JPH0926413A - Method and device for detecting partial change in state of object to be measured - Google Patents

Abstract

(57) [Abstract] [Purpose] Having a first plate portion and a plate surface facing the plate surface of the first plate portion with a gap, and being integral with the first plate portion, Alternatively, the object to be measured is provided with a portion composed of the first plate portion and the second plate portion joined to each other, and the thickness of the first plate portion and the second plate portion of the portion is different, or 1,
The occurrence of defects in the second plate portion is detected. [Configuration] An object to be measured is vibrated at a portion where bending-type and torsion-type vibrations are generated in the portion. Spectral analysis is performed on the stationary vibration wave generated in the DUT. The frequency difference of the spectrum that is divided into two due to the higher-order vibration of the torsional vibration that occurs in the above-mentioned portion in the spectrum group of the stationary vibration wave is calculated. Based on the calculated frequency difference, a change in thickness between the first plate portion and the second plate portion or a defect caused in the first plate portion or the second plate portion is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is, for example, a turbine blade (blade) used in a turbine engine, in which two plate parts face each other with their plate surfaces having a predetermined gap. The present invention relates to a method and an apparatus capable of detecting a change in the thickness of two plate portions caused by a change in the state of the plate surfaces of the two plate portions of an object to be measured having a state portion.

[0002]

2. Description of the Related Art Cracks in structures such as parts of machines and products,
Defects such as cavities and dents that are called "su" may cause various inconveniences. Therefore, parts with defects such as cracks, cavities, and dents can be detected in advance and eliminated. It is desirable to do.

As a method for detecting a crack or the like, a nondestructive inspection method has been conventionally known. For example, an ultrasonic flaw detection method by reflection of an ultrasonic wave or a sound at the time of crack generation by AE (acoustic emission) is known. Detection method by
There are a CCD camera observation method, an X-ray photography method, a color check method, and the like.

[0004]

By the way, in a structure such as a part, in order to reduce the weight and to provide a gas or liquid flow passage therein, a shape in which two plate-like bodies are bonded together is formed. Many have a part (including the case of being configured as one body).

For example, a blade portion of a turbine blade of an aircraft turbine engine has a structure in which two plate-like members facing each other with a predetermined gap therebetween are joined at several bridging portions. Have Then, the space partitioned by each bridging portion is configured to serve as a flow passage for heated air.

Since hot air passes through the blade portion of the turbine blade as described above, the inner wall surface thereof is oxidized.
Then, with use time, a crack or the like is generated in the oxidized portion, the inner wall surface portion is peeled off, and the plate-like body forming the blade portion becomes thin. Therefore, it is important to monitor the thickness of the plate-like body that constitutes the blade portion to determine the deterioration of the turbine blade and the necessity of repair.

However, it takes a very long time to measure the change in the thickness of the blade portion by the above-mentioned conventional nondestructive inspection method.
Sometimes it took time. Further, most of the above-mentioned conventional nondestructive inspection methods are contact type inspection methods in which measurement is performed while the sensor is in contact with the inspection site, and are not suitable for the determination of defects inside the blade portion.

In view of the above points, the present invention has an object to be measured provided with a portion in which the two plate portions as described above face each other with their plate surfaces facing each other with a predetermined gap. It is an object of the present invention to provide a method and an apparatus capable of detecting a defect generated on the inner surface of the portion and detecting the resulting change in the thickness of the plate portion of the portion quickly and easily. .

[0009]

The present invention was created from the results of the research conducted by the inventor of the present invention. That is, the inventor of the present invention vibrates an object to be measured including a portion in which two plate portions as described above are in a state of facing each other with their plate surfaces having a predetermined gap, The resulting vibration of the object to be measured can be picked up in a non-contact manner, and the stationary vibration wave of the object to be measured in the picked up vibration was spectrally analyzed.

Then, spectral peaks appear at some natural frequency positions that are determined according to the shape or structure of the object to be measured, and if one pays attention to the higher order spectrum of the vibration of the torsion system among them, the It was found that the spectrum was divided into two based on the difference in the thickness of the two plate portions of the part, and the frequency difference between the two spectra corresponded to the difference in the thickness.

It is considered that this is because the torsional vibration is caused by a plate having a large thickness having a higher vibration frequency than a plate having a thin thickness. Therefore, if the inside of the plate portion is peeled off due to the occurrence of cracks, the thickness of the plate at that portion is thinned accordingly, so that the frequency difference is expanded. Therefore, by monitoring the frequency difference, it is possible to detect a change in the difference in thickness between the two plate portions of the object to be measured.

The present invention is based on the results of this research. The above-mentioned object to be measured is vibrated at a portion where vibration of bending system and torsional system is generated at the portion, and the object to be measured is generated. The stationary vibration wave is spectrally analyzed, and the frequency difference Δf of the spectrum that is divided into two due to the higher order vibration of the torsional system vibration generated in the portion of the spectrum group by the stationary vibration wave is calculated, and the calculated frequency difference A change in the thickness of the first plate portion and the second plate portion or a defect caused in the first plate portion or the second plate portion is detected based on Δf. Is characterized by.

[0013]

When there is a change in the thickness relationship between the first and second plate portions of the portion of the object to be measured for some reason, the change in the thickness is the first and second The change in the relative thickness of the plate portion is detected by being reflected in the change in the frequency difference Δf.

Then, for example, when the first and second plate portions initially have substantially equal thicknesses to each other, a defect such as a crack occurs inside one of the first and second plate portions, and as a result, peeling of that portion occurs. If it occurs, the frequency difference Δf increases as the peeling increases, due to the change in the thickness between the first and second plate portions. Therefore, by monitoring the frequency difference Δf, the frequency difference Δf
It is possible to detect the occurrence of a defect having a size proportional to.

Even when the outer surfaces of the two plate portions are shaved to reduce the plate thickness and the two plate portions differ in thickness, according to the present invention, the thicknesses of the two plate portions are reduced. It goes without saying that the difference in size can be detected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method and apparatus for detecting a partial change in the state of an object to be measured according to the present invention will be described below with reference to the drawings. The embodiment described below is an example in which the DUT is a turbine blade of an aircraft engine.

The inventor of the present invention has studied the change of state inside the blade portion of a turbine blade made of a material containing titanium as a main component. First, the structure of the turbine blade targeted in this example will be described.

That is, the turbine blade of this example is
For example, it has a shape and structure as shown in FIG.
FIG. 2A is a perspective view of an example of a turbine blade, and FIG. 2B is a cross-sectional view of the blade portion (X-X cross-sectional view of FIG. 2A). As shown in FIG. 2, the turbine blade includes a blade portion 11 and a blade portion 1
It is composed of a platform portion 12 to which 1 is joined and a leg portion 13 continuous with the platform portion 12, and is generally a cast product.

In this case, the turbine blade is not solid inside, and the leg portion 13 is shown by the arrow in FIG. 2A.
As shown in FIG. 2B, a hollow portion is provided as a flow passage 18 for sending air into the blade portion 11 from the side and discharging the air from the blade portion 11.

As shown in the cross-sectional view of FIG. 2B, the blade portion 11 has a streamlined shape as a whole,
Since it has a hollow portion that communicates with the hollow portion of the leg portion 13 inside, it has a structure in which two plate portions 14 and 15 having a streamlined curved surface are adhered in a state of facing each other with a predetermined gap. Then, the plate portion 14 and the plate portion 15 of the blade portion 11
And are connected by several bridging portions 16 so as to form an air flow passage 18.

By the way, the blade portion 11 is formed when the plate portion 14 and the plate portion 15 are formed separately by joining them at the bridging portion 16, and when the blade portion 11 is formed as a whole. In some cases, it is generally generated separately from the platform section 12. And
The blade portion 11 is a surface 12a of the platform portion 12.
On the other hand, the turbine blade is configured by joining the surface 12a and the plate portion 14 and the plate portion 15 in the plate surface direction orthogonal to each other at the joint portion 17.

A heat radiating plate 19 is provided at the tip in the height direction of the gap between the plate portion 14 and the plate portion 15. The position of this heat dissipation plate 19 is slightly lower than the heightwise ends of the plate portion 14 and the plate portion 15.
There is a step between and.

In this case, the plate portion 14 and the plate portion 15
In the case of a non-defective product, the thickness is almost equal in the initial use state. Further, although the plate portion 14 and the plate portion 15 have the same length in the height direction, the platform portion 12
Generally, the lengths of the curved lines of the curved surfaces of the plate portions 14 and 15 in the direction along the surface 12a are different. That is, the plate portion 14 and the plate portion 15 generally have different plate surface areas.

In this embodiment, the turbine blade described above is vibrated by a method such as an impact method, and the resulting vibration wave is picked up by a vibration sensor in a non-contact manner. In this case, the vibration position is a position where the bending vibration mode and the torsional vibration mode are generated with respect to the blade portion 11.

That is, as shown in FIG. 3, when the blade portion 11 is vibrated on a line segment (indicated by a broken line in the figure) connecting the central positions P0 of the second moments of area of the blade portions 11, Only the vibration wave of the vibration mode is generated. further,
When the blade portion 11 is vibrated at the center of gravity, no vibration wave in the bending vibration mode is generated. Therefore, in this embodiment, the blade portion 11 is vibrated at positions other than these positions. For example, in FIG. 3, the blade portion 11 is vibrated by impact at the position indicated by the point P1.

On the other hand, the vibration sensor SS is provided so as to face one end surface 13E of the blade portion 11 of the leg portion 13 of the turbine blade in the curved surface direction. In this case, the center position Pc of the vibration sensor SS is arranged so as to match the center position of the thickness L2 of the end surface 13E of the leg portion 13. Further, the center position Pc of the vibration sensor SS is about 15 mm from the lower end of the platform portion 12,
Downward.

By the impact excitation, as described above, the vibration wave of the bending vibration mode, the vibration wave of the torsional vibration mode, and the stationary vibration wave of both modes are generated in the blade portion 11.

This vibration wave is detected by a vibration sensor SS having a sharp directivity.
Fig. 4
As shown in FIG. 5 and FIG. 5, the spectrum peaks 21, 22, 23, 24, 25, 2 at the frequency positions corresponding to the size of the turbine blade and the components of each of the above vibration modes.
6 and 27 are obtained. Peak 21 of these spectra
The frequencies at which .about.27 stand are f1, f2, f
3, f4, f5, f6, f7, the frequencies f1 to f
The spectrum group of 3 can be a primary spectrum group, and the spectrum group of frequencies f4 to f7 can be a secondary spectrum group. The spectra of the frequencies f1 and f4 are due to the bending vibration mode, the spectra of the frequencies f2 and f5 are due to the torsional vibration mode, and the spectra of the frequencies f3 and f6 and f7 are a mixture of both vibration modes (mainly the torsional mode). System vibration).

Here, the spectrum 2 of frequencies f4 to f7
In the group of 4 to 27, the blade portion 11 is the plate portion 14 and the plate portion 15.
Generally, the dimensions of the blade portion 11 of FIG. 2 of the plate portions 14 and 15 (in this example, the plate portions 14 and 15 are
This is a component caused by the difference in the curved length of the curved surface of. When the blade part 11 is not a plate composed of two plate parts but a plate-shaped part, these groups of spectra 24 to 27 do not occur.

The spectrum of the frequency f3 is a component when the vibration of one of the plate portion 14 and the plate portion 15 transits to the longitudinal vibration of the other plate portion, and the frequency f3
6 and the frequency f7 are considered to be components when the vibration of the other plate portion of the plate portion 14 or the plate portion 15 transits to the vibration of the higher harmonic wave of the one plate portion. The frequency of the spectrum of the vibration of the torsional system in which the torsional vibration mode and the bending vibration mode are mixed is divided into the frequency f6 and the frequency f7.
This is because the vibration frequency of this twisting system starts to be different due to the difference in thickness between the plate portion 14 and the plate portion 15 when the vibration becomes higher than the next.

FIG. 4 shows the spectral distribution of the stationary vibration wave when the turbine blade in the initial state in which the plate portion 14 and the plate portion 15 are not so different in thickness is excited, and FIG. 5 is shown. Steady vibration waves generated when a turbine blade in a state where the inner wall surfaces of the plate portions 14 and 15 are peeled off by use and the difference in thickness between these plate portions 14 and 15 is large is excited. FIG.

Here, comparing the difference Δf between the frequencies f6 and f7 in FIGS. 4 and 5, it can be seen that the frequency difference Δf in FIG. 5 is larger than the frequency difference Δf in FIG. In this embodiment, in order to quantify this frequency difference Δf, a value normalized by the frequency f6 is used. That is, the plate portion 14
And the index indicating the relative thickness difference between the plate portion 15 and
Then, Ig = (f7−f6) / f6 (1)

It can be seen that the greater the index Ig, the greater the difference in thickness between the plate portion 14 and the plate portion 15.
As described above, since the turbine blade is a non-defective product and has the same thickness in the initial state, a large index Ig means that the peeling caused mainly by the cracks formed on the inner wall surface of the plate portion 14 or the plate portion 15. Means that
This means that the occurrence of cracks is substantially detected.

It is needless to say that the detection is made including the case where the outer wall surfaces of the plate portions 14 and 15 are not shaved and the thicknesses of the plate portions 14 and 15 are changed. Absent.

By the way, in the turbine blade which is the object to be measured of this embodiment, when the thickness of the plate portion 14 and the plate portion 15 becomes thin, the bending vibration modes of the respective frequencies f1 to f1.
It was found that f7 was affected, and therefore it was found that the above-mentioned arithmetic expression for defect detection could not make accurate determination.

That is, according to the research conducted by the inventor of the present invention, the frequencies at which the first-order spectrum 21 and the second-order spectrum 24 due to the vibration waves in the bending vibration mode stand even when the thickness of the plate portions 14 and 15 changes. Since f1 and f4 correspond to the area dimensions of the plate surfaces of the plate portion 14 and the plate portion 15,
Almost no change, but the frequencies f2, f3, f5, f6 and the frequency f7 of the spectrum due to the vibration of the torsion system
Was found to shift to a lower frequency as the plate thickness decreased. That is, the frequency difference between the frequencies f1 and f3 and the frequency difference between the frequencies f4 and f6 are
It has been found that the thickness of Nos. 4 and 15 becomes smaller and therefore becomes smaller.

Therefore, in the arithmetic expression (1), the plate thicknesses of the plate portions 14 and 15 are thinned, so that the frequency difference Δf is reduced, and the accurate plate portions 14 and 15 are affected.
It may not be possible to quantitatively evaluate the difference between the sheet thickness and the sheet thickness.

Therefore, in this embodiment, the following formula (2) is used instead of the index Ig represented by the formula (1).
The difference in thickness between the plate portion 14 and the plate portion 15 is expressed by using the index IG IG = {(f7-f6) / f6} ÷ {(f6-f4) / (f3-f1)} (2) Make a quantitative evaluation of.

That is, in the arithmetic expression (2), (f6
The term −f4) / (f3-f1) is a component of the ratio of the thicknesses of the plate portions 14 and 15, and when the plate portions 14 and 15 have the same thickness, the value is “1”. Therefore, by normalizing the calculation result of the calculation formula (1), the plate portion 1
It is possible to eliminate the influence of the change in the plate thickness of Nos. 4 and 15.

Next, an embodiment of a device for detecting a partial state change of an object to which the above-described method is applied will be described with reference to the drawings. FIG. 1 shows an embodiment of the apparatus of this example, and 31 is an object to be measured, which is the turbine blade described above in this example. Reference numeral 32 is a vibration device, and 33 is a control device having, for example, a microcomputer. DUT 3
1 is mounted on a measurement stage 34 made of a cushion material.

The control device 33 drives the vibration device 32,
The measured object 31 is vibrated. In this example, the vibration device 32
Is, for example, a pendulum-like impacting object such as a weight, which impacts the DUT 31 with an impulse, for example. The drive mechanism of the weight is configured by a cam mechanism or the like so that the weight is immediately separated from the object to be measured after the impact. It should be noted that the vibration may be performed a plurality of times instead of once, and moreover, a plurality of different parts may be vibrated. However, the vibration position is
As described above, both the bending vibration mode and the torsional vibration mode necessarily occur.

The DUT 3 vibrated as described above
The vibration No. 1 is contactlessly detected by the vibration sensor 36 of the output vibration receiving device 35, converted into an electric signal, and subjected to predetermined signal processing by the signal conditioner 37. Any sensor can be used as the sensor 36 as long as it can detect vibration, and a displacement meter or the like can also be used. However, in order to prevent noise and vibration from the surroundings to be picked up as much as possible, it is preferable to have a sharp directivity in the direction of the DUT 31.

In the signal conditioner 37, the electric signal is amplified, and unnecessary high and low frequency components are removed (trends are removed).

The electric signal from the output vibration receiving device 35 is
It is supplied to the arithmetic processing / determination device 40. This calculation process
The determination device 40 has, for example, a microcomputer,
The calculation processing and the determination operation described later are performed by software, and this processing is shown in a functional block diagram of FIG.
become that way.

By the way, the vibration which is a problem here is the natural vibration of the shape of the object to be measured. However, when the measured object is forcibly vibrated, the forced vibration and the like are mixed with the natural vibration (longitudinal vibration as a standing wave).
Therefore, it is desirable to remove as much as possible other than these natural vibrations. In this example, this requirement is satisfied as follows.

With respect to the forced vibration, the influence is removed by setting the measurement start point of the signal from the sensor 35 to the time point when a predetermined time has elapsed after the vibration. That is, when the object 31 to be measured is vibrated by the impulse impact method, the measurement is started from a point in time just after a short time has passed immediately after vibrating by giving an impact or the like.

In this case, the time from the time of impact to the start of measurement can be determined as follows. That is, the velocity c of the sound wave propagating through the DUT 31 depends on the Young's modulus E (elastic coefficient) and the density ρ of the object, and has a relationship of c ² = E / ρ. Then, for example, in the case of the impulse impact method of this example, the time-series waveform of the vibration picked up immediately after the impact is as shown in FIG. 6A.

As can be seen from the waveform of FIG. 6A, since the vibration after the vibration is the same as that of the seismic wave, the longitudinal wave and the slow wave having a high velocity are mixed as described above, and the vibration However, the forced vibration remains, and the natural vibration waveform peculiar to the shape of the DUT 31 is not formed. It is considered that the natural vibration wave peculiar to this shape is observed shortly before the stop, for example, in the “small motion” of the top. For this reason, we set a rectangular wave window W1 as shown in Fig. 6B,
In this example, an oscillating wave is extracted by this window W1.

That is, the electric signal input to the arithmetic processing / determination device 40 is supplied to the gate means 41. Then, by the window signal W1 from the window W1 forming means 42, the object to be measured 31 after being vibrated, that is, impacted.
A natural vibration component of the shape of the object 31 to be measured is extracted from the vibration. The window forming means 42 receives the information on the start of vibration from the control device 33, and immediately after the impact, the window W
Set the time until the start-up of 1 and the window width. In the example of the case of FIG. 6, the window W1 is started at the time point 20 msec has passed immediately after the impact and the window width of 200 msec is set.

As described above, the natural vibration component of the shape of the object 31 to be measured is extracted by the window W1. Then, the natural vibration portion is converted into digital data by the A / D conversion means 43 and written in the memory means 44. Then, this digital data is read out from the memory means 44, supplied to the spectrum analysis means 45, and spectrum-analyzed.

The frequencies f1 to f7 detecting means 46 detect the peaks 21 to 27 of the spectrum from the spectrum obtained by the spectrum analyzing means 45 and obtain the frequencies f1 to f7 of the peaks 21 to 27 of each spectrum. The peaks 21 to 27 of the spectrum are detected in a predetermined frequency range, for example, a frequency range of 20 kHz or less, from the peak of the spectrum in order from the largest value, and the peak 21 is sequentially detected from the lowest frequency. , Peak 22, ..., Peak 27 are determined. Then, the frequencies f1 to f7 of the peaks 21 to 27 are obtained.

The frequencies f1 to f obtained by the detecting means 46
7 is supplied to the calculation / determination means 47, and the calculation of the above-mentioned calculation formula (2) is performed. Then, the calculation / judgment means 47 judges the difference in thickness between the plate portion 14 and the plate portion 15 of the turbine blade. This judgment is
When the value IG of the result of the arithmetic expression (2) is, for example, a predetermined value or more, it means that the object to be measured is defective, or a defect has occurred inside. And the judgment result,
The value IG of the calculation result of the calculation means 47 is used as the control device 33.
Send to

The control device 33 sends the value IG and the determination result to the output means 50. The output unit 50 displays the value IG and information on the determination result on a display or prints out on recording paper. Alternatively, voice notification is given.

By displaying or printing out the output means 50, a defect on the inner wall surface of the plate portion 14 or the plate portion 15 due to the defect occurs and the plate portion 14 or the plate portion 1 due to the defect.
The change in plate thickness of No. 5 can be quantitatively known.

[0055]

As described above, according to the present invention, the object to be measured is vibrated, the stationary vibration wave generated in the object to be measured is picked up in a non-contact manner, and the spectrum analysis is performed on the stationary vibration wave. The change in the thickness of the two plate portions and the change of the plate portion in the portion where the two plate portions of the object to be measured face each other with the plate surfaces of each of the two plate portions having a predetermined gap therebetween. Not only the outer wall surface but also the inner wall surface can be detected.

Further, according to the present invention, it suffices to excite the object to be measured and pick up the resulting vibration with a sensor in a non-contact manner to analyze the spectrum. Such inconvenience does not occur, and stable and reliable detection can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a detection apparatus for a partial state change of an object to be measured according to the present invention.

FIG. 2 is a diagram for explaining an example of an object to be measured which is an object of the present invention.

FIG. 3 is a diagram for explaining an example of a vibration position of an object to be measured which is an object of the present invention.

FIG. 4 is a difference in thickness between the two plate portions of the object to be measured in a state where the two plate portions face each other with their plate surfaces facing each other with a predetermined gap. It is a figure which shows the spectrum distribution of a stationary vibration wave when is small.

FIG. 5 is a difference in thickness between two plate portions of the object to be measured in a state where the two plate portions face each other with their plate surfaces having a predetermined gap therebetween. It is a figure which shows the spectrum distribution of a stationary vibration wave when is large.

FIG. 6 is a diagram for explaining a part of the embodiment of FIG.

[Explanation of symbols]

 11 Blade part 14 Plate part 15 Plate part 31 Object to be measured 32 Vibrating device 33 Control device 34 Output vibration receiving device 45 Spectral analysis means 46 Frequency f1 to f7 detection means 47 Calculation / judgment means

Claims (2)

[Claims] 1. A first plate portion, and a plate surface facing the plate surface of the first plate portion with a gap, and the first plate portion.
The object to be measured, which is integrated with the plate part of or of the second plate part joined to the first plate part, at a site where bending and torsional vibrations occur at the part. Then, the stationary vibration wave generated in the object to be measured is subjected to spectrum analysis, and the frequency difference of the spectrum divided into two due to the higher order vibration of the torsional vibration generated in the portion in the spectrum group of the stationary vibration wave is calculated. Then, based on the calculated frequency difference, the first plate portion,
A method of detecting a partial state change of an object to be measured, which detects a change in thickness with the second plate portion or a defect generated in the first plate portion or the second plate portion. 2. A first plate portion, and a plate surface facing the plate surface of the first plate portion with a gap, and the first plate portion.
The object to be measured, which is integrated with the plate part of or of the second plate part joined to the first plate part, at a site where bending and torsional vibrations occur at the part. Vibrating means, pickup means for picking up the vibration of the object to be measured and converting it into an electric signal, means for receiving a signal from the pickup means, and analyzing the stationary vibration wave of the object to be measured, A means for calculating a frequency difference between spectra that are divided into two due to a higher-order vibration of a torsional vibration occurring in the portion of the spectrum group due to the stationary vibration wave, and the first frequency difference calculated based on the calculated frequency difference. Board part,
A change in the thickness of the second plate portion or a means for quantitatively detecting a defect generated in the first plate portion or the second plate portion, Detection device.