JPH0381082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fatigue test piece crack tip position detecting device for detecting the crack tip position of a fatigue test piece used for metal materials.

[Conventional technology]

For fatigue measurement of metal materials, the shape and dimensions are B.S5762.
−1979（Methods for crack opening
displacement testing), etc.
A fatigue test piece (hereinafter abbreviated as test piece) 1 with a crack (fatigue crack) 2 as shown in FIG. 1 was used. In addition, this test piece 1 is one in which a crack 2 of a predetermined length is inserted from the tip of a mechanical notch (hereinafter abbreviated as notch) 3 machined in the center of the test piece 1 using a fatigue testing machine. Therefore, in the machining operation of the crack 2, it is necessary to monitor the length of the crack 2, that is, the position of the tip of the crack.

By the way, there is a device for detecting the position of the crack tip as disclosed in Japanese Patent Application No. 12098/1983, for example.
In this method, a test piece with a marked line as a reference line is set in a fatigue testing machine, and a load is repeatedly applied to the test piece. Note that this load has an amplitude of several hundred μ and a frequency of approximately 30 Hz. While such a load is being applied, the surface of the test piece is illuminated and imaged with an ITV camera (industrial television camera) through a microscope. The video signal output from this ITV camera is then processed to detect the distance between the tip of the crack that occurs on the test piece and the marking line to determine the degree of fatigue.

[Problem that the invention seeks to solve]

However, in the above apparatus, since the test piece is illuminated with continuous light, the obtained image of the test piece will be blurred. In other words, as mentioned above, the load has an amplitude of several hundred μ and a frequency of approximately 30Hz, but in contrast, the field of view when capturing images with an ITV camera must be approximately several mm in consideration of resolution. Therefore, if an image is taken using continuous illumination, the image will be blurred due to the vibration of the test piece, making it impossible to detect the crack tip position with high precision.

Furthermore, the width of a crack that occurs in a test piece varies from several microns to several tens of microns depending on the internal and surface conditions of the test piece. Therefore, if a particularly narrow part of a crack is not illuminated with appropriate illuminance, it may not be imaged and cannot be detected.

Therefore, in order to solve the above problems, the present invention has the following features:
It is an object of the present invention to provide a highly accurate fatigue test piece crack tip position detection device capable of accurately detecting the crack tip position without image blurring.

[Means for solving problems]

In order to achieve the above object, the present invention provides an imaging means that images the crack and the reference line of a fatigue test piece on which a reference line for obtaining the position of the crack tip has been formed in the same field of view, and irradiates illumination light onto the surface of the fatigue test piece. A strobe illumination device, a lighting control means for controlling the light emission timing of the strobe illumination device to a desired timing, and a video signal from an imaging means, and the luminance level is integrated in the same direction as the reference line direction to find the maximum level. The video signal from the reference line detection means detects the reference line position and the imaging means is subjected to binarization processing of the brightness level in the direction perpendicular to the crack direction, and then the continuity of the high level value is determined to detect the tip of the crack. A crack tip position detection means for detecting the position, and a crack tip position detection means for calculating the distance from the reference line to the crack tip position from the reference line position determined by the reference line detection means and the crack tip position determined by the crack tip position detection means. This is a fatigue test piece crack tip position detecting device comprising a tip position calculation means.

[Effect]

The present invention is provided with the above-mentioned means, so that when the fatigue test piece is irradiated with illumination light from the strobe lighting device, the fatigue test piece is imaged by the imaging means, and the reference line and crack tip are detected from the video signal obtained at this time. The position is detected and the distance between these reference lines and the crack tip position is calculated.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an external view of a fatigue test piece crack tip position detection device, and FIG. 2 is a specific configuration diagram thereof. In each figure, reference numeral 10 is a test piece, in which a notch 11 is formed as shown in FIG. is pulled into place. This marked line 13 becomes the target position for inserting the crack 12 in the COD test piece. Further, the surface of this test piece 10 is polished with fine particles of diamond or the like, and is formed into a state almost identical to a mirror surface.

Reference numerals 20 and 21 are microscopes, which are provided to obtain enlarged images of both surfaces of the test piece 10. ITV camera heads 22 and 23 are attached to these microscopes 20 and 21, and are controlled by ITV camera controllers 24 and 25, respectively, to take magnified images through the microscopes 20 and 21, and transmit the video signals to a signal processing device. The signal is sent to a marking line detecting means 32 and a crack tip position detecting means 33 via a camera changeover switch 31 of 30.

Furthermore, 26 and 27 are strobe illumination devices, which irradiate the surface of the test piece 10 with illumination light R from a position having a predetermined angle θ, for example, 30° with respect to the optical axis G of each microscope 20 and 21. It is something. By the way, the emission timing of these strobe lighting devices 26 and 27 is determined by each ITV camera head 22 and 23.
This is done at a time interval in which the afterimage is sufficiently attenuated. Specifically, each ITV camera controller 24,
A synchronization signal generation circuit 34 that sends a synchronization signal to 25
A frequency dividing circuit 35 receives the synchronization signal from the synchronous signal and divides the frequency at a predetermined frequency division ratio, and each strobe lighting device 26, 27 receives the frequency divided output of this frequency dividing circuit 35.
A strobe controller 36, 3 that operates to emit light.
It consists of 7. The camera changeover switch 31 receives the divided output of the frequency dividing circuit 35 and alternately passes video signals from the ITV camera heads 22 and 23 in synchronization with the flashing operation of the strobe lighting devices 26 and 27. There is.

Next, the marking line detection means 32 integrates the brightness level of the video signal in the same direction as the marking line 13 in the image to obtain the maximum brightness level, and calculates the position of the marking line 13 from this maximum brightness level position. It has a detection function and is composed of a horizontal direction integration circuit 38 and an integral value peak position detection section 39.

Further, the crack tip position detection means 33 converts the video signal into a binary signal, and then high-level values are continuously generated from the image data obtained from the binary signal, and this satisfies a certain continuity condition. The filter circuit 40 and the binarization circuit 41 have the function of detecting a crack 12 by determining whether
and a noise removal circuit 42.

The distance detecting section 43 has a function of determining the distance between the marking line position determined by the respective means 32 and 33 and the crack tip position, and this distance is displayed on a display section 44, for example, a monitor television. It is becoming more and more common.

In addition, this device has a preset value for the distance between the marking line 13 and the crack tip position (including when the crack tip position reaches the marking line) for stopping the fatigue testing machine (not shown). A stopping distance setting circuit 45 and a fatigue testing machine stop signal generating circuit 46 for sending a stop signal K to the fatigue testing machine are provided.

Next, the operation of the apparatus configured as described above will be explained. The images of the marking lines 13 and cracks 12 magnified by the microscopes 20 and 21 are shown on the ITV
Enter the camera head 22, 23 into the fourth screen.
Adjustments such as the position are made so that the image is as shown in Figure a. Also, strobe lighting devices 26, 27
The illuminance and the like are variably adjusted so that the marking lines 13 and cracks 12 are emphasized and imaged. In other words, the diffusely reflected light from the marking line 13 and the crack 12 is imaged. In addition, the colors are reversed in FIG. 4a.

Now, in this state, the synchronization signal generation circuit 34
When a synchronization signal is sent from the ITV camera controllers 24 and 25, each ITV camera head 22 and 23 starts imaging and outputs the video signal.

At the same time, the synchronizing signal is frequency-divided by a frequency dividing circuit 35, and is transmitted to, for example, the ITV camera heads 22, 23.
It is output as a frequency-divided signal with a period twice as long as the afterimage time. Therefore, by alternately sending this frequency-divided signal to each strobe controller 36, 37, each strobe lighting device 26, 27 will alternately emit light in synchronization with the frequency-divided signal. As a result, each strobe lighting device 26, 27 is
The light is emitted at a cycle longer than the afterimage time of the ITV camera heads 22 and 23. In this manner, video signals when the strobe lighting devices 26 and 27 emit light are sent through the camera changeover switch 31 to the marking line detection means 32 and the crack tip position detection means 33.

In the scribe line detecting means 32, first, the integrated value of the luminance level of the video signal is determined by the horizontal integration circuit 38. That is, the integrated value of the luminance level is determined in the same direction as the scribe line 13 in the image shown in FIG. 4a. Then, the brightness level in the horizontal direction as shown in FIG. Here, since the crack 12 is imaged in white, the brightness level is high, but in order to integrate in the direction of the marking line 13, the brightness level due to the crack 12 is removed.

On the other hand, at the same time as the marking line detecting means 32 operates, the crack tip position detecting means 33 performs the following operation. That is, A- shown in FIG.
The video signal on A' has a high level value in the crack portion, as shown in FIG. 5a. The video signal is passed through a filter circuit 40 in order to emphasize this crack part and to prevent it from being affected by changes in the overall brightness level due to changes in the measurement target or the like. This filter circuit 40
The video signal passed through has a waveform as shown in FIG. 5B, for example, and the crack 12 is detected by sending this signal to the binarization circuit 41 and binarizing it. That is, the binarization circuit 41 detects the maximum value of the video signal in each scanning line, and places a crack 12 at the position on the scanning line where the maximum value is detected.
is detected as existing. However, since it is meaningless to detect the maximum value on a scanning line where crack 12 does not exist, a certain threshold level L is set, and maximum value detection is performed only for signals above this threshold level L. . In this way 2
The image obtained from the converted signal is the image shown in Figure 5c, but at the threshold level L it is not possible to sufficiently extract only the crack 12, and the image contains noise components. . This noise component is, for example, a polishing flaw that occurs when the test piece 10 is polished, or a waveform of the same type as the waveform detected in the crack part in the scribe line 13, and these polishing flaws and the same type of waveform are erroneously detected as noise. It is to be done.

Therefore, the noise component is removed by the noise removal circuit 42. That is, the noise removal circuit 42 uses a window as shown in FIG. 6a. This window is based on a certain point B and has a predetermined length horizontally and vertically from this point B, and the number of high levels (maximum value) in this window, that is, the density of points in the window is greater than or equal to a predetermined value. If it is, the function determines that point as part of a crack, and if it is less than a predetermined value, it is erased as noise. Therefore, it is determined whether the high level portions are occurring continuously. Figure 6b
shows the binarized signal level in the noise component portion Q1 shown in FIG. 7, and the high level portion (different color in FIG. 6b) is irregular. Further, FIG. 6c shows the crack 12 at Q2, where a high level is continuously generated. When the noise components are removed in this way, the image becomes
It will be as shown below. Then, the tip position 12a of the crack 12 is detected. After this, a window is applied again to determine a crack, but this window has a lowered window density threshold, which lowers the probability that even a crack 2 will be determined as noise. There is.

Then, the marking line position and the crack tip position determined by each means 32, 33 are sent to the distance detecting section 43, where the distance from the marking line 13 to the crack tip position 12a is determined and displayed on the display section 44. will be displayed. When this distance becomes less than or equal to the distance set in the stop distance setting circuit 45, the fatigue test stop signal generation circuit 46 sends a fatigue test stop signal K to the fatigue testing machine. Note that the display section 44
The image displayed on each strobe lighting device 26, 2
7 is an image when the light is emitted, so it is an intermittent image. Therefore, by providing an image memory and configuring it to store one frame of image data, the surface image of the test piece 10 can be displayed as a still image without causing any monitoring problems to the operator. Finish.

In this way, in the above embodiment, when the fatigue test piece 10 is irradiated with strobe illumination light by the strobe illumination devices 26 and 27, the fatigue test piece 10 is imaged by the ITV camera heads 22 and 23, and the images obtained at this time are Since the marking line 13 and the crack tip position 12a are detected from the video signal and the distance between them is calculated, the captured image of the fatigue test piece 10 is not blurred and the crack tip position 12a can be accurately determined. Can be measured. In other words, the test piece 1 at the moment when the strobe lighting devices 26 and 27 emit light.
Since the image is taken at 0, even if the test piece 10 is vibrating, it is not affected by the vibration and a blur-free image can be taken. Furthermore, since the light emission timing of the strobe lighting devices 26 and 27 is set at intervals equal to or longer than the afterimage time of the ITV camera heads 22 and 23, measurements can be made without being affected by afterimages. That is, since television cameras generally have afterimages of several fields, the strobe lighting devices 26 and 27 are connected to the ITV camera heads 22 and 23.
When the test piece 10 is imaged by emitting light every time in synchronization with the field scanning, the following afterimage occurs.
That is, after one field has elapsed from the current image shown in FIG. 8a, the image becomes an image in which the scribe line 13 and crack tip position 12a have changed position due to vibration as shown in FIG. 9. Therefore, if this is imaged with a conventional device using continuous illumination, the image will be superimposed as shown in FIG. 10 due to the afterimage of the ITV camera head. In this case, the marking line 13'
is detected, but the crack tip position is at 12 of the afterimage.
may be detected, making it impossible to accurately detect the position of the crack tip.

However, in the device of the present invention, since images are taken at a time interval longer than the afterimage time, it is possible to accurately detect the crack tip position 12' without being affected by the afterimage.
The distance between a and a can be measured accurately.

Furthermore, this device can provide the following effects.

The position of the crack tip can be measured automatically and in a non-contact manner.

Since the crack tip position 12a can be measured completely unaffected by differences in the shape and steel type of the test piece 10, there is no need for calibration even if the type of the test piece 10 is changed.

Cracks on both sides of the test piece 10 can be detected, and the average value of the crack tip positions on both sides can be measured as the crack tip position of the test piece 10.

Furthermore, it is also possible to perform the detection for two ITV camera heads individually, and when detecting cracks 12 on both sides of one test piece 10 in this way, two cracks can be detected from the images obtained by the two ITV camera heads. It is also possible to determine the distance by determining the distance between the marked lines and detecting the average warpage value.

Note that the present invention is not limited to the above-mentioned embodiment, and can be modified without departing from the spirit thereof.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to provide a highly accurate fatigue test piece crack tip position detecting device that can eliminate image blur and accurately detect the crack tip position.

[Brief explanation of drawings]

Fig. 1 is an external view showing an embodiment of the fatigue test piece crack tip position detection device according to the present invention, Fig. 2 is a specific configuration diagram of the device of the present invention, and Fig. 3 is an example of the device applied to the device of the present invention. Side view of fatigue test piece, Figure 4a
is a diagram showing an image of a test piece obtained by the apparatus of the present invention, FIG. 4b is a brightness distribution diagram for detecting marked lines, and FIGS. 5a to 5d are diagrams for explaining the crack detection operation. Figures 6a, b, c to 7 are diagrams for explaining noise component removal in the device of the present invention, and Figures 8 to 10 are ITV
Diagram for explaining the afterimage of the camera head, No. 11
The figure is a side view of a fatigue test piece. 10... Fatigue test piece, 20, 21... Microscope,
22, 23...ITV camera head, 24, 25
...ITV camera controller, 26, 27...
Strobe lighting device, 30...Signal processing device, 31
...Camera changeover switch, 32...Marking line detection means, 33...Crack tip position detection means, 34
... Synchronization signal generation circuit, 35 ... Frequency division circuit, 3
6, 37... Strobe controller, 43... Distance detection section.

Claims (1)

[Scope of Claims] 1. An imaging means for capturing an image of a crack of a fatigue test piece on which a reference line for obtaining the crack tip position is provided and the reference line in the same field of view, and a strobe for irradiating illumination light onto the surface of the fatigue test piece. An illumination device, a lighting control means for controlling the emission timing of the strobe illumination device to a desired timing, and a video signal from the imaging means to integrate the luminance level in the same direction as the reference line direction to find the maximum level. and a reference line detecting means for detecting the reference line position by using a reference line, and a video signal from the imaging means is subjected to a binarization process of the brightness level in a direction perpendicular to the crack direction, and thereafter, continuity of high level values is determined. crack tip position detection means for detecting the crack tip position by
crack tip position calculation means for calculating a distance from the reference line to the crack tip position from the reference line position obtained by the reference line detection means and the crack tip position obtained by the crack tip position detection means. A device for detecting the crack tip position of a fatigue test piece. 2. The fatigue test specimen crack tip position detection device according to claim 1, wherein the strobe lighting device is installed at a predetermined angle with respect to the surface of the fatigue test specimen so that a predetermined amount of diffusely reflected light is generated from the crack and the reference line. 3. The fatigue test piece crack tip position detection device according to claim 1, wherein the illumination control means causes the strobe illumination device to emit light at a time interval longer than the afterimage time of the imaging means.