SU1388772A1 - Method of controlling quality of acoustic contact in ultrasonic checking of an article - Google Patents

Abstract

The invention relates to the field of non-destructive testing and is aimed at increasing the authenticity of the control of the acoustic contact (AK) between the piezo transducer (P) of the flaw detector and the product being monitored. The essence of the proposed method lies in the fact that the state of AK is judged by the ratio of input acoustic impedances P to the monitored product in the zone AK, and the ratio of input acoustic impedances is determined by the measured input electrical impedance at the antiresonant frequency taking into account the design formula, .1 Il . i cl

Description

The invention relates to non-destructive testing of products and can be used in the ultrasonic flaw detection of various materials and products.

The aim of the invention is to increase the reliability of control of the acoustic contact by taking into account the value of the coefficient of the electromechanical coupling of the piezoplate.

The drawing shows a functional, national scheme of the device for implementing the proposed method.

The device contains a harmonic signal generator 1 whose frequency is equal to the antiresonant frequency of the piezoplate 2 of the piezoelectric transducer with switches S and S of the flaw detector 3, the voltage indicator 4, the voltage ratio meter 5 and the load resistor 6, Position 7 denote the product.

Monitoring the state of the acoustic contact is carried out as follows.

After installing the piezoelectric transducer of the defectoscale 3 on the monitored product 7, it is disconnected from the receiving and transmitting path of the flaw detector 3 and connected to the acoustic contact control device, the switches S, and S are switched to the position a. From generator 1 to the piezoplate 2, an excitation signal is applied. In this case, the ratio meter 5 records the ratio Ui / U J of the amplitude values of the voltages at the output of the generator 1 and the load resistor 6, the resistance R, which is recorded by the voltage indicator 4. The module Z of the input electrical impedance at the antiresonance frequency of the piezoplastic 2 transducer can be determined by the measured ratio and, / and, since

 R (

uj and.

about.

(I)

On the other hand, it is known that the module Z thus measured. The input electrical impedance is related to the ratio Z of the input acoustic impedances of the monitored product 7 and piezoplate 2 with the following functional dependence: I

TO,

4K:

where K, is the experimental ratio of the input acoustic impedances of the product and piezo-pastaine;

K is the coefficient of electromechanical coupling of piezomaterial piezopastins; K - damping coefficient

piezoplates; x, „- 1/2 | G D ,,. f CCI-, respectively, anti-resonant frequency and static capacitance of a piezoplate.

The disturbance of the acoustic contact between the product 7 and the piezoplate 2 of the transducer, by the nature of the effect on the input electrical impedance of the piezoplate, is equivalent to a decrease in the input acoustic impedance Zl of the material of the product 7 in the acoustic contact zone. Therefore, the relative deviation (coefficient 1) of the experimentally determined ratio K from the known value of the ratio Z, / Z about the acoustic wave resistances of the material of the tested product 7 and the piezoplate 2 of the diezoelectric transducer can be represented as

Tk

Zj / Zo - K

z: 7z

(3)

which allows to judge the reliability of the acoustic contact of the piezo transducer - controlled product. Taking into account (2, the fusion (3) takes the following form:

. Zo G 4 k1 1

1. (z; 7x ;: r- -J

(four)

The coefficient of damping is the passport parameter of the piezoelectric transducer and can be determined experimentally.

A sign of the absence of disturbances in the acoustic relation ZJ / Z and the a priori known state of the wave acoustic impedances of the object and piezoelectric transducer studied is fk

A sign of complete absence of acoustic contact is the value

The value of the coefficient j depends

only on the state of acoustic contact of the piezoplates of the transducer and the product under test, as well as on the accuracy of determining the parameter Z, Xo K, K, is practically independent of the state of the surface and the profile of the rear side of the product 7, which makes it possible to increase the accuracy of control of the acoustic contact.

If it is required to estimate the state of acoustic contact, for example, between piezoelectric plate from piezoelectric ceramic PZT-19 and an aluminum product (Zo / Zj 1.83, kt 0.45, Xo 25o ", R" 25th Ki - 0.1), then (2), expression (4) can be rewritten as follows:

1-1.83

0,

 pg - CC

0.1 (5)

Thus, indicator 4, connected to the output of the gauge 5 of the ratios and, and, and, with appropriate calibration of the scale, records the final result, i.e. the coefficient is taq, which makes it possible to judge the state of the acoustic contact. Studies carried out by the method of DGS diagrams using the UD-23UM flaw detector on a standard plexiglas sample showed that the CA value, corresponding to a satisfactory contact, is of the order of 0.1. Observance of a condition of 0.1% of the error due to the contact napshen is about 15% of the nominal value of the working error.

Claims (1)

Invention Formula The method of controlling the quality of acoustic contact with ultrasonic testing of products, which are fixed in that they install a piezoelectric transducer on the product, excite the ultrasonic oscillations in the product by applying an electrical signal to the piezoelectric transducer plate, measure the electrical parameters of the piezogastine, which determine the quality of the acoustic contact, differing from that, in order to increase the reliability of the control, the modulus of its input is measured as an electrical parameter of a piezoplate Nogo electrical impedance at the antiresonance frequency, and quality of acoustic contact is determined by the value of v, defined by the expression of 4Kt   -zT where is z WITH - the module of the input electrical impedance of the piezoelectric transducer of the piezoelectric transducer mounted on the product; to. where is z - coefficient of electromechanical communication of piezo-material piezoplates; Zg and Z are the acoustic wave impedances, respectively, of the piezoplate materials and the product;  Z -the damping coefficient of the piezoplates, X .o l / 2Trf GC; f, Cd-, respectively, the antiresonant frequency and the static capacity of the piezoplate. five/  R ha / s -f- 1 S2 j