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Ultrasonic Testing (UT)

Ultrasonic testing is one of the elemental NDT methods. UT enables to detect presence of the internal discontinuities even if they are in high depth under surface. UT is able to detect imperfection in furthest positions.

UT is used mainly for inspection of the forged products (forgings, rods, plates, ...), welds and castings. The method has an important role in inspection of nonmetal materials - plastics, composites; ... The advantage of the UT is possibility of the process automation especially in case of simply shaped semiproducts (like pipes, plates, rods etc.). The ultrasonic testing is able to detect planar or volumetric imperfections in contact with surface as well as under the surface. Another advantage is, that inspection result is displayed immediately.

Physical background

The principle of the ultrasonic testing operates with the fact, that the solid materials (metallic as well as nonmetallic) are good conductors of acoustic waves. Ultrasound waves emitted into the material are reflected by any interface in the material - so also from the internal imperfections (inhomogeneity). The minimal size of detectable imperfection is in reciprocal proportion to the frequency of the wave. Frequencies from 0,5MHz to 25MHz are used for NDT applications.

The development of the UT testing methods is still under progress. Current testing methods are improved by usage of the digital equipment, possibility of connection with computer allows computer aided evaluation, or usage of special probes. Completely new approaches to the testing are being developed too.

One of the new approaches is the PHASED ARRAY technique. This method is based on usage of a probe set, in combination with special electronic circuits, which could shape the beam. PHASED ARRAY probe consist of the set of miniature piezoelectric transducers. Setting of output parameters for each transducer separately forms the beam. This equipment has standard output signal in shape of the A-scan.

One of the basic advantages is, that only one probe could generate the beam with different output angle. This allows covering much bigger area of the examined part without any move with probe. It results into the spatial resolution improvement and finally into more exact evaluation of the imperfection.
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