JP6241657B2 - Bolt damage detection device - Google Patents

Description

  The present invention relates to a bolt damage detection device for detecting damage of a bolt in use.

  In general, bolts are widely used to connect a plurality of members. For example, when a bonnet (lid) is attached to the end of the casing of the steam turbine valve, the bonnet is fixed to the end of the casing with a plurality of bolts.

  By the way, when a bolt is used over a long period of time, the bolt itself may deteriorate over time, and the bolt may be damaged, for example, the bolt may crack or break. When the bolt is damaged in this way, the fastening force by the bolt is reduced or lost. Therefore, it is necessary to replace the damaged bolt with a new bolt. However, since the damage of the bolt usually occurs at a portion inserted into the member, it is difficult to determine only by the appearance. Moreover, when it attaches with the some volt | bolt, even if one or some of those volt | bolts are damaged, the coupling | bonding of members can be maintained only with the remaining volt | bolt. However, when the number of damaged bolts increases, the maintenance of the connection is suddenly lost when the minimum number of healthy bolts necessary to maintain the connection is exceeded.

  On the other hand, an apparatus for confirming the state of aging deterioration of the material of a structural material used in a nuclear reactor as shown in Patent Document 1 has been proposed. With this device, the growth rate of a crack in a structural material can be measured and monitored.

JP-A-2-280042

  However, in the apparatus described in Patent Document 1 described above, since the lead wire must be directly connected to the part to be measured, if it is attempted to detect the damage of the bolt in use, the structure becomes complicated and practically applied. It may be difficult to do.

  The present invention has been made in consideration of the above-described conventional problems, and provides a bolt damage detection apparatus that can easily detect damage to a bolt without removing the bolt with a simple configuration. It is an object.

In order to solve the above problems, the present invention proposes the following means.
The bolt damage detection apparatus according to the first aspect of the present invention is a bolt that penetrates a bolt hole formed in the first member, protrudes in one direction from the bolt hole, and extends in the one direction of the first member. A bolt having one end fixed to the second member disposed; and a second end protruding in the other direction opposite to the one direction from the bolt hole; and the other end of the bolt in the other direction. A contact member that is urged toward the contact member, a contact member that is disposed away from the other end portion of the bolt in the other direction, and a contact between the other end portion of the bolt and the contact member. Contact detection means.

  According to the bolt damage detection device having such a configuration, when the bolt breaks, the portion on the other side of the broken portion moves toward the other direction by the biasing force of the biasing member, and the other end of the bolt is moved. It contacts the contact member. Then, contact between the other end portion of the bolt and the contact member is detected by the contact detection means, thereby detecting that the bolt is broken.

  Moreover, in the above-described bolt damage detection device, it is more preferable to include a restricting member that restricts a moving range of the other end of the bolt in the bolt radial direction.

  According to the bolt damage detection device having such a configuration, when the portion on the other side of the broken portion of the bolt moves toward the other direction by the biasing force of the biasing member, the restriction member moves the bolt in the radial direction of the bolt. Movement is restricted. Thus, when the bolt breaks, it is possible to prevent the portion on the other direction side from the broken portion of the bolt from coming off the contact member and scattering.

  Further, in the above-described bolt damage detection device, the contact detection unit includes an energization detection unit that detects energization between the other end of the bolt made of a conductive material and the contact member made of a conductive material. It is more preferable.

  According to the bolt damage detection device having such a configuration, when the bolt breaks and the other end of the bolt contacts the contact member, the other end of the bolt made of a conductive material and the contact member made of a conductive material Is energized, and the energization detection unit detects this to detect the breakage of the bolt.

  Furthermore, in this bolt damage detection apparatus, it is further preferable that the contact member is provided on the first member or the second member via an insulating member having electrical insulation.

  According to the bolt damage detection apparatus having such a configuration, even if the contact member is provided on the first member or the second member, the insulating member is provided between the contact member and the first member or the second member. Since electrical insulation is ensured, when the other end of the bolt and the contact member are separated from each other, energization between the bolt and the contact member is reliably interrupted.

  In the above-described bolt damage detection apparatus, a potential difference detection that detects a change in the potential difference by measuring a potential difference between the other end of the bolt made of a conductive material and the second member made of a conductive material. More preferably, means are provided.

  According to the bolt damage detection apparatus having such a configuration, when the bolt breaks or a crack occurs in the bolt, the potential difference between the other end of the bolt and the second member changes. Therefore, the potential difference detecting means measures the potential difference between the other end of the bolt and the second member and detects the change in the potential difference, thereby detecting not only the bolt break but also the bolt crack.

  Furthermore, in this bolt damage detection apparatus, it is further preferable that an insulating sleeve having electrical insulation is disposed in the bolt hole, and the bolt is inserted into the insulating sleeve.

  According to the bolt damage detecting device having such a configuration, the first member and the bolt are reliably electrically insulated by the insulating sleeve, so that the bolt caused by the electrical connection between the first member and the bolt The change in potential difference between the other end of the second member and the second member is suppressed.

  The bolt damage detection device according to the second aspect of the present invention is a bolt that penetrates a bolt hole formed in the first member, protrudes in one direction from the bolt hole, and is the one of the first member. A bolt having one end fixed to the second member disposed in the direction, and the other end protruding from the bolt hole in the other direction opposite to the one direction, and the bolt made of a conductive material. And a potential difference detecting means for measuring a potential difference between the other end and the second member made of a conductive material and detecting a change in the potential difference.

  According to the bolt damage detection apparatus having such a configuration, when the bolt breaks or a crack occurs in the bolt, the potential difference between the other end of the bolt and the second member changes. Therefore, the potential difference detecting means measures the potential difference between the other end of the bolt and the second member and detects the change in the potential difference, thereby detecting not only the bolt break but also the bolt crack.

  According to the bolt damage detection device according to the present invention, it is possible to easily detect damage of the bolt with a simple configuration without removing the bolt.

It is a typical sectional view of a bolt damage detection device for explaining a first embodiment of the present invention, and is a figure showing a state before bolt fracture. It is a typical sectional view of a bolt damage detection device for explaining a first embodiment of the present invention, and is a figure showing a state after bolt fracture. It is typical sectional drawing of the volt | bolt damage detection apparatus for demonstrating 2nd embodiment of this invention. It is typical sectional drawing of the bolt damage detection apparatus for demonstrating 3rd embodiment of this invention. It is a typical sectional view of a bolt damage detection device for explaining a 4th embodiment of the present invention. It is a typical perspective view of the volt | bolt damage detection apparatus for demonstrating 5th embodiment of this invention.

  Hereinafter, the first to fifth embodiments of the bolt damage detection device of the present invention will be described with reference to the drawings as appropriate.

[First embodiment]
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. In the following description, the downward direction in FIGS. 1 and 2 may be referred to as “one direction”, and the opposite side, that is, the upward direction in FIGS. 1 and 2 may be referred to as “the other direction”. Moreover, the direction along the axis O of the following bolt 2 may be described as “axial direction”, and the direction perpendicular to the axis O of the bolt 2 may be described as “radial direction”.

  First, the configuration of the bolt damage detection apparatus 1 according to the present embodiment will be described.

  A bolt damage detection apparatus 1 shown in FIG. 1 is an apparatus for detecting damage, particularly breakage, of a bolt 2 that fastens a first member 11 and a second member 12. As an example of the bolt to which the bolt damage detection device 1 is applied, for example, a bolt for fastening a bonnet (first member 11) of a steam turbine valve to a casing (second member 12) may be mentioned. The damage detection apparatus 1 can be applied to bolts at various locations, and is not limited to bolts at specific locations.

  As shown in FIG. 1, the schematic configuration of the bolt damage detection apparatus 1 according to the present embodiment includes a bolt 2, an urging member 3, a contact member 4, and a contact detection means 5.

  The bolt 2 is a so-called stud bolt made of a conductive material such as a metal material, and is disposed through the bolt hole 13 formed in the first member 11. An end portion on one side of the bolt 2 (a lower end portion in FIG. 1, hereinafter referred to as “one end portion 2 a”) is fixed to a second member 12 disposed on one direction side of the first member 11. More specifically, a female screw hole 14 communicating with the bolt hole 13 of the first member 11 is formed on the upper end surface of the second member 12, and one end 2 a of the bolt 2 protruding from the lower end of the bolt hole 13. Is screwed into the female screw hole 14. Further, the end portion on the other direction side of the bolt 2 (the upper end portion in FIG. 1, hereinafter referred to as “the other end portion 2 b”) protrudes from the upper end of the bolt hole 13 in the other direction. A nut 20 is screwed to the other end 2 b of the bolt 2. In addition, it is preferable that the diameter of the bolt hole 13 is larger than the outermost diameter of the bolt 2, and the bolt 2 is not in contact with the inner peripheral surface of the bolt hole 13.

  The urging member 3 is a member that urges the other end 2b of the bolt 2 in the other direction, and includes a spring such as a coil spring, for example. The urging member 3 is attached to the other end 2b of the bolt 2 so that the bolt 2 is inserted into the inside of the urging member 3, and the lower end of the nut 20 and the upper end opening edge of the bolt hole 13 of the first member 11 are mounted. It is sandwiched between the surroundings. In a state where the bolt 2 fastens the first member 11 and the second member 12, the biasing member 3 is compressed in the axial direction by the nut 20 and the first member 11 as shown in FIG. 1. As a result, the nut 20, and consequently the other end 2 b of the bolt 2, is urged upward by the elastic restoring force of the urging member 3.

  The contact member 4 is a member made of a conductive material such as a metal material, and is disposed away from the other end 2b of the bolt 2 in the other direction. More specifically, the contact member 4 is a cover-like member disposed so as to cover the other end 2 b of the bolt 2, and the schematic configuration of the contact member 4 is relative to the axis O of the bolt 2. A contact portion 40 that is arranged in a vertical direction and faces the upper end surface of the bolt 2 with a space therebetween, and a support portion 41 that is arranged in parallel to the axis O of the bolt 2 and supports the contact portion 40. The support portion 41 is located on the side of the other end portion 2b of the bolt 2 and can regulate the range of movement of the other end portion 2b of the bolt 2 in the radial direction. The upper end of the support part 41 is integrally connected to the contact part 40, and the lower end of the support part 41 is attached to the first member 11 via an insulating member 6 having electrical insulation. Examples of the insulating member 6 include a member made of a rubber material or a synthetic resin material. The insulating member 6 is bonded to the surface of the contact member 4 and the surface of the first member 11 by, for example, insert molding, ultrasonic welding, an adhesive, or the like.

  The contact detection means 5 detects contact between the other end 2 b of the bolt 2 and the contact portion 40 of the contact member 4. The schematic configuration of the contact detection means 5 is detected by an energization detection unit 50 that detects energization between the other end 2b of the bolt 2 made of a conductive material and the contact member 4 made of a conductive material, and an energization detection unit 50. A data logger 51 for recording the recorded information. The energization detection unit 50 is electrically connected to the contact part 40 of the contact member 4 by the first lead wire 52 and electrically connected to the bolt 2 by the second lead wire 53. The end of the second lead wire 53 on the bolt 2 side is joined to the other end 2 b of the bolt 2. For example, the bolt 2 side end portion of the second lead wire 53 is joined to the outer peripheral surface of the portion of the other end portion 2 b of the bolt 2 that protrudes to the other side of the nut 20.

  Next, the operation of the bolt damage detection apparatus 1 having the above-described configuration will be described.

  In the bolt damage detection apparatus 1 having the above-described configuration, when the bolt 2 is broken due to, for example, aging deterioration or external impact, a portion on the other direction side (upper portion) from the broken portion X as shown in FIG. Is pushed up by the urging force of the urging member 3, and the other end 2 b of the bolt 2 contacts the lower surface of the contact portion 40 of the contact member 4. If it does so, electricity will be supplied between the other end part 2b of the volt | bolt 2 which consists of electroconductive materials, and the contact part 40 of the contact member 4 which consists of electroconductive materials. This energization is detected by the energization detection unit 50 via the first lead wire 52 and the second lead wire 53, and the information is recorded in the data logger 51. Therefore, it is detected that the bolt 2 is broken based on the data regarding the energization detection recorded in the data logger 51, that is, the data indicating that the other end 2b of the bolt 2 is in contact with the contact member 4.

  Moreover, in the bolt damage detection apparatus 1 which consists of an above-described structure, since the contact member 4 and the 1st member 11 are reliably electrically insulated by the insulating member 6, it contacts with the other end part 2b of the volt | bolt 2. When the member 4 is separated, the energization between the bolt 2 and the contact member 4 is reliably interrupted.

  Next, the effect of the bolt damage detection apparatus 1 having the above-described configuration will be described.

  According to the bolt damage detection apparatus 1 described above, the data recorded in the data logger 51 of the contact detection means 5 is monitored, for example, online, so that the bolt 2 can be removed with a simple configuration without removing the bolt 2. Can be easily detected.

  In particular, according to the above-described bolt damage detection device 1, the insulating member 6 ensures the energization between the bolt 2 and the contact member 4 in a state where the other end 2 b of the bolt 2 is not in contact with the contact member 4. Since it is shut off, erroneous detection of the breakage of the bolt 2 is prevented, and high detection accuracy can be realized.

  In the bolt 2, stress is often concentrated in the vicinity of the lower and upper opening edges of the bolt hole 13. Therefore, the breakage of the bolt 2 is caused by the vicinity of the lower opening edge and the upper opening edge of the bolt hole 13. It often occurs in the vicinity. Here, in the bolt damage detection apparatus 1 having the above-described configuration, the end portion on the bolt 2 side of the second lead wire 53 is joined to the other end portion 2b of the bolt 2 protruding from the bolt hole 13 to the other side. Therefore, even if the rupture of the bolt 2 occurs near the opening edge on the upper side of the bolt hole 13, the rupture of the bolt 2 can be detected by the contact detection means 5.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. In addition, about the component similar to 1st embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  As shown in FIG. 3, the bolt damage detection device 1 according to the present embodiment is located on the side of the other end 2 b of the bolt 2 and restricts the movement range in the radial direction of the other end 2 b of the bolt 2. A regulating member 7 is provided. More specifically, the contact member 4 is provided with a hook-shaped regulating member 7 that hangs down from the contact portion 40. The restricting member 7 is disposed at a position facing the support portion 41 of the contact member 4, and the other end 2 b of the bolt 2 is disposed between the restricting member 7 and the support portion 41 of the contact member 4. However, the regulating member 7 is inclined with respect to the axis O of the bolt 2, and the interval between the regulating member 7 and the support portion 41 of the contact member 4 is gradually reduced as it goes upward. The regulating member 7 may be formed integrally with the contact member 4 or may be a separate component from the contact member 4 and attached to the contact member 4.

  According to the bolt damage detection apparatus 1 having the above-described configuration, when the bolt 2 is broken and the portion on the other side of the broken portion X is pushed up by the biasing force of the biasing member 3, the broken portion of the bolt 2 is broken. The restricting member 7 restricts the movement in the radial direction so that the portion on the other direction side than X is not scattered. Thereby, when the bolt 2 is broken, the other end portion 2b of the bolt 2 is reliably in contact with the contact portion 40 of the contact member 4, and it can be reliably detected that the bolt 2 is broken.

[Third embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG. In addition, about the component similar to 1st or 2nd embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  As shown in FIG. 4, the bolt damage detection apparatus 1 of the present embodiment measures the potential difference between the other end 2b of the bolt 2 made of a conductive material and the second member 12 made of a conductive material. A potential difference detecting means 8 for detecting a change in the potential difference is provided. The schematic configuration of the potential difference detection means 8 includes a current source / potential meter 80 for passing a current (I) and measuring a potential difference (V), and a data logger for recording data of the potential difference measured by the current source / potential meter 80. 81. The current source / potentiometer 80 is electrically connected to the second member 12 by a third lead wire 82 and is electrically connected to the other end 2 b of the bolt 2 by a fourth lead wire 83. The end of the fourth lead 83 on the bolt 2 side is joined to the other end 2 b of the bolt 2. For example, the bolt 2 side end portion of the fourth lead wire 83 is joined to the outer peripheral surface of the portion of the other end portion 2 b of the bolt 2 that protrudes to the other side of the nut 20.

  The data logger 81 of the potential difference detection unit 8 is a data logger shared with the data logger 51 of the contact detection unit 5. That is, the detection data from the energization detection unit 50 and the measurement data from the current source / potentiometer 80 are recorded in one data logger 51 (81). The measurement of the potential difference by the current source / potentiometer 80 is performed at regular intervals, for example, once every 24 hours.

  According to the bolt damage detection apparatus 1 having the above-described configuration, a current is passed between the other end 2b of the bolt 2 and the second member 12 by the current source / potentiometer 80, and the potential difference is measured at regular intervals. Thus, it is possible to detect the breakage or crack of the bolt 2. More specifically, the potential difference between the other end 2b of the bolt 2 and the second member 12 is (V), the current passed by the current source / potentiometer 80 is (I), and the bolt 2 and the second member 12 When the resistance is (R), the relational expression of V = IR is established. When the bolt 2 is cracked or the bolt 2 is broken, the resistance (R) increases. Therefore, if the current (I) is constant, the potential difference (V) also increases. Therefore, by continuously measuring the potential difference (V) at a constant interval and monitoring the measured value (potential difference) recorded in the data logger 81, for example, online, etc., not only the bolt 2 breaks but also the bolt 2 cracks easily. It is possible to detect.

  Note that the resistance (R) described above also varies depending on the temperature of the bolt 2 and the second member 12, and therefore the potential difference (V) is preferably monitored under a certain temperature condition. In this respect, for example, in the case of a steam turbine or the like, since the temperature is usually adjusted to a constant temperature, the temperature often does not cause a problem. However, when the temperature of the bolt 2 or the second member 12 changes, it is preferable to evaluate the temperature together with the measurement of the potential difference (V). For example, the actual temperature is measured by a thermocouple, or the temperature is estimated by comparing the measurement time of the potential difference (V) with the plant operation history, and temperature correction based on the temperature is performed.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIG. In addition, about the component similar to 1st, 2nd, or 3rd embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

  As shown in FIG. 5, in the bolt damage detection device 1 of the present embodiment, an insulating sleeve 9 having electrical insulation is disposed in the bolt hole 13. The insulating sleeve 9 is a cylindrical member that is fitted into the bolt hole 13 and penetrates the first member 11. Bolts 2 are inserted inside the insulating sleeve 9. Examples of the material of the insulating sleeve 9 include a rubber material and a synthetic resin material.

  According to the bolt damage detection apparatus 1 having the above-described configuration, the first member 11 and the bolt 2 are reliably electrically insulated from each other by the insulating sleeve 9. A change in potential difference between the other end 2b of the bolt 2 and the second member 12 due to the smooth connection is suppressed. Thereby, the detection precision of the damage of the volt | bolt 2 based on the change of the electrical potential difference between the other end part 2b of the volt | bolt 2 and the 2nd member 12 can be improved.

[Fifth embodiment]
Next, a fifth embodiment of the present invention will be described with reference to FIG. In addition, about the component similar to 1st, 2nd, 3rd or 4th embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted suitably.

As shown in FIG. 6, the bolt damage detection device 10 according to the present embodiment is different from the first, second, third, or fourth embodiment described above, and the biasing member 3, the contact member 4, and the contact detection. The device 5 is not provided, and is a device that detects the damage of the bolt 2 only by the potential difference detection means 8. The bolt damage detection device 10 is a device for monitoring a plurality of bolts 2 in particular. This bolt damage detection device 10, the potential difference at its initial state by a bolt 2 to be monitored (V ₀₎ are different, the ratio of the potential difference measured potential difference (V ₀₎ in the initial state (V) ( The time change of the dimensionless value normalized by V / V ₀ ) is monitored. Note that such a monitoring method for the plurality of bolts 2 can also be applied to the above-described third embodiment.

  As mentioned above, although embodiment of the bolt damage detection apparatus which concerns on this invention was described, this invention is not limited to above-described embodiment, In the range which does not deviate from the meaning, it can change suitably.

  For example, in the above-described embodiment, the contact member 4 is attached to the first member 11 via the insulating member 6. However, in the present invention, the contact member 4 is attached to the second member 12 via the insulating member 6. May be. Further, in the present invention, the contact member 4 may not be provided on the first member 11 or the second member 12, and the contact member 4 may be supported by a portion other than the first member 11 and the second member 12. Good.

  Further, the present invention may be configured not to include the insulating member 6, and in this case, the contact portion 40 of the contact member 4 and the first member 11 or the second member 12 are reliably electrically insulated. Thus, for example, it is preferable to form all or part of the support portion 41 of the contact member 4 with a material having electrical insulation.

  In the second embodiment described above, the regulating member 7 is suspended from the contact member 4. However, in the present invention, the regulating member 7 may be supported other than the contact member 4. The regulating member 7 may be erected on the upper surface of the member 11. Note that the position and angle of the restricting member 7 can be changed as appropriate as long as the bolt 2 is broken and the moving range in the radial direction of the portion on the other side of the broken portion is restricted.

  In the third embodiment described above, the data logger 81 of the potential difference detection means 8 and the data logger 51 of the contact detection means 5 are shared data loggers. The data logger 81 and the data logger 51 of the contact detection means 5 may be provided separately.

  Further, in the above-described fourth embodiment, the insulating sleeve 9 extends over the entire length of the bolt hole 13, but in the present invention, the insulating sleeve 9 is formed in a part of the length direction of the bolt hole 13. May be provided only. Further, the insulating sleeve 9 may not be a tubular member having a circular cross section, and may be a sleeve having a C-shaped cross section, for example. Further, the insulating sleeve 9 may be a sleeve divided into a plurality of segments.

  In the fifth embodiment described above, a configuration for monitoring a plurality of bolts 2 is described. However, the present invention includes an urging member 3, a contact member 4, and a contact detection means 5. Alternatively, in the device that detects the damage of the bolt 2 only by the potential difference detecting means 8, the device that monitors only one bolt 2 may be used. An urging member such as a spring washer may be disposed under the nut 20 that is screwed onto the bolt 2. Thereby, when the bolt 2 is broken, the broken portion is pulled away by the biasing member, and contact of the broken surface of the bolt 2 is prevented. As a result, when the bolt 2 breaks, the change in potential difference becomes more reliable and clear, and the breakage of the bolt 2 can be easily detected.

  In addition, in the range which does not deviate from the main point of this invention, it is possible to replace suitably the component in above-mentioned embodiment with a well-known component, and you may combine the above-mentioned modification suitably.

DESCRIPTION OF SYMBOLS 1, 10 Bolt damage detection apparatus 2 Bolt 2a One end part 2b Other end part 3 Energizing member 4 Contact member 5 Contact detection means 6 Insulation member 7 Control member 8 Potential difference detection means 9 Insulation sleeve 11 First member 12 Second member 13 Bolt Hole 50 Current detection part 51 Data logger

Claims (7)

A bolt penetrating a bolt hole formed in the first member, protruding in one direction from the bolt hole, and fixed to the second member disposed in the one direction of the first member; A bolt having a second end projecting in the other direction opposite to the one direction from the bolt hole;
A biasing member that biases the other end of the bolt toward the other direction;
A contact member disposed in the other direction away from the other end of the bolt;
Contact detection means for detecting contact between the other end of the bolt and the contact member;
A bolt damage detection device comprising: In the bolt damage detection device according to claim 1,
A bolt damage detection device comprising a restricting member for restricting a movement range of the other end of the bolt in the bolt radial direction. In the bolt damage detection device according to claim 1 or 2,
The bolt damage detection device, wherein the contact detection means includes an energization detection unit that detects energization between the other end of the bolt made of a conductive material and the contact member made of a conductive material. In the bolt damage detection device according to claim 3,
The said damage member is provided in said 1st member or said 2nd member through the insulating member which has electrical insulation, The bolt damage detection apparatus characterized by the above-mentioned. In the bolt damage detection device according to any one of claims 1 to 4,
Bolt damage comprising a potential difference detecting means for measuring a potential difference between the other end of the bolt made of a conductive material and the second member made of a conductive material and detecting a change in the potential difference. Detection device. In the bolt damage detection device according to claim 5,
An insulation sleeve having electrical insulation is disposed in the bolt hole, and the bolt is inserted into the insulation sleeve. A bolt penetrating a bolt hole formed in the first member, protruding in one direction from the bolt hole, and fixed to the second member disposed in the one direction of the first member; A bolt having a second end projecting in the other direction opposite to the one direction from the bolt hole;
A potential difference detecting means for measuring a potential difference between the other end of the bolt made of a conductive material and the second member made of a conductive material and detecting a change in the potential difference;
A bolt damage detection device comprising:

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