RU2365911C2 - Ultrasonic transducer of shear waves - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: use: for non-destructive examination of metalworks. The ultrasonic transducer contains two piezoceramic plates of shear waves installed on the mechanical impulse neutraliser, spring-actuated on the longitudinal axis, encapsulated in the metal case with the constant annular magnet, connected by the radio-frequency cable with the converter of signals providing serial measurement of time delays of echo pulses of ultrasonic shift waves, having mutually perpendicular directions of polarisation.

EFFECT: increase of accuracy and reliability of voltage determination in controllable installation.

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Description

The invention relates to the field of non-destructive testing (NDT) and can be used to control the stress state of metal structures, including the non-uniform distribution of stresses in the region of welds, in pipes, various metal profiles, oil and gas pipelines, etc.

The reliability assessment (and, therefore, ensuring safe operation) of numerous working objects is not complete without a reliable idea of their stress-strain state [1]. Among modern non-destructive testing methods, methods based on the analysis of the parameters of elastic waves transmitted through a controlled medium are developing intensively [1]. The analyzed information is averaged over the area determined by the acoustic contact zone. To control a uniaxial stress state, shear waves are used, introduced into the controlled object normally on its surface with polarization vectors oriented in two mutually perpendicular directions, and the delays (propagation time) of elastic waves are measured [2]. By known methods determine the stress state. In practice, one of the following methods for emitting and receiving elastic shear waves is usually implemented:

1) a sensor containing one emitter (receiver) is measured, orienting the sensor with a polarization vector along the current voltage, then the sensor is rotated 90 ° and the measurements are repeated,

2) use a shear wave sensor containing in one housing two shear piezoelectric transducers oriented by polarization vectors at an angle of 90 ° to each other.

The disadvantage of the first control option is the need to change the position of the sensor in the control process. This takes extra time. But a more significant drawback is the likelihood of a measurement error associated with the inaccuracy of installing the sensor in a new position and the inaccuracy of the rotation angle (other than 90 degrees).

When implementing the second method, shear converters are installed in one housing, oriented at an angle of 90 degrees, as close as possible to each other. Measurement on a small base becomes relevant when the voltage change is significant within the acoustic sensor [4], the real maximum and minimum voltages acting on the basis of the sensor will differ from the results obtained by averaging over the area of the sensor.

A complex ultrasonic sensor [3] is known, comprising a housing with three holes made in it, in which ultrasonic transducers spring-loaded along their longitudinal axis are mounted, connected by a radio-frequency cable to a signal transducer and providing simultaneous measurement of the time delays of reflected pulses of ultrasonic waves of various types from a controlled section. In this case, one of them has a longitudinal polarization of the emitted ultrasonic wave, and the other two have a transverse polarization of the emitted ultrasonic wave in mutually perpendicular directions.

This technical solution [3], as the closest in technical essence and the achieved result, is taken as a prototype.

The disadvantages of the prototype is the low accuracy of control of the complex spatial distribution of stresses. For example, in the area of the weld, the stresses vary significantly over a length of several millimeters. Averaged results obtained over the area of the sensor lead to a measurement error.

The task of the invention is to reduce the error, increase the accuracy and reliability of determining stresses in a controlled object.

The claimed technical solution is illustrated by drawings. Figure 1 shows a cutting scheme of a workpiece made of polarized thickness piezoelectric ceramics having electrodes 3. Figure 2 shows the location of the piezoelectric plates (polarization direction). Figure 3 shows a section of a shear wave sensor in a vertical plane.

To solve this problem, a sensor design is proposed, consisting of two piezoelectric ceramic emitters (receivers) of shear waves, with mutually perpendicular polarization. The plates are cut from a thick billet (the thickness is not less than the dimensions of the shear wave sensors) polarized by the thickness of the piezoceramics. The direction of cut 2 coincides with the direction of polarization 1. The cutting scheme is presented in figure 1. The thickness of the cut is determined

where V is the velocity of elastic shear waves in piezoceramics,

f _p is the frequency of the mechanical resonance of the emitted elastic waves.

After cutting on the surface of the piezoelectric plates by the method of vacuum deposition, conductive layers are applied, to which the conductors are subsequently soldered. Such a piezoelectric plate allows one to radiate (receive) shear waves perpendicular to the surface of the controlled object. As a contact layer, a viscous medium such as epoxy resin without hardener or a special contact liquid is used.

To manufacture such a sensor, a 5 × 5 mm piezo-plate is cut diagonally. Next, one of the triangular plates is rotated 180 degrees in a plane normal to its surface (in figure 2, the arrows show the direction of polarization of the piezoelectric plates 4, 5). As a result of this action, the polarization directions of the piezoelectric plates are 90 degrees with respect to each other. To obtain a stable and reliable acoustic contact, the emitting planes of the piezoelectric plates must lie at the same level. From the side opposite to the plane of the acoustic contact (Fig. 3), a radio frequency cable 7 is soldered to the piezo plates and a mechanical damper 8 is glued in the form of a pyramid. The damper is made of plasticized epoxy resin, into which a filler of tungsten balls with an average diameter of 0.05 mm is introduced in a volume ratio of 1: 1. A sufficiently high density of the material of the pyramid provides its high damping properties, and the density gradient created along the height of the pyramid reduces the effect of spurious re-reflections of elastic waves from the side faces of the mechanical damper. A density gradient is created during the hardening of the resin. The sensor is shielded by an all-metal screen 10. A permanent magnet 6 is installed inside the metal screen 6. Such a magnet together with the spring 9 provides a fixed acoustic contact with a controlled structure, which also increases the accuracy of measuring stresses in the object.

The ultrasonic sensor operates as follows. A thin layer of viscous liquid is applied to the surface of the area to be monitored, a sensor is installed in such a way that the direction of polarization of one of the piezoelectric plates of the ultrasonic transducer is parallel to the acting voltage. Then, electrical pulses are fed through the radio frequency cable to the piezoelectric plates 4, 5, which alternately emit shear wave pulses perpendicular to the surface of the controlled sample. The same piezoelectric plates receive elastic waves, which again are converted into electrical impulses. After this, the time delays of the reflected pulses of the ultrasonic waves emitted by the piezoelectric plates 4, 5 are measured in turn. Using the measured delays, using known methods and equations of acoustoelasticity, the stresses in the controlled area are determined.

Information sources

1. Non-destructive testing: Handbook / Ed. V.V. Klyueva. M .: Mechanical Engineering, 2004.V.4 - 736 p.

2. RF patent No. 2057330, IPC G01N 29/00, Acoustic method for determining internal mechanical stresses in solid materials / V.T. Vlasov, B.N. Marin, E.S. Yurchuk, Yu.A. Korovkin, V.E. .Udartsev, published 1996.03.27.

3. RF patent No. 2240552, IPC G01N 29/04, Integrated ultrasound sensor / A. L. Uglov, V. M. Andrianov, O. Yu. Batalia, published 2004.11.20.

4. Vinokurov V.A. Welding strain and stress. - M.: Mechanical Engineering, 1968 .-- 236 p.

Claims (4)

1. An ultrasonic sensor containing two piezoelectric shear wave plates mounted on a mechanical damper, spring-loaded along its longitudinal axis, enclosed in a metal housing with a permanent ring magnet, connected by a radio frequency cable with a signal converter, which provides an alternate measurement of the time delays of reflected pulses of ultrasonic shear waves, having mutually perpendicular directions of polarization. 2. The ultrasonic sensor according to claim 1, characterized in that the shear wave transducers are obtained from a square shear wave piezoelectric plate, cut diagonally. 3. The ultrasonic sensor according to claim 1, characterized in that the triangular piezoelectric plates are rotated 180 ° with respect to each other in a plane normal to their surface and glued to a mechanical damper. 4. The ultrasonic sensor according to claim 1, characterized in that the spring and the ring magnet create a constant clamp and provide a fixed acoustic contact.

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