SU987512A2 - Acoustic method of flaw detection - Google Patents

Description

(54) ACOUSTIC DETECTION METHOD The invention relates to a destructive testing and can be used to control the integrity and uniformity of products. According to the main author. St. No. 819709, a known acoustic method of flaw detection, is that in controlled and reference objects, resonant acoustic oscillations are excited, the frequency difference between the main resonant peak corresponding to the reference sample and the additional resonant peak judged by the defect sizes Cl are determined. The sensitivity of the known method is limited by the possibility of separate registration of two closely spaced resonant peaks. If there is a small size defect in the product, adjacent frequency peaks cannot be separately registered, which reduces the sensitivity of the known method. The purpose of the invention is to increase the sensitivity of the control. The goal is achieved by the fact that, according to the acoustic method of defectoscopy, a static non-uniform field of mechanical stresses is preliminarily created in the reference and controlled samples. FIG. 1 shows a scheme for implementing the method, FIG. 2 main and additional resonant peaks b, in accordance with reference and controlled samples, respectively, the presence in them of a non-uniform field of static mechanical stresses. The scheme of the implementation of the method contains a series-connected generator of ultrasonic vibrations, radiating piezoelectric converter 2, rod-conductor 3, controlled sample 4, core-conductor 5, receiving transducer 6, amplifier 7, driver of 8 standard pulses, frequency meter 9 connected to generator 1. Loader unit 10 mechanical ki is connected to the rod mi zvukoprovodi 3 and 5.

The method is carried out as follows.

Using a loading unit 10, cores 3 and 5 are connected to sample 4 with a force of 5-2 O N. Due to this, a static non-uniform field of mechanical stresses is created in the sample. The oscillator 1, whose oscillation frequency varies within pre-selected limits, excites a piezoelectric transducer 2 mounted on a rod-duct 3. Oscillations from the piezoelectric transducer 2 propagate along the sound-operation rod 3 and excite oscillations of sample 4 recorded through the core-sound conductor 5 by the transducer 6. When the frequency of the oscillator 1 coincides with the resonant frequencies of the sample, the amplitude of the oscillations of the latter increases sharply, which leads to an increase in electrical voltage on the piezoelectric transducer 6. This is The stresses are amplified by the amplifier 7i and fed to the driver 8, which produces a standard pulse that starts the frequency counter 9,

Thus, at the moment of passage through the resonance, the resonant frequency is recorded by a frequency meter 9.

When interacting, the field of dynamic forces occurring at resonant

oscillations in a sample with a non-uniform field of static mechanical stresses in it, in the frequency spectrum of the samples, an additional resonant peak b or v occurs, whose frequency differs from the frequency of the main resonant peak a by an amount exceeding the width of the resonant peaks (Fig. 2).

The presence of a defect leads to a change in the difference between the main and additional frequency peak by the value of Af ,. depending on the size of the defects.

The use of the invention allows to increase the sensitivity of the control and detect defects of small sizes.

Claims (1)

1. USSR author's certificate No. 819709, cl. G 01 N 29 / O4, 1979 (prototype).