JPS5824827A - Method for measuring stress distribution - Google Patents

Abstract

PURPOSE:To measure the stress distribution without contact by alternately applying compressing and tensile loads to a body to be measured, and performing raster scanning on an image spot of an infrared ray detector at the timing of the maximum load. CONSTITUTION:The body to be measured 1 is fixed to chucks 2 and 2' of a load testing machine, and the compressing and tensile loads are alternately applied to it. The infrared rays irradiated from the body to be measured 1 are detected by the infrared ray detector 3. The signal from an optical scanner 4 which scans the image spot of the detector 3 is sent to a CRT display 6. The signal is converted into the digital signal by an A/D converter 7 and stored in data memories 12 and 13. A computer 19 samples the detected signal values corresponding to the position which is separated by a specified distance from the initial point of each raster for every raster at the timing of the maximum compressing and tensile loads, obtains a data, and prepares the stress distribution image based on the data.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel stress distribution measurement method using an infrared imaging device that performs raster scanning.

When creating mechanical parts, etc., care must be taken to ensure that the stress due to the load does not concentrate on a specific part, and for this reason, the stress distribution is measured using a real object or a model close to it. The conventional method for measuring stress distribution is to attach one or more strain gauges to each part of the object to be measured, and then make a judgment by integrating the output from each gauge.However, installing strain gauges is a labor-intensive process. Not only is it time-consuming, but the number of measurement points is limited due to the size of the strain, making it impossible to accurately measure the stress distribution.

Therefore, a method has recently been proposed that uses an infrared imaging device that performs raster scanning to measure the 1ζ stress distribution in a short time without contact. This method focuses on the fact that it rises when a load is applied and falls when it receives an inverse tensile load. This method takes advantage of the fact that when this object to be measured is photographed with an infrared imaging device that performs raster scanning while the temperature is repeatedly changed, a striped pattern appears in the stress concentration area of the acquired infrared image due to the repeated temperature changes.

However, although this proposed method can determine the presence or absence of a stress concentration area based on the presence or absence of a striped pattern, it is extremely difficult to determine the strength and density of the striped pattern in a fixed manner over the entire field of view. It is. The present invention has been made in view of this point, and it is an object of the present invention to provide a method that can measure stress distribution in a fixed curve by adding simple processing to an infrared image signal. It is possible to take infrared images asynchronously with the repeated application of loads.
There is this characteristic. The present invention will be explained in detail below using the drawings.

FIG. 1 shows an example of a device for carrying out the method of the present invention. In the figure, 1 is an object to be measured whose both ends are fixed to the load i7ρ#2, and 6 is the radiation emitted from the object to be measured 1. An infrared detector 4 for detecting infrared rays is an optical scanner for forming an image spot S of the detector B on the object to be measured and raster scanning the image spot S within a field of view Z. The infrared image signal obtained from the detector 3 through the field of view scanning 1 of the image spot S by the scanner 41 is sent to the cathode ray tube display device 6 via the amplifier 5. Horizontal and vertical synchronization signals 81 generated
(Since the scanning is performed in synchronization with the SV, the infrared image of the object to be measured 1 is displayed on the screen as shown in FIG. 2, 1b+).

The above-mentioned infrared video signal is sent to the display device 6.
- It is converted into a digital signal by the D converter 7, and the timing signal I from the timing circuits 8 and 9 is turned ON.
Two data memories 1 having a storage capacity to store one screen worth of video signals via switches 10 and 11 that are turned off.
2 or 16 and stored. 14 is a counter for giving information regarding the address f to be stored at that time, and this counter receives the horizontal synchronizing signal S from the scanner 4.
H is counted and cleared by the vertical synchronizing signal SvI.

Reference numeral 15 denotes a strainage attached to an appropriate part of the object to be measured 1, 16 a peak detection circuit for detecting the positive peak of the distortion signal of the strainage 15, and 18 a peak detection circuit for detecting the negative peak. 019 is a peak detection circuit, and the timing circuits 8 and 9 create a timing signal based on the output signal of the detection circuit 17.18 and the horizontal synchronization signal SH.
211 stored! data (after performing smoothing processing, calculate the difference between the two, and store the result in the data memory 12
t second computer 20 stores data in the memory 12;
This is a readout circuit for repeatedly reading out the stored results and displaying them on the cathode ray tube 21.

In such a configuration, suppose that the load tester is applying compressive force and tensile force alternately to 11 objects to be measured at a repetition frequency of, for example, 5 Hz, as shown in FIG. 3(a). ,
In humans, the stress concentration area of the object to be measured 1 is synchronously
As shown in FIG. 1b+i, during the compression period t1, the temperature is higher than that during the thermal load, and during the tension period t2, the temperature is lower than the temperature during the thermal load. Considering the case where the detector image spot S raster-scans the part A where the high temperature period and low temperature period are repeated in synchronization with the load application f repeated once in this way,
If we assume that raster scanning is performed 1 to 10 times during one cycle of load application, Figure 2 1b is an enlarged view of section A.
As shown in +, raster scanning is performed five times during the high temperature period t1,
During the low temperature period t21, raster scanning is performed five times. At this time, raster scanning is also performed on the display device 6 in synchronization with the display device 6.
The five rasters in the period tl are displayed at a high temperature (high brightness), and the five rasters in the period t2 are displayed at a low temperature (low brightness).
Is displayed. Therefore, in the temperature distribution image of the object to be measured 1 displayed on the screen of the display device 6, a striped pattern of shading is generated, as shown in FIG. 2, 1cl.

The difference in the charcoal density of this stripe is the temperature difference between the high temperature period and the low temperature period, and although it is possible to know the magnitude of stress from this difference in shading, it is difficult to understand it quantitatively. That's right.

In this example, we focus only on the raster at the timing when the compressive load is maximum and the raster when the tensile load is at maximum lζ in one screen, and the starting point of each raster is 1 for each raster at the timing when the compressive load is at maximum 1. The video signal data corresponding to the position the same distance away from is sampled and stored as the first data group, and the same distance as noted from the starting point of each raster is sampled for each raster at the timing when the tensile load reaches the maximum. Quantitative understanding can be done by sampling the corresponding video signal data at distant positions and storing it as a second data group, and after performing broken line approximation processing for each data group, finding the difference between both data groups. is possible.

That is, let us now consider the change in temperature along a straight line f perpendicular to the raster, a distance l from the left edge of the screen, as indicated by L on the screen shown in FIG. 2(C)1. If one screen is made up of, for example, 240 rasters, the temperature change along L can be expressed as a series of 240 points (data) as shown in Figure 4 (al). At this time, the load change f is as shown in the same figure (hl I shown r, same figure -), and the data A and -An of the timing when the compressive load is maximum are extracted. l
Similarly, if you extract the data B1 to Bn at the timing when the tensile load reaches a maximum of 1, it will look like the same figure (dl).The difference in the density of the stripes corresponds to the stress value (data of cl and data of tdl). If we take the difference between the two, we should be able to find the stress change along Ll, but since the positions of each data are shifted, there is no data for the other party to find the difference in.
Figure 240 (e), ffl, etc. is obtained by performing a broken line approximation based on the data of icl and tdl.
Create data for the entire rask of points, and use this tel and ffl
By finding the difference between the data, it is possible to obtain 240 points of data indicating stress changes along the f-L as shown in +gl in the same figure.

Furthermore, if there is no synchronous relationship between the raster scanning of the optical scanner 4 and the load application cycle, then (thinking about it further, in the image obtained in the next one screen scan, the position of the stripes will be in the vertical direction. Because of the shift, the temperature change along the same straight line L is also 4th.
It deviates from the figure +a+. Therefore, when scanning the next screen, data 11 to An', n, l to no' are extracted at the timing of the maximum compressive and tensile loads in the same way as above, and the previously stored data A, -An and B1~Bn(
Figure 4+
1++, +1+ are obtained, and if this is repeated one more time, the data will increase by another f, so the accuracy of the broken line approximation will be extremely improved, and the obtained stress distribution will be exactly one.

In this embodiment, based on this idea, a large number (for example, 200) of straight lines are set in one screen to obtain stress distribution data for the entire screen. Immediate entry-1
) The converter 7 converts one raster I from the corresponding video signal to two
The data of 00 points is sampled and converted into digital data, and the data memories 12 and 16 are memories represented by a matrix of 200 columns and 240 rows to store 200 pieces of data per raster in 240 rasters on a plane. Each has its own area (Figure 5). From the detection circuit 16, a strain signal (Fig. 3 (C)) obtained by measuring the load as shown in Fig. 1 (when the maximum compressive load is reached), Fig. 3 +
A timing pulse as shown in dl is generated, and similarly, when the strain signal reaches a minimum of 1 from the peak detection circuit 18 (when the tensile load reaches its maximum), a timing pulse as shown in te+1 in the figure is generated. occurs. Based on the timing pulse and the horizontal synchronizing signal 8H, the timing circuits 8 and 9 perform the first scan after the krE timing pulse is generated after the horizontal scanning repeatedly performed by the scanner 4, as shown in FIG. 3 (fl). Create a timing signal (Figure 3+gl and (h)) that specifies the period of one horizontal scan,
The timing signals are sent to switches 10 and 11, respectively. Since the switches 10 and 11 are ON only during the period specified by the timing signal 1, the 200 video signal data for one raster at the maximum compressive load during each high temperature period are transferred to the data memory via the switch 10. 12, and 200 video signal data for one raster at the maximum tensile load during each low temperature period are sent to the data memory 16 via the switch 11. At that time, a counter 1 indicating which raster each video signal data belongs to is stored in each data memory 12 and 13.
A count value of 4 is supplied, and each video signal data is stored in the corresponding row of the matrix shown in FIG. 5 at the raster position indicated by its column I value. Therefore, at the time one screen scan is completed, each data memory stores sampled raster data in rows corresponding to the raster position, as shown by diagonal lines in FIG. . Data extracted from an arbitrary column, for example column P, in this state corresponds to 1cl or ldll in FIG. After one screen scan is completed, the computer 191 uses the partial data stored once for each column in the matrix to scan the fourth Zlcl as described above.
To avoid the possibility of going from rat to rat, if you create and store the blank data in the matrix by performing exactly the same approximation process as the approximation process from 1dl to lfl in the same figure, there will be no blank data in the matrices of the two memories, and the fourth Figure (C).

Igl is calculated from the difference between lfl. If the data obtained by calculating the difference between the two data groups stored in the two memories here is stored in the memory 12, one of the memories 12 will have the entire screen 200. Data representing the stress distribution over x240=48000 points f will be obtained.

When the stress data of the entire screen is sequentially and repeatedly read out from the readout circuit 20i and sent to the cathode ray tube 21 in the form of a video signal, a stress distribution image with brightness or hue corresponding to the stress is displayed on the screen. Therefore, it is possible to clearly determine the location of stress concentration, needless to say, to the extent of stress concentration.The above was a case in which a stress distribution image was created using data from one screen scan, but the optical scanner 4I performs extensive scanning and load application. If there is no synchronization between them, the same operation is performed every time the screen is scanned multiple times, as shown in FIG. 4(h).

Just like +i+, the amount of original data in the memory matrix increases, improving approximation accuracy and creating a stress distribution image with good resolution (
data) can be obtained.

In addition, since the present invention calculates the difference between the data stored in two memories, the temperature change that exists in the measured object when no load is applied is canceled by calculating the difference, and therefore only information regarding stress is obtained. It can be taken out.

J: As described in detail, the present invention allows stress distribution to be grasped quantitatively, and even in the simplest state, where there is no synchronous relationship between scanning by an optical scanner and load application, resolution is improved. This provides an extremely excellent effect of making it more directional.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the method according to the present invention, and FIG. 2 is a diagram for explaining the generation of stripes.
FIG. 3 is a waveform diagram for explaining the operation of the device, FIG. 4 is a diagram for explaining the basic idea of the present invention, and FIG. 5 is a diagram for explaining the matrix in the data memory. . 1: Object to be measured, 5: Infrared detector, 4: Optical scanner, 6
: Cathode ray tube display device, 7: A-D converter, 8.9: Timing circuit, 10.11: Switch, 12.15:
Data memory, 14: Counter, 15 Nistorange, 16: Detection circuit, 17.18: Peak detection circuit, 1
9: Computer, 20: Output circuit, 21: Cathode ray tube 〇 To Tadao Kase, representative of JEOL Ltd., patent applicant ^ U2 S z g CQ6
9? q dimension′″′ touch

Claims (1)

[Claims] L im + Alternately and repeatedly applying a compressive load and a tensile load to the object to be measured, tbl Raster scanning an image spot of an infrared detector on the object to be measured to obtain a detection signal, let A certain distance from the start point of each raster for each raster when the compressive load is maximum! Sampling detection signal values corresponding to distant positions and storing them as a first data group; detecting signals corresponding to positions a certain distance l away from the starting point of each raster for each raster at the timing when the ldl tensile load is maximum; Sampling signal values and storing them as a second data group; Creating first broken line approximation data based on the first data group; 1 based on the second data group: A stress distribution measuring method comprising: creating the same number of second broken line approximation data as the broken line approximation data in memory 1; 1g) determining the difference between the first broken line approximation data and the second broken line approximation data. 2. The stress distribution measuring method according to claim 1, wherein the detection signal value at 11cl ptdl before λ is sampled and stored for a plurality of screen scans.