JP2019164024A - Strain detector - Google Patents

Abstract

To provide a strain detector which does not require a sophisticated, complicated, or expensive power source or electric wiring, allows a visual confirmation or a confirmation by a low-price device of a displacement generated in an inspection target such as a building, and can easily detect a generation of a displacement due to a load larger than the acceptable stress on an inspection target object or the direction of a generated displacement.SOLUTION: A strain detector 10 includes: a flat plate 12; a plurality of attachment sites 16 located in a plurality of corners 14 of the back surface 12b of the flat plate 12; a thin site 18 in the center of the flat plate 12, of which planar shape is geometric; and a plurality of stress focusing part 20 corresponding to the sides of the flat plate 12, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a strain detector, for example, a strain detector suitable for measuring a displacement generated in a metal frame, a pressure vessel, a concrete structure, a reinforced concrete structure, or the like. Note that “displacement” may be referred to as “strain” or “distortion” or may be described together. The terms “distortion” and “distortion” include distortion as a phenomenon and distortion as a physical quantity, and when the distortion is clearly indicated, it is described as “distortion”.

  Conventionally, there is a strain detection device described in Patent Document 1 as a strain detection device for measuring mechanical strain and displacement of a building or structure, and a device described in Patent Document 2 as an apparatus for evaluating fatigue damage of a structure. There is a fatigue damage evaluation device for structures. Generally, such a building or structure is constructed so that its main stress is supported by a structure made of steel.

  There is mild steel (SS400 etc.) as a steel material mainly used for construction, and with a tensile strength of 426 Pa, the safety factor is 3 (140 MPa) for a long-term static load, and the safety factor is 5 (85 MPa) for a single swing repeated load. Designed. Moreover, the yield point (proof stress) of mild steel is 245 MPa.

  Since the Young's modulus of mild steel is about 200 GPa, the amount of elastic deformation strain at each stress is 0.07%, 0.04%, and 0.12%. If it can be detected, it is effective in evaluating the degree of damage to the structure. However, since the amount of distortion is very small, an advanced and complicated measuring device as described below is necessary for detection.

  The strain detection apparatus described in Patent Literature 1 is attached to a structural member such as a building or a structure, and a lever mechanism that scales the amount of distortion or displacement generated in the structural member, and a displacement that is enlarged or reduced by the lever mechanism. It consists of a strain detector that detects the quantity.

  The fatigue damage evaluation apparatus described in Patent Document 2 includes a deformation amount detection unit that detects a deformation amount of the evaluation target structure, and a fatigue damage rate of the evaluation target structure according to the deformation amount detected by the deformation amount detection unit. Fatigue damage rate detection means for detecting, and fatigue damage rate integration means for integrating the fatigue damage rates detected by the fatigue damage rate detection means.

JP 2000-065508 A JP 2002-014014 A

  The strain detector of the strain detection apparatus described in Patent Document 1 is necessary, and since switches such as a microswitch are used as the strain detector, wiring to a power source and various sensors is necessary, detection work, etc. Is troublesome.

  Since the deformation amount detection means of the fatigue damage evaluation apparatus described in Patent Document 2 only requires a mechanical structure, it does not require a power source or wiring, but is composed of a first fixed plate, a second fixed plate, a movable rod, and a rotating shaft. Therefore, the structure is complicated.

The present invention has been made in view of such problems, and an object thereof is to provide a distortion detector that exhibits the following effects.
(A) The displacement generated in the object to be inspected such as a structure can be confirmed with an inexpensive device or visually without requiring an advanced, complicated and expensive power supply or electric wiring.
(B) It is possible to easily detect the occurrence of displacement due to a load exceeding the allowable stress on the inspection object and the direction of the generated displacement.

[1] A strain detector according to the present invention includes a flat plate, a plurality of attachment portions provided at a plurality of corners of one main surface of the flat plate, and a planar shape provided at a central portion of the flat plate. Has a thin-walled portion having a geometric shape and a plurality of stress concentration portions corresponding to each side of the flat plate.

  Of the object to be inspected, the surface on which the strain detector is attached and the flatness of the strain detector itself are not perfect, so fixing at three points is fundamental. When there are more than three fixing points, there is a concern that not all fixing points exhibit the same fixing force, which may affect the uniform evaluation of the strain direction. Therefore, it is preferable to fix to the object to be inspected through three portions of the flat plate of the strain detector.

  As a result, when a load is applied to the object to be inspected and, for example, a predetermined displacement (strain) occurs in the object to be inspected, a predetermined displacement also occurs in the strain detector, and the stress concentration portion is selectively destroyed. become. Further, by confirming whether or not the stress concentration portion is broken, it is possible to confirm whether or not a predetermined displacement has occurred in the object to be inspected. Furthermore, this confirmation can be easily performed with the naked eye because it is only necessary to confirm whether or not a crack has occurred in the thin-walled portion.

  Therefore, by using the strain detector according to the present invention, an expensive and complicated power source and electric wiring are not required, and even if the distortion generated in the object to be inspected over a long period of time is visually (binoculars). Etc.) and simple presence / absence of an electrical signal can be easily detected at low cost. In addition, it is possible to easily detect the occurrence of displacement due to a load exceeding the allowable stress on the object to be inspected and the direction of the generated displacement.

[2] In the present invention, the stress concentration portion preferably has a corner portion. Since the stress concentration part has corners, cracks are likely to occur in thin-walled parts, and it can be easily confirmed whether or not a predetermined displacement has occurred in the object to be inspected. The direction of the force can be easily confirmed.

[3] In the present invention, it is preferable that a width of the stress concentration portion is 5 mm or less. Strain detection accuracy can be improved by setting the width of the stress concentration portion to 5 mm or less, and the strain detection sensitivity of the strain detector can be appropriately changed by changing the width of the stress concentration portion. . Therefore, it is possible to easily set the strain detection sensitivity suitable for the object to be inspected according to the material of the object to be inspected. More preferably, the width of the stress concentration portion is 3 mm or less.

[4] In the present invention, it is preferable to have a curved surface (fillet) at a boundary portion between the main surface of the flat plate and the thin portion.

  If the boundary part between the main surface of the flat plate and the thin part is square, crack marks are likely to occur along the boundary part, so the direction of the force applied to the strain detector is detected by the crack marks generated in the thin part. In this case, it is preferable to have a curved surface (fillet) at the boundary between the main surface of the flat plate and the thin portion.

[5] In the present invention, it is preferable that the attachment portion has a circular pedestal integrally.

  Accordingly, it is possible to avoid having a specific fixing characteristic with respect to an arbitrary pulling direction generated in the object to be inspected, and preventing the attachment site (adhesion surface) from expressing the sensing directionality. This is preferable in detecting the direction of the force applied to the strain detector.

[6] In this invention, it is preferable to have a curved surface (fillet) in the boundary part of one main surface of the said flat plate, and the said attachment site | part. By providing a curved surface at the boundary portion between one main surface of the flat plate and the attachment site, cracks are unlikely to occur at the boundary portion, which is preferable in detecting the direction of the force applied to the strain detector.

[7] In the present invention, the thickness of the thin portion is preferably 0.03 mm or more, 0.45 mm or less, or 40% or less of the thickness of the flat plate. Furthermore, it is more preferable that the thickness of the thin portion is 0.05 mm or more and 0.28 mm or less.

  The strain detector is provided with a thin window portion, that is, a thin portion at the center. The direction of the force applied to the strain detector can be detected from the crack mark formed in the thin portion. In this case, it is preferable that the thickness of the thin portion is set to a thickness capable of maintaining a stable shape while maintaining a thickness that does not hinder stress concentration. Specifically, it is preferably 0.03 mm or more, 0.45 mm or less, or 40% or less of the thickness of the flat plate. Furthermore, it is more preferable that the thickness of the thin portion is 0.05 mm or more and 0.28 mm or less.

[8] In the present invention, the geometric shape is any one of a regular triangle shape, a square shape, a regular pentagon shape, a regular hexagon shape, a regular nine-angle shape, a regular decagonal shape, a regular ellipsoidal shape, and a circular shape. There may be. Since the positions of the stress concentration portions are in an even relationship, there is almost no directivity in the detection direction of the strain detector, which is advantageous when it is desired to detect the direction of the force applied to the strain detector.

[9] In the present invention, it is preferable that the material of the flat plate, the attachment part, and the thin part is zirconia.

The strain detector according to the present invention has the following effects.
(A) The displacement generated in the object to be inspected such as a structure can be confirmed with an inexpensive device or visually without requiring an advanced, complicated and expensive power supply or electric wiring.
(B) It is possible to easily detect the occurrence of displacement due to a load exceeding the allowable stress on the inspection object and the direction of the generated displacement.

FIG. 1A is a perspective view showing the strain detector according to the present embodiment as seen from the front side, and FIG. 1B is a perspective view showing the strain detector from the back side. 2A is a plan view showing the strain detector as viewed from the back side, and FIG. 2B is a cross-sectional view taken along the line IIB-IIB in FIG. 2A. 3A is a plan view showing a state in which a strain detector is fixed to an object to be inspected, and is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. FIG. 4A is a cross-sectional view illustrating an example of a formation position of a thin portion, and FIG. 4B is a cross-sectional view illustrating another example of a formation position of the thin portion. 5A is a plan view showing the configuration of samples 1 and 2 according to the first experimental example, and FIG. 5B is a cross-sectional view taken along the line VB-VB in FIG. 5A. 6A is a plan view showing the configuration of samples 3 and 4 according to the first experimental example, and FIG. 6B is a cross-sectional view taken along the line VIB-VIB in FIG. 6A. 7A is a plan view showing the configuration of samples 5 and 6 according to the first experimental example, and FIG. 7B is a cross-sectional view taken along the line VIIB-VIIB in FIG. 7A. FIG. 8A is a plan view showing a state in which the strain detector is fixed on the steel material, and FIG. 8B is a view as seen from an arrow A in FIG. 8A. It is explanatory drawing which shows the example which changes the width | variety of a stress concentration part in the 2nd experiment example. It is a top view which shows the example of the other planar shape of an attachment site | part. FIG. 11A is a plan view showing the strain detector according to the first modified example as viewed from the back side, and FIG. 11B is a plan view showing the strain detector according to the second modified example from the back side. It is explanatory drawing which shows nine examples (a)-(i) which detect the direction of the force applied to the to-be-inspected object from the crack trace which generate | occur | produced in each distortion detector, when arranging two distortion detectors. .

  Hereinafter, embodiments of the strain detector according to the present invention will be described with reference to FIGS. 1A to 12. In addition, in this specification, "-" which shows a numerical range is used as the meaning containing the numerical value described before and behind that as a lower limit and an upper limit.

  The strain detector 10 is made of ceramic which is a brittle material, and has a flat plate 12 having a triangular planar shape as shown in FIGS. 1A to 2B. The flat plate 12 has a flat surface 12a. The back surface 12 b of the flat plate 12 has a plurality of attachment portions 16 provided corresponding to the plurality of corner portions 14. The strain detector 10 is provided at the center of the flat plate 12, and has a thin-walled portion 18 having a geometric plan shape and a plurality of stress concentration portions 20 provided corresponding to the sides of the flat plate 12. .

  As shown in FIGS. 3A and 3B, this strain detector 10 is attached to, for example, a plate-shaped metal inspection object 22 and is generated by application of a load to the inspection object 22. Due to the deformation of 22, the strain detector 10 is broken to detect the occurrence of strain in the elastic deformation region generated in the inspection target 22.

  The object 22 to be inspected is basically a flat metal member, but even if it is a curved surface, it can be detected if the part to which the strain detector 10 is attached approximates to a plane. For example, the case of being approximated to a plane includes the following cases.

(A) The unevenness | corrugation between the three attachment positions where the distortion | strain detector 10 is attached among the to-be-inspected objects 22 shall be less than +/- 1.5mm.
(B) When the strain detector 10 is attached to the inspection object 22 using an adhesive, the region to which the strain detector 10 is attached can be in close contact with a resin adhesive having a thickness of 0.03 to 0.48 mm. What?

  The material constituting the strain detector 10 is a solid brittle material, and it is preferable that the linear expansion coefficient with respect to a temperature change is equivalent to that of the inspection object 22. For example, if the constituent material of the inspection object 22 is, for example, a steel material, it is preferable to use, for example, zirconia having substantially the same linear expansion coefficient as that of the steel material.

  Of the object 22 to be inspected, the surface 22a (upper surface, lower surface, side surface, etc.) to which the strain detector 10 is attached and the flatness of the strain detector 10 itself are not perfect, so three-point bonding (fixing) is fundamental. In the case of having three or more adhesion points, there is a concern that all the adhesion points do not exhibit an equal adhesion force, which may affect the uniform evaluation of the strain direction. Therefore, as a simple structure, the outer shape of the strain detector 10 is a triangular shape, and is adhered to the object 22 to be inspected through, for example, three corner portions 14 (top portions).

  The strain detector 10 has a thin plate-like window, that is, a thin portion 18 at the center. It is possible to detect the direction of the force applied to the inspection object 22 from the crack mark formed in the thin portion 18.

  That is, when a strain occurs in the strain detector 10 and the stress concentration portion 20 breaks (primary fracture), the fracture (secondary fracture) is induced starting from the fracture, and the thin wall portion 18 is cracked. Traces will be produced. Thereby, it is possible to confirm whether or not a predetermined distortion has occurred in the inspection target object 22 by confirming a crack mark generated in the thin portion 18. This confirmation can be easily made with the naked eye.

Examples of the position where the thin portion 18 is formed include the positions shown in FIGS. 4A and 4B.
(A) As shown in FIG. 4A, the one main surface 18 a of the thin portion 18 is formed to be the same as the surface 12 a of the flat plate 12.
(B) As shown in FIG. 4B, the thin portion 18 is formed in the thickness direction center of the flat plate 12 or in the vicinity of the center.
Of course, it may be between the position shown by (a) and the position shown by (b).

  As shown in FIG. 2B, it is preferable that the thickness ta of the thin portion 18 is set to a thickness capable of maintaining a stable shape while being thin enough to prevent stress concentration. Specifically, it is 0.03 mm or more and preferably 0.45 mm or less or 40% (for example, 0.3 mm) or less of the thickness tb of the flat plate 12. Furthermore, it is more preferable that the thickness ta of the thin portion 18 is 0.05 mm or more and 0.28 mm or less.

  As for the planar shape of the thin portion 18, since the outer shape of the flat plate 12 is a triangular shape, the planar shape of the thin portion 18 is preferably a regular triangle shape, a regular hexagonal shape, or a regular nine-sided shape. Of these, a hexagonal shape is most preferable. This makes it easy to detect the direction of the force applied to the strain detector 10.

  Other shapes and circles can be used. However, since the corner of the thin portion 18 with respect to each side of the outer shape of the flat plate 12, that is, the position of the stress concentration portion 20 does not have an equal relationship, strain detection is possible. When it is not desired to provide directivity in the detection direction of the detector 10, that is, when it is desired to detect the direction of the force applied to the strain detector 10, it is better to consider a more suitable design.

  When the number of corners of the planar shape of the thin-walled portion 18 is 9 or more, it is approximated to a circular shape, so that the stress concentration portion 20 is not easily broken. Therefore, it is desirable that the number of corners of the planar shape of the thin portion 18 is smaller than the number of sides of the outer shape of the flat plate 12.

  Moreover, it is preferable to have the 1st curved surface 24a (fillet) in the boundary part of the back surface 12b and the thin part 18 of the flat plate 12. FIG.

  Note that the amount of strain when the planar shape of the thin portion 18 is circular or elliptical has a correlation with the stress intensity factor. For example, in one design, due to this correlation, the amount of distortion when the planar shape of the thin-walled portion 18 is a regular hexagon is expected to increase about 1.7 times that of a circular shape, and the amount of distortion of a regular triangle is a circle. An increase of about 2 times the shape is expected.

  Here, the first experimental example will be described. In this first experimental example, the magnification of the strain amount in two directions (first direction and second direction) orthogonal to each other was confirmed for samples 1 to 6.

  As shown in FIGS. 5A and 5B, the samples 1 and 2 used the strain detector 10 in which the planar shape of the thin portion 18 is circular. The size of the strain detector 10 is such that the length La of one side of the equilateral triangle along the outer shape of the flat plate 12 is 80 mm, the thickness tb of the flat plate 12 is 0.5 mm, and the radius r of the planar shape (circular shape) of the thin portion 18. Is 20 mm, the diameter φa of the attachment portion 16 (circular shape) is 16 mm, and the thickness tc of the attachment portion 16 (total with the thickness tb of the flat plate 12) is 3 mm. Further, the radius of curvature of the first curved surface 24a formed at the boundary between the thin portion 18 and the flat plate 12 is 0.4 mm, and the radius of curvature of the second curved surface 24b formed at the boundary between the mounting portion 16 and the flat plate 12 is. 1 mm.

  As shown in FIGS. 6A and 6B, the samples 3 and 4 used the strain detector 10 in which the planar shape of the thin portion 18 is triangular. The size of the strain detector 10 is substantially the same as that of the samples 1 and 2 described above, but the length Lb of one side of the equilateral triangle which is the planar shape of the thin portion 18 is 10 × (√3) mm.

  As shown in FIGS. 7A and 7B, the samples 5 and 6 used the strain detector 10 in which the planar shape of the thin portion 18 is a regular hexagonal shape. The size of the strain detector 10 is substantially the same as that in FIG. 2A and samples 1 and 2 described above, but the length Lc of one side of the regular hexagon that is the planar shape of the thin portion 18 is 20 mm.

  And as shown to FIG. 8A and 8B, about the samples 1-6, the distortion detector 10 was adhere | attached and fixed to the upper surface 26a of the rectangular parallelepiped steel material 26 (test object 22) with the adhesive agent. At this time, in each of the samples 1 to 6, one side 10a of the strain detector 10 and one side 28a of the steel material 26 were fixed in parallel.

  For each steel material 26, of the four side surfaces 30a to 30d, a side surface 30a including the one side 28a parallel to one side 10a of the strain detector 10 is defined as a first fixed surface 32a, and the first fixed surface 32a. The side surface 30b opposite to the first displacement surface 34a. Further, one side surface 30c adjacent to the first fixed surface 32a is defined as a second fixed surface 32b, and a side surface 30d facing the second fixed surface 32b is defined as a second displacement surface 34b.

  Three distortion evaluation positions P1, P2, and P3 were set for samples 1 to 6, respectively (see FIGS. 5A, 6A, and 7A).

  First, the first fixing surface 32a is fixed for each of the samples 1, 3 and 5, and a constant tensile load is applied to the first direction, that is, the first displacement surface 34a. The amount of strain at P2 and P3 was measured. When the strain amount of Sample 1 was used as a reference, Samples 3 and 5 were 1.6 times and 1.4 times, respectively (see Table 1 below).

  Next, for the samples 2, 4 and 6, the second fixed surface 32b is fixed, and a constant tensile load is applied to the second direction, that is, the second displacement surface 34b, so that the strain evaluation positions P1, P2 respectively. And the amount of strain at P3 was measured. When the strain amount of Sample 2 was used as a reference, Samples 4 and 6 were 2.0 times and 2.3 times, respectively (see Table 1 below).

  Thus, when viewed comprehensively, the shape of the thin portion 18 having a regular hexagonal shape has a higher rate of increase in strain than that of a planar shape having a circular shape or a regular triangle shape.

  This is because, when the planar shape of the thin portion 18 is an equilateral triangle, the structure has a side that linearly connects the three corners that are the stress concentration portions, and thus the progress of cracks occurring in the thin portion 18 is limited. There is a high risk. The regular hexagonal shape does not have such a restriction. Therefore, it is considered that the regular shape of the thin portion 18 is most preferably a regular hexagon.

  Since the attachment part 16 for attaching the strain detector 10 to the inspection object 22 is preferably point contact rather than surface contact, it is required to be as small as possible. If there is, it is necessary to have an area that can secure the adhesive force).

For example, when an S6 type sheet-like adhesive manufactured by Dai Nippon Printing Co., Ltd. is used, it is desirable to have an area of 75 mm ² or more per one attachment site 16. Furthermore, it is desirable to have an area of 200 mm ² or more per one attachment site 16.

  Further, the surface shape of the attachment portion 16 may be any shape, but it does not have a specific fixing characteristic with respect to an arbitrary pulling direction generated in the inspection object 22, that is, the attachment portion (adhesion surface) is sensing. From the viewpoint of avoiding the development of the directivity of the above, a circular shape is desirable.

  In the above-described example, an example in which the planar shape of the thin portion 18 is a regular hexagonal shape is shown. However, as shown in FIG. 9, the planar portion of the thin portion 18 and the side corresponding to the corner portion are connected. The shortest distance may be changed. That is, the width W of the stress concentration portion 20 may be changed.

  Here, the second experimental example will be described. In this second experimental example, the distortion amount magnification in the first direction in the first experimental example described above was confirmed for sample 1 and samples 7 to 10.

  In the sample 7, in the strain detector 10 having the same size as the sample 5 described above, the width W of the stress concentration portion 20 is set to 5 mm. Similarly, Samples 8, 9, and 10 are the strain detector 10 having the same size as Sample 5 described above, and the width W of the stress concentration portion 20 is set to 3 mm, 1.5 mm, and 0.5 mm.

  Then, when the magnification of the strain amount in the first direction was confirmed in the same manner as in the first experimental example described above, when the strain amount of Sample 1 described above was used as a reference, Samples 7 to 10 were 1.1. Times, 1.4 times, 2.3 times, and 3.3 times (see Table 2 below).

  As described above, the strain detection sensitivity of the strain detector 10 can be appropriately changed by changing the width W of the stress concentration portion 20. Therefore, the strain detection sensitivity suitable for the inspection target 22 can be easily set according to the material of the inspection target 22 and the like.

  The ceramics constituting the strain detector 10 preferably contains zirconia. Further, by providing the stress concentration portion 20, the strain detector 10 can be broken with strain within a range in which the inspection target 22 is elastically deformed, for example, 0.1% or 0.2%. Moreover, since zirconia has a thermal expansion coefficient substantially the same as that of carbon steel (mild steel material) or reinforced concrete, it can compensate for the temperature change. This leads to the ability to detect distortion without being affected by temperature changes, and is advantageous for improving detection accuracy.

  Next, a manufacturing method of the strain detector 10 will be briefly described below.

  First, the manufacturing method of the strain detector 10 is not particularly limited, and may be any method such as a doctor blade method, an extrusion method, a gel casting method, a powder pressing method, an imprinting method, and the like. Particularly, for a complicated shape in which the thin portion 18 and the stress concentration portion 20 are formed, the gel casting method is particularly preferably used. In a preferred embodiment, a slurry containing a ceramic powder, a dispersion medium, and a gelling agent is cast, and the slurry is gelled to obtain a molded body, and the molded body is sintered to detect strain. Can be obtained (see JP 2001-335371 A).

As a constituent material of the strain detector 10, a raw material obtained by adding ₃ mole% yttria (Y ₂ O ₃ ) assistant to the zirconia powder is particularly preferable. As the auxiliary agent, yttria is preferable, but calcia (CaO), magnesia (MgO) and the like can also be exemplified.

The gel casting method includes the following methods.
(1) Along with inorganic powder, a prepolymer such as polyvinyl alcohol, epoxy resin, phenol resin or the like, which becomes a gelling agent, is dispersed in a dispersion medium together with a dispersant to prepare a slurry. The slurry is solidified by crosslinking and gelation.
(2) The slurry is solidified by chemically bonding an organic dispersion medium having a reactive functional group and a gelling agent. This method is the method described in Japanese Patent Application Laid-Open No. 2001-335371 of the present applicant.

  It should be noted that the strain detector according to the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

  That is, in the above example, the planar shape of the attachment portion 16 is a circular shape, but it may be configured by other shapes, for example, a plurality of arcs. For example, as shown in FIG. 10, the first arc 40 a constituting a part of the outer periphery of the strain detector 10 and the second arc 40 b facing inward of the attachment portion 16 may be used. FIG. 10 shows an example in which the radius of curvature of the first arc 40a is smaller than the radius of curvature of the second arc 40b.

  In the above-described example, the planar shape of the flat plate 12 is a triangular shape, and the planar shape of the thin portion 18 is a hexagonal shape, a circular shape, or a triangular shape, but the other is shown in the first modified example of FIG. 11A. As described above, the flat shape of the flat plate 12 may be circular, and the flat shape of the thin portion 18 may be triangular, or the flat shape of the flat plate 12 may be quadrangular and the thin portion 18 as shown in the second modification of FIG. 11B. The planar shape may be a quadrangular shape.

  In the above-described example, the case where one strain detector 10 is bonded to the inspection target object 22 is shown. However, the plurality of strain detectors 10 are arranged on the inspection target object 22 in a tile shape, for example. The direction of the force applied to 22 may be detected. In this case, the direction of force can be detected with higher accuracy than when only one strain detector 10 is installed.

  For example, as shown in FIG. 12, two strain detectors may be arranged with one side facing each other. In FIG. 12, the crack mark is indicated by a thin line Lc (solid line), the approximate direction of the force applied to the strain detector is indicated by a broken line Ld, and the main direction of the force applied to the strain detector is indicated by a thick line Le (solid line). . FIG. 12 shows that the patterns are classified into nine patterns (a) to (i) depending on the occurrence positions of crack marks.

  Patterns (a), (b), (f), and (i) show examples in which only the approximate direction of the force applied to the strain detector is known. Patterns (c), (d), (e), (g) and (h) show examples in which the main direction of the force applied to the strain detector is also known.

  With only one strain detector, three directions can be detected as main directions of the force applied to the strain detector. On the other hand, in the example in which two strain detectors are arranged, as can be seen from FIG. 12, four directions can be detected as main directions of the force applied to the strain detector.

DESCRIPTION OF SYMBOLS 10 ... Strain detector 10a ... One edge | side 12 ... Flat plate 12a ... Front surface 12b ... Back surface (one main surface) 14 ... Corner | angular part 16 ... Attachment part 18 ... Thin-walled part 20 ... Stress concentration part 22 ... Test object 24a ... 1st curved surface 24b ... 2nd curved surface 26 ... Steel material 26a ... Upper surface 32a of steel material ... 1st fixed surface 32b ... 2nd fixed surface 34a ... 1st displacement surface 34b ... 2nd displacement surface

Claims (9)

A flat plate,
Among the one main surface of the flat plate, a plurality of attachment sites provided at a plurality of corners,
Provided in the central part of the flat plate, and the planar shape is a thin-walled portion having a geometric shape;
A strain detector comprising a plurality of stress concentration portions corresponding to each side of the flat plate. The strain detector of claim 1, wherein
The strain detector, wherein the stress concentration part has a corner part. The strain detector according to claim 1 or 2,
A strain detector, wherein the stress concentration portion has a width of 5 mm or less. The strain detector according to any one of claims 1 to 3,
A strain detector comprising a curved surface at a boundary portion between the main surface of the flat plate and the thin portion. In the distortion detector according to any one of claims 1 to 4,
The attachment part has a circular pedestal integrally, and is a strain detector. The strain detector of claim 5, wherein
A strain detector having a curved surface at a boundary portion between one main surface of the flat plate and the attachment site. In the distortion detector according to any one of claims 1 to 6,
The thickness of the thin part is 0.03 mm or more, 0.45 mm or less, or 40% or less of the thickness of the flat plate. The strain detector according to any one of claims 1 to 7,
The geometric shape is any one of a regular triangle, a square, a regular pentagon, a regular hexagon, a regular nine, a regular decagon, a regular eleven, and a circle. Detector. In the distortion detector according to any one of claims 1 to 8,
The strain detector is characterized in that the flat plate, the attachment part and the thin part are made of zirconia.

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