JPS6236526B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily measuring the distribution of stress applied to an object to be measured.

Measuring the magnitude of stress that occurs in each part of various machines and structures is a safe and economical method by selecting the shape of each part, the dimensions of the materials used, the materials, etc. when designing the machine or structure. This is extremely important to enable flexible design. Accordingly, various methods have been developed to measure stress distribution. The main conventional methods include, for example, methods in which stress is measured by gluing a resistance wire etc. to the object to be measured and detecting the strain occurring in the object from changes in the resistance value of the resistance wire, and optical methods. The transparent resin makes it easy to measure.
There are methods such as creating a model that is close to the real thing, actually applying a load to this model, and measuring the stress distribution.

However, the former method not only requires specialized skills to bond the resistance wire to the object to be measured, but is also troublesome. Therefore, considerable effort and equipment are required to measure the stress distribution by bonding resistance wires to multiple locations on the object to be measured.

Furthermore, the latter method requires the creation of a model close to the object to be measured, making it impossible to easily measure the stress distribution.

The present invention solves the shortcomings of such conventional stress measurement methods and provides a novel method that can quickly and easily measure the stress distribution of a measured object to which a time-varying load is applied without contact. The present invention will be described in detail below with reference to the drawings.

Devices that measure the temperature of a test sample by detecting infrared rays emitted from the test sample include radiation thermometers, thermography devices, and infrared vidicons. The temperature of the surface of the test sample was measured when a compressive load and a tensile load were repeatedly applied to the test sample. Incidentally, a test sample whose emissivity ε was extremely close to 1 was selected as the test sample so that the output signal of the thermography device was accurately proportional to the temperature of the test sample.

As a result, the surface temperature of the test specimen at the stress-concentrated area does not simply rise, but synchronizes with the application of a load and has a period in which it rises above the temperature when no load is applied, and a period in which it falls. I found that it was repeated alternately.

In other words, when a load with a sinusoidal waveform as shown in Figure 1a is applied to a sample, the surface temperature of a specific part of the sample is a sinusoidal waveform synchronized with the load application as shown in Figure 1b, and no load is applied. This resulted in alternating periods of higher and lower temperatures than the average temperature.

This phenomenon occurs when a load is applied at a speed that is sufficiently faster than the time required for this part whose temperature is measured to exchange heat with other parts inside the test sample or with the surroundings of the test sample. This is thought to be due to the repeated rise and fall of temperature as a result of this part being compressed and expanded in a process that can be considered an adiabatic process.

This means that, for example, if only compressive force is applied in a rectangular waveform as shown in Figure 1c, only a temperature rise in the rectangular waveform synchronized with it as shown in Figure 1d will occur;
It was also confirmed that when only a tensile force was applied as shown in figure e, only a temperature drop occurred as shown in figure f.

As a result of repeated experiments by changing only the applied load, it was found that there is a proportional relationship between the amount of temperature change and the amount of stress change, as shown in the experimental results shown in Figure 2a. Furthermore, as a result of repeating the experiment while varying the temperature of the object to be measured, the experimental results shown in Figure 2b were obtained, indicating that there is a proportional relationship between the amount of temperature change and the temperature of the object to be measured. There was found. That is, the amount of change in stress has the following relationship.

△P=A・△T/T ₀ ...(1) However, △T is the amount of temperature change at the measurement point, T ₀ is the temperature when no load is applied to the test sample, and △P is the temperature change of the measured object. The amount of stress change, A, is a constant related to the material. Therefore, a load that changes over time (preferably a repeated load) is applied to the object to be measured, and the amount of temperature change ΔT of a specific part of the object at that time is measured,
Also, measure the surface temperature T ₀ of the specific part when no load is applied to the object to be measured, and further calculate △T as T ₀
By dividing the amount by Furthermore, if this specific area is horizontally scanned for removal, the distribution of stress changes along the scanning line can be found, and if the position of the scanning line is gradually moved in the vertical direction, the two-dimensional distribution in the scanning area can be obtained. It is possible to measure the stress distribution.

Embodiments of the present invention applying this principle will be described below with reference to the drawings.

FIG. 3 is a schematic diagram of one embodiment, and 1 in the figure is a vibrator. Although the vibrator 1 is not shown, it is periodically driven by a hydraulic mechanism driven by a motor or the like. It has pistons 2 and 3 that reciprocate and mechanisms 5 and 6 that fix the object to be measured. Measured object 4
The vibrator 1 applies a load as shown in FIG. 4a, for example. However, in the figure, a portion larger than the 0 level represents a compressive load, and a portion smaller than the 0 level represents a tensile load.
7 is a synchronous signal generation circuit, and the synchronous signal generation circuit 7 receives, for example, a signal obtained by detecting the movement of the piston of the vibrator 1 or the rotation of a motor, or a signal attached to the object to be measured. Based on these signals, the circuit 7 determines the moment when the compressive load applied to the object to be measured peaks, the moment when the tensile load peaks, and the load. A synchronizing pulse having a small time width t is generated as shown in FIG. The synchronization pulse from the synchronization signal generating circuit 7 is supplied to an optical scanning mechanism 8. The optical scanning mechanism 8 has a scanning mirror and its driving source as main components, and oscillates the mirror based on a synchronization signal having a short time width shown in FIG. The image is scanned, for example, on line H of the object to be measured 4 as shown in FIG. 4c. However, in FIG. 4c, the vertical axis represents the distance from the scanning start point on line H, and the horizontal axis represents time. The output signal from the infrared detector 9 is supplied to a linearity correction circuit 11 via an amplifier 10.
The linearity correction circuit 11 corrects the signal from the infrared detector into a signal proportional to the temperature at the detection point of the object to be measured. The output signal of the linearity correction circuit 11 is converted into a digital signal by an A/D converter 12. The output terminal of the A/D converter 12 is connected to first, second, and third adder circuits 13a, 1
It is connected to one input end of 3b and 13c.
Each of the adder circuits 13a, 13b, 13c has a first, a second, and a third memory 14a, 14b, 14.
connected to c. The output terminals of the memories 14a and 14b are connected to the subtraction circuit 15,
The output terminal of c is connected to one input terminal of the divider circuit 16. These memories 14a, 14b, 1
The output terminal of 4c is the adder circuit 13a, 13b, 1
3c. Furthermore, the output terminal of the subtraction circuit 15 is connected to the other input terminal of the division circuit 16, and the subtracted signal is sent to the memory 14c.
divided by the output signal of The output signal of the divider circuit 16 is supplied to a vertical deflection coil 20Y of a cathode ray tube 19 via a D/A converter 17 and an amplifier 18. On the other hand, the synchronization signal from the synchronization signal generation circuit 7 is supplied to the controller 21. The controller 21 causes each of the memories 14a, 14b, and 14c to have a fourth memory based on the supplied synchronization signal.
Control signals shown in FIGS. d, e, and f are supplied to control the writing of signals into these memories 14a, 14b, and 14c, and the reading of signals that have already been stored. Furthermore, the controller 21
When the integration of the signals in these memories 14a, 14b, 14c is completed, it sends a periodic read command signal to these memories 14a, 14b, 14c, and also sends a periodic signal synchronized with the supply of the signal as a scanning signal. It is supplied to the creation circuit 22. In the scanning signal generation circuit 22, the controller 2
1 generates a scanning signal for amplitude (deflection) modulation display of the signal from the amplifier 18 on the surface of the cathode ray tube.

When using the device configured as described above and applying a load as shown in FIG. As shown in FIG. 4c, a line H on the object to be measured 4 is scanned. As a result, the infrared rays emitted from each point on the line H are sequentially guided to the infrared detector 9 via the optical scanning mechanism 8. As a result, a scan performed during the period when the largest compressive load is applied, as indicated by A in FIG. 4c, produces a temperature signal as shown in FIG. 5a, and also as indicated by C in FIG. Figure 5c was obtained by scanning during a period when such a load was not applied.
A temperature signal as shown in FIG. 5B is detected by scanning the period during which the largest load is applied as shown in FIG. 4C, and a temperature signal as shown in FIG. 5B is detected. When performing a scan as shown by A in FIG. 4c, the controller 21 sends a control signal as shown in FIG. 4d to the memory 14a, and a control signal as shown in FIG. The detection signal is stored in the memory 14a. At the same time, the signals already stored in the memory 14a are also read out in synchronization with the scanning, and the adding circuit 13a
Since the linearity correction circuit 11
The newly supplied signal is added to the signal stored in the previous scan and stored in the memory 14a. Therefore, the detection signals obtained by the scanning indicated by A in FIG. 4c are accumulated a plurality of times and stored in the memory 14a. In exactly the same way, the memories 14b and 14c have the information in FIG. 4e,
A control signal from the controller 21 as shown in FIG. 4f is supplied, and in FIG.
Signal writing is performed during the period in which the detection signal obtained by the scanning indicated by is supplied. Therefore, detection signals as shown in FIGS. 5b and 5c are accumulated and stored a plurality of times in the memories 14b and 14c, respectively.
After completing the scanning over a certain period of the applied load, the controller 21 sends the same periodic read command signal to the memories 14a, 14b, 14c.
At the same time, a signal synchronized with the read command signal is supplied to the scanning signal generation circuit 22. As a result, the subtraction circuit 15 is supplied with a signal obtained by integrating the signal shown in FIG. 5a a plurality of times and a signal obtained by integrating the signal shown in FIG. A signal as shown in FIG. 5d (more precisely, a signal multiplied by the number of integrations of this signal) obtained by subtracting both integrated signals is output and supplied to the divider circuit 16. On the other hand, since the signals stored in the memory 14c are read out at the same time, the division circuit 16 is supplied with a signal obtained by integrating the signals shown in FIG. 5c a plurality of times. As a result, the division circuit 16 divides the output signal of the subtraction circuit 15 by the output signal of the memory 14c as shown in FIG.
A signal as shown in (more precisely, a signal approximately times the number of integrations of the signal) is output. The signal is sent to D/A converter 1
After being converted into an analog signal at 7, it is passed through an amplifier 18 to a vertical deflection coil 20 of a cathode ray tube 19.
Supplied to Y. In synchronization with the periodic supply of signals to the cathode ray tube 19, periodic scanning signals from the scanning signal generation circuit 22 are applied to the horizontal deflection coil 2.
Since the cathode ray tube is supplied with
A profile representing the magnitude of stress change on line H from which the influence of the surface temperature of the object to be measured 4 has been removed as shown in the figure is displayed.

For example, when bending stress is applied to an object to be measured, compressive force may be applied to one side of the object and tensile stress may be applied to the other side. The broken portion is represented by waveforms above and below the 0 level of the display screen. Therefore, by observing this waveform, it is possible to accurately measure the distribution of the amount of change in stress applied to the object 4 to be measured, including its type.

The embodiment described above is only one embodiment of the present invention, and other embodiments may be adopted when implementing the present invention. For example, in the above embodiment, when a load is repeatedly applied to the object to be measured, the line H is scanned in synchronization with the timing when the load applied to the object becomes 0, and when no load is applied. The temperature along the line H of
It is also possible to detect and store the temperature along the range, and to lead the stored signal to the division circuit 16.

Further, in the above-described embodiment, all temperatures along the line H are measured when no load is applied to the object 4 to be measured. In this way, since one end of the object to be measured 4 is heated, the stress change along line H can be adjusted even if the base temperature along line H when no load is applied is significantly different. The distribution of quantities can be determined with great precision. However, if the base temperature of the object to be measured is approximately uniform, it is sufficient to measure the temperature at one representative point on the object to be measured and use the signal to divide the output signal of the subtraction circuit 15. It is.

Furthermore, in order to measure the temperature only at a representative point, a contact type detection means such as a thermistor may be used instead of detecting and measuring infrared rays.

Further, in the above-described embodiment, signal integration is performed to improve the S/N ratio, but it is also possible to perform scanning once at a time without performing integration.

In addition, although the one-dimensional stress change distribution of the object to be measured is measured, the measuring section may be any one point or multiple points on the object to be measured, and furthermore, the measurement section may be located at any one point or multiple points on the object to be measured.
By scanning also in the vertical direction, two-dimensional distribution can also be measured. Further, in such a case, the signal from the amplifier 18 may be displayed by brightness modulation.

In addition, in the embodiment shown in Fig. 3, Fig. 4b
Although only one horizontal line was scanned during the time width t shown in (this t is selected to be short enough to allow negligible changes in the load applied to the object to be measured), two-dimensional When measuring a distribution, one field may be scanned within this time width t.

In addition, in the above-mentioned embodiment, two temperature signals obtained when different loads are applied are subtracted using a subtraction circuit in order to obtain the width of temperature change when the load changes, but other methods may be used. can also be taken.

For example, when the applied load is periodic and is as shown in FIG. 7a, the signal from the detector 9 based on the infrared radiation from the measuring point P of the object to be measured 4 as shown in FIG. Figure 7b synchronized with said load.
If the signal is guided to the synchronous detection circuit 23 to which a synchronous signal as shown in FIG. At this time, if the signal from the detector is passed through an amplifier 24 whose amplification factor is automatically changed according to the temperature signal when no load is applied to the object to be measured, the temperature of the object becomes the base.
A signal proportional to the value obtained by dividing the temperature width ΔT by T ₀ can be obtained.

Furthermore, if the optical scanning mechanism 8 scans so that the measurement point P is moved at such a speed that the movement of the point P during the period in which the applied load is repeated for a plurality of cycles, the synchronous detection signal as described above can be used. hand,
It is also possible to display a one-dimensional or even two-dimensional distribution of the amount of stress change in the object to be measured.

Further, regarding the direction of the load, it may be applied only in the compression direction or the tension direction as shown in FIG.

Further, the waveform of the load is not limited to a sinusoidal waveform, but may be a rectangular waveform.

Furthermore, the present invention can be applied in exactly the same way to objects to be measured to which repeated loads are applied, even if the loads are not applied repeatedly by a vibrator, such as a part of a working machine. .

Furthermore, although the above-mentioned embodiments have been described in which a load is repeatedly applied to the object to be measured, it can also be applied to cases where the load applied to the object to be measured only changes at a high speed and does not change repeatedly. ,
The amount of stress change in the object to be measured can be determined by scanning the same line of the object to be measured at least once during a short period of time when different loads are applied, and obtaining a difference signal between two detection signals based on the scanning. distribution can be measured. Furthermore, even if a recorder is used in place of the display device, exactly the same results can be obtained.

In addition, if the test sample is ideally close to a perfect black body, the infrared detection signal of a thermography device, etc. will be a signal proportional to the temperature T of the part to be measured, as a result of correcting the signal with a linearizer etc. KT(K
is a constant of proportionality), but if the test sample is not ideal, the signal actually obtained is I=KεT+K(1-ε)Ta...(2) (However, Ta is The temperature of the surrounding object, ε, is the emissivity of the part to be measured, 0ε1).

From equation (2), the change in signal amount △I when the temperature of the part to be measured changes by △T becomes Kε△T, so I ₀
Assuming that is a signal obtained by detecting the temperature T ₀ of the part to be measured when no load is applied to the measured object, the above equation can be calculated using the following error on the actual detection signal. It is given including. That is, △P=A・Kε△T/I ₀ =A・Kε△T/KεT ₀ +K(1−Kε)Ta =A・△T/T ₀ (1/ε−1)Ta ……(3) However, As is clear from this formula, T ₀ ≫
In the case of Ta, the amount of stress change can be measured with almost no error even for a measured object whose emissivity is not close to 1 without applying special emissivity correction to the detection signal.

As described above, according to the present invention, the amount of stress change in a desired portion of an object to be measured can be measured quickly and easily in a non-contact manner.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram for explaining the principle of the present invention, Figure 2 is a diagram showing the relationship between load and temperature change, and the relationship between ambient temperature and temperature change, and Figure 3 is a diagram for implementing the present invention. FIG. 4 is a schematic diagram showing an example of a device for scanning, FIG. 6 is a diagram for explaining the temperature waveform, FIG. 6 is a diagram for illustrating the display waveform on the cathode ray tube surface, and FIG. 7 is a diagram for illustrating the relationship between the load waveform and the synchronization signal in another embodiment. FIG. 8 is a diagram showing another example of an apparatus for carrying out the present invention. 1: Vibrator, 2, 3: Piston, 4: Measured object, 5, 6: Fixing mechanism, 7: Synchronous signal generation circuit,
8: optical scanning mechanism, 9: infrared detector, 10,
18, 24: Amplifier, 11: Linearity correction circuit, 12: A/D converter, 13a, 13b, 1
3c: addition circuit, 14a, 14b, 14c: memory, 15: subtraction circuit, 16: division circuit, 17:
D/A converter, 19: cathode ray tube, 21: controller, 22: scanning signal generation circuit, 23: synchronous detection circuit.

Claims (1)

[Claims] 1. Infrared rays emitted from the same part or substantially the same part of the object to be measured to which a time-varying load is applied is detected at least at two timings when different loads are applied. and obtain a signal corresponding to the temperature change width of the part when the different loads are applied,
Stress measurement, wherein a signal is obtained based on the signal by substantially dividing the signal by a signal proportional to the temperature of the part when no load is applied, and the obtained signal is displayed or recorded. Method. 2. The stress measuring method according to claim 1, wherein the same portion of the object to be measured is in the form of a point. 3. The stress measuring method according to claim 1, wherein the same portion of the object to be measured is linear. 4. The stress measuring method according to claim 1, wherein the same portion of the object to be measured is planar. 5. The stress measuring method according to claim 1, wherein the obtained signal is displayed or recorded as an amplitude modulated signal. 6. The stress measuring method according to claim 4, wherein the obtained signal is displayed or recorded as a brightness modulation signal. 7. The stress measuring method according to claims 1 to 6, wherein the load that changes over time is a load that changes repeatedly. 8. The stress measuring method according to any one of claims 1 to 7, wherein the load that changes over time is a compressive load and/or a tensile load. 9. The stress measuring method according to any one of claims 1 to 7, wherein the load that changes over time is a load obtained by superimposing a variable amount on a constant load.