JP2012057709A - Axial force control bolt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial force control bolt with which a fastened object can be fastened with a predetermined axial force or axial force for reaching to a plastic region, and with which whether the bolt is before or after plastic deformation can be sorted simply.SOLUTION: The axial force control bolt has a shaft 1A and a screw 1c, and a head 1b and enables control of axial force acting in the axial direction, wherein an axial force detection material 2 to be destroyed when an axial strain amount of the bolt 1 exceeds a predetermined value is attached on at least an outer surface of the axial part 1A of the bolt 1, and the axial force detection material 2 is attached while axial tension is previously applied to the bolt 1.

Description

  The present invention relates to an axial force management bolt for fastening an object to be fastened, and more particularly to an axial force management bolt capable of managing an axial force generated in the axial direction of a bolt at the time of fastening.

  In general, when two members are tightened with a bolt and a nut, the two members which are fastened bodies receive a tightening compression force from the bolt and the nut. On the other hand, an axial force in the tensile direction is generated in the bolt due to the reaction. If this axial force is weak, there is a risk of causing looseness, and if it is too strong, there is a risk of causing destruction of the fastened member.

  In order to appropriately apply this axial force to a bolt, a torque management method is generally used in which tightening is performed while managing the tightening torque using a tightening tool having a torque detection function such as a torque wrench.

  However, the relationship between the axial force and torque at the time of bolt fastening greatly depends on the influence of the friction coefficient at two locations of the contact portion between the male screw and the female screw and the contact portion between the bolt head and the fastening member. When the friction coefficient is small, the gradient of the axial force with respect to the torque increases, and when the friction coefficient is large, the gradient of the axial force with respect to the torque decreases. Thus, in the torque management method, the relationship between the torque and the axial force of the bolt varies depending on the lubrication condition of the contact portion described above. Therefore, even if the bolt is tightened with a predetermined torque, the axial force of the bolt is insufficient or conversely high. There was a problem of becoming too much.

  For this reason, as a more accurate bolt fastening method, a rotational angle method in which a predetermined axial force is obtained by rotating a bolt by a predetermined angle after being tightened once to a predetermined light torque (snugg torque), or rotation of a bolt Tighten the bolt while monitoring the angle and tightening torque, and stop the tightening when it detects that the bolt reaches the plastic range and the torque increases less than the rotation angle of the bolt. A torque gradient method to be obtained is disclosed (for example, see Patent Document 1). In addition, a method is also disclosed in which the elastic wave generated by tightening the bolt is continuously monitored by an acoustic emission method (hereinafter referred to as AE method), and the tightening of the bolt is terminated by detecting that the plastic region has been reached (for example, Patent Document 2).

JP-A-6-79552 JP 2006-55989 A

  In the bolt fastening method described above, the rotation angle method is initially tightened with a snug torque that is a tightening torque necessary to bring the bolt head and the seating surface into close contact with each other. The axial force may be different even with the same tightening torque. Therefore, there is a case where a predetermined axial force is not obtained even when tightening at the same rotation angle from the position tightened with the snag torque.

  In the torque gradient method, a stable axial force can be obtained by detecting a state where the bolt has reached the plastic region. Therefore, the axial force can be managed with higher accuracy than other methods. However, it is necessary to measure the rotation angle and tightening torque of the bolt and calculate the fluctuation rate of the tightening torque with respect to the rotation angle, which can be applied only to limited places and the tightening device is expensive. It was.

  Further, since the AE method detects an elastic wave generated when the material is plastically deformed, it can accurately grasp that the bolt is plastically deformed. However, depending on the material, an elastic wave is hardly generated even if the material is plastically deformed. Some were not available for all bolts. Further, since the elastic wave generated when the material is plastically deformed is detected, there is a problem that it cannot be applied to tightening up to an elastic region, for example.

  Furthermore, since the bolt tightened up to the plastic zone is stretched from the initial state, it is not desirable to use it again after it has been loosened, but it can be distinguished whether the bolt is before plastic deformation or after plastic deformation. There was a problem that it was difficult.

  The present invention has been made based on the above matters, and the object thereof can be fastened with a predetermined axial force or an axial force reaching a plastic region without using an expensive instrument or device, The present invention provides an axial force management bolt capable of easily selecting whether a bolt is before plastic deformation or after plastic deformation.

  In order to achieve the above object, the first invention is an axial force management bolt including a shaft portion, a screw portion, and a head, and capable of managing an axial force acting in an axial direction, wherein the bolt An axial force detection material that breaks when the axial strain amount exceeds a predetermined value is attached to at least the outer surface of the shaft of the bolt, and the axial force detection material applies an axial tension to the bolt in advance. It shall be attached in the state of being applied.

  The second invention is characterized in that, in the first invention, the axial force detection substance has a brittle substance attached thereto.

  Furthermore, the third invention is characterized in that, in the first or second invention, the destruction of the axial force detection substance is detected by an acoustic emission sensor.

  According to a fourth invention, in the first or second invention, the destruction of the axial force detection substance is detected by an acoustic pickup.

  Furthermore, the fifth invention is characterized in that, in the first or second invention, the destruction of the axial force detection substance is detected by an endoscope.

  According to the present invention, there is provided a bolt in which a brittle substance is attached to the shaft portion of the bolt in a pre-tensioned state and hardened, and a detecting means for detecting the breakage of the brittle substance. The object to be fastened can be fastened by an axial force or an axial force reaching the plastic region. Further, by confirming the fracture / non-destructive state of the brittle substance, it is possible to easily select whether the bolt is before plastic deformation or after plastic deformation. As a result, misuse of the bolt after plastic deformation can be prevented.

It is a front view which shows 1st Embodiment of the axial force management volt | bolt of this invention. It is a front view which shows in a partial cross section an example of the method of attaching an axial force detection substance in 1st Embodiment of the axial force management bolt of this invention. It is a front view which shows in a partial cross section the other example of the method of attaching an axial force detection substance in 1st Embodiment of the axial force management bolt of this invention. It is a front view which shows the tightening state of a volt | bolt in 1st Embodiment of the axial force management volt | bolt of this invention in a partial cross section. It is a front view which shows an example of the method of detecting destruction of the axial force detection substance which comprises 1st Embodiment of the axial force management bolt of this invention in a partial cross section. It is a front view which shows the other example of the method of detecting destruction of the axial force detection substance which comprises 1st Embodiment of the axial force management bolt of this invention in a partial cross section. It is a front view which shows 2nd Embodiment of the axial force management volt | bolt of this invention. It is a front view which shows 3rd Embodiment of the axial force management volt | bolt of this invention in a partial cross section. It is a front view which shows 4th Embodiment of the axial force management volt | bolt of this invention. It is a front view which shows 5th Embodiment of the axial force management volt | bolt of this invention.

Hereinafter, embodiments of the axial force management bolt of the present invention will be described with reference to the drawings.
1 to 3 show a first embodiment of an axial force management bolt according to the present invention, and FIG. 1 is a front view showing the first embodiment of the axial force management bolt according to the present invention. FIG. 3 is a front view showing a partial cross-sectional view of an example of a method for attaching the axial force detection substance 2 in the first embodiment of the axial force management bolt of the present invention, and FIG. 3 shows the first of the axial force management bolt of the present invention. It is a front view which shows in a partial cross section the other example of the method of attaching the axial force detection substance 2 in embodiment.

  As shown in FIG. 1, the first embodiment of the axial force management bolt according to the present invention includes a shaft 1A, a head 1B provided on one side of the shaft 1A, and a male screw provided on the other side of the shaft 1A. A bolt 1 having a portion 1C and an axial force detection substance 2 made of a brittle substance in the axial direction are attached and cured on the outer surface of the shaft 1A of the bolt 1 in an axial direction. As the axial force detection substance 2, for example, a brittle substance such as liquid glass 2A or a photo-curing resin is used. The liquid glass 2A is, for example, a material called perhydropolysilazane (PHPS) that is hardened under a normal temperature / air atmosphere, and can be easily subjected to on-site work such as brushing. This liquid glass 2A is known to exhibit physical properties similar to quartz glass after curing. The photo-curing resin is a resin that rapidly cures when irradiated with light of a specific wavelength such as ultraviolet rays. In the following description, a case where liquid glass 2A is used as the axial force detection substance 2 will be described as an example.

In general, glass has a feature that it is easily broken by a tensile force, hardly broken by a compressive force, and hardly plastically deforms. For example, quartz glass which is the main component of the liquid glass 2A has a compressive strength of 1150 [N / mm ² ] with respect to a tensile strength of 50 [N / mm ² ]. For this reason, after the liquid glass 2A is simply adhered and cured as the axial force detection substance 2 on the outer surface of the shaft portion of the bolt 1, when the member to be fastened is fastened with the bolt 1, the shaft portion 1A of the bolt 1 is tightened. Since the liquid glass 2A is stretched, the liquid glass 2A cured before reaching a predetermined axial force is broken. Therefore, the liquid glass 2A is adhered and cured under a state where a predetermined load is applied to the bolt 1 in advance and the shaft portion 1A is extended. As a result, even if the load is removed from the bolt 1 after the liquid glass 2A is adhered and hardened, the liquid glass 2A adheres to the outer surface of the shaft 1A without breaking even if the shaft 1A is reduced.

FIG. 2 is a diagram for explaining an example of a method for applying a pretension when the axial force detection substance 2 is attached to the bolt 1.
The pre-tensioning jig 3 used in the present embodiment connects the ceiling plate 4a supporting the lower surface of the head 1B of the bolt 1, the bottom plate 4b facing the ceiling plate 4a, and the ceiling plate 4a and the bottom plate 4b. A frame structure 4 composed of at least two opposing side plates 4c, 4c, a load cell 5 placed and fixed on the bottom plate 4b of the frame structure 4, and a male screw portion 1C of the bolt 1 fixed to the top of the load cell 5 And a connecting member 5A in which a female thread portion is formed. As shown in FIG. 2, the center of a hole 4 d formed in a diameter that penetrates the shaft 1 </ b> A of the bolt 1 but does not penetrate the head 1 </ b> B of the bolt is connected to the ceiling plate 4 a of the frame structure 4. It is provided so as to coincide with the center of the female screw portion formed on the member 5A.

  Further, as shown in FIG. 2, the space inside the frame structure 4 is formed by the ceiling plate 4a, the side plates 4c and 4c, and the connecting member 5A, and the vertical direction in the drawing is an open state, so that the bolt 1 is a hole. When screwed into the connecting member 5A via 4d, the exposed upper portion of the shaft portion 1A and male screw portion 1C of the bolt 1 can be approached from the opening side.

  First, the internal thread portion 1C of the bolt 1 is inserted into the hole 4d of the ceiling plate 4a of the frame structure 4 of the jig 3 and screwed into the internal thread portion of the connecting member 5A. Thereafter, the bolt 1 is screwed. At this time, by performing screwing while monitoring the output of the load cell 5, a predetermined pretension can be applied to the bolt 1 as indicated by a symbol X in FIG. 2. Specifically, after the bolt 1 is screwed into the connecting member 5A and the lower surface of the head 1B of the bolt 1 comes into contact with the upper surface of the ceiling plate 4a, the output of the load cell 5 that is the pretension of the bolt 1 is displayed. Is done.

  After screwing up to a predetermined pretension (axial force), the liquid glass 2A is applied to the outer surface of the shaft 1A of the bolt 1 with, for example, a brush from the opening, and left in this state, whereby the liquid glass 2A Is cured.

  After the liquid glass 2 </ b> A is cured, the bolt 1 is unloaded by turning it in the direction of loosening the connecting member 5 </ b> A, and the bolt 1 is taken out from the jig 3. Thereby, in the state where the bolt 1 is not tightened, the attached liquid glass 2A is in a compressed state. As described above, since the glass has sufficient strength against the compressive force, the liquid glass 2A is not broken in this state.

  FIG. 3 is a front view showing another example of the method of attaching the axial force detection substance 2 in the first embodiment of the axial force management bolt of the present invention, and is below the load cell 5 shown in FIG. A hydraulic cylinder 6 is provided. A connecting member 5 </ b> A is connected to the load cell 5 and a rod of the hydraulic cylinder 6 is connected to the lower side. By pulling the bolt 1 with the hydraulic cylinder 6, a predetermined axial force can be applied to the bolt 1. Further, instead of the hydraulic pressure of the hydraulic cylinder 6, it is also possible to pull by a mechanical method such as a feed screw.

  Next, the tightening operation in the first embodiment of the axial force management bolt of the present invention will be described in detail with reference to FIG. FIG. 4 is a front view showing a partially tightened state of the bolt in the first embodiment of the axial force management bolt of the present invention. In FIG. 4, the same reference numerals as those shown in FIGS. 1 to 3 are the same parts, and detailed description thereof is omitted.

  As shown in FIG. 4, when the fastened object 7 including the upper fastened object 7A and the lower fastened object 7B is tightened with the bolt 1 and the nut 10, the lower surface of the head 1B of the bolt 1 and the upper fastened object. A fastening force P2 and a reaction force P1 are generated at the contact portion between the upper surface of 7A and the contact portion between the upper surface of the nut 10 and the lower surface of the lower article 7B. This reaction force P1 extends the shaft portion 1A of the bolt 1 and the male screw portion in which the nut 10 is screwed to generate an axial force FB. At this time, the liquid glass 2 </ b> A attached to the outer surface of the shaft portion 1 </ b> A is stretched along with the elongation of the bolt 1. At this time, since the liquid glass 2A is deformed together with the bolt 1, the strain value εb of the bolt 1 and the strain value εg of the liquid glass 2A are equal.

Assuming that the axial force value of the bolt 1 is Fb [N], the stress value σbj [N / mm ² ] at the shaft portion 1A of the bolt 1 is represented by the cross-sectional area of the shaft portion 1A of the bolt 1 as Aj [mm ² ] (several It is obtained by the formula of 1).

Assuming that the elastic coefficient of the bolt 1 is Eb [N / mm ² ] from the relationship between the stress and the strain, the strain value εbj of the shaft portion 1A of the bolt 1 is obtained by the equation (Equation 2).

  As described above, since the strain value εg of the liquid glass 2A and the strain value εb of the bolt 1 are equal, the strain value εgj of the liquid glass 2A at the shaft portion 1A of the bolt 1 is expressed by the equation (3). It is obtained by

Assuming that the elastic coefficient of the liquid glass 2A is Eg [N / mm ² ], the stress value σgj [N / mm ² ] of the liquid glass 2A at the shaft 1A of the bolt 1 is obtained by the equation (Equation 4).

  Substituting the equations (Equation 1), (Equation 2), and (Equation 3) into the equation (Equation 4) yields the equation (Equation 5).

When the axial force value Fb [N] of the bolt 1 is increased by tightening, the stress value σgj [N / mm ² ] of the liquid glass 2A obtained from the equation (Equation 5) is also increased. On the other hand, as described above, the liquid glass 2A hardly undergoes plastic deformation. For this reason, when the stress value σgj [N / mm ² ] of the liquid glass 2A exceeds the tensile strength of the liquid glass 2A, the liquid glass 2A breaks.

When the liquid glass 2A is attached, a pretension value Fpr [N] is given to the bolt 1, and after the liquid glass 2A is cured, the pretension value Fpr [N] of the bolt 1 is unloaded, A compression response value −σgjpr [N / mm ² ] corresponding to the amount unloaded from the bolt 1 is generated. This compressive stress value −σgjpr [N / mm ² ] is obtained by replacing the axial force value Fb [N] of the bolt 1 in the equation (Equation 5) with the pretension value Fpr [N] of the bolt 1 (Equation 6). ).

That is, in the bolt 1 in the untightened state after finishing the above-described attachment of the liquid glass 2A and unloading of the pretension value Fpr [N], the stress value σgj [N / mm ² ] of the liquid glass 2A is It is in a state equivalent to the compression response value −σgjpr [N / mm ² ] obtained from (Equation 6). Next, the object to be fastened is tightened with the bolt 1, and the stress value σgj [N / mm ² ] of the liquid glass 2 A when the bolt 1 is stretched is calculated from the equations of (Equation 5) and (Equation 6): 7).

By substituting the stress value [N / mm ² ] corresponding to the tensile strength of the liquid glass 2A into σgj and the target axial force value [N] of the bolt 1 into Fb in the equation (Equation 7), the pretension The value Fpr [N] can be calculated.

  Under the condition that the calculated pretension value Fpr [N] is applied to the bolt 1, the liquid glass 2A is adhered and cured to the outer surface of the shaft portion 1A, and then unloaded, thereby the bolt 1 for axial force management. Form. By tightening the object to be fastened with the bolt 1 and tightening until the liquid glass 2A is broken by the axial force of the bolt 1, the object to be fastened can be fastened with a target axial force value.

  When it is desired to plastically fasten the object to be fastened with the bolt 1, the pretension value Fpr [N] is set to a value slightly lower than the bolt 1 starts plastic deformation, and the liquid glass 2A is placed on the outer surface of the shaft portion 1A. Adhesive cure. As a result, when an axial force value obtained by adding an axial force value corresponding to the tensile strength of the liquid glass 2A to the pretension value Fpr [N] is applied to the bolt 1, the liquid glass 2A is broken. Therefore, by tightening the bolt 1 until the liquid glass 2A is broken, it is possible to fasten the article to be fastened with the axial force value at the start of plastic deformation.

  Next, a method for detecting a breakage of the axial force detection substance in the first embodiment of the axial force management bolt of the present invention will be described with reference to FIGS. FIG. 5 is a front view showing a partial cross-sectional view of an example of a method for detecting the destruction of the axial force detection substance constituting the first embodiment of the axial force management bolt of the present invention, and FIG. 6 is an axial force management of the present invention. It is a front view which shows the other example of the method of detecting destruction of the axial force detection substance which comprises 1st Embodiment of a bolt in a partial cross section. 5 and 6, the same reference numerals as those shown in FIG. 1 to FIG. 4 are the same parts, and detailed description thereof is omitted.

  As shown in FIG. 5, when the acoustic pickup 8 is installed in the vicinity of the upper bolt fastening portion of the upper article to be fastened 7 </ b> A, and the liquid glass 2 </ b> A that is the axial force detection substance 2 attached to the bolt 1 is broken. There is a method to detect the sound of. At this time, the output from the acoustic pickup 8 is amplified by an amplifier (not shown), and a sound is output from a speaker (not shown). It can be detected that the axial force of 1 has reached a predetermined value.

  In addition, as shown in FIG. 6, when a small hole can be provided in the side portion of the upper article to be fastened 7A, an illuminated endoscope 9 is inserted into the hole and the shaft of the bolt 1 is inserted. It is possible to optically detect that the liquid glass 2A, which is the axial force detection substance 2 attached to the outer surface, breaks, and to detect that the axial force of the bolt 1 due to tightening has reached a predetermined value. In addition, an acoustic pickup 8 is inserted instead of the endoscope 9 into a small hole provided in the side portion of the upper fastening object 7A, and the axial force of the bolt 1 by tightening becomes a predetermined value from the detection of sound. Can also be detected.

  Furthermore, as another method, there is a method using an AE sensor as shown in Patent Document 2 described above. In Patent Document 2, since an elastic wave generated when the bolt material is plastically deformed is detected by an AE sensor, there is a problem that it is difficult to apply this method to a bolt made of a member that hardly generates an elastic wave.

  In the first embodiment of the axial force management bolt of the present invention, the liquid glass 2A which is the axial force detection substance 2 attached to the outer surface of the shaft portion 1A of the bolt 1 is broken by tightening up to a predetermined axial force. Therefore, the elastic wave of the liquid glass 2A can be generated when the liquid glass 2A is broken without depending on the material of the bolt 1. As a result, the generation of elastic waves at the time of plastic deformation of the liquid glass 2A does not depend on the material of the bolt, and even if the bolt 1 is tightened within the elastic range where the plastic glass is not plastically deformed, the elastic wave at the time of plastic deformation of the liquid glass 2A is generated. Since it is generated, it can be used within such a tightening range.

  Further, in the first embodiment of the axial force management bolt of the present invention, the attached liquid glass 2A is broken when tightened with a predetermined axial force, so that the bolt 1 once used can be discriminated. . Even if it is prohibited to reuse the bolt 1 that has been used once, such as plastic fastening, in order to ensure the safety of the structure, the first implementation of the axial force management bolt of the present invention In the form, it can be easily determined whether or not it is used.

  According to the first embodiment of the axial force management bolt of the present invention described above, the bolt 1 in which the liquid glass 2A, which is a brittle substance, is attached and cured on the outer surface of the shaft portion 1B in a state in which a pretension is applied; Since the detecting means for detecting the breakage of the liquid glass 2A, which is a brittle substance, is provided, the bolt 1 can be used to fasten the object to be fastened with a predetermined axial force or with an axial force reaching the plastic region. Further, by confirming the fracture / non-destructive state of the liquid glass 2A which is a brittle substance, it is possible to easily select whether the bolt 1 is before plastic deformation or after plastic deformation. As a result, misuse of the bolt 1 after plastic deformation can be prevented.

  FIG. 7 shows a second embodiment of the axial force management bolt of the present invention. In the first embodiment shown in FIG. 1, since the liquid glass 2 </ b> A is used as the axial force detection substance 2, when a predetermined axial force is generated in the bolt 1, the liquid glass 2 </ b> A is broken. For example, in the case of the fastening configuration shown in FIG. 4, the broken pieces of the liquid glass 2 </ b> A are sealed in the inner hole of the body 7 to be fastened by the head 1 </ b> B of the bolt 1 and the nut 10, and are not scattered to the outside. When the fastening of the bolt 1 and the nut 10 is loosened in order to release the fastening of the fastened object 6, the pieces of the liquid glass 2 </ b> A are scattered from the inner hole of the fastened body 7 to the outside. Therefore, when a device or the like that does not allow foreign matters to be mixed is disposed in the lower portion of the bolt 1, measures for preventing foreign matters from being mixed are required. In the present embodiment, as shown in FIG. 7, the liquid glass 2 </ b> A as the axial force detection substance 2 is adhered and cured on the outer surface of the shaft 1 </ b> A of the bolt 1, and then flexible so as to cover the liquid glass 2 </ b> A. A coating material 11 made of resin or the like is applied to the shaft portion 1A of the bolt. As a result, it is possible to prevent the liquid glass 2A fragments as described above from being scattered outside.

  FIG. 8 shows a partial cross section of a third embodiment of the axial force management bolt of the present invention. In the first embodiment shown in FIG. 1, the liquid glass 2A is adhered and hardened on the upper outer surface of the shaft 1A of the bolt 1 as the axial force detection substance 2, but in this embodiment, FIG. As shown in FIG. 3, liquid glass 2A as an axial force detection substance 2 is adhered and cured in the axial direction from the shaft portion 1A of the bolt 1 to the upper outer surface of the male screw portion 1C. The site for adhering and curing the axial force detection substance 2 is not limited to the upper outer surface of the shaft portion 1A of the bolt 1, but is an upper portion of the male screw portion 1C, for example, a portion that does not screw with the nut 10 or the like. You may adhere and harden on the outer surface of the part.

  FIG. 9 shows a fourth embodiment of the axial force management bolt of the present invention. In the first embodiment shown in FIG. 1, the liquid glass 2A is attached and cured as the axial force detection substance 2 on the outer surface of the entire upper periphery of the shaft portion 1A of the bolt 1, but in this embodiment, As shown in FIG. 9, it is configured to adhere and harden only on the four outer surfaces in the upper circumferential direction of the shaft portion 1A of the bolt 1. Since the destruction of the axial force detection substance 2 is detected by sound, optics, an AE sensor or the like as described above, the axial force detection substance 2 may be adhered and cured at such a site.

  FIG. 10 shows a fifth embodiment of the axial force management bolt of the present invention. As described in the fourth embodiment, if the destruction of the axial force detection substance 2 can be reliably detected, it is not necessary to limit to the four directions in the upper circumferential direction of the shaft portion 1A of the bolt 1; If the means is an acoustic pickup or the like, it may be adhered and cured in one direction in the upper circumferential direction of the shaft portion 1A of the bolt 1.

  In the embodiment of the present invention, the case where the liquid glass 2A is used as the axial force detection substance 2 has been described. However, the present invention is not limited to this. For example, even a photo-curing resin has the same properties as liquid glass and can be used as the axial force detection substance 2 in the same manner as the liquid glass 2A.

DESCRIPTION OF SYMBOLS 1 Bolt 1A Shaft part 1B Head part 1C Male thread part 2 Axial force detection substance 2A Liquid glass 3 Jig 4 Frame structure 5 Load cell 5A Connection member 6 Hydraulic cylinder 7 Fastening object 8 Acoustic pick-up 9 Endoscope 10 Nut 11 Coating material

Claims (5)

An axial force management bolt comprising an axial portion, a screw portion, and a head, and capable of managing axial force acting in the axial direction,
An axial force detection substance that breaks when the amount of axial strain of the bolt exceeds a predetermined value is attached to the outer surface of at least the shaft portion of the bolt,
The axial force management bolt is characterized in that the axial force detection substance is attached in advance in a state where an axial tension is applied to the bolt. The axial force management bolt according to claim 1, wherein the axial force detection substance has a brittle substance attached thereto. The axial force management bolt according to claim 1 or 2, wherein the destruction of the axial force detection substance is detected by an acoustic emission sensor. The axial force management bolt according to claim 1 or 2, wherein the destruction of the axial force detection substance is detected by an acoustic pickup. The axial force management bolt according to claim 1 or 2, wherein the destruction of the axial force detection substance is detected by an endoscope.

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