JPH04186102A - Method and device for detecting damage of structural member - Google Patents

Abstract

PURPOSE:To highly precisely detect a crack depth by decomposing a detected voltage every frequency band, detecting the size of the crack of a structural member, converting each detected amount to a damage amount by a predetermined calibration curve, and displaying it. CONSTITUTION:A current having an AC constant current waveform of each frequency band oscillated from a function generator 1 is applied to each current supplying terminal 4a, 4b through a high-speed current amplifier 2. When a structural member W has a damage part Wa by crack, the voltage is detected by each voltage measuring terminal 5a, 5b, and this output voltage is inputted to a high-speed Fourier transformation analyzer 7 through a transfer 6, Fourier- transformed, and spectrum-decomposed into the voltage of each frequency band. Then, the voltage data of each frequency band is inputted to an arithmetic device 9 through a transmitter device 10. In the device 9, the voltage data of each frequency band is decomposed every frequency band on the basis of a preliminarily inputted data, the size and form of the crack Wa are detected, and each crack detected amount is converted into a damage amount by a predetermined calibration curve and displayed 11.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to structural members (inspected objects) used in high temperature and high pressure atmospheres, such as stator blades and rotor blades of gas turbines. body)
cracks due to thermal fatigue, corrosion due to high temperature oxidation, and structural members (
The present invention relates to a method and apparatus for detecting damage to a structural member using a non-destructive alternating current potential difference method in a coating layer (film) of an object to be inspected.

(Prior Art) In general, structural members such as stationary blades and rotor blades of gas turbines for power generation are used at extremely high temperatures of, for example, 1,300 to 1,500°C for long periods of time, and on the other hand, they are used during startup and shutdown. In the structural members of power generation equipment, where thermal stress is frequently applied, many thermal fatigue cracks occur and grow due to repeated thermal stress caused by temperature fluctuations.
Not only is there a risk of destruction, but in addition to thermal stress, there are problems such as corrosion due to high-temperature oxidation, thinning, erosion, peeling, and changes in structure within the coating layer of the structural member, making it unusable. .

Conventionally, tissue observation using a microscope has been widely used as a means for detecting damage to structural members (objects to be inspected).
This microscopic structure observation means requires manpower and time, and the microscopic structure observation means of a structural member provided with a coating layer (film) has drawbacks such as the need to peel and remove the coating layer.

On the other hand, although methods for detecting damage to workpieces using ultrasonic detection means using high-frequency oscillators and means for detecting damage to workpieces using X-ray detection means have already been proposed, there are problems such as difficulty in quantitative evaluation or inability to apply them to coating materials. .

On the other hand, conventionally, as one of the potential difference methods, DC potential difference means,
This DC potential difference method is widely used because it is easy to analytically determine the calibration relationship between potential difference and crack length, and the measurement principle and equipment are relatively simple. Since this method detects average data (information) on the cross section of a target object, it is difficult to apply it to measuring the distribution of microcracks on the surface of the object to be measured or the shape of the tip of a crack.

On the other hand, this type of "crack depth detection device" (Japanese Unexamined Patent Publication No. 57
-24804) has already been proposed.

In other words, the above-mentioned "crack depth detection device" detects minute cracks on the surface of the measured object by passing a high-frequency current through the measured object, and this high-frequency current flows close to the surface of the measured object. It is designed to detect.

In other words, the crack depth detection device described above is a crack inspection device that applies a current to the object to be measured and detects the depth of the crack based on the potential difference. an AC constant current device, an input terminal connected to the AC constant current device and installed near a crack in the object to be measured, an amplifier connected to the signal generator via a transformer, and the signal generator. One end of the lock-in amplifier is connected to the lock-in amplifier, which is adjusted to amplify the generated potential difference at the same frequency, and the other end is connected between the input terminals and near the crack in the object to be measured. The depth of the crack in the object to be measured is detected using an output terminal installed in the lock-in amplifier and a voltmeter that reads the potential difference between the lock-in amplifiers.

(Problem to be Solved by the Invention) However, since the crack depth detection device described above uses alternating current of a single frequency, there are many cracks with different sizes and shapes distributed on the surface of the object to be measured. In the case of crack measurement or buried defects, it is necessary to measure many times by changing the frequency, which requires a lot of time and effort. When a fixed object is coated with a coating, it is necessary to determine the coating layer of the object, and the above-mentioned single frequency measurement method requires even more time and effort. In addition to being complicated, measurement errors occur, making it difficult to detect crack depth etc. with high accuracy.

The present invention has been made in view of the above-mentioned circumstances, and effectively and appropriately utilizes the skin effect of alternating current to prevent cracks, oxidation corrosion, and microstructures that occur and propagate on the surface of a structural member as an object to be measured. An object of the present invention is to provide a method and apparatus for detecting damage to a structural member, which enables highly accurate and efficient measurement of the size (dimensions), shape, position, distribution, etc. of a damaged area, such as changes in damage area.

, -6- [Structure of the Invention] (Means for Solving the Problem) The present invention connects a high-speed current amplifier to a function generator that generates an AC constant current waveform in each frequency band so as to amplify the current waveform. A current supply terminal connected to the high-speed current amplifier is brought into contact with the structural member so as to apply an alternating current to the structural member, and a voltage measurement terminal is brought into contact with a structural member beside the current supply terminal to detect the voltage. A transformer that amplifies the detected voltage is connected to this voltage measurement terminal, and a fast Fourier transform analyzer that decomposes the amplified voltage into each frequency band is connected to this transformer. It is constructed by connecting an arithmetic device equipped with a storage device for numerically analyzing voltage data decomposed into frequency bands, and connecting a display device to this arithmetic device.

(Function) The present invention applies an AC constant current from a high-speed current amplifier to a current supply terminal that is in contact with a structural member, and detects a voltage from a voltage measurement terminal that is in contact with a structural member beside the current supply terminal. Then, this voltage is input to a calculation device equipped with a display device and a storage device through a transformer, a fast Fourier transform analyzer, and a transmission device, and the voltage is decomposed into each frequency band based on the data input in advance to this calculation device. The size, shape, position, and distribution of cracks in the structural member are detected, and the detected amount of each crack is converted into a damage amount using a predetermined calibration curve, which is displayed on the display device. This is a structural damage detection method.

(Example) Hereinafter, the present invention will be described with reference to an illustrated embodiment.

In FIGS. 1 to 3, reference numeral 1 denotes a function generator that generates an AC constant current waveform in each frequency band. This high-speed current amplifier 2
A plurality (a pair in the figure) of current supply terminals (input terminals) 4a and 4b held by the positioning and holding member 3 are connected to the terminals.

Moreover, as shown in FIG.
A plurality of (
In the figure, a pair of voltage measurement terminals (output terminals) 5a and 5b are attached so as to come into contact with each other to detect voltage. Furthermore, a transformer 6 is connected to each of the voltage measurement terminals 5a, 5b so as to amplify the detected voltage, and the voltage amplified by the fast Fourier transform analyzer 7 is connected to the transformer 6 in each frequency band. They are connected in such a way that they can be taken apart. In addition, this fast Fourier transform analyzer 6 includes:
An arithmetic device 9 equipped with a storage device 8 is connected to perform numerical analysis of voltage data decomposed into each frequency band through a transmission device 10, and a display device 11 is connected to this arithmetic device 9. There is.

In particular, as shown in FIG. 2, the arithmetic unit 9 first calculates the reference voltage Eo measured at the same position of the structural member W of the same shape without cracks, which is inputted and stored in the storage device 8 in advance. Then, the ratio E/E o of the voltage E of the structural member W as a damaged material transmitted from the high-speed toggle conversion analyzer 7 is calculated for each frequency band.

On the other hand, E/Eo, which was determined in advance by measuring a sample with artificial cracks, and the size, shape, and position of the crack,
Calibration curve data with crack parameters such as crack density is retrieved from the storage device 8, and the input value of E/Eo is determined. At this time, the frequency band of the calibration curve between the E/Eo data and the crack parameters is selected so that they match under the most sensitive conditions.

Furthermore, calibration line data representing the correlation between the crack parameters and the amount of damage (in the case of fatigue, expressed as a ratio between the number of repetitions and the number of fatigue fractures) is read from the storage device 8, and the Determine the amount of damage. This amount of damage is displayed on the display device 11 (see FIG. 2).

Hereinafter, the effects of the present invention will be explained.

Therefore, each current supply terminal 4a%4b and each voltage measurement terminal 5a, 5b are brought into contact with the surface of the structural member W in advance.

Next, since the AC constant current waveform of a plurality of frequency bands is oscillated from the function generator 1, the current of the AC constant current waveform of the plurality of frequency bands includes many frequencies. A rectangular wave as shown in Figures (A) and (B) is applied. The current of the AC constant current waveform in each frequency band is amplified by the high speed current amplifier 2, and then the AC constant current from the high speed current amplifier 2 is applied to each current supply terminal 4a, 4b in contact with the structural member W. By applying voltage, if there is a damaged part Wa due to a crack in this structural member W, each of the voltage measurement terminals S a s5b that is in contact with the structural member W beside each of the current supply terminals 4a and 4b detects the voltage,
This output voltage is amplified by the transformer 6 and inputted to the fast Fourier transform analyzer 7, which fast Fourier transform analyzer 7 Fourier transforms the input voltage.
Spectrum decomposition into voltages in each frequency band. This spectrum-decomposed voltage data of each frequency band is inputted through the transmission device 10 to an arithmetic device 9 equipped with a display device] 1 and a storage device 8.

In this way, the voltage data of each frequency band input to the calculation device 9 is obtained by decomposing the voltage into each frequency band based on the data input to the calculation device 9 in advance, as described above. The size, shape, position, and distribution state of the cracks Wa in the structural member W are detected, and the detected amount of each crack is converted into a damage amount using a predetermined calibration curve and displayed on the display device 11. ing.

Next, in another embodiment of the present invention shown in FIGS. 4 to 6, for example, a structural member W as an object to be measured having a crack Wa caused by a stator blade of a gas turbine is Damaged parts are detected by applying alternating current.

That is, in FIGS. 4 to 6, an AC amplifier 12 capable of amplifying up to IMHz is connected to a function generator 1 that generates an AC constant current waveform in each frequency band so as to amplify the current waveform. A plurality of current supply terminals (input terminals) 4a and 4b (a pair in the figure) held by the positioning and holding member 3 are connected to the AC amplifier 12. or,
The current supply terminals 4a, 4b are attached so as to apply an alternating current to a structural member W, which is an object to be measured, which has a crack Wa caused by, for example, a stator blade of a gas turbine. A plurality of (a pair in the figure) voltage measurement terminals (
The output terminals 5a and 5b are attached so as to be in contact with each other to detect voltage.

Further, a transformer 6 is connected to each of the voltage measurement terminals 5a, 5b so as to amplify the detected voltage, and a fast Fourier transform analyzer 7 is connected to the transformer 6.
are connected so that the amplified voltage is decomposed into each frequency band. Also, this fast Fourier transform analyzer 7
, the computer 14 equipped with the disk device 13 is
The computer 14 is connected to perform numerical analysis of voltage data decomposed into each frequency band through a P-IB interface 15, and a CRT display device 6 is connected to the computer 14.

-13-,l Therefore, each current supply terminal 4a, 4b and each voltage measurement terminal 5a, 5b are brought into contact with the surface of the structural member W in advance.

Next, by applying a rectangular wave AC constant voltage of, for example, 50H2 from the function generator to flow a constant current, the current of this rectangular wave AC constant voltage waveform is as shown in FIGS. 5(A) and (B). As shown in , the result of Fourier analysis of the constant current voltage waveform shows a rectangular wave, and since this rectangular wave continuously contains many frequency components, the current of the AC constant voltage waveform in each frequency band are amplified by the AC amplifier] 2, and then connected to the respective current supply terminals 4a, 4 that are in contact with the structural member W.
By applying an alternating current constant current from the high-speed current amplifier 2 to b, if there is a damaged part Wa in this structural member W due to a crack, each voltage that comes into contact with the structural member W beside each of the current supply terminals 4a and s4b is reduced. The measurement terminals 5a and 5b detect the voltage, and this output voltage is amplified by the transformer 6 and inputted to the fast Fourier transform analyzer 7, which performs Fourier transform on the input voltage,
Frequency - ] 4 - Spectrum decomposition into wave number band voltages. This spectrally decomposed voltage data of each frequency band is
- input to the computer 14 equipped with the second disk drive 13 through the IB interface 15;

In this way, the voltage data of each frequency band manually entered into the computer 14 is stored in advance in this computer]4.
Based on the input data, the voltage is decomposed into each frequency band to determine the size of the crack Wa in the structural member W,
The shape, position, and distribution state of cracks are detected, and the amount of each detected crack is converted into the amount of damage using a predetermined calibration curve.
It is designed to be displayed on the display device 16.

As shown in FIG. 6, the computer 14 first receives spectrum data of the reference voltage Eo measured at the same position of the structural member W, which is a static vane of the same shape without cracks, from the disk device 13. Then, the ratio E/E o of the structural member W as damaged material to the voltage E is calculated for each frequency band.

On the other hand, the calibration curve data of the optimum frequency band E/Eo, the maximum crack size, and the crack density at E/Eo, determined in advance by measuring artificially cracked samples, is used in the disk device. Call from 13.

In particular, in this specific example, the maximum crack length is as shown in the graph showing the relationship between voltage ratio and maximum crack length in Figure 7.
There is a linear relationship with E/Eo in the low frequency band of 500 Hz, and crack density has a linear relationship with E/Eo in the high frequency band of 5 kHz, as shown in the graph showing the relationship between voltage ratio and crack density in Figure 8.
There is a linear relationship with E o.

Therefore, the frequency band of the calibration curve for detecting the maximum crack length is called from the data in the low frequency band of 500 Hz, and the frequency band of the calibration curve for detecting the crack density is called from the data in the high frequency band of 5 KHz. ,E/
From the measured spectrum data of Eo, select data for each frequency band to determine each crack parameter.

Furthermore, as shown in the graph showing the relationship between maximum crack length and fatigue damage in Figure 9 and the graph showing the relationship between crack density and fatigue damage in Figure 10, the maximum crack length β and fatigue damage n/ The relationship between Nf (n is the number of repetitions, Nf is the number of fatigue failures of the material) and the relationship between crack density and fatigue damage n/Nf are called up, the fatigue damage value is calculated from each crack parameter, and the fatigue damage value is displayed on the CRT display device 16. The crack distribution state and damage evaluation results of the structural member W of the object to be measured as the stationary blade are displayed.

On the other hand, FIGS. 11 and 12 show, for example, a structural member W made of a conductor as an object to be measured that has cracks Wa or oxidized corrosion parts Wc caused by the rotor blades of a gas turbine. Prevents oxidation and corrosion, e.g. Pt
- It is coated with a corrosion-resistant coating wb having different electrical conductivity, such as a coating formed by diffusion of Al or a coating formed by thermal spraying of CoCrAIY. was formed.

A structural member W made of a conductor is used as an object to be measured that has cracks Wa or oxidized corrosion parts We caused by the rotor blades of a gas turbine.
Based on the specific example shown in FIG. Damage detection can be detected and displayed on the CRT display device 16.

Furthermore, when the structural member W made of a conductor is an object to be measured that has a crack Wa or an oxidized corrosion part Wc caused by the rotor blade of a gas turbine shown in FIGS. 11 and 12, when the corrosion-resistant coating wb peels off, the As shown in the graph of the relationship between voltage and defect location from the blade surface in Figure 13, the voltage corresponding to a high frequency (e.g., 5 kHz) with a penetration depth that best matches the location where delamination has occurred is Low frequency (
For example, since the voltage changes significantly compared to the voltage corresponding to 500 Hz, the presence of peeling can be confirmed. Furthermore, when the change is uniform over a relatively wide area such as in a degraded layer, the current supply terminals 4a and 4b and the voltage measurement terminals 5a and 5b are moved and scanned together by the positioning holding part 3. By measuring while moving, defects can be locally detected.

In the structural member W coated with the film wb in this manner, damaged parts such as cracks, thinning, peeling, and altered layers can be detected non-destructively, efficiently, easily, and with high precision.

〔Effect of the invention〕

As described above, according to the present invention, an alternating current constant current from a high-speed current amplifier is applied to a current supply terminal in contact with a structural member, and a voltage measurement terminal in contact with a structural member adjacent to the current supply terminal is applied with an AC constant current from a high-speed current amplifier. Detects the voltage, inputs this voltage through a transformer, a fast Fourier transform analyzer, and a transmission device to an arithmetic unit equipped with a display device and a storage device. The size of the crack in the structural member is determined by disassembling each
The shape, position, and distribution state of cracks are detected, and each detected amount of cracks is converted into damage amount using a predetermined calibration curve and displayed on the display device, so the surface of the structural member as the object to be measured is Not only can the depth of damage areas such as cracks, oxidation corrosion, and changes in structure that occur and propagate in the substrate be detected with high precision and efficiency, but the detection means can detect them all at once in each frequency band, so it can be detected in a short time. without spending any effort on
Moreover, it is possible to detect the crack depth with high precision without error, and also to detect the size of the crack in the coated structural member.
It has excellent effects such as being able to nondestructively detect oxidation, peeling, deterioration, and damage states.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the structural member damage detection method and apparatus of the present invention, and FIG. 2 is a diagram for explaining the structural member damage detection method of the present invention and an arithmetic unit incorporated in the apparatus. , FIG. 3 is a perspective view showing a crack state of a gas turbine stationary blade as an example of a structural member as an object to be measured;
Figure 5 is a block diagram showing another embodiment of the present invention.
Figures (A) and (B) are diagrams showing the results of frequency analysis of voltage and rectangular wave current and the relationship between voltage and frequency, and Figure 6 is a diagram showing the method and apparatus for detecting damage to structural members of the present invention. Figure 7 is a graph showing the relationship between voltage ratio and maximum crack length. Figure 8 is a graph showing the relationship between voltage ratio and crack density. Figure 9 is a graph showing the relationship between voltage ratio and crack density. A graph showing the relationship between length and fatigue damage, FIG. 10 is a graph showing the relationship between crack density and fatigue damage, and FIG. 11 is a graph showing the relationship between crack density and fatigue damage.
71I is a side view showing a gas turbine rotor blade as another example of a structural member as a treasure; FIG. 12 is an enlarged sectional view taken along the chain line A-A in FIG. 11; FIG. It is a graph showing the relationship between the voltage ratio in the blade and the defect position from the blade surface. 1...Function generator, 2...High speed current amplifier, 4 a
%4b...Current supply terminal, 5a %5b...
Voltage measurement terminal, 6...Transformer, 7...Fast Fourier transform analyzer, 8...Storage device, 9...Arithmetic device,]
0... Transmission device, 11... Display device, 12... AC amplifier, 13... Disk device, 14... Computer, 15... GP-IB interface, 16
...CRT display device. Fig. 3■ -----1g -to-m-, -1 Frequency kHz (A) Fig. 4 Time t, m5eC (B) Fig. 5 14 Shadow? ] 1st side - Reloading device FE
＼-E's Spectrum EO's Spectrum-Loview 1 N-Kusetsu-1 EE. 500Hz ”” 1E/EO spectrum ゛E/Eol
1 Maximum crack length (L) mm l II o3. Original frequency f Go0' Fig. 7 Fatigue damage n/N f Fig. 9 Fig. 11 Fatigue damage n/Nf Fig. 10 Fig. 12

Claims (1)

[Claims] 1. A constant AC current from a high-speed current amplifier in each frequency band is applied to a current supply terminal in contact with a structural member, and a voltage measurement terminal in contact with a structural member beside the current supply terminal; This voltage is input to a calculation device equipped with a display device and a storage device through a transformer, a fast Fourier transform analyzer, and a transmission device. The size, shape, position, and distribution of cracks in the above-mentioned structural member are detected by breaking it down into bands, and the detected amount of each crack is converted into the amount of damage using a predetermined calibration curve, which is displayed on the above-mentioned display device. A method for detecting damage to a structural member, characterized in that: 2. A function generator that generates an AC constant current waveform in each frequency band, a high-speed current amplifier that is connected to this function generator and amplifies the current waveform, and a high-speed current amplifier that is connected to this high-speed current amplifier and applies AC current to the above structural members. A current supply terminal contacts a structural member near the current supply terminal to detect voltage, and a voltage measurement terminal connects to this voltage measurement terminal to amplify the detected voltage. a fast Fourier transform analyzer connected to this transformer that decomposes the amplified voltage into each frequency band, and a fast Fourier transform analyzer that is connected to this fast Fourier transform analyzer and performs numerical analysis of the voltage data decomposed into each frequency band through a transmission device. What is claimed is: 1. A damage detection device for a structural member, comprising: an arithmetic device having a storage device for storing information; and a display device connected to the arithmetic device.