DE2701054C3 - Procedure for the determination of defects in materials with high ultrasound scattering - Google Patents

Description

The invention relates to a method according to the preamble of the claim. The increasing application Austenitic materials, especially those of higher wall thicknesses, throw up in the ultrasonic flaw test big problems. The useful displays are accompanied by scatter displays from the structure The amplitudes this interference structure can, depending on the size of the error to be detected, the amplitude of the Reach or even exceed the useful signal.

In the course of previous investigations it was attempted to increase the useful signal with the help of communication technology methods compared to the scattered background. These are the correlation and the inverse filtering. A known useful signal are increased compared to white noise, with inverse filtering it is time-dependent overlapping signals separated according to arrival time and amplitude

Both methods did not provide any significant success because the structural noise is a coherent noise, d. H. has the same frequency content as the useful signal

Ultrasonic scattering

If you put an ultrasonic pulse into a metallic sample, the energy of the wave increases with Path used up by absorption and scattering. In the structural area covered by the sound beam, the Crystallites stimulated to vibrations that overlap and spread out in all directions. the Scattered energy can thus also be received by the sending probe as a function of time.

The measurement setup and the general ones that are customary when determining the structure by means of ultrasonic scattering The course of the curves obtained is in DE-PS 25 11 750 described.

Measurement structure

The apparatuses used to carry out the measurements are shown in FIG. I and 2 shown as a block diagram slide. Fig. 1 shows the general basic structure. The transceiver unit with the test head PK is via an impedance matching with the

Data processing system connected. The analog signals are digitized in an AD converter ADC with a maximum conversion rate of 100 MHz and added up in an average value computer

The resulting signal can be digitized in the Form can be put on punched tape or read out via a teletype. Furthermore there is the possibility to pick up the signal again in analog form and to display it using an X-Y recorder or, after digitizing again, to be processed in the connected computer.

In the case of location averaging, an ultrasonic pulse device with analog outputs for the signal in high-frequency The sample is used under the test head via a stepper motor-controlled Slide moves

The frequency averaging is done in a frequency generator a sinusoidal voltage is generated, the frequency of which in the attached wobbler in preselectable steps is varied by the set center frequency. Above the downstream burst generator, power amplifier and probe, the ultrasonic pulse reaches the sample, which in this case is fixed by the Receiving amplifiers are fed the signals into the data processing system outlined above

Determine the experimental conditions

A central problem is the choice of suitable test parameters. When averaging the location, the Probe position can be varied over the reflector of interest; in the case of frequency averaging, however, is to change the excitation frequency to suit the center frequency.

The parameters - height Ar of the stroke, Ay of the angle or width Afae.% Frequency interval - can be obtained from the corresponding echo dynamics curves (FIG. 3).

The useful signal drop is plotted as a function of the probe position relative to the center of the error or the excitation frequency or the angle of incidence.

If one considers the possible ranges of oscillation, e.g. B. at 6 dB drop, there is also the dependency the height of lift from the depth of the defect. As given by the sound field structure, the Lifting height for the shallower defect depth is smaller than for the defect of greater depth.

The relationships in frequency averaging are very similar. Here comes as an additional parameter add the width of the excitation pulse; with increasing pulse width, the dynamic curves getting closer.

Measurements

The representation of the measurement results for the location averaging is shown in Fig. 4 for the testing of coarse grains austenitic materials.

Which was only determined by adding up the interference patterns at two different probe positions The curve is still identical to the first display. A fourfold addition does not show any either significant improvements. However, if one goes over to 32-fold or 64-fold summation, this is Back wall echo sequence can already be clearly displayed up to the 4th echo.

For this purpose 4 sheets of drawings

Claims (1)

Claim: 27 Ol 054 Procedure for the determination of defects in materials with high ultrasound scattering by measuring the Sound pressure amplitude as a function of the travel time of the sound waves in the sample and Improvement of the signal-structure-noise ratio, characterized in that the Interference pattern of the coherent scattering background due to local changes and / or changes in the angle of incidence of the sounder and / or change of the sound frequency is changed and the corresponding values of the propagation time-dependent sound pressure amplitudes of at least two of the interference pattern changed in this way are summed up.