JP2001188028A - Infrared-ray stress image device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared-ray stress image device which can detect the phase where temperature variation with stress becomes maximum at higher S/N than before and speedily and accurately detect the difference between a specific phase (e.g. maximum, zero, or minimum phase, etc.) of a signal syn chronizing with a load and the phase where the stress of a sample becomes maximum. SOLUTION: The infrared-ray stress image device which obtains a stress distribution image by determining the difference between the specific phase of the signal synchronizing with the load and the phase where the stress of the sample becomes maximum by placing the load on the sample in specific cycles, and then integrating and measuring temperature variation on the sample surface resulting from thermoelastic effect by an infrared-ray camera divisionally into a plus temperature image and a minus temperature image in timing to the phase difference and finding the difference image between the two integrated temperature images giving the same sign to specific areas of the difference image including an area where stress is converged and/or an area where ghost is generated and integrating the temperature values given the same sign.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an image of a stress distribution by applying a load to a sample at a predetermined cycle and measuring a temperature change of the sample surface based on a heat generation / absorption action by a thermoelastic effect with an infrared camera. In particular, a phase difference between a predetermined phase (for example, a maximum phase, a zero phase, a minimum phase, etc.) of a synchronization signal synchronized with a load and a phase at which the stress of the sample becomes maximum. The present invention relates to an infrared stress imaging apparatus capable of easily determining the image.

[0002]

2. Description of the Related Art Measuring the magnitude of stress generated in each part of an object to which a load is applied is a matter of selecting the shape of each part, the dimensions of the material used, the material, etc. when designing a machine or structure. Thus, it is extremely important to enable a complete and economical design. Therefore, conventionally, a strain gauge has been attached to an object to be measured, a strain generated in the object to be measured has been detected, and a stress distribution has been measured.

[0003] However, there is a problem that the attachment of the strain gauge to the object to be measured is troublesome and takes a lot of time for the measurement. On the other hand, when a compression / tensile load is repeatedly applied to the object, a heat generation / endothermic phenomenon based on the thermoelastic effect appears. When the heat generation and heat absorption are repeated in a relatively short cycle, the surface temperature of the stress concentration portion changes in an adiabatic state in which diffusion of heat to the surroundings or inflow of heat from the surroundings is cut off. Since there is a direct relationship between the amount of temperature change and the amount of stress change, a method of measuring the stress distribution by measuring the amount of change in the surface temperature of the object to which a load is applied using an infrared camera. Has been proposed. According to such a stress distribution measuring method, it is possible to measure a stress distribution quickly and easily in a non-contact manner as compared with a conventional stress distribution measuring method using a strain gauge or the like.

[0004]

The change in stress (or change in temperature) of the sample when a compressive / tensile load is repeatedly applied to the sample depends only on the actuator system or the test machine to which the load is applied. In addition, depending on the material and shape of the sample, a predetermined phase shift that cannot identify the cause occurs with respect to the phase of the synchronization signal synchronized with the load. The amount of stress change (that is, the amount of temperature change) is obtained from the temperature difference between the highest temperature and the lowest temperature generated when a load is applied to the sample, and the temperature data is obtained in synchronization with a synchronization signal synchronized with the load. Therefore, it is necessary to determine the phase of the synchronization signal that gives the maximum value and the minimum value of the detected temperature change signal, measure the temperature data at that time, and obtain the difference.

However, since the actually obtained temperature change signal does not form a smooth curve but has a jagged waveform on which noise and the like are superimposed, it is not possible to determine the phase of the synchronization signal that gives the maximum and minimum values of the temperature. It's not easy. Therefore, conventionally, the detection signal is integrated to improve the S / N ratio, and the timing of the temperature data measurement is automatically adjusted to the phase of the synchronization signal that gives the maximum and minimum values of the temperature. An adjustment scheme has been proposed.

In the stress measurement method using an infrared camera, when the temperature difference between the maximum temperature and the minimum temperature is calculated, an apparent temperature difference due to a temperature image shift caused by a position shift of the sample due to application of a load. A signal, a so-called ghost, occurs. Since the phase in which the ghost is maximized and the phase in which the stress is maximized almost coincide with each other, the phase in which the ghost is maximized is detected, and the phase is automatically adjusted by adjusting the temperature image acquisition timing to the phase. The method is also generally performed.

However, these automatic phase adjustment methods use, for example, as shown in FIG. 1, a predetermined one-point pixel in a temperature image of a measured object measured by an infrared camera.
Or, at a plurality of pixels in the vicinity including the point or a plurality of pixels in a predetermined range arranged on the same scanning line, a phase of a synchronization signal that gives a maximum temperature change is obtained, and the timing of temperature data acquisition is determined as the phase. The phase adjustment method automatically adjusts the phase, so if you do not know in advance where the stress is concentrated in the temperature image or where the ghost occurs in the temperature image, the phase There was a problem that a measurement point for alignment could not be determined. Further, in the conventional automatic phase adjustment method, since the temperature data of a limited number of measurement points are merely integrated, the S / N ratio is insufficient, and it takes time for the automatic phase adjustment, or the accurate phase adjustment is performed. There was a problem that they could not be matched.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to increase the phase at which the temperature change due to stress is maximum, to a higher S / S than in the prior art.
The phase difference between a predetermined phase (for example, a maximum phase, a zero phase, a minimum phase, and the like) of a synchronization signal detected by an N ratio and a load and synchronized with a load is quickly and quickly determined. An object of the present invention is to provide an infrared stress imaging device that can be accurately determined.

[0009]

In order to achieve this object, an infrared stress imaging apparatus according to the present invention applies a load to a sample at a predetermined cycle, and sets a predetermined phase of a synchronization signal synchronized with the load with a predetermined phase of the sample. After determining the phase difference of the phase that maximizes the stress, the temperature change of the sample surface due to the thermoelastic effect is divided into a plus temperature image and a minus temperature image at the timing that matches the phase difference, and integrated measurement with an infrared camera Then, in the infrared stress imaging apparatus configured to obtain a stress distribution image by obtaining a difference image between the two integrated temperature images, a predetermined image of the difference image including a region where stress is concentrated and / or a region where ghost occurs is obtained. By encoding the temperature values in the region of the same, and integrating the same encoded temperature values,
A phase difference between a predetermined phase of the synchronization signal synchronized with the load and a phase at which the stress of the sample is maximized is determined.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram illustrating an embodiment of the infrared stress imaging apparatus. When a load is repeatedly applied to the DUT 1 at a predetermined cycle by the repetitive load generator 2,
The temperature of the portion where the stress is concentrated rises and falls in synchronization with the cycle of the repeated load due to the thermoelastic effect. Since the value of the temperature change accompanying the normal stress change in the solid is very small, the temperature image data is repeatedly taken in synchronization with the load application timing at a predetermined phase while taking an image with the infrared camera 3, and the integration is performed. The temperature change is extracted as a signal.

That is, as shown in FIG. 3, the timing on the plus side and the timing on the minus side of the synchronization signal synchronized with the load (strictly, the timing is adjusted to the maximum and minimum timings of the temperature change. , Which coincides with the minimum timing) and data in a predetermined range before and after that (for example, a range from the maximum stress value and the minimum stress value to about 70% of those stress values) and sampled and integrated. On the plus temperature image integrating memory 4 and the minus temperature image integrating memory 5, the plus temperature image and the minus temperature image integrated for each pixel are obtained. Then, the subtraction means 6 performs subtraction between the two temperature images to obtain a stress image 7 corresponding to the amount of change in temperature.

In such a configuration, in order to efficiently obtain a stress distribution image, as shown in FIG. 3, the phase is shifted by a predetermined phase from the period of the synchronization signal synchronized with the load applied to the measured object. It is necessary to match the temperature image acquisition timing to the positions of the maximum value and the minimum value of the temperature signal. Conventionally, as shown in FIG. 1, a pixel at a predetermined point in a temperature image of an object to be measured measured by an infrared camera, or pixels at a plurality of nearby points including the point, or aligned on the same scanning line In a plurality of pixels in a predetermined range, the phase of the synchronization signal that gives the maximum temperature change is obtained, and the timing of temperature data measurement is automatically adjusted to that phase. As shown in FIG. 4, by setting the entire temperature difference image of the measured object or a predetermined range including the compression / tensile portion and the ghost occurrence portion, the absolute value of the temperature difference data of each pixel of the temperature difference image is obtained. The operation of integrating the absolute value over the entire set range is performed for various phases of the synchronization signal, and the entire temperature difference image of the measured object, or a predetermined range including a compression / tensile portion or a ghost occurrence portion is included. Temperature Calculated temperature difference absolute value of the integral value of the synchronizing signal so as to maximize the phase of the data of the image, so timing the temperature image acquisition to the phase.

Here, the reason for taking the absolute value of the temperature difference data is that if a plus portion and a minus portion are present in the temperature difference data during the integration, they will be offset each other, so that this is prevented. That's why. Therefore, this operation is replaced with an operation having an effect equivalent to obtaining the absolute value of the temperature difference data, for example, an operation of converting the temperature difference data to a value of the same sign by squaring or squaring the temperature difference data. It is also possible. By these operations, the phase at which the absolute value of the temperature change due to the stress is maximum is detected at a higher S / N ratio than before, and the predetermined phase of the synchronization signal synchronized with the load (for example, the maximum phase, zero phase) And the phase at which the stress of the measured object becomes the maximum can be quickly and accurately determined.

FIG. 5 shows the flow of operation of such an automatic phase adjustment method according to the present invention. First, in a predetermined temperature image region set in advance, a phase for acquiring a temperature image is determined for phase determination. Next, a plus temperature image is obtained at a predetermined timing on the plus phase side of the compression / tensile load, and a minus temperature image is obtained at a predetermined timing on the minus phase side of the compression / tensile load. Next, the obtained plus temperature image and minus temperature image are converted into a temperature difference image by subtraction means. Next, the temperature difference data for each pixel of the obtained temperature difference image is converted into an absolute value and integrated over the entire set area. Next, it is determined whether or not the integration result is the maximum. If the integration result is not the maximum, the process returns to the first step, the phase for acquiring the temperature image is reset, and the same determination operation is repeated. If the integration result is the maximum, the acquisition phase of the temperature image is determined to be the phase.

The determination as to whether or not the value of the integration result is the maximum can be easily made by comparing the value of the integration result of the temperature difference image measured at the phase before and after that phase. .

[0016]

As described above, according to the infrared stress imaging apparatus of the present invention, the temperature difference data of the temperature difference image of the surface temperature change observed with the application of the load to the measured object is encoded, By integrating over the entire set area, the phase at which the temperature change of the surface temperature is maximized is determined, so that the optimal phase for acquiring the temperature image can be detected at a high S / N ratio, and the phase can be quickly detected. And the phase of temperature image acquisition can be accurately determined. Further, since the phase matching is performed based on the temperature data of the wide temperature image area, it is not necessary to know in advance the specific part where the stress is concentrated or the specific part where the ghost occurs.

[Brief description of the drawings]

FIG. 1 is a diagram showing characteristics of a phase adjustment method of a conventional infrared stress imaging apparatus.

FIG. 2 is a diagram showing one embodiment of an infrared stress imaging apparatus.

FIG. 3 is a diagram showing a phase relationship between a load change and a temperature change.

FIG. 4 is a diagram showing characteristics of the phase adjustment method of the infrared stress imaging apparatus of the present invention.

FIG. 5 is a flowchart of a phase adjustment method in the infrared stress imaging apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measurement object, 2 ... Repeated load generator, 3 ... Infrared camera, 4 ... Plus temperature image accumulation memory, 5 ...
Minus temperature image accumulation memory, 6 ... subtraction means, 7
..Stress images.

Claims (1)

[Claims] A load is applied to a sample at a predetermined cycle, and a phase difference between a predetermined phase of a synchronization signal synchronized with the load and a phase at which the stress of the sample is maximized is determined. At the timing, the temperature change of the sample surface due to the thermoelastic effect is divided into a plus temperature image and a minus temperature image, integrated and measured with an infrared camera, and a difference image between the two integrated temperature images is obtained to obtain a stress distribution image. In the infrared stress imaging apparatus configured as above, the temperature values of a predetermined area of the difference image including the area where the stress is concentrated and / or the area where the ghost is generated are coded the same, and the coded temperature values are integrated. The infrared stress imaging apparatus according to claim 1, wherein a phase difference between a predetermined phase of the synchronization signal synchronized with the load and a phase at which the stress of the sample is maximized is determined.