RU1770892C - Method of locating surface acoustic wave source - Google Patents

Abstract

The invention relates to ultrasonic testing of materials and can be used to determine the location of a surface acoustic wave source in one- and two-dimensional objects, as well as on the surface of three-dimensional objects. The purpose of the invention is to improve the accuracy of determining the location of a surface acoustic wave source. The location of the source of acoustic waves is determined by the average value of the coordinates of the absorber of acoustic vibrations, when located in which the absorber, the amplitude of the acoustic vibrations changes sharply, recorded by a directional receiver of acoustic waves, 6 ill.

Description

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The invention relates to the field of ultrasonic monitoring of materials and can be used to locate a source of surface acoustic waves, in particular a source of acoustic emulsion (AE), in one- and two-dimensional objects, as well as on the surface of three-dimensional objects.

There is a known method for determining the coordinates of an acoustic emission source, which consists of installing non-directional acoustic wave receivers connected to electronic equipment on the surface of the object, determining the moments of arrival of acoustic emission pulses to each of the receivers, and then using the connection between the wave velocity and its time the movement from the source to the receiver and the distance from the source to the receiver determine the coordinates of the acoustic emission source.

Closest to the technical nature of the proposed method is a method for determining the location of a surface source of acoustic waves, which consists in. that with the help of a directional receiver of acoustic waves, acoustic emission signals are perceived, the receiver is oriented so that the axis of its radiation pattern passes through the source of surface acoustic waves, the receiver is moved along the contour of the controlled area in such a way. so that the axis of the radiation pattern and the tangent to the contour are a right angle, the lines are fixed that coincide with the axis of the radiation pattern at the time of registration of acoustic emission signals, and the coordinates of the emission source are determined as the intersection point of these lines.

A disadvantage of the known method is its low reliability in the presence of

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two or more sources of AE on a controlled surface.

The aim of the invention is to improve the accuracy of determining the coordinates of a surface wave source by eliminating errors in the presence of several sources of AE.

The goal is achieved in that using a directional receiver of surface acoustic waves, waves from the source are recorded and the receiver is oriented so that its axis of the radiation pattern passes through the source of surface acoustic waves. An absorber of surface acoustic waves is placed on the axis of the radiation pattern of the receiver, it is moved along this axis, and the location of the source of surface acoustic waves is judged by the average coordinates of the points of the absorber, at which the amplitude of the received oscillations changes sharply.

In FIG. Figures 1-6 show the arrangement of the receiver, absorber, and AE source for their various combinations.

A directional receiver of acoustic surface waves 2 mounted on the surface of the monitored object 1 is connected to a measuring device, for example, an oscilloscope (not shown), with which the amplitude of the surface acoustic wave can be measured. The axis of the radiation pattern 3 of receiver 2 passes through the source of acoustic surface waves 4 and the absorber of acoustic surface waves 5, the X axis, parallel to the axis 3 of the radiation pattern of receiver 2, serves to more clearly demonstrate the coordinate of the intersection point of the axis of the radiation pattern 3 of receiver 2 and the one closest to it the boundaries of the acoustic contact zone of the surface wave absorber 5 and the controlled object 1.

The method is implemented as follows.

During cyclic loading of a steel plate 1 with a thickness of 3 mm, a fatigue crack appeared in it, which is a source of acoustic emission signals. At a selected thickness of the plate, acoustic emission waves in it can propagate in the form of normal and surface waves. Thus, a crack is a source of surface waves. A prismatic piezoelectric transducer is installed on the plate, which is a directional receiver of acoustic surface

waves 2. It is oriented so that its radiation pattern 3 passes through a source of surface acoustic waves 4; the amplitude of the oscillations perceived by the receiver will be maximum. In this way, it is established in which direction the source of surface acoustic waves is.

Then, an absorber of surface acoustic waves 5 is placed on the surface of object 1. An absorber is a body having certain boundaries of the acoustic contact zone with the surface of the object being monitored 1. For example, the absorber may be a steel plate whose surface facing the surface of object 1 is coated with contact liquid (oil). The absorber is placed on the axis 3 of the radiation pattern of the receiver of surface waves 2. In this case, two cases are possible.

In the first case, the absorber 5 is between the emission source 4 and

the receiver 2 (figure 1). This situation is recognized by a sharp decrease in the amplitude of the surface acoustic waves perceived by the receiver when the absorber 5 is mounted on the surface of the object 1.

In order to determine the position of the source 4 in this case, the absorber 5 is removed from the receiver 2 along the axis 3. At the moment when the source 4 is between the receiver 2 and the nearest acoustic contact zone of the absorber 5 and object 1 (Fig. 2), the amplitude of the surface acoustic waves perceived by the receiver 2 will increase sharply. At this moment, Xi is determined - the coordinate of the intersection point of axis 3 and

the boundary of the acoustic contact zone of the absorber 5 and object 1 closest to the receiver 2 (for convenience, the coordinate Xi is indicated on the X axis parallel to axis 3).

Then the absorber 5 is moved in the opposite direction, i.e. bring it closer to receiver 2 along axis 3 until the boundary of the acoustic contact zone of the absorber 5 and object 1 closest to the receiver is between the source of surface acoustic waves 4 and receiver 2 (Fig. 3). At this moment, when the amplitude of the surface acoustic waves perceived by the receiver 2 decreases sharply, the coordinate X2 of the point of intersection of the axis 3 with the nearest acoustic contact between the absorber 5 and object 1 is determined (for convenience, also shown on the axis

X parallel to axis 3).

The location of source 4 is defined as the average between Xi and X2.

In the second case, the absorber 5 is located on the surface of the object 1 so that the source 4 is located between the absorber 5 and the receiver 2 (Fig. 4). This situation is recognized by the fact that the installation of an absorber on the surface of an object does not change the amplitudes of the surface acoustic waves perceived by the receiver. In this case, the absorber 5 is brought closer to the receiver 2 along axis 3 until the amplitude of the surface acoustic wave perceived by the receiver decreases sharply. This will happen at the moment when the boundary of the acoustic contact zone of the absorber 5 and object 1 closest to the receiver 2 is between the source 4 and the receiver 2 (Fig. 5). At this moment, the coordinate Xt of the intersection point of the axis of the radiation pattern 3 and the boundary of the acoustic contact zone of the absorber 5 and object 1 closest to the receiver is determined. Then the absorber 5 is moved in the opposite direction, i.e. remove it along axis 3 from receiver 2 until the amplitude of surface acoustic waves perceived by receiver 2 sharply increases. This will happen when the source 4 is between the receiver 2 and the nearest face 453

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the zone of acoustic contact of the absorber 5 and object 1 (Fig. 6). At this moment, X2 is determined - the coordinate of the point of intersection of the axis of the radiation pattern 3 and the boundary of the acoustic contact zone of the absorber 5 and object 1 closest to the receiver.

The location of the surface acoustic wave source 4 is defined as the average between Xi and Xa.

Claims (1)

SUMMARY OF THE INVENTION A method for detecting the location of a surface acoustic wave source, comprising: using a directional surface acoustic wave receiver, detecting waves from the source and orienting the receiver so that its axis of the radiation pattern passes through the surface acoustic wave source, characterized in that: in order to increase the accuracy of determining the coordinates of the source of surface acoustic waves, an absorber is placed on the axis of the radiation pattern of the receiver surface acoustic waves, it is moved along this axis, and the location of the surface acoustic wave source is judged by the average value of the coordinates of positioning point absorber in which sharply varies the amplitude of the received receiver oscillations. X / X J Figure 1 X / X2 fig.Z X J 4 FIG. 5 Editor S. Stenina Compiled by L. Levitan Tehred M. Morgenthal -UJ ./ / g / Proofreader M. Keretsman