JPH05223717A - Instrument for automatically measuring extending dimension of crack - Google Patents

Abstract

PURPOSE:To automatically, very accurately, and easily measure the extending dimension of a crack even when the surface of a test piece is scratched or contaminated. CONSTITUTION:A video camera 34 takes pictures of a crack generated in a test piece 10 and a picture processor 48 fetches the pictures gn of the crack at prescribed time intervals, forms differential pictures from the pictures gn-gn-1, detects the maximum absolute value Dmax of luminance in the differential pictures, and binarizes the differential pictures, and then, a picture measuring instrument 52 measures the position of the front end of the crack on the pictures by detecting the front end on the differential pictures. A computer 50 calculates at least the extending dimension of the crack as the sum of the displacement amounts of the front end measured in each cycle. When the maximum value Dmax exceeds a reference value, the computer 50 does not calculate the extending dimension, but increases 'r' by '1' in the next cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automatically measuring the size of cracks developed in a test piece in a fracture mechanical test of a material, and more particularly to an automatic measuring device for the size of crack growth. Pertain.

[0002]

CT, which is one of the fracture mechanical tests for materials
As one of the devices for automatically measuring the size of cracks in the test, Japanese Patent Application No. 4- (Reference No. A) filed by the same applicant as this applicant and another applicant.
T-4779), a test piece support device that supports a test piece and applies a load to the test piece, an imaging device that images a crack generated in the test piece and converts it into an electrical crack image, and an imaging device. An image processing device that takes in a crack image at every predetermined time, subtracts a crack image of a predetermined cycle from the crack image of the current cycle, and forms and stores a differential image that has undergone low resolution processing and a difference, An image measuring device that detects the tip of the crack on the image and measures the position of the crack tip on the difference image, and a signal indicating the position of the crack tip from the image measuring device is input, and at least the amount of displacement of the crack tip is input. There has been proposed an automatic measuring device for a crack growth dimension, which has an arithmetic and control unit for calculating the crack growth dimension as a total of the above.

According to the automatic measuring device according to the above-mentioned proposal, even if there are scratches or stains other than cracks on the surface of the test piece, those portions are located at the same position in the crack image of each cycle. Since it appears, scratches and stains are erased by subtraction of the image when forming the difference image, and only the changed portion between the two cycles, that is, the newly developed portion of the crack is left in the difference image. Therefore, it is possible to reliably detect the tip of the crack in the differential image subjected to the low resolution processing by the image measuring device and accurately measure the position of the crack tip on the differential image. Even if there are scratches or stains other than the cracks on the cracks, the progress dimension of the cracks can be measured very accurately and easily and automatically.

[0004]

Particularly when a CT test is performed in a vibration mode in which a tensile load is repeatedly applied to a test piece, cracking occurs when the maximum tensile load is applied to the test piece. As shown in FIG.
As shown in FIG. 5, the image acquisition timing Tg of the image processing apparatus is various response delay time ΔT from the time Tp at which the control signal output from the control apparatus to the load generating apparatus such as the hydraulic cylinder reaches the maximum value in the pulling direction. In consideration of the above, the time is set to a later time point.

However, the response delay time ΔT is not always a constant value, but varies within a certain range due to various factors as shown in FIG. Thus, when the response delay time ΔT fluctuates, the position of the crack of the test piece with respect to the imaging device slightly fluctuates, so that the image can be subtracted in the state where the cracks and the like are accurately aligned when forming the difference image. However, depending on the degree of misalignment between the two images, the tip of the crack may not be detected by the image measurement device, or scratches or stains other than the crack may be erroneously determined to be a part of the crack. In this case, the tip of the crack cannot be reliably detected and its position cannot be accurately measured, which may cause a failure to accurately measure the progress dimension of the crack.

In view of the above-mentioned problems in the automatic measuring device according to the above-mentioned proposal, the present invention erroneously detects the tip of the crack on the difference image and measures its position inaccurately. It is an object of the present invention to provide an improved automatic measuring apparatus for crack growth size, which can prevent the above and thereby automatically and very accurately measure the crack growth size.

[0007]

According to the present invention, there is provided a test piece supporting device for supporting a test piece and applying a load to the test piece, and an image of a crack generated in the test piece. An imaging device that converts this into an electrical crack image, and the crack image is taken in from the imaging device at predetermined time intervals.
Is a positive integer, r is a positive integer less than n, and n-r cycle crack images are subtracted from n cycle crack images to form a difference image, and the maximum value Dmax of the absolute value of the brightness in the difference image is formed. An image processing device that detects and reduces the resolution of the difference image to form and store the difference image subjected to the resolution reduction, and detects the tip of the crack on the difference image subjected to the resolution reduction. An image measuring device that measures the position of the crack tip on the difference image, and a signal indicating the position of the crack tip from the image measuring device is input, and the crack progress dimension is calculated as the total amount of displacement of at least the crack tip. When the maximum value Dmax exceeds a predetermined value, the arithmetic and control unit does not calculate the crack extension size in the cycle, and the image processing apparatus in the next cycle. Increase the r by 1 It is accomplished by the automatic measuring apparatus crack growth dimension, characterized in that is configured to form a differential image by.

[0008]

[Function] In the crack image, the brightness of the crack portion where the reflected light amount is low is negative and the brightness of the portion other than the crack where the reflected light amount is high is positive. If the position of the crack in the gap occurs, the brightness of the part where the part of the crack is subtracted from the part other than the crack when forming the difference image becomes a positive high value, and conversely the part other than the crack than the part of the crack. The luminance of the portion where is subtracted becomes a high negative value, and the absolute value of any of these values becomes higher than the absolute value of the luminance of the portion other than the crack and the portion of the crack in the original crack image. Therefore, by detecting the maximum value of the absolute value of the brightness in the difference image and determining whether or not the maximum value exceeds the reference value, the cracks in the two crack images provided for forming the difference image are detected. It is possible to determine whether the positional deviation is within the allowable range, that is, whether the difference image is properly formed.

According to the above-mentioned structure, the difference image is formed by subtracting the n-r cycle crack image from the n cycle crack image, and the difference image is subjected to the low resolution process to obtain the low resolution. Since the differential image that has been subjected to the digitization process is formed and the tip of the crack is detected in the differential image, if there is no deviation between the two crack images, there are scratches or stains other than the crack on the surface of the test piece. However, those parts do not appear in the difference image, only the newly developed part of the crack appears in the difference image, and scratches and dirt other than the crack are erroneously identified as part of the crack. Never.

Further, according to the above configuration, the maximum value Dmax of the absolute value of the brightness in the difference image is detected, and when the maximum value Dmax exceeds the predetermined value due to the displacement between the two crack images, the cycle concerned. In this case, the crack growth size is not calculated and r is incremented by 1 in the next cycle to form a differential image. Therefore, in the differential image that was not properly formed, that is, a flaw other than a crack is formed. The crack extension dimension is not calculated based on the position of the tip of the crack detected in the difference image in which dirt or stains may be erroneously identified as a part of the crack.

Therefore, according to the above-described structure, the difference image is a difference image formed by subtracting two crack images that are not displaced from each other, that is, scratches or stains other than the crack are part of the crack. There is no risk that it will be erroneously identified as being, the progress dimension is calculated based on the position of the tip of the crack that was detected and the position was measured in the properly formed difference image, so the crack on the surface of the test piece Even if there are scratches or stains other than the above, the crack propagation dimension can be automatically measured very accurately and easily.

[0012]

[Supplemental Description of Means for Solving the Problems] According to one detailed feature of the present invention, the image pickup device and the test piece support device are arranged so that the image pickup device moves in the direction of crack propagation relative to the test piece. A moving device for moving at least one relative to the other is provided, and when the crack tip exceeds a predetermined position in the difference image, the moving device is operated by the arithmetic and control unit so that the imaging device or the test is performed. The one-sided support device is configured to be moved by a predetermined relative movement amount. With this configuration, it is not necessary to constantly monitor whether the tip of the crack protrudes from the visual field, and the visual field is automatically updated. The difference image is not formed in the cycle immediately after the moving device is operated.

Further, when the moving device is incorporated as described above, the arithmetic and control unit causes the total amount of displacement of the crack tip generated in each cycle after the moving device is finally operated and the image pickup device or the test piece support. It may be configured to calculate the crack propagation dimension as the sum of the total relative movement of the device, in which case the accuracy of the moving device and within the range of measurement error due to image distortion error factors only. It is possible to accurately and easily automatically measure the crack growth size.

Generally, since the difference in the displacement amount of the crack tip between successive cycles is very small, the arithmetic and control unit determines the position of the crack tip in the n cycle and the n-r cycle when the moving device is not operated. The amount of displacement of the crack tip is calculated as a deviation from the position of the crack tip at the time, and when the moving device is operated, the amount of displacement of the crack tip calculated one cycle before is regarded as the amount of displacement of the crack tip in the current cycle, The crack propagation dimension may be calculated as the total amount of displacement of the crack tip in each cycle, in which case the crack propagation dimension is measured accurately and easily without depending on the accuracy of the moving device. Is possible, and the moving device does not have to be highly precise.

The resolution lowering process in the present invention means that the brightness level of the difference image is reduced based on a predetermined brightness such as 2 gradations rather than 20 gradations.

[0016]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing one embodiment of an automatic measuring apparatus for crack growth dimensions according to the present invention, FIG. 2 is an enlarged front view showing a test piece, and FIG. 3 is taken along line III-III in FIG. It is a plane sectional view of a test piece.

In FIG. 1, reference numeral 10 denotes a test piece to be subjected to a CT test. The test piece 10 has an upper arm 14 and a lower side of a CT test apparatus 12 as a test piece supporting device at the upper and lower ends, respectively. It is supported by the arm 16 via pins not shown in FIG. Upper arm 14 is C
The lower arm 16 is fixed to a frame 18 of the T-test device 12, and the lower arm 16 is connected to a hydraulic cylinder 20. The hydraulic pressure of the hydraulic cylinder 20 is controlled by the hydraulic control device 22 so that the vertical static tension load or the repeated load (vibration load) is applied to the test piece 10. As shown in FIGS. 2 and 3, the test piece 10 has a substantially rectangular plate shape and has an apex angle 60 for facilitating crack initiation.
It has a chevron notch 24 of 0 ° and two pin insertion holes 26 and 28 on both sides of the notch for receiving pins not shown in FIG.

A table 30 is fixed to the frame 18 of the CT test apparatus 12, and a three-dimensional stage device 32 is provided on the table. The stage device 32 includes a main body 32a fixed to the table 30 and a moving member 32b that is displaced relative to the main body. A video camera 34 as an imaging device is fixed to the moving member 32b, and an optical microscope 36 is attached to the video camera 34. The optical microscope 36 includes an objective lens barrel 38,
A light source device 40 that irradiates the test piece 10 with light through the objective lens barrel, and a naked eye 42 looks into the test piece 10 before the test is started to roughly position the optical microscope 36 and the video camera 34 with respect to the tip of the notch of the test piece. And an eyepiece lens barrel 44 for.

The moving member 32b of the stage device 32 is relative to the main body 32a in the X direction (direction perpendicular to the plane of FIG. 1), the Y direction (vertical direction), and the Z direction (direction perpendicular to the X and Y directions). The stage control device 46 controls the relative movement and positioning of the moving member 32b with respect to the main body 32a in units of μm. Thus, the stage device 32 and the control device 46
The video camera 34 according to the progress of cracks in the test piece.
A moving device is configured to move relative to the test piece.

The video camera 34 takes an image of the test piece and the crack generated in the test piece, and converts it into an electric signal of a crack image of 20 gradations consisting of an image signal (voltage ± 10 V) and a position signal (x, y). Then, the electric signal is output to the image processing device 48. The image processing device 48 receives a crack image g _n from a video camera at predetermined time intervals based on an instruction from a personal computer 50 (hereinafter referred to as “personal computer”).
Of the electric signal of g _n −g _nr (r =
A difference image G _N is formed by subtracting a positive integer), and a positive constant voltage offset is given to the electric signal of the difference image G _N by kV (k is a positive integer). Further, the image processing device 48 detects the maximum value Dmax of the absolute value of the brightness in the offset image thus offset and outputs it to the personal computer 50, and binarizes the difference image to generate an image signal (voltage 0V). , 1V) and position signal (x,
y) is converted into an electric signal of a difference image that has been binarized, and the electric signal is converted into an electric signal.
It is designed to output to 4.

Especially when a cyclic load is applied to the test piece, there is a delay in the response of the hydraulic cylinder 20 and the like to the control signal from the hydraulic control device 22, so the test piece 1
In order that the crack image is captured at the time when the maximum tensile load is applied to 0, the timing of capturing the image by the image processing device 48 is more than that at the time when the control signal from the hydraulic control device 22 reaches the maximum value in the tensile direction. It is set to a time point that is later by a predetermined time in consideration of the response delay. Further, in the difference image formed by the image processing device 48, the part common to the images g _n and g _nr is deleted by subtraction, so
Of the crack 56 as shown in FIG.
During the cycle, only the newly developed portion 56a appears, and no portion of the crack that has developed up to the previous cycle, scratch 58a on the surface of the test piece, dirt, etc. appear.

Further, in the offset processing by the image processing device 48, the crack portion and the portion other than the crack are clearly distinguished, and the tip of the crack is surely detected by the image measuring device 52 in FIG. As shown, the difference image is shifted from the black side to the white side, that is, to the high brightness side. Further, in the binarization processing by the image processing device 48, the voltage of the crack portion is processed to be 0V and the voltage of the portion other than the crack is 1V, whereby the monitor 54 is displayed as shown in FIG. The part 56 of the crack is black and the part 58 other than the crack is
Is displayed in white with two gradations. It is also possible to reverse the display by inverting the black and white of the monitor.

The image measuring device 52 can take out the 0V signal in the binarized difference image and store the position thereof, thereby detecting the tip 60 of the crack and detecting the tip of the crack on the difference image. The position (x, y) is measured and a signal indicating the measurement result is output to the personal computer 50 and the monitor 54.

The personal computer 50 has a general structure having a main body 62 having functions such as calculation and storage, a keyboard 64, and a color monitor 66, and outputs a control signal to the hydraulic control device 22 to cause a CT test device to operate. 12 controls the start and stop of the operation of the stage 12, and also controls the stage controller 46.
A control signal is output to control the relative movement of the video camera 34 and the optical microscope 36 with respect to the crack generated in the test piece. Further, the personal computer 50 calculates the crack growth dimension L _N in the X direction based on the signals from the image processing device 48 and the image measurement device 52, and outputs a signal indicating the crack growth dimension L _N to the printer 68 and the plotter 70 as described later. It is designed to output to.

When measuring the crack propagation dimension in the CT test in the vibration mode using the automatic measuring device thus constructed, the test piece 10 is first set in the CT test device 12, and the video camera 34 and An optical microscope 36 is positioned in a position substantially aligned with the tip of the notch in the specimen. Then, by inputting a measurement start command to the personal computer 50 via the keyboard 64, the CT test and the measurement of the crack propagation dimension are started according to the flowcharts shown in FIGS. 6 and 7.

Next, the operation of the illustrated first embodiment will be described with reference to the flow charts shown in FIGS. 6 and 7. In these figures, N indicates the number of cycles of vibration applied to the test piece 10 by the hydraulic cylinder 20 of the CT test device 12, and m indicates the number of stage movements, that is, the video by the stage device 32 and the control device 46. The number of times the camera 34 is moved relative to the test piece 10 is shown, and n is the number of cycles after the stage is moved. Further, r indicates a cycle difference when forming a difference image, and a flag F relates to whether or not the stage has been moved.
Indicates that the cycle is immediately after the stage is moved.

First, in step 10, various initial settings are performed. That is, as shown in FIG. 5, the measurement start line 72 on the screen is the tip 24 of the notch 24 of the test piece.
The position x _c0 on the screen of the first measurement start line is set so as to coincide with a, and the position x _cm (m = 1, 2, 3, ...) of the measurement start line on the screen after the stage movement is set. The position x _s of the field-of-view change line 74 on the screen as a criterion for determining whether or not the stage needs to be moved is set, the measurement cutoff length L _c is set, and the cycle numbers N and n and the stage movement number m are Each is set to 0, and the cycle difference r and the flag F are set to 1.

In step 20, the vibration of the test piece 10 by the hydraulic cylinder 20 is started, and in the next step 30, whether or not the present time is the image acquisition timing based on the control signal from the hydraulic control device 22. If it is determined that it is not the image capture timing, step 30 is repeatedly executed, and if it is determined that it is the image capture timing, step 4 is executed.
The process proceeds to 0, and the cycle numbers N and n are each incremented by 1.

In the next step 50, the video camera 3
The image g _n (raw image) picked up by No. 4 is taken into the image processing device 48, and it is judged in step 60 whether the flag F is 1 or not, and it is determined that F = 1. When the determination is made, the flag F is reset to 0 in step 70 and then the process returns to step 30, and when it is determined that F = 1 is not satisfied, the process proceeds to step 72. In step 72, it is determined whether or not the cycle difference r is less than n-1, and when it is determined that r <n-1 is not satisfied, the process returns to step 30 and r <n-1. When it is determined that the value is, the process proceeds to step 80.

The image g from the image g _n is At a step 80
By subtracting _{nr, a} difference image G _N is formed,
In step 85, k is applied to the electric signal of the difference image G _N.
Positive offset processing is performed at V. In step 90, it is determined whether or not the maximum value Dmax of the absolute value of the brightness in the offset-processed difference image is equal to or less than the reference value Dc, and it is determined that Dmax≤Dc. Sometimes, the routine proceeds to step 95, and when it is determined that Dmax ≤ Dc is not satisfied, the cycle difference r is incremented by 1 at step 91 and then the routine proceeds to step 92.

In step 92, it is determined whether or not the cycle difference r is 4, and when it is determined that r = 4 is not satisfied, the process returns to step 30 and r = 4 is determined. When the determination is made, the process proceeds to step 93. r = 4
The case where the determination is made means that the image misalignment when forming the difference image occurs twice in succession, which means that the image capture timing is not appropriate.
In step 93, the test piece 1 by the hydraulic cylinder 20
The vibration for 0 is stopped, and in step 94, an alarm is displayed on the monitor 66 of the personal computer 50 to the effect that the CT test and the measurement of the crack development dimension are not performed properly, and then in FIGS. 6 and 7. The control according to the flowchart shown is ended.

In step 95, it is determined whether or not the cycle difference r is 1, and when it is determined that r = 1 is not satisfied, the cycle difference r is 1 in step 96.
After being reset to step 100, the process proceeds to step 100, and when it is determined that r = 1, step 100 is performed as it is.
Go to.

In step 100, the electric signal of the offset-processed difference image G _N is binarized by the image processor 48 to form and store the binarized difference image. .. In step 110, the tip position x _n of the crack in the difference image is detected by the image measuring device 52, and x _n is output to the personal computer 50.

In step 120, the total amount of cracks propagated in the same field of view, that is, the total amount I _n of cracks propagated in each cycle after the last stage movement is performed is the following number. Calculated according to 1. In step 130, the crack propagation dimension L _N is calculated according to the following equation 2 and stored in the storage device.

## EQU1 ## I _n = x _n -x _cm

## EQU2 ## L _N = I _n + ΣS _m (m = 1 ... m)

In step 140, for example, x _n is x
_It is determined whether or not the tip of the crack has crossed the field-of-view change line by determining whether or not _s has been exceeded, that is, whether or not there is a need to move the stage, and there is no need to move the stage. When the determination is made, step 190
When it is determined that the stage needs to be moved, the process proceeds to step 150.

In step 150, the stage movement number m is incremented by 1, and in step 160, the tip of the crack is located at the position x _{cm of} the next measurement start line set in step 10 in the difference image. The stage movement amount S _m is calculated according to the following equation 3 so as to move to, and then the process proceeds to step 170.

[Equation 3] S _m = x _n −x _cm

In step 170, the image is step 1
The video camera 34 is moved relative to the test piece 10 by the stage device 32 and the controller 46 so that the video camera 34 moves in the direction opposite to the crack propagation direction by the value S _m calculated in 60. Then, in step 180, the cycle number n is reset to 0 and the flag F is set to 1. Then, the process returns to step 30.

In step 190, the crack propagation dimension L _N is set to the measured cutoff length L set in step 10.
_If it is determined whether or not it is greater than or equal to _c , and if it is determined that L _N ≧ L _c is not satisfied, then the process returns to step 30 and L
_If it is determined that _N ≧ L _c , step 2
Proceed to 00. In step 200, the hydraulic cylinder 20
Vibration of the test piece 10 due to is stopped, and step 2
In No. 10, the crack propagation dimension L _N (N = 1, 2, 3, ...
6) is output to the printer 68 and the plotter 70, and FIG.
And the control by the flowchart shown in FIG. 7 is ended.

Thus, according to this first embodiment, FIG.
As shown in FIG. 4, the position of the measurement start line 72 in the X direction is set to coincide with the tip 24a of the notch 24 of the test piece in the N = n = 0 cycle, and in the N = n = 1 cycle. Position x ₁ of the tip 60 of the crack 56 is detected,
The total crack growth amount I ₁ (= x ₁ −x _c0 ) and the crack growth dimension L ₁ (= I ₁ ) are calculated. If it is determined that the maximum value Dmax of the absolute value of the brightness in the difference image exceeds the reference value Dc in N = n = 2 cycles, the position x ₂ of the tip of the crack is not detected and the crack is not detected. The total amount I ₂ of cracks and the size L _{2 of} crack growth are not calculated.

As shown in the figure, when the position of the tip of the crack exceeds the visual field changing line 74 in N = n = 3 cycles,
This At a cycle is detected crack image g ₃ from cracking image g ₁ is located x ₃ of the tip of the crack At a difference image G ₃ formed by being subtracted progress quantity I ₃ cracks (=
x ₃ −x _c0 ) and the crack _propagation dimension L ₃ (= I ₃ ) are calculated, and the field of view is S ₁ (= x ₃ −) in this cycle.
x _c1 ) is moved in the crack propagation direction. N = 4 (n =
1) In the cycle, the position x ₁ of the crack tip is not detected, and therefore the total amount I ₁ of crack growth and the crack growth dimension L ₄
Is not calculated.

In the N = 5 (n = 2) cycle, the position x ₂ of the tip of the crack is detected, and the total amount I ₂ (= x of the progress of the crack) is detected.
₂₋ x _c1 ) and the crack growth dimension L ₅ (= I ₂ + S ₁ ) are calculated, and the position x ₃ of the crack tip is detected in N = 6 (n = 3) cycles, and the crack growth is detected. Quantity I ₃ (= x ₃ −
x _c1 ) and the crack growth dimension L ₆ (= I ₃ + S ₁ ) are calculated, and the crack growth dimension L _N is measured and the cut-off length L _c is obtained by performing the same processing as in the case of the cycles thereafter. L _N is automatically calculated until the above.

In this embodiment, the position x _cm of each measurement start line on the screen after the stage is updated can be arbitrarily set. However, the position x _cm of the measurement start line on the screen can be set.
_cm may be set to a constant value such as x _c0 described above.

FIGS. 9 and 10 are flow charts showing a control flow in the second embodiment of the automatic measuring apparatus for crack growth dimensions according to the present invention. In addition, in these figures, FIG.
Steps corresponding to the steps shown in FIG. 7 are given the same step numbers as those given in FIGS. 6 and 7.

In the initial setting of step 10 of this embodiment, the position x on the screen of the first measurement start line is set so that the measurement start line on the screen coincides with the tip of the notch of the test piece.
_c0 is set to x ₀ , the amount of stage movement S (constant) on the screen is set, and the position x _s of the visual field changing line 74 on the screen as a criterion for determining whether or not the stage needs to be moved.
Is set, the measurement cutoff length L _c is set, the cycle numbers N and n and the stage movement number m are set to 0, respectively, and the cycle difference r and the flag F are set to 1 respectively.

In step 120, the total amount of crack propagation I
_n is calculated according to the following expression 6, and in step 130, the crack propagation dimension L _N is calculated according to the following expression 7 and stored in the storage device.

## EQU6 ## I _n = x _n -x ₀

(7) L _N = I _n + m × S

In step 145, the reference amount x ₀ used to calculate the total amount I _n of crack propagation in step 120 after the next cycle is calculated according to the following equation 8.

X ₀ = x _n −S

In step 170, the image is step 1
The video camera 34 is moved relative to the test piece 10 by the stage device 32 and the control device 46 so as to move in the direction opposite to the crack propagation direction by the length S set at 0. The other steps of this embodiment are the same as those of the first embodiment.
It is executed in the same manner as the corresponding step of.

Thus, according to this second embodiment, FIG.
As shown in FIG. 1, in the N = n = 0 cycle, the position of the measurement start line 72 in the X direction is the notch 24 of the test piece.
The position x ₁ of the tip 60 of the crack 56 is detected in N = n = 1 cycles, and the total amount I ₁ (= x ₁ −x ₀ ) of the crack and the crack are set. The development dimension L ₁ (= I ₁ ) of is calculated. If it is determined that the maximum value Dmax of the absolute value of the brightness in the difference image exceeds the reference value Dc in N = n = 2 cycles, the position x ₂ of the tip of the crack is not detected and the crack is not detected. The total amount I ₂ of cracks and the size L _{2 of} crack growth are not calculated.

As shown in the figure, when the position of the tip of the crack exceeds the visual field changing line 74 in N = n = 3 cycles,
This At a cycle is detected by the position x ₃ in the difference image G ₃ formed Te at the crack tip by cracking image g ₁ from the crack image g ₃ is subtracted, the total advance amount I crack
₃ (= x ₃ −x ₀ ) and crack growth dimension L ₃ (= I ₃ ).
Is calculated, and in this cycle, x ₀ (= x ₃ −S) in the next cycle is calculated, so that the field of view is a constant value S.
It is moved only in the crack propagation direction. N = 4 cycles (n
= 1), the position x ₁ of the tip of the crack is not detected, and therefore the total amount I ₁ of crack growth and the size L _{4 of} crack growth are not calculated.

In N = 5 (n = 2) cycles, the position x ₂ of the tip of the crack is detected, and the total amount I ₂ (= x of the progress of the crack) is detected.
₂₋ x ₀ ) and the crack growth dimension L ₅ (= I ₂ + S) are calculated, and the position x ₃ of the crack tip is detected in N = 6 (n = 3) cycles, and the crack growth amount is calculated. I ₃ (= x ₃ −x
₀ ) and the crack growth dimension L ₆ (= I ₃ + S) are calculated, and the crack growth dimension L _N is measured as the cutoff length L by performing the same processing as in the case of the subsequent cycles.
L _N is automatically calculated until it becomes more than _c .

In each of the above embodiments, the difference image G _N
Is offset with a positive constant voltage, the image g _n may be offset with a positive constant voltage to the high brightness side as shown in FIG. may be offset processing to the low-brightness side image g _nr is at a constant negative voltage, as shown in, even image g _nr offset processed image g _n is at a constant positive voltage
May be offset with a negative constant voltage. In each of these cases, the parts common to the images g _n and g _nr are substantially erased by the subtraction in forming the difference image,
Since it is completely erased by the binarization process, only the newly developed portion between the n cycle and the n-r cycle of the crack appears as in the case of the above two embodiments, and No scratches, stains, etc. on the surface of the test piece and the parts that have progressed up to the n−r cycle appear. Therefore, the tip of the crack is accurately detected and the position is accurately measured in the binarized difference image. It

Further, in each of the above-described embodiments, for the purpose of facilitating the description, the tip 60 of the crack is the visual field changing line at the third cycle after the measurement of the crack propagation dimension is started or the stage is moved. However, in reality, the distance between the measurement start line 72 and the visual field changing line 74 is much larger than the amount of crack growth in each cycle. Alternatively, the number of cycles in which the amount of progress of cracks is measured between the stage movement and the next stage movement is several tens to several hundreds.

Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to these embodiments, and various other embodiments are also possible within the scope of the present invention. It will be apparent to those skilled in the art that

For example, the offset process itself does not form the subject of the present invention, and thus step 85 in the above-mentioned two embodiments may be omitted. Similarly, the procedure itself for calculating the crack progress dimension does not form the subject of the present invention, and as long as the crack progress dimension is calculated as at least the total displacement of the crack tip, for example, the same application as the applicant of the present application A procedure other than the calculation procedure in the above-described embodiment as in the third embodiment described in Japanese Patent Application No. 4- (Reference No. AT-4779) related to the application of a person and another applicant. The crack propagation dimension may be calculated at.

Further, the automatic measuring device of the present invention is suitable for the case where the test piece is subjected to the CT test in the vibration mode. In each of the above-mentioned embodiments, the test piece is subjected to the CT test in the vibration mode. However, the automatic measuring apparatus of the present invention may be applied to the case where the test piece is CT-tested in the tensile mode, in which case, for example, in step 30 of each of the above-described embodiments, The timer measures a constant time, and in step 50, an image is captured at a constant time.

[0057]

As is apparent from the above description, according to the present invention, a difference image is formed by subtracting an n-r cycle crack image from an n cycle crack image, and a brightness image in the difference image is formed. When the maximum absolute value Dmax of the cracks is detected and the two crack images are displaced and the maximum value Dmax exceeds the predetermined value, the crack extension dimension is not calculated in the cycle and the next cycle is calculated. Since r is increased by 1 to form a differential image, the differential image is a differential image formed by subtracting two crack images that are not mutually displaced, that is, a flaw or stain other than the crack. Since there is no risk of being erroneously identified as a part of a crack, the progress dimension is calculated based on the position of the tip of the crack that was detected and the position was measured in a properly formed difference image. Scratches and dirt on the surface of It can be automatically very accurately 且 easily measure the progress dimensions of the crack even if present.

Further, according to the present invention, even if scratches or stains other than cracks are present on the surface of the test piece as described above, the crack propagation dimension can be measured very accurately without being affected by these. As a result, the surface finishing of the test piece can be simplified, and the CT test can be efficiently performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an automatic measuring apparatus for crack growth dimensions according to the present invention.

FIG. 2 is an enlarged front view showing a test piece to be CT tested.

FIG. 3 is a plan sectional view of the test piece taken along line III-III in FIG.

FIG. 4 is an explanatory diagram showing an example of a procedure for forming a difference image, offset processing, and binarization processing.

FIG. 5 is an explanatory diagram showing an example of initial setting performed at the start of measurement of a crack growth dimension.

FIG. 6 is a flowchart showing a part of a control flow in the first embodiment of the automatic crack growth dimension measuring apparatus according to the present invention.

FIG. 7 is a flowchart showing the remaining part of the control flow in the first embodiment of the automatic crack growth dimension measuring apparatus according to the present invention.

FIG. 8 is an explanatory diagram showing a procedure of automatic measurement of a crack growth dimension according to the first embodiment.

FIG. 9 is a flowchart showing a part of a control flow in a second embodiment of the automatic crack growth dimension measuring apparatus according to the present invention.

FIG. 10 is a flowchart showing the remaining part of the control flow in the second embodiment of the automatic crack growth dimension measuring apparatus according to the present invention.

FIG. 11 is an explanatory diagram showing a procedure of automatic measurement of a crack growth dimension according to a second embodiment.

FIG. 12 is an explanatory diagram showing another example of a procedure for forming a difference image, offset processing, and binarization processing.

FIG. 13 is an explanatory diagram showing still another example of a procedure for forming a difference image, offset processing, and binarization processing.

FIG. 14 is an explanatory diagram showing a relationship between a control signal to the load generator and a load generated by the load generator.

FIG. 15 is an illustrative graph showing a variation of the response delay time ΔT shown in FIG.

[Explanation of symbols]

 10 ... Test piece 12 ... CT test device 20 ... Hydraulic cylinder 22 ... Hydraulic control device 32 ... Stage device 34 ... Video camera 36 ... Optical microscope 46 ... Stage control device 48 ... Image processing device 50 ... Personal computer 52 ... Image measuring device

Claims (1)

[Claims] 1. A test piece support device for supporting a test piece and applying a load to the test piece, an image pickup device for picking up an image of a crack generated in the test piece and converting the image into an electrical crack image, and the image pickup device. The crack image is taken in every more predetermined time, and n
Is a positive integer, r is a positive integer less than n, and n-r cycle crack images are subtracted from n cycle crack images to form a difference image, and the maximum value Dmax of the absolute value of the brightness in the difference image is formed. An image processing device for detecting and reducing the resolution of the differential image to form and storing the differential image subjected to the resolution reduction, and detecting the tip of the crack on the differential image subjected to the resolution reduction. An image measuring device that measures the position of the crack tip on the difference image, and a signal indicating the position of the crack tip from the image measuring device is input, and the crack progress dimension is calculated as the total amount of displacement of at least the crack tip. When the maximum value Dmax exceeds a predetermined value, the arithmetic and control unit does not calculate the crack extension size in the cycle, and the image processing apparatus in the next cycle. Increase the r by 1 Automatic measuring apparatus crack growth dimension, characterized in that it is configured to form a differential image by.