JP2008139273A - Method and system for measuring strain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for readily measuring a strain (deformation) of a wood, metallic or resin material or the like by effectively using retroreflective beads. <P>SOLUTION: In the case where a strain of an article is measured, retroreflective beads are uniformly adhered to the measuring face of the article to be measured. The surface having the adhered retroreflective beads is irradiated with a light, the reflection amount before occurrence of strain is compared with that after the occurrence of the strain, thereby measuring the strain. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for measuring strain (deformation) of various objects made of wood, metal, or other materials, and a system for performing the method.

  Because wood, metal materials, synthetic resin materials, concrete materials, and other materials used in buildings and other structures or their components are subject to creep deformation over time due to external forces, etc., eventually leading to destruction Knowing the state of strain (deformation) during use, and knowing the remaining life until breakage are extremely important for long-term stable use.

  Various measuring methods are known as methods for measuring the strain of an object. The most common method for measuring strain (deformation) is to measure the dimensional change, and the method of measuring the change in the distance between the marks by marking two or more marks on the surface of the object is an old method. Has been adopted. However, since it is difficult to measure local deformation in these dimensional measurements, the surface of the measured portion of the material is polished to extract carbides on the surface, and its distribution is used as a strain measurement method for the minute portion. There are also methods for observing and measuring the state with an electron microscope, but there are problems such as how the change appears depending on the material, and measurement with sufficient accuracy unless it approaches the end of life.

  On the other hand, there is a proposal to use a method for measuring the deformation of a minute portion by a speckle pattern for measuring the amount of creep deformation. With this speckle pattern strain measurement method, for example, fine unevenness is given to the surface of the object, the reflected light image is pre-photographed, and after the stress is applied and deformed, the reflected light image is imaged again, This is a method of measuring the displacement by the digital image processing technique from the difference between the two images and knowing the magnitude and distribution of the strain. However, according to this method, depending on the material, the surface state changes greatly over a long period of use, and the reflected light is greatly affected. Therefore, in order to avoid the influence of the surface change, a stable thin film (such as platinum foil) that is not affected by the environment is attached to the surface of the part to be measured, and the minute distortion of the target part is measured by measuring the speckle pattern change of the film. A method for measuring the above has also been proposed. (See Patent Document 1 and Non-Patent Document 1 below). In this case, a platinum foil is welded to the portion to be measured, and a speckle pattern formed by surface irregularities of the platinum foil is used. Platinum does not oxidize on the surface during use at high temperatures for a long time. If it is made into a foil and welded to the surface of a metal member to be measured, it deforms according to the deformation of the member. It is described that measurement is possible by the measurement method.

  In addition, a method using a strain gauge for electrically measuring the elongation and shrinkage of a test body is also well known. For example, in a strain sensor that measures the strain amount of a test piece, the super magnetostrictive material installed in the portion for measuring the strain amount of the test piece, and the super magnetostrictive material in the vicinity of the super magnetostrictive material are installed in a non-contact state. A coil that induces a current by electromagnetic induction of a magnetic field generated by the deformed super magnetostrictive material following the test piece and measuring the current value of the current. A method of calculating the strain amount of a test piece from the relationship between the strain amount of the magnetostrictive material and the current value is known (see Patent Document 2 below). This makes it possible to measure static, dynamic and impact stress, but cannot measure the strain beyond the elastic region.

  For measuring strain beyond the elastic region, it is preferable to use an optical measurement method having advantages of high accuracy, non-contact, high speed and full-field measurement. As an example of such an optical measurement method, at least two measurement jigs each provided with a fixed part that is fixed to a test material and a measurement part that is formed integrally with the fixed part, and a measurement that is opposed to the measurement jig. Using a measuring device consisting of measuring means (laser length measuring machine) that measures the displacement between the parts with a laser beam, a fixing part of a measuring jig is attached to the test point of the test piece, and the laser oscillator of the laser length measuring machine A method has been proposed in which the measurement part is irradiated with laser light from the side, and the displacement between the measurement points of the test piece is measured by measuring the displacement between the measurement parts by receiving and detecting with a detector ( See Patent Document 3 below). However, in general, the optical measurement method is not widely used because it takes time to understand the principle and an easy-to-use apparatus is not commercially available.

  JP 2005-291979 A   JP 2004-219105 A   JP-A-10-89950   R. van Vulpen et al., “Creep Monitoring of Repair Welds in High Temperature Components”

The conventional measurement methods as described above are difficult to measure the accurate deformation amount for each local area, require expensive measurement means such as platinum foil, or require large-scale instruments and devices for measurement. There are problems such as cost.
An object of the present invention is to solve such problems of the conventional measuring method and to provide a highly accurate measuring method that can easily and accurately measure the strain of a material.

The inventor of the present invention paid attention to retroreflective beads as a result of intensive studies to achieve the above-mentioned object. Here, “retroreflective” refers to a reflection phenomenon in which light emitted from the light source returns to the light source again on the surface coated with the reflective material. Such retroreflective beads are widely used for road markings, road signs, and the like. In the present invention, wood coated with retroreflective beads having such properties (hereinafter sometimes simply referred to as “reflective beads”) is used. By applying a load to the material, etc. and observing the lateral compression deformation, even if the wood exceeds the elastic region, by observing the change in the reflected light from the reflective beads applied to the surface, the strain of the wood ( It has been found that it is possible to measure deformation.
Based on this knowledge, further research was conducted to complete the method of the present invention that can easily and accurately measure strain (deformation).
In other words, it is expected that there will be an error between the point being observed and the distortion of the entire object to be measured such as wood, and the relationship between the distortion of the entire object to be measured displayed by the testing machine and the change in reflected light due to the reflective beads. As a result, the behavior of the reflective beads uniformly attached to the surface of the object to be measured is linked to the deformation (strain) of the object, and when the compressive load is applied and the object surface contracts, it is applied to the surface of the object. The interval between the reflective beads is reduced, the total area occupied by the reflective beads per unit area of the surface is increased, and the distribution density is increased. Therefore, the intensity of reflected light (the amount of reflected light) also increases. As a result, when the object is irradiated with light and the compression proceeds, the intensity of the reflected light (the amount of reflected light) at the compressed portion also increases. By measuring this, the distortion can be measured quantitatively. Further, when bending deformation occurs, the total area of the reflective beads per unit area changes locally according to the deformation, and by measuring this, the state of strain due to bending can be known.

Thus, according to the present invention, the following measuring method is provided.
(1) When measuring the strain of an object, retroreflective beads are uniformly attached to the surface of the object to be measured, and the surface is irradiated with light to examine changes in reflected light from the retroreflective beads. A strain measuring method characterized by measuring strain.
(2) Apply the adhesive uniformly to the surface of the object to be measured, and make the retroreflective beads uniformly on the surface of the object to be measured by bringing the gas in which the retroreflective beads are dispersed into contact with the adhesive application surface. The strain measuring method according to claim 1, wherein the strain is attached.
(3) It is characterized in that the reflected light from the surface where the reflective beads are attached is photographed with a digital camera when distortion occurs, and the change in the reflected light is examined by calculating the total area of the reflective beads per unit area from the photographed image. The method for measuring strain according to claim 1.
(4) The strain measuring method according to claim 1, wherein the reflected light from the reflecting beads is photographed with a digital camera before and at the time of occurrence of the strain, the photographed images are synthesized, and the history of the strain is observed. .
Furthermore, according to the present invention, the following measurement system is provided as means for carrying out the above method.
(5) means for irradiating light on the surface of the object to be measured with retroreflective beads attached, means for photographing the reflected light from the retroreflective beads into a digital image, and analyzing the photographed digital image And a means for calculating the total area of the reflective beads per unit area.
(6) A means for irradiating light on the surface of the object to be measured with the retroreflective beads attached, a means for photographing the reflected light from the retroreflective beads into a digital image, and a composite of the photographed digital image And a means for displaying an image of the background of the distortion.

  According to the method and system of the present invention, it is possible to easily and accurately measure the strain of an object by effectively using retroreflective beads.

<About the material to be measured>
The measurement method according to the present invention can accurately measure strain (deformation) caused by external force in materials such as wood, metal materials, and synthetic resin materials, and there are limitations on the size and material of the material to be measured. Absent.

<Regarding the application of retroreflective beads to the material to be measured>
According to the method of the present invention, first, retroreflective beads are uniformly attached to the surface of the material to be measured. As the retroreflective beads (hereinafter, sometimes simply referred to as “reflective beads”), transparent glass beads alone or glass beads having a reflective film in a partially embedded portion can be used. The diameter of the reflective beads is usually 40 to 200 μm, preferably 50 to 150 μm. Such retroreflective beads are widely used for road marking, road signs, and the like, and are easily available.
The reflective beads are partially embedded in the surface of the material to be measured and bonded so that incident light can be reflected in that direction.
For this reason, the adhesive is uniformly applied to the surface of the material to be measured, and the reflective beads are uniformly spread and adhered to the adhesive application surface, and the reflective bead dispersion gas in which the reflective beads are scattered on the surface. For example, a method of attaching the reflective beads by contacting them is adopted.
The adhesion density of the reflective beads should be appropriately selected according to the material to be measured. In many cases, the range of about 1000 to 10,000 is appropriate per 1 cm ² of the surface area of the material to be measured.

<Measurement of light irradiation and reflected light>
In the present invention, usually, at least twice before and after the occurrence of strain, the surface of the object to be measured which is provided with the reflective beads is irradiated with light, and the reflected light is measured. In the measurement of reflected light, the amount of reflected light at each location is seen, but this is proportional to the total area of the reflective beads per unit area, so the amount of reflected light can also be known by obtaining the total area.
As the light irradiation means, for example, a vertical epi-illumination device (LSGA oblique illumination device, SZ-VIA / vertical epi-illuminator attachment, TL-3-100 6V20W type transformer) or the like is adopted, but the present invention is not limited to these. Absent. When irradiating light, adjustment is made so that the light beam is incident at a right angle to the reflective bead attachment surface of the object to be measured.
In order to see the amount of reflected light, it is preferable to photograph the light-irradiated surface with a digital camera. When photographing with a digital camera, the amount of reflected light varies depending on the reflective bead adhesion area on each specimen and the total reflected bead area per unit area that changes with compression. difficult. Therefore, it is preferable to adjust the color tone by storing a white balance suitable for the actual shooting situation in the digital camera with the test piece before compression each time.
These photographing operations can also be performed in the course of strain generation of the test piece. For example, the strain can be measured by photographing each load while applying a load that increases stepwise to the object to be measured.

<Measurement of strain>
The strain is measured by measuring the amount of reflected light per unit area (in other words, the total area of the reflective beads) from the reflected light. For example, as a pre-measurement process, an image photographed in a program mode with a digital camera is taken into a PC, processed with image analysis software (Adobe Photoshop 6.0 or the like), and each image is converted to gray scale. Then, the intensity of the reflected light can be indirectly quantified by measuring the total area of the reflective beads in the imaging range using image analysis software (Scion Image or the like). In this method, for example, when there is a considerable time difference between the time of capturing an image before deformation and the time of capturing an image after deformation, the area is measured in this way to determine the intensity of reflected light (the amount of reflected light). The obtained one has the advantage that it is less susceptible to changes in the intensity of illumination light and environmental conditions.
FIGS. 6 to 9 are images taken in this way, FIGS. 6 and 7 are images before and after compression deformation, and FIGS. 8 and 9 are images before and after bending deformation. By measuring and comparing the total area occupied by the reflective beads per unit area in the images before and after the deformation, that is, the density of the reflective beads, the distortion of each part can be known.

<Image display of strain change by image composition>
If the deformation measurement using the reflective beads is viewed from a different viewpoint, it is possible to focus on the behavior of the reflective beads and to visualize the force distribution at the time of strain generation.
For example, when a material compression test is performed and a plurality of images obtained by photographing with a digital camera for each compression condition are combined by using a layer function such as Adobe Photoshop 6.0, the reflective beads are deformed by wood. Along with this, various patterns are created as if showing the distribution of force.

  As an example, FIG. 10 shows a photographic image synthesized with reference to the center of wood before compression and wood distorted to some extent. In FIG. 10, although the part where the reflective bead does not draw a pattern can be confirmed, it may be considered that the part is not deformed by the wood. In this photographic image, it can be seen that in the case of lateral compression, the force is transmitted from the soft early material on the load side to the hard late material, and the force is transmitted to the next annual ring field. In the composite photograph image of FIG. 10, the annual ring world runs from the upper left to the lower right. There is a part in which the behavior of the reflective bead cannot be confirmed in an opposite manner. In this part, the annual ring field is not orthogonal to the load direction, so it is considered that the time during which force is transmitted to each annual ring is different. That is, it can be estimated that the portion where the behavior of the reflective bead does not occur takes time to transmit the force even when a load is applied, and the portion where the behavior of the reflective bead is large is transmitted quickly and is distorted.

  Also, the photograph in FIG. 13 is a photograph of a plate surface subjected to a bending test, and is a composite of images before applying a load and before the breakage, and this image is also superimposed and synthesized at the center of the test piece. is there. In the composite photograph of FIG. 13, the behavior of the reflective bead is not seen in the central part, and it seems to move while drawing an arc from the tension side to the load side so as to avoid the central part. These are considered to indicate the distribution of force applied to the wood. Establishing this photosynthesis method can be applied to materials other than wood, and can be a new deformation measurement that replaces expensive and time-consuming methods such as photoelasticity experiments.

  Hereinafter, experimental examples measured according to the method of the present invention will be described in detail. However, the scope of the present invention is not limited by these experimental examples.

[Example 1]
<Experimental equipment>
As an experimental apparatus, as shown in FIG. 1, a digital camera (Olympus E-300) was attached to the crosshead portion of a Shimadzu universal testing machine (Shimadzu Corporation, AGS-H). When the test machine starts to compress, the digital camera moves with the movement of the crosshead. At that time, even if the observation position after the initial observation position and the crosshead movement are different, the vertical movement mechanism can always be used. Attached. A close-up lens and vertical epi-illuminator (LSGA oblique illumination device, SZ-VIA / vertical epi-illuminator attachment, TL-3-100 6V20W transformer) are attached to the digital camera so that the retroreflected light of the reflective beads can be photographed. . Since it was found from the preliminary experiment that the test piece itself was greatly deformed in the tangential direction when the test piece was compressed, the deformation was restrained by an aluminum frame (inner dimensions 40 × 40 × 40 mm, thickness 10 mm).

<Sample material>
Sugi (Cryptomeria japonica D. Don) was used as a test material. As shown in FIG. 2, the dimensions of the test piece are (a) fiber direction 40 mm, tangential direction 39.5 mm, radial direction 39 mm and (b) fiber direction 40 mm, tangential direction 39 mm, radial direction 39 mm. Types were prepared (the test piece of size a was RED, the test piece of size b was BLUE, and the test pieces were distinguished). The reason why the radial direction is 1 mm smaller than the inner dimension of the aluminum frame is to guide the compression jig smoothly. Two types of test specimens were prepared in order to know whether the friction with the compression jig would change when the dimensions in the tangential direction were changed, and to know whether a difference appears in the load-strain curve. In addition, it was found that a narrow space with the aluminum frame was more convenient for focusing at the time of shooting, so silicon pad aerosol was sprayed on the inner surface of the jig in order to reduce friction generated in a narrow gap.
A spray paste (“3M spray paste 55” manufactured by Sumitomo 3M Co., Ltd.) is applied to the surface of the lip of each test piece evenly for about 1 second, and the self-reflective glass that is one of the test piece and the retroreflective beads. The beads (manufactured by Union Co., Ltd., self-reflection union beads UB-24MSJ, average diameter 45 μm, composition BaO—SiO 2 —TiO glass, refractive index 1.93 ± 0.01, specific gravity 4.02 ± 0.1) In the ball-type spraying device shown in FIG. 3, the reflective beads were rolled up by air spray, and adhered so that the reflective beads fell on the upper surface of the test piece.

<Compression test>
Using a Shimadzu universal testing machine (Shimadzu Corporation, AGS-H), a lateral compression load was applied in the radial direction of the test piece. The compression speed was constant at 0.5 mm / min, and a lateral compression test was performed up to a strain of 0 to 50%.

<Photographing>
In parallel with the compression test, the surface of the test piece to which the reflective beads were attached was photographed every 5% with a digital camera equipped with a close-up lens. The shooting location was set at the center of the mouth. The imaging surface is illuminated by a vertical epi-illumination device (LSGA oblique illumination device, SZ-VIA / vertical epi-illuminator attachment, TL-3-100 6V20W type transformer), and the brightness adjustment scale makes it easy to confirm reflected light even with the naked eye. 6 was set. The camera was focused in an unloaded state, and the shooting range was 11.5 mm in length and 15.5 mm in width. The maximum close-up magnification (1 pixel: 0.216 μm) that can be read by the micrometer during image analysis was used.
When photographing with a digital camera, the amount of reflected light varies depending on the total area of the reflective beads in each test piece and the total area of the reflective beads that changes due to compression, so it is difficult to keep such a subtle change in hue constant. Therefore, the white balance appropriate for the actual shooting situation was stored in the digital camera with the test piece before compression each time.
As the compression proceeds, the total area of the reflective beads per unit area on the upper surface of the test piece increases, and the amount of reflected light also increases. At that time, in order to make the reflected light purely visible, the image was taken in the manual (M) mode in which the aperture and shutter speed can be set by itself. Even if the reflected light increased, the image was taken without changing the aperture and shutter speed, and the light intensity of the image was judged with the naked eye. Next, immediately after shooting in manual (M) mode, shooting was also performed in program (P) mode in which the camera automatically sets an appropriate aperture and shutter speed according to the brightness of the subject. Even if the amount of reflected light increases, it is possible to accurately calculate the total area of the reflective beads when performing image analysis later by photographing with appropriate exposure. The two modes were photographed with no time difference and stored as images for each strain.

<Measurement of strain>
As a pre-measurement step, an image photographed in the program (P) mode was taken into a PC and processed with image analysis software (Adobe Photoshop 6.0). Each image was grayscaled, divided into four crosses, and each was saved in TIFF format. Subsequently, the total area of the glass beads in the imaging range was measured using image analysis software (Scion Image). The measurement results at the four divided locations were added together to obtain the total area (see the flowchart in FIG. 4).

<Condition settings for image analysis software>
In performing image analysis, only the portion of the reflective bead must be selected from the image. For this reason, the brightness distribution range (Density Slice value) was set. This is an operation of designating a specific brightness distribution range in the target image on the image. By designating an upper limit and a lower limit of the brightness distribution, only a certain brightness range can be extracted.
Using a randomly selected test piece (BLUE 17), the lower value is fixed to 1 and the upper value is changed every 8 gradations, and the reflection at the time of strain 0%, 25%, 51.61% (maximum load) The change in bead layer area was measured. The results are shown in Table 1. When the measured numerical value was confirmed by a graph, as shown in FIG. 5, the reflective bead area at each strain increased stably up to the Upper value of 96. However, after that, the reflective bead area followed an increasing trend. Here, it can be estimated that a brightness distribution other than the reflective beads is selected. Accordingly, pixels extracted within the range of 1 (black side) to 96 (white side) out of 256 gradations are used as reflected light by the reflective beads.

<Measurement of total area of reflective beads>
The image was composed of pixels, and the area of the pixel of the reflected bead portion was measured and converted to the reflected bead area. Since the reflected light of the reflective beads varies depending on the angle of the reflective film, the number of pixels of the minimum bead reflected light area is set to 1 pixel. Similarly, the distortion progresses and the reflective beads are densely packed to increase the area. The number of pixels of the reflected light area was set to 99999 pixels.

<Observation of specimen>
8, 9, 11, and 12, photographs are taken with a digital camera by attaching beads to the end surface of the test pieces BLUE2 and 13RED6 (after manual mode (M) and gray scale), and shining light on the surface. FIGS. 8 and 9 are photographic images before and after the compression test, and FIGS. 11 and 12 are photographic images before and after the bending test. The total area of the reflective beads was measured using such an image. As the strain increased, the early wood part was compressed, the reflective beads were dense, and a striped pattern appeared along the annual ring. Further, it was found that the pattern does not appear uniformly in the image but gradually occurs from the top of the test piece. This time, the center of the specimen's mouth was observed at a fixed point, so it can be said that the reflective beads, which were distorted sequentially from the top of the specimen, entered the image. It was clearly confirmed by the naked eye that the reflected light became brighter as the distortion progressed and the reflective beads became dense.

<Analysis results>
First, two reflective beads were selected as top and bottom marks in the image, and the distance between the beads was measured for each strain. The distance at which the distortion is not generated _{A 0,} to calculate the strain imaging range the distance and An from _{(A 0 -An) × 100 /} A 0 when the strain occurs. As a result, as shown in FIG. 6 (relation between the bead area increase rate and the imaging range distortion with respect to the tester display distortion), it was found that there was some error in the overall distortion and the imaging range distortion. Meanwhile reflection bead area when the strain is not generated B _0, strained was calculated reflection bead area increase rate of the glass beads area from the _{Bn (Bn-B 0) ×} 100 / B 0 when the resulting (below (See Table 2). The tester display strain is an average strain of the entire test piece displayed by the universal tester.

  As shown in FIG. 6, the total area of the reflective beads (hereinafter abbreviated as “bead area”) hardly changed at the time when the strain of the entire test piece displayed by the universal testing machine was small even when compression started. However, the bead area gradually increased when the strain exceeded 10%, and rapidly increased when the strain exceeded about 20%. This proves that glass beads that are distorted in order from the compression side have entered the image. In other words, it can be said that there is a time difference between the overall strain and the local strain.

Next, when the relationship between the observation range strain and the bead area increase rate was examined, it was as shown in Table 2 and FIG. 7 (relationship between the imaging range strain and the reflective bead total area). When approximate curves were given to these two relationships, a quadratic function curve was drawn instead of a proportional relationship.
From the compression test results, the order of the early materials to be crushed is unpredictable, but detailed data for each strain can be obtained by analyzing the tendency of the quadratic function curve or mathematical expression.
However, some test specimens expand in the tangential direction when they exceed the elastic region of wood because a compression jig is used together. For this reason, when the compression progresses, there is a problem that the camera is out of focus and cannot be correctly analyzed. As a solution to this problem, a strain gauge is used in the elastic area, and the camera is focused when the elastic area is exceeded.

The series of experiments detailed above confirmed the following.
1) From the photographed image, the early wood is crushed and the reflective beads are dense, and a striped pattern can be observed from the top of the test piece.
2) From the result of image analysis, the area of the reflective bead increases as the test piece is compressed. In addition, there is a time difference between the overall strain and the local strain.

[Example 2]
Considering the measurement of deformation of wood using reflective beads from a different point of view, we thought that we could focus on the behavior of reflective beads themselves, and conducted the following experiments.
That is, a compression test was performed in the same manner as described above, and at the same time, images were taken with a digital camera. When the obtained images were overlaid using the layer function of Adobe Photoshop 6.0, the reflection beads produced various patterns as if they showed the distribution of force as the wood deformed. The specimen was Cryptomeria japonica D. Don, and the dimensions were set to 1 mm in the fiber direction, 1 mm in the tangential direction, and 2 mm in the radial direction. An image synthesized based on the center of the uncompressed wood and the wood distorted to some extent is the photograph in FIG. In this photograph, the part where the reflective bead does not draw a pattern can be confirmed, but it is thought that the part has no wood deformation. In the case of lateral compression, it is considered that the force is transmitted from the soft early material on the load side to the hard late material, and the force is transmitted to the next annual ring field. In addition, in the photograph of FIG. 10, the annual ring world runs from the upper left to the lower right. There is a part in which the behavior of the reflective bead cannot be confirmed in an opposite manner. That is, since the annual ring field is not orthogonal to the load direction, it is considered that the time during which the force is transmitted to each annual ring is different. It can be estimated that it takes time to transmit the force by applying a load to the portion where the behavior of the reflective bead does not occur, and that the portion where the behavior of the reflective bead is large is transmitted quickly and is distorted.

On the other hand, the photograph in FIG. 13 was obtained by photographing the surface of the plate in a bending test and synthesizing images before applying a load and immediately before breaking, and this image was also superimposed at the center of the test piece. Sugi (Cryptomeria japonica D. Don) was used for the test piece, and the dimensions were set to 300 mm in the fiber direction, 12 mm in the tangential direction, and 12 mm in the radial direction. The span was set to 280 mm. Interestingly, the behavior of the reflective bead is not seen in the center, and it can be seen that it moves while drawing an arc from the tension side to the load side so as to avoid the center. These are very interesting as they show the distribution of force on the wood.
From the above experiments, it was found that the pattern representing the force distribution applied to the material can be confirmed by observing the behavior of the reflective bead in the composite image.

  According to the present invention, it is possible to easily measure the strain of a structural material or member made of wood, metal, or plastics by making good use of reflective beads, and in particular, locally by combining photographic images. Since it is possible to know how to generate a large amount of distortion, it is easy to check the degree of occurrence of distortion for members to be used in advance, and to easily and low-cost the distortion that has already occurred in structural materials that make up structures. Can be measured.

Schematic diagram of the experimental equipment used in the examples Explanatory drawing of the shape and dimensions of the test pieces used in the examples Schematic diagram of the ball-type reflective bead spraying device used in the examples Flow chart of image analysis to calculate total area of reflective beads Graph showing the relationship between specific concentration distribution range and reflective bead area Graph showing the relationship between the increase rate of the bead area and the imaging range distortion against the tester display strain A graph showing the relationship between distortion and shooting area Digital photograph of specimen before compression Digital photograph of the specimen after compression Synthetic entity photo when measuring compression specimen Digital photograph of specimen before bending test Digital photograph of specimen after bending test Synthetic entity photo when measuring bending specimen

Explanation of symbols

1 Universal testing machine 2 Vertical / backward moving device 3 Angle 4 Test piece / Compression jig 5 Digital camera 6 Vertical epi-illumination device

Claims (6)

  In measuring the distortion of the object, the retroreflective beads are uniformly attached to the surface of the object to be measured, the surface is irradiated with light, and the change in the reflected light from the retroreflective beads is examined. A method for measuring strain, comprising measuring strain.   Apply the adhesive evenly to the surface of the object to be measured, and make the retroreflective beads evenly adhere to the surface of the object to be measured by bringing the gas in which the retroreflective beads are dispersed into contact with the adhesive application surface. The strain measuring method according to claim 1.   The reflected light from the reflective bead-attached surface is photographed with a digital camera when distortion occurs, and the change in the reflected light is examined by calculating the total area of the reflective beads per unit area from the photographed image. The method for measuring strain according to 1.   The strain measurement method according to claim 1, wherein the reflected light from the reflective beads is photographed by a digital camera before and at the time of occurrence of the strain, the captured images are synthesized, and the history of the strain is observed.   Means for irradiating light on the surface of the object to be measured with the retroreflective beads attached, means for photographing the reflected light from the retroreflective beads into a digital image, and analyzing the photographed digital image for unit And a means for calculating the total area of the reflective beads per area.   A means for irradiating light on the surface of the object to be measured with the retroreflective beads attached, a means for photographing the reflected light from the retroreflective beads into a digital image, and a combination of the photographed digital images for distortion And a means for displaying an image of the history of the distortion.

Images