SU1379725A1 - Ultrasound transducer of acoustic emission signals - Google Patents

Abstract

This invention relates to the field of non-destructive testing. The aim of the invention is to increase the reliability of control due to the expansion of the receiving polarization pattern of the shear waves of horizontal polarization from acoustic emission sources. The ultrasonic transducer contains a waveguide 1 in the form of a solid cone and a piezoelectric element 2 with electrodes 3 placed on its larger spherical surface. Thanks to polarization of the piezoelectric element 2 around the circumference and dividing it into at least four parts by radially directed slits, selective reception of horizontal-wave waves in polarization is provided in a wide range of controlled area. 3 il.

Description

Source E

(L

CO SO

The invention relates to the field of non-destructive testing of materials and products and can be used to determine the coordinates of the sources of acoustic emission signals in thick-walled vessels.

The aim of the invention is to increase the reliability of quality control of hollow articles with a curved surface due to the expansion of the receiving directional patterns of horizontal polarization shear waves from acoustic emission sources.

FIG. 1 shows an ultrasonic acoustic emission transducer; in fig. 2 shows the piezoelectric element of converter i in FIG. 3 shows section A-A in FIG. 2

The ultrasonic transducer contains a waveguide 1 in the form of a solid truncated cone with a small flat working base of circular cross section, located normally to the axis of the piezoelectric transducer, and a large base limited by a spherical surface whose center is aligned with the center of the small base, and the piezoelectric element 2 in the form of a spherical layer placed on a larger the base of the waveguide 1. In this case, the spherical surface of a smaller radius of the piezoelectric element 2 coincides in shape with the spherical surface of the waveguide 1. On a spherical surface ost of the piezoelement x electrodes were applied 3, limited extension surface of the waveguide 1. In addition, the piezo element 3 is polarized in the circumferential and radial direction is divided

4 slots to the center are not less than four parts.

The material of waveguide 1 (for example, brass) is chosen so that the shear wave propagation velocity in it is less than in the material of the controlled product 5 (for example, stainless steel) C.S.P.I., 3 is the angle between the axis of waveguide 1 and its generator, the radius K, the spherical surface of the waveguide, the radius R of its small base, the length L "p, and the width Hpp of the slits 4 are chosen from the ratios

Finoi.

. Ss.g.i

.R, - 10 5y b5., R ep., L 0.95

 P

 0.02 Rf

where Cjf.p and С are the shear wave velocities of horizontal polarization in the materials of the waveguide and the product under test, respectively

WITH -. the speed of surface waves in the material of the product (controlled vessel); R is the outer radius

walls of the product under test, i is the lowest frequency of the converter pulse;

and „- the radius of the horizontal projection of the piezoelectric element.

The angle ot between the generatrix of the cone-shaped waveguide and its longitudinal axis follows from Snell's law, taking into account the condition that there is no reception of the surface wave from the layer of the product wall, limited by angle 2, which is determined from the ratio

sin | 5 - -

The radius RJ of the spherical surface of the waveguide is selected from the condition of the field formation in the far field of the waveguide. The radius RJ of the small base of the waveguide follows from the condition of the undistorted transmission of the lower frequency of the spectrum of the transformed pulse.

The length bn pI the width nn of the slits of the piezoelectric element is chosen on the basis of the condition of its mechanical strength. In this case, the slits emerge on the surface of the piezoelectric element bounded by the generatrix of the cone of the waveguide.

Ultrasonic transducer acoustic emission works as follows.

The shear wave signals propagating in a controlled zone bounded by an angle of 2p from the source of acoustic emission hit the surface of the small base of waveguide 1. After the shear wave is refracted at the product – waveguide boundary, it propagates through waveguide 1. The latter is in the form of a solid truncated cone allows you to get

The transducer radiation pattern is circular in plan and close to a semicircle in section, which provides control of a fairly wide area of the product wall.

Due to the choice of the angle v between the axis of the waveguide 1 and its forming piezoelement 2, only shear waves of horizontal polarization are received. These waves effectively excite the piezoelectric element 2 in the direction of their polarization due to the fact that it is polarized around the circumference and made with a spherical surface mating with the surface of the waveguide 1. And to perform circular polarization, the piezoelectric element 2 is divided by radially directed slits four.

The electrical signal converted by the piezoelectric element 2 is taken from the electrodes 3 to determine the coordinates of the source of the acoustic emission signals.

Thus, the ultrasonic transducer of acoustic emission signals increases the reliability of the control, since it selectively receives acoustic emission signals in a wide range of the controlled area.

Claims (1)

Invention Formula An ultrasonic transducer for acoustic emission signals containing a waveguide in the form of a truncated cone with a flat small base of circular cross section and a large base, bounded by a spherical surface whose center is aligned with the center of a small base, and a piezoelectric element with electrodes placed on the larger base of the waveguide, which differs from that, in order to increase the reliability of the quality control of hollow products with a curved surface, the waveguide is solid, the piezoelectric element is polarized around the circumference and p The radially directed slits are divided into equal to at least four parts, and the angle L between the axis of the waveguide and its generator, the radius R, the spherical surface of the waveguide, the radius R of its small base, the length Lnp and the width П „p of the slots are chosen from the ratios op Twin s, g, y and sg. s..and r horizontal polarization shear wave velocities in the waveguide materials and the product correspond to CTBeHHoJ the speed of surface waves in the material of the product; radius of the outer wall of the controlled product, the lower frequency of the pulse converter} the radius of the horizontal projection of the piezoelectric element. /// - / polarization3 TA % g, 2 Direction polarization3 Aa TA