JPH0358644B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method and apparatus for automatically measuring the position of the crack tip of a fatigue test piece used for metal materials.

[Technical background of the invention and its problems]

For fatigue measurement of metal materials, the shape and dimensions are B,
S5762−1979（Methods for crack opening
7 stipulated in
A fatigue test piece (hereinafter abbreviated as test piece) 1 with cracks (fatigue cracks) 2 as shown in the figure is 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, examples of devices for detecting the crack tip position include a reading method using a microscope, a crack gauge method, a backplane strain method, an electric potential method, a compliance method, an ultrasonic method, an eddy current method, and an AE method. These methods will be explained below.

First, the reading method using a microscope measures the position of the crack 2 directly using a microscope, and is the only non-contact method among the above methods other than the eddy current method. Must be supervised by a lifeguard.

The crack gauge method uses test piece 1 as shown in Figure 8.
In this method, a gauge 4 is attached to the side of the gauge 4, and changes in the electrical resistance of the gauge 4 are examined. in this way,
It takes time to attach the gauge 4, and the cost of the gauge increases when a large number of test pieces 1 are tested.
Another disadvantage is that the measurement accuracy is low.

The back strain method is a method in which a strain gauge 6 is attached to the back surface of a test piece 5 as shown in FIG. 9, and is mainly used in tensile test types. Furthermore, the electric potential method is a method in which a current is passed through the test piece 1 as shown in FIG. 10, and changes in voltage at both ends of the notch are examined. In addition, the 10th
In the figure, I is an ammeter and V is a voltmeter. Both the back strain method and the electric potential method require calibration depending on the type of test piece 1.

The compliance method is a method of determining the length of the crack 2 from the load applied to the test piece 1 and the displacement of the test piece 1, but the accuracy varies depending on the calculation formula for calculating the length of the crack 2 and the shape of the test piece 1. For this reason, there is a drawback that calibration is required for each type of test piece 1.

In the ultrasonic method, a sensor is brought into contact with the test specimen 1 and moved to measure the position of the crack 2. In this method, the sensor must be moved, and the absolute value of the length of the crack 2 is measured. is difficult to measure. Furthermore, there is a drawback that the vibration of the test piece 1 tends to cause noise during measurement.

Although the eddy current method is a non-contact method, it has the disadvantage that the measurement depends on the magnetic properties of the test piece 1.

Furthermore, the AE method has problems with variations in AE mode, sound speed, and AE energy depending on the sample.

As described above, each of the above methods has its own problems. Here, as a condition for measuring the crack tip position, non-contact is desired, and of the above-mentioned methods, only the reading method using a microscope and the eddy current method are non-contact. However, since the long eddy current method has the above-mentioned problems, it is desired to automate the reading method using a microscope, which is currently the most commonly used reading method.

[Purpose of the invention]

The present invention was made based on the above circumstances, and
The object of the present invention is to provide a method and apparatus for automatically measuring the position of the crack tip of a fatigue test piece with high precision, which can automatically measure the position of the crack tip using a microscope.

[Summary of the invention]

The present invention integrates the luminance level in the same direction as the reference line from the image signal obtained by imaging cracks and the reference line that have occurred on a fatigue test piece to which a reference line has been applied, and then converts the maximum luminance level to the reference line. The system is characterized by determining the position, converting the image signal into a binary signal, detecting the crack tip position by determining the continuity of high level values, and then calculating the distance between the reference position and the crack tip position. This is an automatic method for measuring the crack tip position of a fatigue test specimen.

Further, the present invention provides a method for detecting a crack generated in a fatigue test piece on which a reference line has been provided for determining the position of the crack tip, and detecting a crack in the same direction as the reference line from an image signal obtained by imaging the reference line. The luminance level is integrated to obtain the reference line position from the maximum luminance level, and the crack tip position detecting means converts the image signal into a binary signal and determines the continuity of the high level value to detect the crack tip. detect the position,
This is an automatic measuring device for the crack tip position of a fatigue test piece, in which the crack tip position calculation means calculates the distance between the reference line position and the crack tip position detected by these detection means.

[Embodiments of the invention]

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

FIG. 1 is a configuration diagram of an automatic measuring device for the position of the crack tip of a fatigue test piece to which the method of the present invention is applied. In the figure, reference numeral 10 is a test piece, on which a notch 11 is formed as shown in FIG. being pulled into place.

Note that this marking line 13 becomes the target position for inserting the crack 12 in the COD test piece 10.

20 and 21 are microscopes, respectively, and test piece 1
These microscopes 20 and 21 are equipped with an industrial television.
ITV camera heads 22, 23 are provided.
These ITV camera heads 22, 23 are controlled by ITV camera controllers 24, 25, and the specimen 10 is magnified through each microscope 20, 21.
The video signal is sent to the signal processing device 30 via the ITV camera controllers 24 and 25.
The signal is further sent to the marking line detection means 32 and the crack tip position detection means 33 via the camera changeover switch 31 of the signal processing device 30. Note that 26 and 27 are lighting devices that illuminate the surface of the test piece 10, and 34 is a lighting device that illuminates the surface of the test piece 10.
This is a synchronization signal generation circuit that sends synchronization signals to the ITV camera controllers 24, 25 and camera changeover switch 31.

Now, 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 detects the position of the marking line from this maximum brightness level position. It is composed of a horizontal direction integration circuit 35 and an integral value peak position detection section 36.

On the other hand, 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, which satisfies a certain continuity condition. The filter circuit 37 and the binarization circuit 38
and a noise removal circuit 39.

40 is a distance detection section, which is connected to each means 3.
It has a function of calculating the distance between the scribing line 13 and the crack tip position from the crack tip position and the scribing line position determined by 2 and 33,
This distance is displayed on the display section 41.

This device also includes a stopping distance setting circuit 42 in which a set value is set for the distance between the marking line 13 and the crack tip position for stopping the fatigue testing machine (not shown), and a stopping distance setting circuit 42 that sends a stop signal to the fatigue testing machine. A fatigue testing machine stop signal generation circuit 43 is provided.

Next, the operation of the apparatus configured as described above will be explained. Marking lines 13 and cracks 12 on the surface of the test piece 1 magnified by the microscopes 20 and 21
is within one screen of the image captured by the ITV camera heads 22 and 23, and its position etc. is adjusted so that it becomes an image as shown in FIG. 3a, and
The illumination intensity etc. of each illumination device 26, 27 is varied and adjusted so that the marking line 13 and the crack 12 are uniformly imaged in white. Note that the colors are reversed in FIG. 3a.

The video signals of such images are each ITV
The signal is sent via the camera controllers 24 and 25 and the camera changeover switch 31 to the marking line detection means 32 and the crack tip position detection means 33.

In the scribe line detection means 32, first, the horizontal integration circuit 35 calculates the integrated value of the luminance level of the video signal. That is, in the image shown in FIG. 3A, the integrated value of the luminance level is determined in the same direction as the scribe line 13. Then, a horizontal brightness distribution as shown in FIG. 3b is obtained, and the integral value peak position detecting section 36 detects the maximum brightness level from this brightness distribution to determine the position of the scribe value 13. Here, since the clutch 12 is also imaged in white, its brightness level is high, but since integration is performed in the direction of the scribe line 13, the brightness level due to the clutch 12 is removed.

On the other hand, the crack tip position detecting means 33 performs the following operation. That is, the video signal on line A-A' shown in FIG. 3a has a high level value in the crack portion, as shown in FIG. 4a. The video signal is passed through a filter circuit 37 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. The video signal that has passed through this filter circuit 37 is, for example, shown in FIG.
The waveform becomes as shown in , and by sending this signal to the binarization circuit 38 and binarizing it, crack 1
2 is detected. That is, the binarization circuit 38 detects the maximum value of the video signal in each scanning line,
A crack 12 is detected as existing at the position on the scanning line where this maximum value was detected. However, since it is meaningless to detect the maximum value on a scanning line where no crack 12 exists, a certain threshold level L is set and maximum value detection is performed only for signals above this threshold level L. The image obtained from the binarized signal in this way is the image shown in Figure 4c, but at the threshold level L it is not possible to sufficiently extract only the crack 12, and the image contains noise components. It's summery. This noise component is
For example, the polishing scratches that occur when polishing the test piece 10, or the waveforms at the scribe line 13, are the same as the waveforms detected in the cracked parts, and these polishing scratches and similar waveforms are falsely detected as noise. .

Therefore, the noise component is removed by the noise removal circuit 39. In other words, the noise removal circuit 39 uses a window as shown in FIG. 5a. This window is based on a certain point A and has a certain length horizontally and vertically from that point,
If the number of high levels (maximum values) in this window, that is, the density of points in the window, is above a certain value, that point is judged to be part of a crack, and if it is below a certain value, it is judged to be noise. It is something to be erased.

That is, it is determined whether high level portions occur continuously. FIG. 5b shows the binary signal level in the noise component portion Q1 shown in FIG. 6, and the high level portion (different color in FIG. 5b) is irregular. Further, FIG. 5c shows a portion Q2 of the crack 12, where a high level is continuously generated. When the noise components are removed in this way, the image becomes as shown in FIG. 4d. There, the tip position 12a of the crack 12 is detected. After this, a window is applied again to determine the crack, but this window has a lowered window density threshold.
This reduces the probability that even crack 2 will be determined as noise.

Then, the marking line position and the crack tip position determined by each means 32, 33 are sent to the distance detecting section 40, and the distance detecting section 40 calculates the distance from the marking line 13 to the crack tip position 12a. are displayed on the display section 41. When this distance becomes less than or equal to the distance set in the stop distance setting circuit 42, the fatigue testing machine stop signal generation circuit 43 sends a fatigue test stop signal K to the fatigue testing machine.

As described above, in the above embodiment, the marking line detection means 32 detects the position of the marking line 13 by determining the maximum value of the brightness level from the video signal of the test piece 10 imaged through each microscope 20, 21, On the other hand, the crack tip position detecting means 33 converts the signal into a binary signal, judges the continuity of the high level value, extracts the crack 12, and detects the crack tip position. Since the distance detecting section 40 is configured to determine the distance from the marking line 13 to the crack tip position from the position and the crack tip position, the following effects can be achieved. That is, by setting the position of the marking line 13 on the test piece 1 in advance, the position of the crack tip on the test piece 1 can be automatically measured.

The position of the crack tip can be measured using a non-contact method.

Since the crack tip position can be measured without being affected by the shape of the test piece 10 or the difference in steel type,
Even if the test piece 10 is changed, there is no need for calibration.

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.

Furthermore, in the above-mentioned embodiment, it is also possible to perform the detection using two ITV cameras individually, and when detecting cracks 12 on both sides of one test piece 10 in this way, the detection can be performed using two ITV cameras. The distance can be determined by determining the distance between the two cracks and the marking line from the captured image and detecting the average value. Note that the present invention is not limited to the above-mentioned embodiment, and can be modified without departing from the spirit thereof. For example, the device takes an image signal, determines the reference line position from its maximum brightness level, and detects the crack tip position by determining the continuity of the high level value.
Any configuration may be used as long as it calculates the distance between the next detected reference line position and the crack tip position.

〔Effect of the invention〕

As described in detail, according to the present invention, it is possible to provide a method and apparatus for automatically measuring the position of the crack tip of a fatigue test piece with high precision, which can automatically measure the position of the crack tip using a microscope.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an automatic measuring device for the position of the crack tip of a fatigue test piece according to the present invention;
Fig. 2 is a side view of a fatigue test piece used in the apparatus of the present invention, Fig. 3a is a diagram showing an image of the test piece obtained by the apparatus shown in Fig. 1, and Fig. 3b is a diagram showing the detection of marked lines. Luminance distribution diagrams for Figures 4a to 4
Figure d is a diagram for explaining the crack detection operation.
Figures 5a, b, c and 6 are diagrams for explaining the removal of noise components in the crack detection operation, Figure 7 is a side view of the fatigue test piece, and Figures 8 to 10 are the conventional crack tip. FIG. 3 is a diagram for explaining a position detection method. 1... Fatigue test piece, 20, 21... Microscope, 2
2, 23...ITV camera head, 30...signal processing device, 32...marked line detection means, 35...
Horizontal direction integration circuit, 36... Integral value peak position detection unit, 33... Crack tip position detection means, 37
...Filter circuit, 38...Binarization circuit, 39...
...Noise removal circuit, 40...Distance detection section, 43...
...Fatigue tester stop signal generation circuit.

Claims (1)

[Scope of Claims] 1. A method of integrating the luminance level in the same direction as the reference line from an image signal obtained by imaging a crack that occurred in a fatigue test piece to which a reference line has been applied and the reference line, and then determining the maximum luminance level. The reference line position is determined from the brightness level, the image signal is converted into a binary signal, the crack tip position is detected by determining the continuity of high level values, and then the crack tip position is determined from the reference line position and the crack tip position. An automatic method for measuring the position of a crack tip of a fatigue test specimen, the method comprising calculating the distance between the cracks. 2. An imaging means for imaging the crack of the fatigue test piece on which a reference line has been applied to obtain the position of the crack tip and the reference line in the same field of view, and a video signal obtained by imaging the imaging means in the same direction as the reference line. a reference line detecting means for detecting the reference line position by integrating the luminance level in the crack direction and finding the maximum level; a crack tip position detection means that detects the crack tip position by determining the continuity of the high level value; and a crack tip position detection means that detects the crack tip position by determining the continuity of the high level value; 1. An automatic measuring device for measuring a crack tip position of a fatigue test specimen, comprising a crack tip position calculation means for calculating a distance from the reference line to the crack tip position based on the crack tip position determined by the crack tip position.