduced from the simulated beam illustrated below, .

 

 

The results are calibrated relatively to the Ø0.5 mm FBH at 30 mm distance.

 

 

CIVA simulation data are close to Krautkramer data with less than 2 dB difference for FBH deeper than the focal depth. For FBH no deeper than the focal depths, CIVA over-estimates the echoes by 2 dB for small (Ø0.5 mm) FBH and large (Ø10 mm) FBH and up to 8 dB for medium (Ø4 mm) FBH.

 

single element contact probe 2.0 MHz, 24 mm, P0°

For the 24 mm contact probe at 2 MHz, the P0° mode is used for inspection. The input signal frequency is 2.0 MHz, with 59% bandwidth and 0° phase.

The acoustic focusing depth is 51 mm, deduced from the simulated beam illustrated below.

 

 

The results are calibrated versus the great diameter reflector at 100 mm depth.

 

 

A very good agreement is obtained in P0° mode inspection. CIVA estimates the echoes with less than 1 dB difference with Krautkramer data. It can be noted than all the FBH of this experiment are deeper than the focal spot.

 

single element contact probe 2.0 MHz, 24 mm, P0° in water

For the 24 mm probe at 2 MHz, the P0° mode is used for inspection in water. The input signal frequency is 2.0 MHz, with 40% bandwidth and 0° phase.

The acoustic focusing depth is 184 mm, deduced from the simulated beam as illustrated below.


 

 

The results are calibrated versus the Ø2.4 mm FBH at 590 mm depth.

 

 

A good agreement is obtained in P0° mode inspection. CIVA estimates the echoes with often less than 2 dB difference with Krautkramer data. Close to the focal depth, discrepancy is up to 4 dB.

CONCLUSION

For each FBH diameter, there is a very good agreement for the FBHs echoes amplitudes in the far field where the specular echo amplitude linearly decreases with the depth on the figures, but there are discrepancies for the highest diameters at the smallest depths.

 

Continue to Conclusion and discussion about the limitations

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