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Article No. VK-IND01

IND01 Non-Destructive Testing (NDT)

To localize and determine the size of discontinuities in accordance with the pulse echo method

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Subject matter of the experiment

In order to localise and determine the size of discontinuities in accordance with the pulse echo method, the ultrasonic device is calibrated for a normal ultrasonic probe. For this, a DGS diagram (distance-gain-size) is compiled and a horizontal evaluation line is set in the DGS diagram for a series of equally sized replacement reflectors of different depths using time gain control (TGC).

Keywords: Sound velocity, reflection, pulse echo method, discontinuity, replacement reflector, normal probe, DGS diagram, time gain control

Theoretical and practical aspects of the experiment

For ultrasonic tests according to the pulse echo method with perpendicular sound coupling, standard normal probes are used. The localisation of discontinuities is here carried out by reflection of the sound wave, with the time of flight of acting as a measure of the depth of the discontinuity. In contrast, an exact determination of size is usually problematic due to material attenuation and sound field characteristics. The size of discontinuities of large spatial extension can be determined by scanning. The size of small discontinuities is determined by comparison with idealised replacement reflectors from a distance-gain-size diagram. In the experiment, such a DGS diagram is to be produced using a test block with defined replacement reflectors (drilled holes of different size and depth).

Results

In the DGS diagram, the echo amplitudes of the replacement reflectors are presented in relation to the amplitude of an infinitely extended reflector in the spacing zero and its distances x relative to the zero field length xN. For the series of the diagonally arranged, equal-sized replacement reflectors, a horizontal evaluation line was determined and entered using TGC (time gain control).

Amplitude scan with echos from a discontinuity and the test block bottom

Amplitude scan with echos from a discontinuity and the test block bottom


Measurements at the test block with 2 MHz ultrasonic probe

Measurements at the test block with 2 MHz ultrasonic probe

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