JPS6140932B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel stress measuring device that can accurately obtain stress values or stress distributions applied to a test sample in a short time.

When creating mechanical parts, etc., care must be taken to ensure that stress due to loads does not concentrate on specific parts. Therefore, in applications where durability is particularly important, a load is actually applied to the actual object or a model close to the actual object and the stress in each part is measured. Installing strain gauges and monitoring the output of each gauge was a large-scale and time-consuming process.

The present invention has been made in view of this point,
Stress can be measured accurately by determining the temperature change based on the load change, and by attaching a single strain detection element to the test sample and making corrections based on the signal from the detection element. The purpose of this invention is to provide a measuring device. The present invention will be explained in detail below using the drawings.

When the temperature of the surface of the test sample was measured when compressive and tensile loads were repeatedly applied to the test sample, the inventor found that the surface temperature did not simply increase in areas where stress was concentrated, but that the surface temperature increased with the application of load. It has been found that periods in which the temperature rises above the ambient temperature (more accurately, the sample temperature at zero load) and periods in which it falls below the ambient temperature are alternately repeated. That is, when a sinusoidal waveform load as shown in Figure 1a was applied to the sample,
As shown in Figure b, the surface temperature of the stress concentration area of the sample has a sinusoidal waveform synchronized with the load application, resulting in alternating periods of higher temperature than the ambient temperature and periods of lower temperature than the ambient temperature. ing.

This is because heat generation occurs at the stress concentration area during the period when compressive force is applied, and endothermic effect appears during the period when tensile force is applied, and this heat generation is repeated in relatively short cycles, so that heat is not transferred to the surroundings. The surface temperature of the stress concentration area changes in an adiabatic state in which diffusion or inflow of heat from the surroundings is cut off.
For example, if only compressive force is applied in a rectangular waveform as shown in Fig. 1c, only a temperature rise in the rectangular waveform synchronized with it will occur as shown in Fig. 1d, and only a tensile force will be applied as shown in Fig. 1e. This was also confirmed by the fact that only a temperature drop occurred when the voltage was applied, as shown in figure f.

As a result of repeated experiments under various conditions, it was found that there is a proportional relationship between the amount of temperature change and the stress change (more precisely, the amount of displacement due to stress). FIGS. 2a and 2b are diagrams showing the proportional relationships between load and temperature change and between ambient temperature and temperature change, which were actually determined through experiments.

Based on this relationship, by sequentially applying different loads to the object to be measured and detecting the range of surface temperature change of a specific part at that time, it is possible to know the stress applied to that part.
Moreover, by gradually scanning the measurement site horizontally, the stress distribution along the scanning line can be determined.
In addition, by gradually moving the scanning line position in the vertical direction, it is possible to measure the two-dimensional stress distribution in the scanning area.

Furthermore, by using an infrared camera to obtain temperature distribution images of the test sample under different loads (in the form of video signals) and finding the pattern of the difference between the two images, that is, the pattern that indicates the degree of temperature change, this can be done. The pattern shows the range of temperature change at each point on the sample,
Stress distribution can be obtained in an extremely short time.

The present invention provides such a novel stress measuring device, in which a strain detection element such as a strain gauge is attached to one point on a sample, and the measurement results obtained by the above method are corrected based on the detection signal obtained from the detection element. It is characterized by FIG. 3 shows the configuration of an embodiment of the present invention, in which numeral 1 represents a vibrator. The vibration exciter 1
are hydraulically driven pistons 2, 3 and holding mechanisms 5, 6 for fixing the test sample 4 between the pistons.
It is equipped with

7 is a radiation thermometer for detecting the temperature of a specific point on the sample 4; an amplifier 12 for amplifying the detected signal;
The detection circuit 13 includes a synchronous detection circuit 13 that performs detection in synchronization with the chopping, and a linearizer 14 that corrects the detection output from the detection circuit 13 so that it becomes a temperature signal having a linear relationship with the temperature.

Only the AC component of the temperature signal obtained from the linearizer 14 is extracted through a DC component removal circuit 15 such as a filter or a level shift circuit, and the AC component is converted into a synchronous signal synchronized with the load application generated from the vibrator 1. 16 is sent to the synchronous detection circuit 17 to which the signal 16 is supplied. The output signal of the detection circuit 17 is selectively sent to an arithmetic circuit 19 or 20 by a switch 18. The other input terminal of the arithmetic circuit 19 receives the output of a detection circuit 22 that determines the stress value at a predetermined position of the sample 4 based on a detection signal from a strain detection element 21 such as a strain gauge attached to the sample 4. Supplied. The arithmetic output of the arithmetic circuit 19 is transmitted to the arithmetic circuit 2 through a hold circuit 23.
Sent to 0. 24 and 25 are meters and numerical displays for displaying the output values of the arithmetic circuit 20.

In the above configuration, if compressive load and tensile load are applied alternately to the test sample 4 in a rectangular waveform as shown in FIG. 4a by the pistons 2 and 3, the surface temperature of each part of the sample is As mentioned above, the ambient temperature changes as shown in FIG. 4b, for example, with a range corresponding to the compressive load and tensile load applied to each part. Therefore, the output of the thermometer 7 that measured the temperature change at a specific point P on the sample also shows a waveform change corresponding to b in the same figure, and the change in the output (AC signal)
is taken out via the removal circuit 15 as shown in FIG. 4c. Then, the circuit under test 17 transmits the AC signal to the vibrator 1.
Since synchronous detection is performed based on the synchronous signal (Fig. 4 d) generated from the synchronous signal, a DC signal Ap corresponding to the amplitude of the AC signal is obtained as an output, as shown in Fig. 4 e. As mentioned above, the DC signal corresponds to the range of temperature change at the observation point, that is, the stress value applied to that point.

However, even if the stress value is the same for this DC signal value,
It varies depending on the emissivity and material of the sample, and if the gain of the circuit system fluctuates due to changes over time, voltage changes, etc., it changes accordingly, resulting in errors. Therefore, in the present invention, the correct stress value applied to the same place as the observation point P by the thermometer 7 is detected using the strain detection element 21 and the detector 22, and the obtained detection signal Bp
The ratio of the DC signal Ap corresponding to the stress obtained using the thermometer 7, that is, the correction coefficient, is determined in the arithmetic circuit 19, and the measured values of other parts are corrected using the obtained coefficient.

That is, prior to measurement, the switch 18
9 side, and the observation point of the thermometer 7 is set at the mounting position of the strain detection element 21 or a position very close to it. The arithmetic circuit 19 calculates the ratio K=Bp/Ap between the detection signal Ap sent via the switch 18 and the detection signal Bp sent via the detector 22, and the ratio K is sent to the hold circuit 23 as a correction coefficient.
held by.

After the correction coefficient is held, the switch 18
If the observation point of the thermometer 7 is moved to a desired position on the sample 4 at the same time, the detection signal A regarding the desired position is sent to the arithmetic circuit 20;
At 0, the signal A is multiplied by the correction coefficient K to obtain the correct measured value A·K. The correct measurements obtained are sent to the meter 24 or display 25 for display.

In this way, the stress value at any point can be obtained as a corrected value, but a two-dimensional or one-dimensional optical scanning mechanism 26 is provided in front of the thermometer 7 to gradually move the observation point of the thermometer. Along with scanning,
Along with this, if the measured value obtained from the arithmetic circuit 20 is introduced as a luminance modulation signal or a Y-direction modulation signal to the display device 27 synchronized with the scanning, a stress distribution image or stress distribution waveform having a luminance according to the stress value is generated. Needless to say, it is possible to display

By the way, as mentioned above, the temperature changes at different positions on the sample surface in a range corresponding to the stress value at each point, so a repetitive load as shown in Figure 1 a is applied. During the half period T1 of the compressive load, each point on the sample surface shows a temperature rise (from the ambient temperature) according to the stress value at each point,
Half period T2 of the tensile load should show a temperature drop (from ambient temperature) depending on the stress value at each point. Therefore, by acquiring a temperature distribution image of the sample surface whose temperature has increased during T1, and acquiring a temperature distribution image of the same surface whose temperature has decreased during T2, and finding the pattern of the difference between the two temperature distribution images, The pattern corresponds to the temperature difference, that is, the stress, between the periods T1 and T2 at each point on the sample.
A stress distribution pattern can be obtained at +T2.

FIG. 5 shows the configuration of another embodiment of the present invention based on this idea. In the same figure, 28 is sample 4.
This is an infrared camera that scans and detects the infrared rays generated from the sample and photographs the temperature distribution image of the sample, and the camera intermittently photographs one screen at a time based on the synchronization signal 29 generated from the vibrator 1. . A video signal (temperature signal) for one screen obtained in conjunction with photographing is converted into a digital signal by an A-D converter 30, and then write control is performed by a switch 31 that is switched based on the synchronization signal 29. It is selectively supplied to the circuit 32 or the subtraction circuit 33. The write control circuit writes the supplied temperature signal for one screen into the memory 3 based on the scan synchronization signal 34 of the camera 28.
Store in 5.

The stored temperature signal is then read out by a readout control circuit 36 which operates based on the scan synchronization signal 34 when photographing the next one screen, and sent to the subtraction circuit 33 and also to the level determination circuit 38. The output signal of the subtraction circuit 33 is selectively supplied via a switch 37 to a sample and hold circuit 39 operated based on a command pulse from a level discrimination circuit 38 or to an arithmetic circuit 40.

41 is a detection circuit 22 that sends the output A of the sample hold circuit 39 and the A-D converter 42.
It is an arithmetic circuit that calculates the ratio of the detection signal B from the
The output of the arithmetic circuit 41 is sent to the arithmetic circuit 40 via a hold circuit 42. The output of the arithmetic circuit 40 is sent to a cathode ray tube (CRT) display device 45 which operates based on the scan synchronization signal 34.
It is supplied via the A converter 44 as a brightness modulation signal.

In the configuration as described above, the vibrator 1 applies a rectangular waveform load as shown in FIG. 6a, for example, to the sample 4 at a repetition period of 2 seconds. The vibration exciter 1
A synchronization signal 29 (Fig. 6b) synchronized with the load application is generated, and based on the synchronization signal 29, the camera 28 detects the timing within the compressive load period T1 and the tensile load period T2 at the timing shown in Fig. 6c. 1 time each
Perform screen scanning.

At this time, the switch 31 is switched in synchronization with the load application as shown in FIG. The temperature signal Z2 obtained with one screen scan at T2 is sent to the subtraction circuit 33. The T2 period readout control circuit 36 reads the temperature signal Z1 obtained during the T1 period in synchronization with one screen scan by the camera 28 and sends it to the subtraction circuit 33.
As the output of the subtraction circuit 33, a difference signal between Z1 and Z2 is obtained. That is, a difference signal corresponding to the temperature difference (temperature change) between the temperature during the period T1 and the temperature during the period T2 is obtained for each pixel forming one screen. As mentioned above, this temperature difference signal indicates the stress applied to the minute point on the sample corresponding to each pixel, and if this signal is sent to the CRT display device 45, the brightness will be given according to the stress. A stress distribution image can be obtained.

However, even if the distortion value is the same, this difference signal will show a different value depending on the emissivity of the subject and the material, and if the gain of the circuit changes due to changes over time or voltage changes, it will change accordingly, causing an error. It will happen.
Therefore, in this embodiment, the strain detection element 21 is mounted on the sample within the field of view of the infrared camera 28, and the correct stress value at the mounting location is detected by the element 21 and the detection circuit 22, and the obtained detection signal B and the infrared camera 28 The ratio of the stress to the signal A corresponding to the stress at the installation location obtained using the above method, that is, the correction coefficient, is determined, and the measured values of other parts are corrected using the obtained correction coefficient.

That is, the outer surface of the strain detection element 21 is given a mirror finish, for example, and has an extremely low emissivity compared to the surrounding area.
Therefore, during the period when the surface of the strain detection element 21 is being scanned for both Z1 and Z2, the signal level is extremely lower than before and after that, and as a result, the output signal of the readout control circuit 36 is also During that period, the signal level becomes extremely low. Therefore, the switch 37 is turned to the contact a side during the first cycle of load application, and the readout control circuit 36 obtained during that period is
The level of the output signal is monitored by the discrimination circuit 38, and a command pulse from the discrimination circuit 38 is issued at a timing immediately before or after a period in which the signal level is extremely reduced (in other words, a period in which the distortion detection element is being detected). If the output signal of the subtraction circuit 33 is sampled and held in the hold circuit 39 immediately before or immediately after the period in which the signal level drops extremely, the sampled and held output signal value A will be the output signal of the distortion detection element 21. The stress value corresponds to the stress value in the very vicinity, that is, substantially at the mounting position of the element.

Then, the calculation circuit 41 calculates the ratio K=B/A between the correct measurement value B of the stress value at the mounting position and the measurement value A obtained by the infrared camera 28, and the ratio K
is held by the hold circuit 43 as a correction coefficient.

After the correction coefficient is held in this way, when the switch 37 is switched to the contact b side from the second cycle of load application as shown in FIG. and the arithmetic circuit 4
0, a correct signal is obtained by multiplying the output signal by the correction coefficient K. Since this signal is sent as a luminance signal to the CRT display device 45 via the DA converter 44, a stress distribution image with correct luminance given by correction is obtained on the screen of the display device. As a display method, in addition to the above-mentioned brightness modulation method, for example, a so-called deflection modulation method may be used in which the brightness signal is kept constant and the output signal of the arithmetic circuit 40 is superimposed on the vertical direction deflection signal of the CRT. It goes without saying that other display methods may be used.

The waveform of the applied load is not limited to the rectangular waveform as in the above example, but may be a sine waveform, and the direction of the load may also be applied only in the compression or tension direction as shown in Figure 1c or e. Furthermore, it may be such that a variation is superimposed on a constant load.

The infrared camera may be one that performs optical scanning or one that performs electronic scanning such as an infrared vidicon.

Furthermore, in the above embodiment, the weight application by the vibrator is performed with a constant amplitude, but when the amplitude changes, the correction coefficients other than the measurement points by the strain detection element are changed in accordance with the change in amplitude. Just do it like this.

As described in detail above, according to the present invention, a corrected and precise stress distribution image can be obtained in an order of magnitude shorter time than conventional methods.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram for explaining the principle of the present invention, Fig. 2 is a diagram showing the relationship between load and temperature change, and ambient temperature and temperature change, Fig. 3 and Fig. 5 are one embodiment of the present invention. 4 and 6 are waveform diagrams for explaining the operation. 1: Vibrator, 4: Test sample, 7: Radiation thermometer,
15: DC component removal circuit, 17: Synchronous detection circuit, 1
8, 31, 37: Switch, 19, 20, 40,
41: Arithmetic circuit, 21: Strain detection element, 22: Detection circuit, 23, 43: Hold circuit, 24: Meter, 25: Display, 26: Optical scanning means, 2
7, 45: CRT display device, 28: Infrared camera, 30, 42: A-D converter, 32: Write control circuit, 33: Subtraction circuit, 35: Memory, 36:
Read control circuit, 38: Level discrimination circuit, 39:
Sample and hold circuit, 44: DA converter.

Claims (1)

[Scope of Claims] 1. A means for detecting temperature changes in a sample in synchronization with load changes based on infrared rays generated from a test sample to which different loads are sequentially applied, and a strain detection element attached to the sample; Calculating means for calculating the ratio between the output of the detection element and the output of the temperature change detection means at the same position as the mounting position of the detection element, and means for correcting the output of the temperature change detection means based on the value of the ratio. and display or recording means to which the output of the correction means is supplied. 2. The temperature change detection means comprises a radiation thermometer that measures the sample temperature, a circuit that extracts an AC signal from the output signal of the radiation thermometer, and a circuit that detects the amplitude of the AC signal. The stress measuring device according to scope 1. 3. The temperature change detection means stores an infrared camera for photographing the test sample to which two different loads are sequentially applied, and one screen worth of temperature signals obtained from the infrared camera when one of the loads is applied. Claim 1, which comprises a storage means, and a subtraction circuit that calculates the difference between the temperature signal for one screen obtained from the infrared camera when the other load is applied and the temperature signal stored in the storage means. The stress measuring device according to item 1. 4. The stress measuring device according to any one of claims 1 to 3, wherein one of the different loads is a compressive load and the other is a tensile load. 5. The stress measuring device according to any one of claims 1 to 3, wherein one of the different loads is zero.