KR101449411B1 - Electromagnetic Acoustic Transducer Module for Nondestructive Testing of Composite Materials - Google Patents

Abstract

The present invention relates to an electromagnetic acoustic transducer for a nondestructive test of composite materials and a nondestructive test method using the same, wherein the transducer includes a donut-shaped goniometer (1); a cover (2) located at a lower portion of the goniometer (1) to be inserted into a central through-hole (11) of the goniometer (1) and including a rectangular cover body (22) having an inner space, a circular upper portion, and a rectangular lower portion; an upper plate (3) inserted into a cover space portion (23) inside the rectangular cover body (22) of the cover (2) and having a central through-hole (32) and a plurality of upper plate reinforcing bars (34); a rotary shaft (4) installed by penetrating through the through-hole of the upper plate (3); a lower plate (5) installed at the lower portion of the rotary shaft (4) and having a central groove (53) and two side surface through-holes (52) formed at both side surfaces of the central groove (53); a yoke (6) inserted into two through-holes formed apart from each other at a predetermined interval on the lower plate (5); and a plurality of plate type coils (7) each installed at a lower portion of the yoke (6) and between two bias magnets (8) generating a bias magnetic field to apply a static magnetic field to a ferromagnetic substance and generating and measuring the magnetic field when transmitting and receiving induced ultrasonic waves. Therefore, the transducer performs conversion into horizontal shear wave to be transferred to composite materials and easily be applied to a nondestructive test of the composite materials.

Description

TECHNICAL FIELD [0001] The present invention relates to an electromagnetic acoustic transducer for non-destructive inspection of a composite material, and a non-destructive inspection method using the same.

The present invention relates to an electromagnetic acoustic transducer for nondestructive testing of composites and a non-destructive inspection method using the same, which is used in nondestructive testing of composite materials which are variously applied in aerospace industry and national important industrial facilities.

Guided ultrasound is an elastic ultrasonic wave propagating along the boundary of a structure, and has recently attracted attention as a method for nondestructive evaluation of various objects due to its remote propagation characteristics. Guided ultrasonic waves are difficult to measure and analyze because of their various types and modes depending on the shape of the structure and the dispersion characteristics of waves having different velocities depending on frequency components. The application of nondestructive testing using guided ultrasound is one of the causes of the lack of suitable transducer for the purpose of inspection, since understanding of induced ultrasound propagation phenomenon, mode selection, and post-processing and analysis of measurement signal must be accompanied together. In addition, the SHO mode, which is the only non-dispersive wave existing in the plate structure, is advantageous in terms of signal processing because the velocity is constant regardless of the frequency. However, It is difficult to create.

Recently developed electromagnetic acoustic transducers can not be used in nonmagnetic materials, but they can easily produce shear horizontal waves even in non-magnetic materials with high damping such as composites by using ferromagnetic thin plates.

Korean Patent Laid-Open Publication No. 1020110000527 includes two pole magnets oriented at an oblique angle with respect to the central longitudinal axis of the tool body. The array of sensor coil sets is located between the opposite edges of the two pole magnets and is oriented perpendicular to the central longitudinal axis. Each sensor coil set includes two opposing pairs of receiver coils and transmitter coils gated to receive reflections from the wall of the tubular member. Since the lines of the sensor coil are rotated relative to the magnetic bias field, the receiver coil is in series with the transmitter coil and has the same angular orientation as the transmitter coil. The tool is a pipeline inspection tool that provides enhanced sensitivity to small defects, significant reduction in RF pulse power requirements, total circumferential coverage, self calibration of transmitted signals, and less interference between transmitter coils generated by acoustic rings Technology is disclosed,

In the registered patent publication No. 1010612260000 (20110825), there is disclosed a magnetostrictive transducer module for guided ultrasound conversion, comprising: a case having a tubular shape in which a part is opened and a lead connector connection part is formed on the opposite side of the opening part; A coil installed inside the case for generating a magnetic field generated when guided ultrasonic waves are transmitted or for measuring a magnetic field induced when receiving guided ultrasonic waves; Bias magnets provided on both sides of the coil to generate a bias magnetic field to apply a static magnetic field to the ferromagnetic material; A yoke protruding as a part at both ends of the bias magnet to be engaged with the bias magnets, the support yoke being formed at a center thereof; An inner support which is formed with a yoke insertion groove into which the yoke is inserted and which supports the yoke stably in the case; It can be seen that a magnetostrictive transducer module for guided ultrasound conversion including a ferromagnetic thin plate having strong magnetostriction is disclosed.

1. Korean Patent Laid-Open Publication No. 1020110000527 2. Registered Patent Registration No. 1010612260000 (20110825)

To date, non-destructive testing methods have been applied to reliability evaluation of various materials as well as composite materials. Ultrasonic waves, radiation, heat, etc. are investigated on the object and the physical reactions occurring thereafter are detected to detect damage or defects. Among the inspection methods, internal defects in the composite material, that is, delamination, disbond, and debond, which form the air layer, are easily detected by ultrasonic inspection. The reason is that when the ultrasonic wave travels through the medium, the reflection is most likely to occur at a defect perpendicular to the traveling direction, and a piezoelectric transducer generally used is difficult to generate an SH wave. Even if a lamb wave is used, a wedge And the problem of the inconvenience of adjusting the propagation angle is a problem to be solved by the present invention.

In order to solve the above problems, the present invention is designed to generate a horizontal shear wave using an electromagnetic wave, configure a ultrasonic wave generating and measuring unit as a single module, and rotate the ultrasonic wave generating and measuring unit to measure at all angles, It is an object of the present invention to provide an electromagnetic acoustic transducer for composite non-destructive testing and a non-destructive inspection method using the same, which are used for measuring an SH wave and inspecting an internal defect such as interlayer separation, fiber breakage, etc. of a composite layer plate through a beam radiation pattern, Is a solution to the problem of.

The present invention is applied to non-destructive inspection for generating and measuring shear horizontal waves in a non-magnetic composite material, and has an effect of manufacturing an electromagnetic acoustic transducer module for testing a composite material, which has not been attempted in the past,

  It is designed to generate horizontal shear wave by using electromagnetic wave and to make ultrasonic wave generation and measurement unit as a single module and rotate to be able to measure at all angles. It produces Lamb wave and SH wave according to the relative position of the magnetic field and the static field So that it is advantageous in that the non-destructive inspection can be performed accurately,

  When a ferromagnetic material having a high Curie temperature is used, it can be applied at a high temperature.

It is noteworthy that the structure is simple, the durability is excellent, and that it can be manufactured at a low cost, considering industrial applicability.

1 is an overall view of an electromagnetic acoustic transducer for nondestructive inspection of a composite material according to the present invention
A plan view 1a, a perspective view 1b, a front view 1c, a side view 1d,
2 is an exploded view of an electromagnetic acoustic transducer for nondestructive inspection of a composite material according to the present invention.
3 is an inside view of an electromagnetic acoustic transducer for nondestructive inspection of a composite material of the present invention
The perspective view 3a, the bottom view 3b, the top view 3c,
Fig. 5 Detail view of the goniometer of the present invention
Fig. 6 Detailed view of the cover of the present invention
7 is a top plan view of the present invention
Fig. 8 Detailed rotation axis of the present invention
Figure 9 Detail view of the bottom plate of the present invention
Fig. 10 Details of the yoke of the present invention
Fig. 11 Magnet detail diagram of the present invention
Fig. 12 Detailed drawing of the handle of the present invention
13 shows the result of a short-time Fourier transform (STFT) test when the unidirectional and ultrasonic propagation directions of the composite material of the present invention are the same.
Fig. 14 shows the result of the radiation pattern test of the composite material of the present invention. 24 ply (5a), 48 ply (5b) Fig. 15 Modulation method of EMAT and ultrasonic testing method

The present invention is designed to generate a shear horizontal wave using magnetostriction and to construct a single module of ultrasonic wave generating and measuring unit and to rotate the ultrasonic wave generating and measuring unit so that it can be measured at all angles, The present invention relates to an electromagnetic acoustic transducer for nondestructive inspection of a composite material and a non-destructive inspection method using the same.

The present invention relates to an electromagnetic acoustic transducer module in which a transmitter and a receiver for generating and measuring ultrasonic waves are constituted by one module; Characterized in that the current induced in the ferromagnetic patch by the magnetostriction phenomenon causes the change of the magnetic field to be transmitted to the composite material.

In particular, the magnetostatic field includes a yoke attached to the permanent magnet so as to form a closed loop, and the relative position is fixed, so that the sensitivity does not fluctuate at the time of inspection.

And is sensitive to the propagation characteristics of elastic waves according to the direction of lamination of the composite fibers, so that the module module is configured to rotate independently of the material.

And a circuit for impedance matching with equipment used in generating and measuring ultrasonic waves is integrated in the sensor module.

And the displacement directions of the ultrasonic waves of the ultrasonic wave generating part and the measuring part coincide with each other.

Is an electromagnetic acoustic transducer for nondestructive testing of composites that generates shear horizontal waves using magnetostriction and transfers them to a composite material to perform shear horizontal wave conversion so that it can be easily applied to nondestructive testing of composite materials.

)가 유도되고 정자기장(

)를 가하면 시험편 표면의 입자들은 로렌쯔 힘을 받는다.The electromagnetic acoustic transducer (EMAT) of the present invention is a method using a Lorentz force, and comprises a coil for generating an eddy current and a Bias magnet for applying a static magnetic field. When an electric current is applied to a coil placed on the surface of the composite laminated plate material, eddy current (

) Was induced and the static magnetic field (

), The particles on the surface of the test specimen receive Lorentz force.

(1)

(One)

는 와전류의 밀도,

는 자속밀도,

는 로렌쯔 힘이다.here,

The density of the eddy current,

Magnetic flux density,

Is the Lorentz force.

The present invention relates to a method of NDT-based nondestructive inspection using EMAT,

Generally, unlike bulk ultrasonic waves, which are divided into longitudinal wave and shear wave, induction ultrasonic waves have various types and modes according to waveguide structures. In the plate structure, there are two types of guided ultrasonic waves, Lamb wave and SH wave (shear horizontal wave), depending on the displacement direction of the medium, and infinite modes exist respectively. Among them, the SH wave has the only non-dispersion wave SH0 mode in which the dispersion characteristic does not change even if the frequency is changed, so it is preferable to use the SH0 mode of the SH wave for the nondestructive inspection in the plate.

Also, a piezoelectric transducer generally used is difficult to produce an SH wave, and even if a lamb wave is used, it is inconvenient to adjust the propagation angle by using a wedge.

On the other hand, EMAT is easy to produce Lamb wave and SH wave according to the relative position of the magnetic field and the static field,

It is advantageous in that a transducer suitable for the purpose of inspection can be produced.

In the present invention, the center frequency of 500 kHz and the SH0 mode of the SH wave are used for the 24 ply and 48 ply laminated composite materials tests. For this purpose, an EMAT transducer for composites inspection was fabricated. The transducer was manufactured to be modular so that the position of the transmitting sensor and the receiving sensor was relatively fixed in order to increase the sensitivity of the repetitive measurement, and was manufactured so that it could rotate 360 ° along the rotation axis to transmit and receive ultrasonic waves in all directions Respectively. In order to understand the lamination orientation characteristics of composite laminates, propagation characteristics of ultrasonic waves were measured and analyzed in all directions of the laminates. As a result, the radiation pattern of the composite laminates was measured and it was confirmed that defects could be detected due to the change of the radiation pattern characteristics in the internal defect of the laminates.

Hereinafter, the present invention will be described in detail with reference to examples.

Example

Fixing the EMAT transducer for inspection of the present invention to the upper portion of the composite material,

The EMAT transducer for composite material is attached to the bottom of the transducer using a thin plate of iron-cobalt alloy, and the static magnetic field of the static magnetic field and the coil due to the permanent magnet is vertically arranged to set the frequency to 0.5 MHz and the electric impedance matching circuit When the strain energy of the patch is transferred to the composite material, the strain occurring in the patch is a horizontal strain, so that an SH wave is generated,

)와 탄성파의 파장(

)과의 관계에 따라 구조물로 전파하는 파의 중심 주파수가 결정되며, 코일의 파장(

)과 선간격(

)는 다음과 같은 식을 이용하고,
At this time,

) And the wavelength of the elastic wave (

), The center frequency of the wave propagating to the structure is determined, and the wavelength of the coil

) And line spacing

) Uses the following equation,

(2)

(2)

이면 파가 구조물의 표면을 따라서 전파하고,According to equation (2)

The backside wave propagates along the surface of the structure,

24 ply composite.

Experimental Example

In the present invention, an EMAT transducer was used for SH wave conversion on the surface of a composite material (laminated plate) made of carbon fiber reinforced plastic (CFRP).

24 ply and 48 ply composites (laminates) were prepared and measured with the EMAT transducer manufactured to measure the radiation pattern of the composite plate to evaluate the composites integrity. One sinusoidal wave with a frequency of 0.5 MHz was supplied to the transducer as the excitation signal

The EMAT transducer for composite material is attached to the bottom of the transducer using a thin plate of iron-cobalt alloy, and the static magnetic field of the static magnetic field and the coil due to the permanent magnet is vertically arranged to set the frequency to 0.5 MHz and the electric impedance matching circuit When the strain energy of the patch is transferred to the composite material, the strain occurring in the patch is a horizontal strain, so that an SH wave is generated,

)와 탄성파의 파장(

)과의 관계에 따라 구조물로 전파하는 파의 중심 주파수가 결정되며, 코일의 파장(

)과 선 간격(

)는 다음과 같은 식을 이용하고,
At this time,

) And the wavelength of the elastic wave (

), The center frequency of the wave propagating to the structure is determined, and the wavelength of the coil

) And line spacing

) Uses the following equation,

(2)

이면 파가 구조물의 표면을 따라서 전파하고, 24 플라이 및 48플라이의 복합재(적층판)의 비파괴검사를 하여 도4 및 도5와 같은 결과를 얻었다.
According to equation (2)

The backwaves propagated along the surface of the structure and subjected to nondestructive tests of 24 ply and 48 ply composites (laminates) to obtain the results shown in Figs. 4 and 5.

13 shows the measured signals and the short-time Fourier transform (STFT) when the unidirectional and ultrasonic propagation directions of the 24-ply composite material (laminates) are the same.

FIG. 13 shows that the magnitude of the signal when the propagation direction of the SH wave coincides with the unidirectionality is measured to the greatest, and that the attenuation is large when the direction is normal to the unidirectional direction. Also, it can be confirmed that the arrival time and the frequency characteristic of the wave are changed as the one direction and the propagation angle of the ultrasonic wave are changed. This means that the characteristics of the SH wave measured according to the reflection angle of the SH wave and the defect are different when the air layer or the interlayer break in the composite plate exists. Therefore, it is considered that a transducer using EMAT based on guided ultrasonic wave is applicable when a defect exists in the composite laminated plate.

Fig. 14 shows the radiation patterns of the 24-ply and 48-ply composite laminates. As a result of radiation pattern measurement, propagation of SH wave is easy in one direction, and attenuation becomes more severe as one direction and propagation angle become larger.

Hereinafter, the structure of the present invention will be described with reference to the drawings.

1 is a plan view (1a), a perspective view (1b), a front view (1c) and a side view (1d) of the composite non-destructive inspection of the present invention. 3 is an exploded perspective view of an electromagnetic acoustic transducer for composite nondestructive inspection according to the present invention; FIG. 4 is a perspective view of the electromagnetic acoustic transducer according to the present invention; As a result of the measurement signal and STFT (Short-time Fourier Transform) test result at the same time, the result of the radiation pattern test of the composite material of the present invention, 24 ply 5a, 48 ply 5b Fig. 6 is a schematic diagram of a method of constructing an EMAT of the present invention and an ultrasonic testing method. Fig. 6 is a schematic view showing the configuration of the goniometer 1, the cover 2, the upper plate 3, the rotary shaft 4, The yoke 6, the magnet 8, the coil 7, the handle 10, the central aperture 11 of the goniometer, the cover circular portion 21, the cover rectangular body 22, the cover space portion 23, The body 31, the upper plate central through hole 32, the upper plate reinforcement 34, the rotary shaft body 40, the rotary shaft upper and lower portions 41 and 42, the lower plate body 51, the lower plate central groove 53, The yoke body 61, the yoke lower central groove portion 62, the handle body 100, and the lower portion 110 of the handle.

1 to 12, a composite non-destructive acoustic transducer according to the present invention includes:

A donut-shaped goniometer 1 and a goniometer 1 disposed below the goniometer 1 and inserted into the goniometer central aperture 11 of the goniometer 1 and having a space therein. The upper portion of the circular lower portion is a rectangular parallelepiped- The cover 2 is inserted into the cover space portion 23 of the cover body 22 of the cover 2 and has a central through hole 32 at the center thereof. A rotation shaft 4 installed through the through hole of the upper plate 3 and a lower plate central groove 53 provided at the bottom of the rotation shaft 4 at the center, A lower plate 5 provided with two lower plate side through holes 52 formed in both sides of the lower plate central groove 53 and a yoke 6 inserted into two through holes spaced apart from the lower plate 5 A bias magnetic field is generated in the lower portion of the yoke 6 to apply a static magnetic field to the ferromagnetic material, And a plurality of plate-shaped coils 7 installed between the two bias magnets 8 for generating and measuring a magnetic field during transmission and reception of the induced ultrasonic waves.

As shown in Fig. 3,

The cover circular portion 21 of the cover 2 is made to pass through the goniometer central through hole 11 of the goniometer 1 and the rotary shaft 4 is inserted into the cover rectangular parallelepiped body 22 of the cover 2,

The upper portion 41 of the rotating shaft 4 of the rotating shaft 4 is passed through the upper plate central through hole 32 and the cover circular portion 21 of the upper plate 3 and is exposed through the central through hole 11 of the goniometer 1 ,

The rotary shaft lower portion 42 of the rotary shaft 4 is inserted and fixed in the lower plate central groove 53 of the lower plate 5,

The yoke 6 is inserted into the respective lower plate side through holes 52 formed on both side surfaces of the lower plate central groove 53 and a plurality of plate-shaped coils 7 are inserted into the lower portion of each yoke 6, After locating the magnets 8 on both sides of the coil 7,

The upper part 41 of the abutment shaft exposed to the outside and the lower part 110 of the handle 10 are screwed together to complete assembly.

The yoke 6, the magnet 8, the coil 7, the handle 10, the central aperture 11 of the goniometer 11, the cover 2, the upper plate 3, the rotary shaft 4, the lower plate 5, The cover circular portion 21, the cover rectangular portion 22, the cover space portion 23, the upper plate body 31, the upper plate central through hole 32, the upper plate supporting rib 34, the rotating shaft body 40, The yoke body 61, the yoke lower central groove portion 62, the handle body 100, the handle lower portion 41, the lower plate body 51, the lower plate central groove 53, the lower plate side opening 52, (110),

Claims (2)

An electromagnetic acoustic transducer for nondestructive inspection of composite materials,
A donut-shaped goniometer 1 and a goniometer 1 disposed below the goniometer 1 and inserted into the goniometer central aperture 11 of the goniometer 1 and having a space therein. The upper portion of the circular lower portion is a rectangular parallelepiped- The cover 2 is inserted into the cover space portion 23 of the cover body 22 of the cover 2 and has a central through hole 32 at the center thereof. A rotation shaft 4 installed through the through hole of the upper plate 3 and a lower plate central groove 53 provided at the bottom of the rotation shaft 4 at the center, A lower plate 5 provided with two lower plate side through holes 52 formed on both sides of the lower plate central groove 53 and a yoke 6 inserted into two through holes spaced apart from the lower plate 5 A magnetic field generating unit for generating a bias magnetic field to apply a static magnetic field to the ferromagnetic material, And a plurality of plate-shaped coils (7) installed between the plurality of bias magnets (8) for generating and measuring a magnetic field in the transmission and reception of the induced ultrasonic waves.
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