KR100581762B1 - Magnetostrictive transducer - Google Patents

Abstract

The present invention relates to a device for performing long-distance non-contact inspection of a circular shaft using magnetostrictive effects and guided ultrasound.

According to the present invention, a magnetostrictive transducer for defect inspection of a rotating shaft includes a magnetostrictive member that exhibits a change in length when a magnetic field is applied therein, a permanent magnet that forms a bias magnetic field, and vibrations of the magnetostrictive member remaining. A damping material for damping, a joining element for transmitting vibration between the magnetostrictive member and the rotating shaft, and a variable magnetic field to cause a variable magnetic field to flow inside the magnetostrictive member, and when the magnetostrictive member causes deformation, transmission and reception of an induced current flows. It consists of a coupling means for fastening so that the coil and the contact member and the rotating shaft can be fixed in contact.

Guided-wave, Magnetostrictive Transducer, Terfenol-D, Giant Magnetostrictive Alloy

Description

Magnetostrictive transducers

1 is a view showing the configuration of a magnetostrictive transducer according to a first embodiment of the present invention.

FIG. 2 shows the magnetic field-magnetic strain curve of terphenol-D. FIG.

3 is a view for explaining an initial process of forming a variable magnetic field by a drive current in a rotating magnetostrictive member.

4 shows a shape during driving of the magnetostrictive transducer;

5 is a cross-sectional view of the magnetostrictive transducer in FIG.

6 is a view showing the configuration of a magnetostrictive transducer according to a second embodiment of the present invention.

7 is a sectional view of a magnetostrictive transducer according to a second embodiment;

8 shows an overall system including a magnetostrictive transducer, a rotation axis, and a device for controlling / measuring the transducer.

9 is a diagram showing the group velocity of longitudinal waves propagating in a steel round rod having a diameter of 20 mm according to a frequency of 500 kHz or less.

10 is a diagram showing a group speed of bending waves propagating in a steel circular rod having a diameter of 20 mm according to a frequency of 500 kHz or less.

Fig. 11 shows an example of a tone burst signal in which only a few sine functions are applied for a limited time.

12 shows the dimensions of the joining elements.

FIG. 13 shows a case of attaching a synthetic rubber damping material to a transducer. FIG.

FIG. 14 shows sensitivity for each case of FIG. 13; FIG.

FIG. 15 shows the duration of a pulse for each case of FIG. 13; FIG.

16 is a schematic view of a rotating shaft used in one experiment of the present invention.

FIG. 17 is a diagram illustrating a result of analyzing a signal and time-frequency measured in the rotation axis of FIG. 16. FIG.

(Symbol description of main part of drawing)

10: oscilloscope 20: function generator

30: ultrasonic device 40: DC power supply

50: computer 80: bobbin support

90: rotation axis 100: magnetostrictive transducer

110: magnetostrictive member 120: permanent magnet

130 damping material 140 joining elements

141: contact member 142: receiving member

150: transmission and reception coil 151: transmission and reception coil bobbin

160: coupling means 170: bias coil

175: bias coil bobbin

The present invention relates to a non-destructive testing device, and more particularly to a device for performing long-range non-contact inspection of the circular axis using the magnetostrictive effect and the guided ultrasound.

Most of the ultrasonic non-destructive scanning techniques currently in use focus on local flaw detection of the transducer's location. Therefore, transducers must be moved to perform non-destructive inspection on a wide range of areas. Non-destructive flaw detection using guided ultrasonic waves has been receiving great attention in recent decades as a way to overcome this disadvantage.

Induction ultrasonic flaw detection technique is known to be less accurate than the local flaw detection method, but it is applied to various fields because it has the advantage of being able to efficiently perform a wide range of non-destructive flaw detection. It is useful for nondestructive testing of rotating machines, rotating shafts, and various structural members made of sheet metal.

In addition, when performing nondestructive inspection on critical pipes or members with high risk of accidents in case of destruction, when access is difficult due to covering or underground laying, it is difficult to stop for inspection during operation, or local flaw detection is possible. However, if the time and cost constraints prevent the effective inspection of the entire structure, the guided ultrasonic scanning technique can be very useful.

The transducer using the magnetostriction effect has the advantage of being able to transmit and receive ultrasonic waves without mechanical contact to the object to be measured, thereby securing unique application possibilities in the field where contact is not applicable. Practical applications of the magnetostrictive effects of various ferromagnetic materials have already been introduced in various fields. However, the unique nonlinear behavior and the hysteresis effect of magnetic materials have been a great difficulty in understanding the magnetization process and the behavior of magnetic materials including magnetostrictive effects. There is a lack of systematic research on.

In addition, there has been no report on a method for effectively performing nondestructive inspection using guided ultrasound when non-contact flaw detection such as a rotating shaft is required.

Therefore, when non-contact flaw detection is required, it is necessary to devise a method capable of efficiently performing non-destructive inspection using magnetic deformation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above necessity, and an object thereof is to provide a method and apparatus for inspecting defects of an object by using a magnetostriction effect in an environment requiring non-contact flaw detection.

In particular, an object of the present invention is to provide a method and apparatus for inspecting a defect of the rotating shaft when the target object is the rotating shaft.

Another object of the present invention is to adopt a magnetostrictive member suitable for non-contact flaw detection.

In order to achieve the above object, according to the present invention, the magnetostrictive transducer for flaw detection of the rotating shaft is fixed at a predetermined distance on one side in the longitudinal direction of the magnetostrictive member, has the same cross-sectional shape as the magnetostrictive member, A permanent magnet which forms a bias magnetic field in the magnetostrictive member so that a predetermined magnetic displacement occurs in advance in the magnetostrictive member; A damping material that maintains a predetermined distance between the magnetostrictive member and the permanent magnet and fixes them by adhesion, and attenuates vibrations of the magnetostrictive member remaining after stopping excitation by a variable current; A contact member serving as a medium for transmitting the displacement vibration of the magnetostrictive member to the rotating shaft to be inspected and transmitting the vibration reflected from the rotary shaft to the magnetostrictive member, and a magnetostrictive member for accommodating the magnetostrictive member; A joining element comprising a receiving member having an inner diameter of the same cross section; A variable current flows so that a variable magnetic field is generated inside the magnetostrictive member, and when the magnetostrictive member deforms due to the reflected vibration, an induced current flows, and a predetermined distance is greater than the outer diameter of the receiving member. Transmitting and receiving coils are formed concentrically spaced apart; The inner diameter is formed to be substantially the same as the outer diameter of the contact member and the outer diameter of the rotating shaft, the coupling so that the contact member and the rotating shaft can be fixed in contact with the coupling to rotate the joint element together when the rotating shaft is rotated Way; And an electric device that generates a variable magnetic field inside the magnetostrictive member by flowing a variable current through the transmission / reception coil, and detects the induced current to find a defect in the rotational shaft. The phenol-D element is used, and the magnetostrictive member, the permanent magnet, the damping material, and the joining element rotate together with the rotary shaft and the transmission / reception coil is fixed at the time of flaw detection of the rotary shaft.

The electrical device includes a function generator for generating a waveform desired by a user; An oscilloscope for allowing a user to check the waveform by displaying the generated waveform to the user; It is connected to the transmission and reception coils to generate an induction ultrasonic wave by applying a variable current of the tone burst type to the transmission and reception coil, and transmits a trigger signal to the function generator and the oscilloscope every time the tone burst type variable current signal is applied An ultrasonic apparatus for synchronizing a signal and receiving and amplifying the induced current; And a computer controlling the function generator, the oscilloscope, and the ultrasound apparatus according to a user's command, and receiving and analyzing the signal waveform stored from the oscilloscope.

In order to achieve the above object, according to the present invention, the magnetostrictive transducer for defect detection of the rotary shaft, the displacement vibration of the magnetostrictive member is transmitted to the rotation axis to be inspected, the vibration that is reflected from the rotation axis the magnetostriction A joining element including a contact member serving as a medium for transmitting to the member, and a receiving member having an inner diameter of the same cross section as the magnetostrictive member to accommodate the magnetostrictive member; A damping member bonded to one side of the magnetostrictive member and configured to attenuate vibrations of the magnetostrictive member remaining after the excitation due to a variable current is stopped; A variable current flows so that a variable magnetic field is generated inside the magnetostrictive member, and when the magnetostrictive member deforms due to the reflected vibration, an induced current flows, and a predetermined distance is greater than the outer diameter of the receiving member. Transmitting and receiving coils are formed concentrically spaced apart; A bias coil provided on an outer side of the transmission / reception coil in a concentric manner and configured to form a bias magnetic field in the magnetostrictive member by flowing a direct current; The inner diameter is formed to be substantially the same as the outer diameter of the contact member and the outer diameter of the rotating shaft, the coupling so that the contact member and the rotating shaft can be fixed in contact with the coupling to rotate the joint element together when the rotating shaft is rotated Way; And an electric device that generates a variable magnetic field inside the magnetostrictive member by flowing a variable current through the transmission / reception coil, and detects the induced current to find a defect in the rotational shaft. The phenol-D element is used, and when the defect of the rotating shaft is detected, the magnetostrictive member and the joining element rotate together with the rotating shaft, and the transmission / reception coil and the bias coil are fixed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only the embodiments are to make the disclosure of the present invention complete, and the general knowledge in the art to which the present invention belongs It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

In the present invention, in order to determine how the various factors affect the performance of the transducer in the design of the ultrasonic transducer, an analysis and experiment were performed to provide an index to the design of the magnetostrictive transducer for the guided ultrasonic inspection. Based on these results, it is shown that the structure of the transducer suitable for conducting non-contact induction ultrasonic inspection on the rotating circular axis can be determined.

Accordingly, in the embodiment of the present invention, by using a terfenol-D (terpenol-D) device, a large magnetostrictive alloy, a magnetostrictive transducer capable of transmitting and receiving induction ultrasound can be designed and manufactured to eliminate defects in the rotating steel bar. We present a long-range guided ultrasonic flaw detection technique. For this purpose, the dispersion phenomenon, which is characteristic of guided ultrasound propagating on circular axis, is considered and the mode and frequency suitable for guided ultrasound inspection are selected.

In addition, the structure of the magnetostrictive transducer using the terphenol-D device is presented and electromagnetic and mechanical modeling are performed to analyze it. In addition, the non-destructive testing method using the magnetostrictive transducer proposed in this study can be usefully applied in the situation similar to the actual operating conditions by conducting the long-distance non-contact defect inspection on the steel rod using the designed and fabricated magnetostrictive transducer. Will confirm.

1 is a view showing the configuration of a magnetostrictive transducer 100 according to an embodiment (first embodiment) of the present invention. The magnetostrictive transducer 100 includes a magnetostrictive member 110, a permanent magnet 120, a damper 130, a bonding element 140, a transmission / reception coil 150, and a coupling means 160. It may be configured to include).

The magnetostrictive member 110 is a member made of a material that shows a change in length when a magnetic field is applied thereto. When an object is placed in a magnetic field, its size changes. This is called magnetostriction. In addition, as a reverse phenomenon of the magnetostriction phenomenon, a phenomenon in which the magnetic field inside the ferromagnetic material fluctuates when deformation is caused by stress is called an inverse magnetostriction phenomenon.

In order to overcome the disadvantage that the magnetic strain of ferromagnetic materials such as steel and nickel is very small, it is difficult for practical application. Considering its high strain rate, the Giant Magnetostrictive Alloy (GMA) has been developed to mix these two elements in proper proportions and alloy with iron to produce a large magnetostriction of more than 1500 ppm even at a relatively low magnetic field. Among them, in particular, the substance of Tb _x Dy _1-x Fe _y (x = 0.27-0.3, y = 1.9-2.0) is called Terfenol-D.

The magnetic field-magnetic strain curve of terphenol-D is shown in FIG. 2. The terphenol-D has a large magnetic strain of about 50 times that of nickel and about 10 times that of piezoceramic, and has a high energy density per unit volume. It has the advantage of being able to produce and responding quickly. Therefore, in the present invention, terphenol-D is used as the magnetostrictive member 110.

The magnetostrictive member 110 has a cylindrical shape and, when a magnetic field is applied, mainly causes displacement in the longitudinal direction. The magnetostrictive member 110 is fitted to the cylindrical hole-shaped receiving member 142 provided with the bonding element 140 described later and bonded by epoxy resin or the like.

The permanent magnet 120 is fixed at a predetermined distance on one side of the magnetostrictive member 110 at a predetermined distance, and may have the same cross-sectional shape as the magnetostrictive member. The permanent magnet 120 forms a bias magnetic field in the magnetostrictive member 110 so that a predetermined displacement occurs in advance in the magnetostrictive member 110.

This causes the magnetostrictive member 110 to expand in advance according to the magnitude of the applied bias magnetic field and be located at a certain operating point. When the magnitude of the magnetic field decreases with respect to the point, it acts as if it causes contraction. It is also important to obtain a linear behavior of the magnetic field by applying an appropriate bias magnetic field. Nd (Neodymium Magnet) may be used as the material of the permanent magnet 120.

The damping member 130 maintains a predetermined distance between the magnetostrictive member 110 and the permanent magnet 120 and fixes them by adhesion, and the magnetostrictive member that remains after stopping the excitation by the variable current ( Attenuate the vibration of 110). However, when the damping material 130 is made of polystyrene having an acoustic impedance similar to that of air, it may be regarded as air-backing. The damping material 130 may have the same cross-sectional shape as the magnetostrictive member 110 and the permanent magnet 120.

The bonding element 140 transmits the displacement vibration of the magnetostrictive member 110 to the inspection object 90, and the contact acts as a medium for transmitting the vibration reflected from the inspection object 90 to the magnetostrictive member 110. It may be configured to include a member 141, and the receiving member 142 having an inner diameter of the same cross section as the magnetostrictive member to accommodate the magnetostrictive member 110. The contact member 141 protects the magnetostrictive member 110 and allows for proper acoustic impedance matching. To this end, the thickness of the contact member 141 may be 1/4 of the wavelength at the resonance frequency. In this way, the most effective wave energy can be transmitted by canceling the waveform reflected from the outer surface of the contact member 141.

The contact member 141 and the receiving member 142 are integrally formed of the same material. The material of the bonding element 140 is to use Acrylite GP, which is a kind of acrylic synthetic resin, in consideration of the acoustic impedance of the steel bar, which is the magnetostrictive member 110 and the inspection object 90.

The material forming the magnetostrictive transducer 100 is selected as a nonmagnetic material except for the magnetostrictive member 110 and the permanent magnet 120 to facilitate magnetic field analysis.

Physical properties of the terphenol-D device used in the present invention, Acrylite GP, the steel used in the steel bar, and the material used in the permanent magnet are shown in Table 1 below.

TABLE 1

Terphenol-D Acrylite gp Steel Neodymium Modulus of elasticity E (GPa) 50 2.8 500 186 Density (kg / m ³ ) 9021.4 1190 7800 7481 Poisson's Ratio 0.3 0.3 0.3 - Relative investment 3.007 One 2000-5000 1.08 Propagation velocity of sect at rod C _B (km / s) 2354 1534 5064 - Propagation velocity of longitudinal wave in infinite space C _L (km / s) 2731 1780 5875 - Acoustic Impedance Z (kg / m ² s) 2.114E7 1.825E6 4.583E7 - Wavelength of wave with frequency of 57.9 kHz (mm) 40.66 (C _B ) 30.74 (C _L ) 87.46 (C _B ) -

The transmission / reception coil 150 generates a variable magnetic field inside the magnetostrictive member 110 by flowing a variable current to generate ultrasonic vibration in the magnetostrictive member 110, and according to the generated vibration, the inspection object 90 When the magnetostrictive member 110 deforms due to vibration reflected from the current, a current (hereinafter referred to as induced current) flows due to the deformation. Since the transmission / reception coil 150 should be fixed even when the rotation shaft 90 and the magnetostrictive member 110 rotate, the transmission / reception coil 150 may be formed concentrically at a predetermined interval from the outer diameter of the receiving member 142 among the bonding elements 140. do. To this end, the transmission / reception coil 150 is wound around the transmission / reception coil bobbin 155 having a cylindrical shape whose inner diameter is larger than the outer diameter of the receiving member 142.

As described above, when the non-contact flaw detection of the rotating shaft is required, the transmission / reception coil 150 may provide a separate bobbin to wind the coil around the bobbin and place the bobbin outside the transducer, but requires no contact flaw detection. If not, it may be wound directly on the outer diameter of the receiving member 142.

The coupling means 160 is fastened so that the contact member 141 of the joining element 140 and the inspection object 90 can be contacted and fixed. The coupling means 160 has a cylindrical shape and is designed such that its inner diameter is approximately equal to the outer diameter of the contact member 141 and the outer diameter of the inspection object 90. If the outer diameters of the contact member 141 and the inspection object 90 are different, the inner diameters of both ends of the coupling means 160 may have different sizes depending on the size of the outer diameter of the object to be accommodated. The first screw holes 161a, 161b, etc. and the second screw holes 162a, 162b, etc., which penetrate the thickness direction at predetermined intervals along the outer diameter circumference of the engaging means 160, are provided in two rows. The first screw holes 161a, 161b, and the like are for accommodating and screwing the contact member 141, and the second screw holes 162a, 162b, etc. are for screwing the inspection object 90.

3 is a view for explaining an initial process of forming a variable magnetic field by a driving current in the rotating magnetostriction member 110. When the inspection object 90 rotates, the bonding element 140 contacted and fixed by the coupling means 160 rotates. In addition, the magnetostrictive member 110, the damping material 130, and the permanent magnet 120 bonded in the receiving member 142 of the bonding element 140 also rotate together.

After that, when the bobbin support 80 holding the transmission / reception coil bobbin 155 approaches in the axial direction of the inspection object 90, the transmission / reception coil 150 may move the magnetostrictive member 110 as shown in FIG. 4. It is wrapped in a solenoid form, and then a variable magnetic field is formed in the magnetostrictive member 110 when a variable current flows through the transmission / reception coil 150.

As such, first, while the rotating shaft 90, the bonding element 140 coupled thereto, and the magnetostrictive member 110 are rotating, the transmission / reception coil 150 may change the outer diameter of the receiving member 142 of the bonding element 140. Although the transmission and reception coil 150 may be inserted to enclose, the rotation shaft 90, the bonding element 140, and the magnetostrictive member 110 rotated while the transmission and reception coil 150 is inserted from the beginning. It may be.

5 is a cross-sectional view of the magnetostrictive transducer 100. In FIG. 4, the damping member 130 is exposed to the outside of the receiving member 142. However, the damping member 130 is formed according to the length of the magnetostrictive member 110 and the length of the receiving member 142. It may be accommodated inside the receiving member 142 as shown.

As such, a predetermined distance exists between the outer diameter of the receiving member 142 and the transmission / reception coil 150 among the bonding elements 140, such that the remaining components 110, 120, 130, and 140 of the magnetostrictive transducer 100 are present. Even if the 160 rotates, the transmission / reception coil 15 may be fixedly attached. The magnetostrictive member 110 is in close contact with one surface of the contact member 141 of the bonding element 140, and the inspection object 90 is in close contact with the other surface of the contact member 141. And variable displacement, i.e., vibration, can be transmitted between and the inspection object 90.

6 is a view showing the configuration of a magnetostrictive transducer 200 according to another embodiment (second embodiment) of the present invention. Unlike the first embodiment, the magnetostrictive transducer 200 does not have a permanent magnet 120. Instead, as another method of applying a fixed bias magnetic field, a bias coil 170 and a bias coil 170 for flowing a DC current are wound, and a bias coil bobbin capable of accommodating the outer diameter of the transmission / reception coil bobbin 155 in the inner diameter ( 175). In the second embodiment, the bobbin support 80 does not fix the transmission / reception coil bobbin 155, but fixes the bias coil bobbin 175. The transmission / reception coil bobbin 155 is fixed within the inner diameter of the bias coil bobbin 175.

As such, when the magnetic field is applied using the bias coil 170, a relatively uniform bias magnetic field may be applied to the magnetostriction member 110 than when the permanent magnet 120 is used.

7 is a cross-sectional view of the magnetostrictive transducer 200 according to the second embodiment. In FIG. 7, the bias coil 170 is wound to the outside of the transmitting and receiving coil 150, which is different from FIG. 5. Since the bias current has a much larger value than the driving current, it is preferable to use a larger cross-sectional area of the bias coil 170, but the present invention is not limited thereto.

8 is a schematic diagram of an entire system including a magnetostrictive transducer 200, an inspection object, ie a rotating shaft 90, and a device for controlling / measuring the transducer 200.

The system includes a rotating shaft 90 which may have a crack 91 at any position with the magnetostrictive transducer 200, bearings for guiding the rotation of the rotating shaft 90 and supporting a force perpendicular to the shaft. And electrical devices 10, 20, 30, 40, and 50.

The function generator 20 generates a waveform of a shape desired by a user. The generated waveform is input to the oscilloscope 10 and the ultrasound apparatus 30. An oscilloscope displays the generated waveform to the user so that the user can check the waveform. In addition, the waveform of the current actually excited by the ultrasonic apparatus 30 may be confirmed using a current measuring probe.

The ultrasonic apparatus 30 is connected to the magnetostrictive transducer 200 and generates an induced ultrasonic wave by applying a driving current, for example, a tone-burst signal, to the transducer 200. When generating the guided ultrasonic waves in this way, the ultrasonic device 30 sends a trigger signal to these devices 10 and 20 to synchronize with the oscilloscope 10 and the function generator 20. That is, each time the tone burst signal is applied, the ultrasonic device 30 generates a trigger signal so that the operation of the function generator 20 and the oscilloscope are synchronized, and the ultrasonic device 30 has a crack ( 91) or a signal signal induced by a reflected wave returning from a support (brake, pulley, etc.), the end of the rotating shaft 90, or the like, and amplifying it.

The received and amplified voltage signal is input to the oscilloscope 10 so that the user can check the waveform. The signal input to the oscilloscope may be transmitted to the computer 50 and subjected to signal processing.

Meanwhile, the DC power supply 40 forms a bias magnetic field in the transducer 200 by flowing a bias current through the bias coil 170 of the transducer 200. If the transducer 100 of the permanent magnet 120 type is used as in the first embodiment, the DC power supply 40 should be omitted.

The computer 50 controls other electrical devices 10, 20, 30, and 40 according to a user's command, and receives the signal waveform stored from the oscilloscope 10 and analyzes it.

In the embodiment of the present invention, the ultrasonic device 30 uses 'RAM-5000' manufactured by Ritec Inc. (Ritec Inc.). RAM-5000 is a super heterodyne general purpose high power ultrasonic device, the main specifications of which are shown in Table 2.

TABLE 2

Item Specifications Frequency band 20 kHz to 20 MHz Output 5 kW Normal output impedance 50 Ω Receiver Input Impedance 50 Ω Receiver Output Impedance 50 Ω Pulse width 200 μsec Receiver Amplification Gain 20 dB to 100 dB

Meanwhile, hereinafter, a process of determining parameters required for performing non-contact flaw detection using the magnetostrictive transducers 100 and 200 according to the present invention will be described in detail. Hereinafter, a method for selecting the mode and frequency of the ultrasonic wave excited by the ultrasonic device 30, a method for selecting the waveform of the induced ultrasonic wave, a method for selecting the size of the bonding element and the transducer, and the shape and attachment position of the damping material We describe the process of selecting and finally the results of the non-contact long distance flaw test in this environment.

Mode and Frequency Selection of Inductive Ultrasonic Waves

Group velocity according to a frequency of 500 kHz or less for longitudinal waves and bending waves in guided ultrasonic waves propagating in the longitudinal direction using the physical properties of steel rods (diameter 20 mm), which is the material of the circular axis, which is the object of the present invention. Is shown in FIG. 9 and FIG. 10, respectively. That is, FIG. 9 shows the group speed curve of the longitudinal wave, and FIG. 10 shows the group speed curve of the bending wave.

9 and 10, the group velocity variance curves, L (0,1) mode in the region below 60 kHz and L (0,2) mode around 250 kHz are the fastest and substantially non-speed at that frequency, respectively. The behavior is close to dispersion. However, in case of L (0,2) mode, the displacement distribution in the cross section is not the same direction, so it is not suitable for the long-range flaw detection of defects, and it is considered that it is difficult to excite the transducer to be fabricated in this study. Therefore, the L (0,1) mode with a uniform displacement distribution in the cross section was selected, and the frequency domain was selected around 60 kHz.

Selection of excitation method of induction ultrasound

We will look at the methods needed to have an induction ultrasound in a specific frequency band. BACKGROUND ART Ultrasonic transducers using piezoelectric elements generally use a method of simultaneously applying a wide waveform frequency by applying a spike-like waveform having a high voltage for a short time. This method has the advantage that the resolution of the time domain is good because the piezoelectric element having the natural frequency of the high frequency region is relatively short.

In addition, there is an excitation method for continuously applying a waveform of a specific frequency, which is used in special cases such as thickness measurement, and is used when driving a vibration device of an ultrasonic cleaner, a welding machine, and various tools requiring large power. The continuous excitation method is advantageous in that the resolution in the time domain is low but the characteristics in the frequency domain are good.

The present invention allows the use of a tone-burst method that compromises the advantages of both methods. The tone burst excitation method is a method of applying only a few cycles of a sine function for a limited time as in the example of FIG. 11 (four-cycle sine wave), and is used to improve both the resolution in the time domain and the resolution in the frequency domain.

In the long-range guided ultrasonic flaw detection aimed at the present invention, it is necessary to estimate the position of the defect by measuring the arrival time of the reflected signal from the defect. Therefore, the resolution of the time domain must be good and the L (0,1) mode around 60 kHz is required. Since we want to concentrate on, the resolution in the frequency domain also needs to be high.

Selection of joining elements 140 and transducers 100, 200

Ultrasonic transducers are generally classified into narrow-band transducers and wide-band transducers depending on whether they use resonance. Broadband transducers are mainly used to measure signals in the region lower than the natural frequency, avoiding resonance, which is appropriate when the main objective is to understand the behavior of the measurement object over a wide frequency range such as an accelerometer.

On the other hand, narrowband transducers have the advantage of generating high-intensity ultrasonic waves with relatively little energy by matching the natural frequencies of the active elements with the driving frequency and using the resonance of the active elements. It shows a high efficiency in transmitting and receiving the ultrasonic pulse corresponding to. The objective of the present invention is to detect the micro cracks of the steel round rods, so that a narrow band transducer using resonance of the terphenol-D device, which can increase the sensitivity, is designed.

The first thing to design in an ultrasonic transducer is the length of the active element in relation to the resonant frequency. As described above, in order to fabricate a low frequency transducer with a driving frequency of less than 60 kHz, the length of the terphenol-D device must be determined first.

When the length l of the active element of the ultrasonic transducer corresponds to 1/2 of the ultrasonic wave wavelength λ, it is known that the most efficient operation is possible because the resonance frequency in the longitudinal direction coincides with the frequency of the ultrasonic wave to be generated. . That is, if the resonant frequency is f ₀ , the propagation speed of the longitudinal wave of the terphenol-D device is c _T , and the wavelength corresponding to the resonant frequency is λ _T , the length ( l ) of the terphenol-D device is expressed by Equation 1 below. It can be obtained as

[Equation 1]

In this case, substituting the relationship between the elastic modulus E _T , the mass density ρ _T of the terphenol-D, and the transfer speed c _T of the longitudinal wave in the rod into Equation 1 is as follows.

[Equation 2]

Using Equation 2, the terphenol-D element has a length of 20 mm when the resonance frequency is 58.86 kHz.

In addition, the contact member 141 is required between the terphenol-D element and the iron rod for protecting the terphenol-D element and for proper acoustic impedance matching, and the material of the contact member 141 is as described above. Like Acrylite GP. When the thickness of the contact member 141 becomes 1/4 of the wavelength λ _A corresponding to the resonant frequency f ₀ , the thickness of the contact member 141 cancels the waveform reflected from the outer surface of the contact, thereby enabling the most efficient transfer of wave energy.

At this time, since the thickness t _A of the contact member 141 is relatively thin compared to the wavelength λ _A , the velocity relationship of the longitudinal wave transmitted in the infinite space is used. The transmission velocity C _A of the longitudinal wave of Acrylite GP is expressed by the elastic modulus E _A , the density ρ _A , and the Poisson's ratio ν _A.

[Equation 3]

At this time, the relationship between the thickness t _A of the contact portion and the wavelength λ _A is as follows.

[Equation 4]

Substituting the properties in Equation 4 to calculate the thickness of the contact portion made of Acrylite GP is 7.7 mm.

In the present invention, the diameter of the terphenol-D element of the active element of the magnetostrictive transducer 100 was selected to 10 mm, and a three-dimensional finite element analysis technique was introduced for more accurate analysis. The one-dimensional analysis described in Equations 1 to 4 only considers the motion in the axial direction, which is the direction of wave displacement, which is valid for a shape that can be regarded as a flat plate because the radius of the active element is considerably larger than its thickness. In order to verify the applicability to cylindrical shapes with a diameter of 10 mm and a length of 20 mm, three-dimensional analysis was performed using the finite element method.

The diameter of the contact portion of the magnetostrictive transducer was set to 20 mm equal to 20 mm of the specimen, and the thickness was set to 7.7 mm, which is 1/4 of the wavelength as described above. The thickness of the case is set to 2 mm in consideration of strength and attenuation. Therefore, the inner diameter of the case is 10 mm and the outer diameter is 14 mm. The specification of the bonding element 140 used in the embodiment of the present invention is as shown in FIG.

In order to confirm the dynamic behavior of a terphenol-D element and a contact part, the result of the comparative examination about the case where the terphenol-D element was analyzed separately and the case where the contact part was combined and analyzed is summarized as shown in Table 3.

TABLE 3

Interpretation Method Natural frequency (kHz) 1-D Analysis of Terphenol-D Devices 58.86 Axisymmetric Finite Element Analysis of Terphenol-D Devices 57.97 Three-Dimensional Finite Element Analysis of Terphenol-D Devices 57.94 3D finite element analysis of transducers (except permanent magnets) 54.58 3D finite element analysis of transducers (including permanent magnets) 55.73

As shown in Table 3, it was confirmed that the value of the first axial eigenmode and the corresponding natural frequency is not significantly different from the one-dimensional analysis result. It can also be seen that permanent magnets have little effect on the mechanical behavior. This shows that even when the quantity of the permanent magnets 120 is measured, the change in the natural frequency as the mass of the permanent magnets 120 increases can be ignored. In the present invention, a natural frequency of 57.9 kHz is selected as the driving frequency based on the three-dimensional finite element analysis of the terphenol-D device.

Selection of damping material shape and attachment location

Most ultrasonic transducers apply electrical and magnetic stimulation to active elements to generate mechanical vibrations that propagate waves into adjacent media. For ultrasonic inspection, it is necessary to stop the electromagnetic stimulus and then appropriately damp the residual vibration in order to receive the reflected signal from the defect. However, the vibration of the active element does not immediately disappear, but the inertia tends to continue at a frequency corresponding to the natural frequency. This residual vibration has the side effect of preventing the discrimination of the reflected signal returning from a short distance from the transducer, or making it difficult to distinguish two consecutive pulses. In order to minimize the residual vibration, it is necessary to reduce the duration of the pulse by attaching a damping material 130 having a proper attenuation coefficient and having a high attenuation coefficient.

In this experiment, the synthetic rubber is attached to each part of the magnetostrictive transducer 100 to find the most efficient attachment position of the damping material 130 and evaluate its effect. 13 shows the attached position of the synthetic rubber damping material 130 to each part of the transducer 100, and the experimental results for each case are shown in FIGS. 14 and 15. For this experiment, a bias magnetic field was applied using a permanent magnet 10 mm in diameter and 10 mm long, and the winding frequency was 50 times. Apply a drive current of a two-cycle tone burst function.

In each case, the magnitude of the terminal reflection signal of the steel bar having a diameter of 20 mm and a length of 4 m was measured, and the relative sensitivity and the duration of the pulse were calculated and compared in FIGS. It can be seen that the trend is similar for the waveforms of the two driving magnetic fields. Relative sensitivity was significantly lowered in cases 3, 5, and 6, where the damping material was directly attached to the terphenol-D device, indicating that it most efficiently absorbs the residual vibrations of the terphenol-D device. Also note that the pulse duration was the shortest in case 3 and significantly shorter in cases 5 and 6. This means that the remaining vibrating portion of the waveform of the pulse is attenuated and disappears faster. Case 2, in which the damping material 130 is attached to the outside of the contact portion, has a longer pulse duration than case 1, in which the damping material is not attached, because the output voltage of the pulse is lowered.

In the case of performing actual defect inspection, it is assumed that it is more important to obtain a clean waveform without residual vibration, and the results of FIGS. 14 and 15 can be considered as the most suitable position. In the experiment, it can be seen that the damping material 130 is required by confirming that the performance of the magnetostrictive transducer can be improved by suppressing unnecessary vibration of the terphenol-D device, and according to the first embodiment of the present invention, The same damping material as case 3 was used.

Non-contact Long Range Fault Test

In order to check the non-contact long-range defect flaw detection characteristics of the magnetostrictive transducer manufactured in the present invention, an experiment is performed to transmit and receive ultrasonic waves while making artificial defects on the rotating shaft. A main body consisting of a terphenol-D element and a bias permanent magnet is attached to the end of the rotating shaft to rotate together with the rotating shaft, and the transmission / reception coil can maintain a non-contact state with the main body.

In this experiment, a 20mm diameter, 4m long steel (S45C) rotary shaft was machined to have an artificial defect of 12% cross-sectional loss at 2810 mm from the magnetostrictive transducer and 615 RPM using a pulley and V-belt at the opposite end. It was set to rotate at a speed of. The rotating shaft is supported by the bearing UC204 and a brake is installed at a position 2080 mm from the transducer to rotate while supporting the torsional load. A schematic diagram of the axis of rotation is shown in FIG. 16 and the measured signal and time-frequency analysis results are shown in FIG. 17.

Referring to the result of FIG. 17, an echo signal represented by a brake or a pulley or a terminal may be clearly distinguished from an echo signal due to a crack, and the echo signal due to a crack may be relatively different. It can be seen that the amplitude is small.

In addition, in consideration of the actual situation, when the torsion load acts on the rotating shaft, when the diameter of the rotating shaft changes due to the step machining like the generator turbine shaft, the experiment also occurs when the lateral vibration occurs due to the eccentric mass on the rotating shaft. It can be seen that the whole inspection is possible by performing. In addition, even when the member to be examined has a bent portion rather than a straight line, the whole inspection was possible.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the present invention, it is possible to accurately detect whether or not a defect exists in the rotation axis.

In addition, according to the present invention, it is possible to appropriately determine various parameters influencing the design of the magnetostrictive transducer using the terphenol-D device.

Claims (3)

A magnetostrictive member that exhibits a change in length when a magnetic field is applied thereto; It is fixed with a predetermined distance on one side in the longitudinal direction of the magnetostrictive member, has the same cross-sectional shape as the magnetostrictive member, and forms a bias magnetic field in the magnetostrictive member to cause a predetermined magnetic displacement in advance in the magnetostrictive member. Permanent magnets; A damping material that maintains a predetermined distance between the magnetostrictive member and the permanent magnet and fixes them by adhesion, and attenuates vibrations of the magnetostrictive member remaining after stopping excitation by a variable current; A contact for transmitting the displacement vibration of the magnetostrictive member to the rotation axis to be inspected, and a medium for transmitting the vibration reflected from the rotation axis to the magnetostrictive member, to protect the magnetostrictive member, and to achieve acoustic impedance matching A joining element comprising a member and an accommodating member having an inner diameter of the same cross section as the magnetostrictive member to accommodate the magnetostrictive member; A variable current flows so that a variable magnetic field is generated inside the magnetostrictive member, and when the magnetostrictive member deforms due to the reflected vibration, an induced current flows, and a predetermined distance is greater than the outer diameter of the receiving member. Transmitting and receiving coils are formed concentrically spaced apart; The inner diameter is formed to be substantially the same as the outer diameter of the contact member and the outer diameter of the rotating shaft, the coupling so that the contact member and the rotating shaft can be fixed in contact with the coupling to rotate the joint element together when the rotating shaft is rotated Way; And And an electric device generating a variable magnetic field inside the magnetostrictive member by flowing a variable current through the transmitting / receiving coil, and detecting the induced current to detect a defect of the rotating shaft. Terphenol-D element is used as a material of the magnetostrictive member, and when the defect of the rotary shaft is detected, the magnetostrictive member, the permanent magnet, the damping member, and the matching element rotate together with the rotary shaft and the transmission / reception coil The magnetostrictive transducer for defect detection of the rotating shaft, characterized in that the fixed. The device of claim 1, wherein the electrical device is A function generator for generating a waveform desired by a user; An oscilloscope for allowing a user to check the waveform by displaying the generated waveform to the user; It is connected to the transmission and reception coils to generate an induction ultrasonic wave by applying a variable current of the tone burst type to the transmission and reception coil, and transmits a trigger signal to the function generator and the oscilloscope every time the tone burst type variable current signal is applied An ultrasonic apparatus for synchronizing a signal and receiving and amplifying the induced current; And Magnetic deformation for fault detection of the rotating shaft, characterized in that it comprises a computer for controlling the function generator, the oscilloscope, the ultrasonic device according to the user's command and receives the signal waveform stored from the oscilloscope and analyzes it. Transducer. A magnetostrictive member that exhibits a change in length when a magnetic field is applied thereto; A damping material bonded to one side of the magnetostrictive member and configured to attenuate vibrations of the magnetostrictive member remaining after the excitation due to a variable current is stopped; A contact for transmitting the displacement vibration of the magnetostrictive member to the rotation axis to be inspected, and a medium for transmitting the vibration reflected from the rotation axis to the magnetostrictive member, to protect the magnetostrictive member, and to achieve acoustic impedance matching A joining element comprising a member and an accommodating member having an inner diameter of the same cross section as the magnetostrictive member to accommodate the magnetostrictive member; A variable current flows so that a variable magnetic field is generated inside the magnetostrictive member, and when the magnetostrictive member deforms due to the reflected vibration, an induced current flows, and a predetermined distance is greater than the outer diameter of the receiving member. Transmitting and receiving coils are formed concentrically spaced apart; A bias coil provided on an outer side of the transmission / reception coil in a concentric manner and configured to form a bias magnetic field in the magnetostrictive member by flowing a direct current; The inner diameter is formed to be substantially the same as the outer diameter of the contact member and the outer diameter of the rotating shaft, the coupling so that the contact member and the rotating shaft can be fixed in contact with the coupling to rotate the joint element together when the rotating shaft is rotated Way; And And an electric device generating a variable magnetic field inside the magnetostrictive member by flowing a variable current through the transmitting / receiving coil, and detecting the induced current to detect a defect of the rotating shaft. Terphenol-D element is used as the material of the magnetostrictive member, and when the defect of the rotary shaft is detected, the magnetostrictive member and the matching element rotate together with the rotary shaft, and the transmission / reception coil and the bias coil are fixed. A magnetostrictive transducer for flaw detection of a rotating shaft.

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