UT - SDH: Side Drilled Holes at different depths and Phased-Array probes

This validation experiment also deals with Ø 2 mm SDH at different depths. The measurements are performed upon the planar steel block containing Ø 2 mm SDH from 4 to 60 mm depth with 4 mm steps. As a reminder the steel parameters are: density 7.9, P waves velocity: 5900 m/s and SV waves velocity: 3230 m/s. Since the SDH are inspected perpendicularly to their axis, the SOV interaction model is considered.

The following picture presents the mock-up that is used.

 

 

The 2 phased array probes that are used in Pulse Echo mode are:

 

 

Phased array contact probe of 28 ElEments with 0.7 mm pitch at 5.0 MHz

For the phased array contact probe at 5 MHz, different focal laws are used with SV waves for inspection with 28 active elements out of 48. The first experiment uses a focusing at 20 mm depth and a beam angle from 45° to 60°. The second one uses a beam steering of 45° and a focusing from 4 to 24 mm depth.

 

The acoustic focusing depth is 20 mm for the SV45° beam steering, deduced from the simulated beam as illustrated below.

 

 

The results from the first experiment show the influence of the beam orientation.

The results are calibrated versus the Ø2 mm SDH at 20 mm depth for SV45° waves focused at 20 mm.

 

 

 

 

For all the angles, the amplitudes of the echoes are well estimated with less than 2 dB discrepancies.

The results from the second experiment show the influence of the focusing depth.

The results are calibrated versus the Ø2 mm SDH at 20 mm depth for SV45° waves focused at 20 mm.

 

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With delay laws focusing at different depths, there is a good agreement. The maximum discrepancy is 3 dB for SDH at 8 mm depth and focusing at 20 mm depth, and less than 2 dB in all the other cases.

 

Phase array contact probe of 20 ELEMENTS with a 0.7 MM PITCH at 5.0 MHZ

The phased-array probe is used to generate a P45° beam at 5 MHz with 20 active elements out of 48. The acoustic focusing depth is 20 mm, deduced from the simulated beam as illustrated below.

 

 

The results are calibrated versus the Ø2 mm SDH at 20 mm depth.

 

 

With less than 1 dB discrepancy, there is a very good agreement between experiment and simulation.

 

Results show a very good agreement with less than 2 dB difference in the cases of SDH and contact phased-array probes.