JP2004212210A - Method for measuring shearing load of fastening implement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring sharing load of a fastening implement which measures sharing load exerted on the fastening implement by focusing attention on axial distortion which secondarily occurs in the fastening implement for mechanically fastening a plurality of members. <P>SOLUTION: Plate-like members 1 and 2 are fastened by a bolt 4 and a nut 5, which constitute the fastening implement 3. When load P acts on the members 1 and 2 from the outside, axial distortion occurs due to "Poisson effects" in strength of materials in a form corresponding to compressive stress which occurs when a solid shaft part 7 comes into contact with the inner circumferential surface of a hole for fastening 10. The axial distortion is measured by a distribution sensor 9 embedded in a bottom part 8a of a measuring hole 8 formed in the center axis 4c of the solid shaft part 7 of the bolt 4. By previously relating the amount of the measured axial distortion with the load (sharing force) acting on the fastening implement 3, the sharing load is computed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention measures a shear load applied to a solid shaft portion in a state where a plurality of members are fastened in a fastener such as a bolt, a pin, or a rivet having a solid shaft portion for fastening a plurality of members. The present invention relates to a method for measuring a shear load of a fastener.
[0002]
[Prior art]
BACKGROUND ART Conventionally, a fastening structure for fastening a plurality of members with fasteners such as bolts, pins, and rivets is widely used not only in aircraft and spacecraft but also in general structures. This type of fastening structure is a structure that can also be recognized as a joint, and a fastener such as a bolt, a pin, or a rivet fulfills its fastening function by mainly receiving its axial tensile load. They are largely classified into so-called shear joints, which mainly perform a shearing force to fulfill their fastening function.
[0003]
Generally, a tensile force acts as an axial load on a solid shaft portion such as a bolt, a pin, or a rivet for fastening a plurality of members. For such an axial load, a method of embedding a detector, such as a resistance wire strain gauge or an optical fiber strain sensor, along the axial direction inside a solid shaft portion and measuring based on the detection output of the detector is generally used. It is a target. Such a measuring method is applied to measurement of a bolt tightening force, a load converter (load cell), and the like. This measurement method is a method for exclusively measuring the axial load acting on the fastener for fastening a plurality of members, and is not intended to measure the shear load, and is applicable to the measurement of the shear load. Is not considered.
[0004]
However, when the plurality of members are plate materials in particular, the fastener is used to transmit in-plane stress acting on the plurality of members by shearing force acting on the solid shaft portion. Many. In particular, in aircraft and spacecraft, since the fuselage is configured with a monocoque structure made of lightweight thin plates, multiple plate materials are fastened with fasteners such as rivets, and the shear force that generates in-plane stress on the solid shaft part is reduced. Is transmitted through. In addition to the fastener, mechanical elements such as a shear joint that transmits power acting between a plurality of power transmission components by a shear force of the fastener are also used in various technical fields.
[0005]
In a fastener for fastening a plurality of members as a structural material by a shear force, or in a fastener for transmitting power in the form of a shear force between a plurality of power transmission components such as a shear joint, a shear load applied to the fastener is given. Is generally difficult to measure with conventional techniques. Methods such as estimating the shear stress state by measuring strain on the surface around the joint of the member to be fastened and calculating the shear stress by corresponding numerical simulation have been used, but these methods are not effective. It cannot be said that this is a typical measurement method. In particular, in the case of a fastening structure using a plurality of fasteners, it is important in structural design to calculate the shear load shared by each fastener, but the shear force acting on each fastener is accurately determined. It is virtually impossible to measure and it is difficult to obtain such shear loads experimentally. In addition, conditions and problems are complicated in analysis, and as a result, there are many cases where empirical rules are used.
[0006]
When a fastener breaks due to its shearing force, in most cases, the breakage of the fastener itself, or a crack, plastic yield, damage, etc. occurring around the fastening portion of the member to be fastened becomes the starting point of the failure. Of these, it is generally very difficult to detect the initial stage of plastic yielding and damage that has occurred around the joint. Flying objects such as airplanes and spacecraft are almost always composed of a monocoque structure in which the fuselage, wings, etc., are connected with thin metal plates with many rivets, and detect such plastic yielding and the initial stage of damage. This has been difficult in the past.
[0007]
A bolt provided with a strain gauge having a gauge resistance portion that expands or contracts by receiving a stress in the bolt axis direction in a recess formed in the bolt head and is equipped with a strain sensor capable of detecting loosening of the bolt has been proposed. (See Patent Document 1). In addition, in order to eliminate the effects of mechanical fatigue and temperature that exist in electric resistance type strain gauges, optical strain gauges that use the interference of light reflected by two reflecting surfaces or mirrors that sandwich a gap that expands and contracts by thrust force are used. It has been proposed to measure the bearing thrust of an engine by using it (see Patent Document 2).
[0008]
[Patent Document 1]
JP 2002-236064 A ([0010], FIGS. 1 and 2)
[Patent Document 2]
JP 2000-32030 A ([0009] to [0010], FIG. 1)
[0009]
[Problems to be solved by the invention]
By the way, it is known that when a shearing force acts on a material, an axial strain is also generated in a direction orthogonal to the shearing direction. Therefore, instead of directly measuring the shear force and shear strain by focusing on this phenomenon in material mechanics, it detects the amount of axial strain secondary to the fastener, and based on the amount of axial strain. There is a problem to be solved in measuring the shear load generated on the fastener.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a practical method capable of measuring a shear load applied to a fastener, which has been conventionally difficult, in a fastener for mechanically fastening a plurality of members.
[0011]
[Means for Solving the Problems]
The method for measuring the shear load of a fastener according to the present invention includes embedding a strain sensor for detecting an axial strain amount of the solid shaft portion inside the solid shaft portion of the fastener having a solid shaft portion, Measuring the shear load acting on the solid shaft based on the amount of axial strain detected by the sensor and the Poisson effect.
[0012]
The basic principle of the method for measuring the shear load of a fastener according to the present invention is that, when a fastener such as a bolt, a pin, a rivet is subjected to a shear load, a secondary and localized inside of the solid shaft portion of the fastener is performed as Poisson effect. An object of the present invention is to measure a shear load by detecting an axial strain amount of a fastener which is generated by a strain sensor embedded in a fastener. Corresponding to the shear stress, distortion occurs not only in the shear direction in the solid shaft portion but also in the axial direction as a Poisson effect. Although it is difficult to directly measure the amount of shear strain generated in the fastener, the amount of axial strain can be detected with sufficiently high accuracy by a strain sensor embedded in a solid shaft portion. If the correspondence between the shear load and the axial strain of the fastener is determined in advance, the shear load acting on the fastener can be determined based on the value of the axial strain. The position where the measurement hole is provided is preferably the center axis position of the solid shaft portion which is assumed to be able to avoid bias in terms of stress.
[0013]
In this method for measuring the shear load of the fastener, it is preferable to perform a strain-load calibration that associates the amount of axial strain detected by the strain sensor with the shear load. Since it is difficult to perform the strain sensor and its attachment to the fastener under the same conditions for all fasteners, the strain-load characteristics are slightly different for each fastener. Therefore, load calibration is required to make the load required for measuring the shear load correspond to the output of the strain sensor. Specifically, this load calibration is obtained by mounting the fastener on the calibration tester and applying a load of a actually known value.
[0014]
In the method for measuring a shear load of a fastener, the fastener acting on the solid shaft portion may be a plurality of members fastened in a state where the fastener is engaged with the solid shaft portion at different positions in the axial direction. When a load is transmitted by a shear load, the present invention can be applied to the measurement of the shear load. When a plurality of members are fastened by a fastener, when each member is engaged at a different position in the axial direction with respect to a solid shaft portion, a load acting on some members is changed to a solid shaft of the fastener. It acts as a compressive stress (surface pressure) on the portion, and is transmitted again to another member as a compressive stress (surface pressure) via the inside of the solid shaft portion. If the abutment portion of some members and another member with respect to the solid shaft portion is offset in the axial direction of the solid shaft portion, the inside of the solid shaft portion forms a shear stress between the members. A stress field transmitting the load is formed. This shear stress can be obtained based on the measured axial strain and the Poisson effect. The depth of the measurement hole provided with the strain sensor depends on the configuration of the member to be fastened, but a boundary position between the members can be cited as a candidate.
[0015]
In the method for measuring the shear load of the fastener, when the members are joined by a plurality of the fasteners, the shear load measuring method is used to grasp the distribution of the shear load acting on the fasteners. It can be applied individually to fasteners. A strain sensor is embedded for each fastener, and the shear load acting on the fastener can be directly measured by the shear load measuring method applied to each fastener. The load condition to be grasped includes, for example, calculating a distribution ratio of a load carried by a plurality of fasteners. Since the load distribution carried by each fastener is known, the real-time load distribution of the fastening structure can be grasped, and the optimum arrangement of the fasteners and the load and maintenance management can be easily performed.
[0016]
In the method for measuring a shear load of a fastener, when the fastener generates a surface pressure between the members by an axial tension, the axial strain is determined in a relationship between the axial strain and the shear load. Based on the shear load when the amount starts to occur, a load transmitted by a frictional force generated between the members based on the surface pressure can be obtained from the loads acting on the members. When a frictional force acts between the members based on the axial load of the fastener, a part of the external force acting on the members is transmitted by the frictional force. In such a case, it is preferable to separate the load transmitted by the frictional force from the load transmitted by the surface contact pressure between the member and the fastener. The relationship between the amount of axial strain and the shear load when a frictional force is applied between the members is that Poisson's force is applied only when a load exceeding the frictional force is applied at the beginning of the load, as compared to when no frictional force is applied. A relationship appears in which the amount of axial distortion corresponding to the effect starts to be detected. Therefore, by capturing the change in the relationship between the axial strain and the shear load, and by capturing the shear load when the axial strain begins to occur, the load transmitted by the frictional force is calculated, and the frictional force between the members is calculated. The shear load transmitted by the fastener can be separated.
[0017]
In the method for measuring the shear load of the fastener, the solid shaft of the fastener is determined based on a change in the amount of the axial strain with respect to the shear load in the relationship between the amount of axial strain and the shear load. Non-linear behavior such as plastic yielding and damage of the member generated near the fastening portion due to the contact surface pressure between the portion and the member can be detected. Non-linear behavior such as plastic yielding and damage of the member may occur in the vicinity of the fastening portion due to the contact surface pressure between the solid shaft portion of the fastener and the member. If the initial stage of plastic yielding and damage can be detected when the behavior occurs, it is preferable for the load and maintenance management of the fastening structure. Such a non-linear behavior appears as a phenomenon in which the amount of strain is large despite the small amount of increase in load. Therefore, in the relationship between the axial strain and the shear load, by finding a change in which the axial strain to the shear load sharply increases, the fastening due to the contact surface pressure between the solid shaft portion and the member of the fastener is performed. It is possible to detect plastic yielding, damage, and the like of the member generated near the portion.
[0018]
In the method for measuring the shear load of the fastener, the strain sensor is a resistance wire strain gauge or an optical fiber sensor fixed in a measurement hole formed in the solid shaft portion of the fastener, and A lead extends through the opening of the measurement hole and can be connected to a measurement instrument. Bolts, pins, rivets and other fasteners with a simple structure that forms a measurement hole in the fastener and fixes the strain sensor in the measurement hole, while minimizing the effect on the structural strength of the fastener itself, The shear force acting on the fastener can be effectively measured.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a method for measuring a shear load of a fastener according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example in which the present shear load measuring method is applied to fastening of two plate-like members using a fastener composed of a bolt and a nut, and FIG. 2 illustrates the principle of measuring the shear load of the fastener. FIG. In the application example shown in FIG. 1, the plate-like members 1 and 2 are fastened by a fastener 3 including a bolt 4 and a nut 5. The fastener 3 inserts the bolt 4 into the fastening holes 10 and 11 in a state where the fastening holes 10 and 11 formed in the members 1 and 2 are aligned, and attaches the nut 5 to the threaded portion 4 b of the bolt 4. By screwing in, a fastening state is obtained. Washers 6, 6 are interposed between the bolt head 4a and the member 1 and between the nut 5 and the member 2 for well-known purposes such as loosening prevention and dispersion of a tightening load.
[0020]
The cylindrical solid shaft portion 7 of the bolt 4 is formed with a sensor mounting measurement hole 8 for mounting the sensor from the top surface of the bolt head 4a by machining. It is preferable that the depth of the measurement hole 8 be adjusted to the position of the joining surface of the members 1 and 2 as described later. The measurement hole 8 can be formed as a hole having a depth of a halfway at the position of the central axis 4c of the solid shaft portion 7, but it is formed once in a through hole, and a thermosetting resin is embedded halfway from the penetration destination. In this case, a measurement hole may be formed. The strain sensor 9 is inserted into the measurement hole 8 and fixed to the bottom 8a of the measurement hole 8 by filling with an adhesive or the like. A detection signal from the strain sensor 9 is connected to an external measuring device 13 through a lead wire 12. In order to avoid that the original strength of the bolt 4 serving as a fastener is largely affected by the measurement hole 8 formed for embedding the strain sensor 9 therein, the strain sensor 9 is provided with a solid shaft portion 7 of the bolt 4. It is desirable that the size be small in comparison with the diameter of the object.
[0021]
As the strain sensor 9, a small resistance wire strain gauge, an optical fiber sensor such as a Fabry-Perot interferometer, or the like can be applied. In particular, when applied to a small-diameter fastener, a small-diameter optical fiber sensor having a small diameter of the sensor itself and high sensitivity is preferable.
[0022]
The principle of measuring the shear load of the fastener will be described with reference to FIG. When a tensile force P in the in-plane direction as shown in FIG. 1 is acting on the member 1 and the member 2, all of the applied force is applied from one member (for example, 1) through the bolt 4 to the other member. (For example, 2) is considered. In this case, no force is transmitted between the fastened members 1 and 2 due to frictional force. That is, in general, in a state where the members 1 and 2 are pressed against each other by tightening the nut 5 to the bolt 4, when a tensile force P in the in-plane direction is applied, the surface pressure generated between the members 1 and 2 is reduced. As a result, a frictional force is generated in the in-plane direction, and there is load transmission without the bolt 4. However, in this application example, first, the tightening of the members 1 and 2 by the initial bolts 4 and the nuts 5 is sufficiently small, and all the tensile forces P are handled as being transmitted through the bolts 4.
[0023]
The tensile force P applied from one of the members 1 is a compression surface in a region having a certain spread as a contact portion between the inner peripheral surface 10a of the insertion hole 10 of the member 1 and the outer peripheral surface 7a of the cylindrical portion 7 of the bolt 4. The pressure is transmitted to the bolt 4 in the form of a compressive stress. Similarly, the force acting on the cylindrical portion 7 of the bolt 4 based on the compressive stress is generated at the contact portion between the outer peripheral surface 7a of the cylindrical portion 7 of the bolt 4 and the inner peripheral surface 11a of the insertion hole 11 of the other member 2. It is transmitted to the other member 2 in the form of stress, and furthermore, becomes a tensile force P acting on the member 2.
[0024]
The bolt 4 transmits the force transmitted to the bolt 4 in the form of a compressive stress mainly by a shearing force inside the solid shaft portion 7. At this time, a compressive stress field 14 is generated in the solid shaft portion 7 near the contact portion with each of the members 1 and 2. The region of the compressive stress field 14 extends from the contact portion 15 including the outer peripheral surface 7a contacting the inner peripheral surface 10a to the other contact portion 16 including the outer peripheral surface 7a contacting the inner peripheral surface 11a via the central axis 4c of the bolt 4. It is expanding. The shape of the compressive stress field 14 and the intensity distribution of the stress inside the compressive stress field 14 vary depending on the thickness of the two members 1 and 2 and the combination of materials, and also on the central axis 4c of the bolt 4 along the central axis 4c. ing. The axial strain (shown on the vertical axis) at the depth position D (shown on the horizontal axis) corresponding to the position along the central axis 4c of the bolt 4 is shown in FIG. 9 using the load as a parameter. In the compressive stress field 14, the compressive stress is symmetrically distributed in the axial direction of the solid shaft portion 7, and a shear stress is generated in the compressive stress field 14 in response to such a change in the compressive stress. The force P is transmitted between the members 1 and 2 via shear stress.
[0025]
The principle of the shear load measurement according to the present invention is that the amount of axial strain (tensile strain) of the bolt 4 generated in a form corresponding to the compressive stress generated on the center axis 4c of the bolt 4 is stored inside the cylindrical portion 7 of the bolt 4. It is based on the measurement by the embedded strain sensor 9 and the correspondence between the axial strain measured by the strain sensor 9 and the external force obtained on the fastener 3, that is, the shear load. The generation of the axial strain according to the lateral compressive stress acting on the bolt 4 is due to the so-called “Poisson effect” in the material dynamics. The effect of Poisson's ratio ν on the axial strain distribution is shown in FIG. The distribution of the axial strain shown on the vertical axis at the depth position D shown on the horizontal axis changes depending on the value of the Poisson's ratio ν. The shear load acting on the bolt 3 can be measured by measuring the amount of axial strain. In this shear load measurement principle, it is found from numerical calculations and the like that the greater the degree to which the shear stress generated in the compressive stress field 14 changes in the axial direction of the solid shaft portion 7, the greater the amount of axial strain is measured. are doing.
[0026]
Although the intensity distribution of the axial strain on the center axis 4c of the bolt 4 caused by the external force differs in each case, in many cases, the strength distribution on the plane 17 where both members 1 and 2 are in contact with the bolt 4 At the intersection of the center axis 4c. Therefore, by embedding the strain sensor 9 in this vicinity, the measurement sensitivity of the shear load can be improved. In order to accurately and accurately calculate the optimum embedding position of the strain sensor 9 in advance, a simulation analysis using a numerical calculation such as the finite element method is effective. It is also possible to ask.
[0027]
FIG. 3 is a schematic cross-sectional view showing an example of a fastening test specimen for calibration. In FIG. 3, a fastening specimen 20 fastens plate-like members 1 and 2 a with two ordinary fasteners 3 and 3 including the bolts 4 and the nuts 5 described above. And is fastened by the calibrating fastener 23. The calibration fastener 23 is formed by combining a calibration member having the same material and thickness as the fastener 3 to be applied, and the bolt 24, the nut 25, It comprises a strain sensor 9 and the like. After fixing both sides of the fastening test piece 20 to the chuck portion of the material testing machine, when the load (tensile force P) is gradually increased while controlling the testing machine, the strain amount generated in the calibration fastener 23 by the strain sensor 9 ( The amount of distortion of the bolt 24 in the axial direction) is detected. The value of this strain is recorded together with the value of the tensile force P, and the calibration curve of the fastener 3 is obtained by associating them with each other.
[0028]
This calibration curve is specific to the calibration fastener 23 after the strain sensor 9 has been embedded, and calibration must be performed individually. This is because the sensitivity of the strain sensor 9 to the load P is not always the same due to differences in the embedding conditions and the like. In this calibration, the fastening force of the calibration fastener 23 must be small enough that the frictional force acting between the members 1 and 2 can be ignored. This is to eliminate the load transmission due to the frictional force between the members 1 and 2, and to transmit all the load through the contact portion between the members 1 and 2 and the bolt 24.
[0029]
Each of the calibrated fasteners 3 and 3 is applied to a joint for fastening the members 1 and 2 at multiple points (two points in FIG. 4) as shown in FIG. It is possible to measure the load shared by the fasteners 3,3. Not only in aircraft and spacecraft, but also in general building structures, many structural members such as plate members are connected using fasteners such as bolts, pins, and rivets. In the structure using the fastener of the above, it is practically impossible to accurately grasp the load acting on each fastener. In such a structure, the failure of one fastener affects the load of the other fastener, so that the load management must be strict. Therefore, according to empirical rules, measures have been taken to increase the plate thickness or increase the number of fasteners. As a result, the weight of the structure tends to increase more than necessary. On the other hand, in this shear load measuring method, by detecting the shear load acting on each fastener 3 one by one, not only grasping the load state of the structure but also individual information of the fastener 3 leading to breakage in real time. Since it can be grasped, it can be used to determine its optimum arrangement with the smallest possible number of fasteners 3 and to prevent damage to the structure.
[0030]
As shown in FIG. 5, in the fastener 3 using the bolt 4 and the nut 5, the members 1 and 2 which are the members to be fastened are made using the tensile force in the axial direction of the bolt 4 generated by tightening the nut 5. When a compressive force Pa in the thickness direction is applied, a part of the load P is transmitted by a frictional force Pf generated between the members 1 and 2 near the fastening portion when the load P is applied from the outside. If the magnitude of the frictional force Pf cannot be ignored, the detected output of the strain sensor 9 does not accurately reflect the external load, and the external load cannot be directly obtained from the detected output. Therefore, it is necessary to separate the shearing force from the frictional force.
[0031]
When an external load is applied beyond the limit of the load transmitted by the frictional force Pf, the load is transmitted by the contact between the fastener 3 and the members 1 and 2, and the load of the portion exceeding the frictional limit load is generated. As for the method, a shear load measuring method using a principle based on the above-described amount of axial strain and Poisson effect can be applied. FIG. 6 shows a change in the amount of axial strain detected by the strain sensor 9 embedded in the fastening body 3 with respect to a gradually increasing external load P. The limit load of the frictional force is Pf. There is no change in the amount of strain under the following loads. However, when the load exceeds Pf, the excess of the load is transmitted by the contact between the fastener 3 and the members 1 and 2, and the amount of distortion is gradually increased. Thus, the load P can be separated into a load shared by the frictional force Pf and a shear load Pc shared by the contact between the fastener 3 and the members 1 and 2.
[0032]
When the frictional force Pf is zero, the external load P and the amount of axial strain are substantially proportional, but as the load P increases, as shown in FIG. , 16 in the vicinity, the fastening portion 18 of the members 1 and 2 may cause nonlinear behavior such as plastic yielding and damage. In such a case, the amount of axial strain measured by the strain sensor 9 clearly changes as shown in FIG. The graph shown in FIG. 7 is a characteristic curve showing a case where the amount of axial strain increases sharply despite little increase in load due to plastic yielding and damage. The figure shows a smoothly changing characteristic curve that gradually deviates from the proportional relationship. Depending on the type of the material, the characteristic curve may appear as a clear bending point. In the figure, the plastic yield and damage start point are indicated by A. As shown in FIG. 8, such a change causes the members 1 and 2 to be pushed out of the plane by plastic yielding or damage near the fastening portion 18 shown by B in the drawing, and this is pushed out by the head (bolt head) of the fastener 3. By pushing up the portion 4a), a tensile force as shown by C in the drawing is provided to the fastening body 3. By finding this change point, it is possible to detect plastic yielding and damage of the members 1 and 2 in the vicinity of the fastener 3.
[0033]
【The invention's effect】
As described above, the method for measuring the shear load of a fastener according to the present invention includes a strain sensor for detecting an axial strain amount of the solid shaft portion inside the solid shaft portion of the fastener having the solid shaft portion. And the shear load acting on the solid shaft portion is measured based on the amount of axial strain detected by the strain sensor and the Poisson effect, so that the Poisson effect is applied to the solid shaft portion corresponding to the shear stress. Can be detected with sufficiently high accuracy by the strain sensor embedded in the solid shaft portion. If the correspondence between the external force acting as the shear load and the axial strain of the fastener is determined in advance, the shear load acting on the fastener can be determined based on the value of the axial strain. Conventionally, it has been difficult to directly measure the amount of shear strain generated in a fastener, but the shear load applied to the fastener can be quickly and easily and practically measured.
[0034]
According to the method for measuring a shear load of a fastener according to the present invention, in addition to the above, it is possible to obtain a load calibration for associating a load required for practical measurement of a shear load with an output of a strain sensor. When a plurality of members are fastened by the fastener, a load acting on the member can be obtained from a shear load acting on the fastener. Also, in the case of a structure in which a plurality of members are fastened by a plurality of fasteners, it has not always been possible to clearly analyze what kind of load each fastener shared, but each individual fastener was By applying the present shear load measuring method to the present invention, it is possible to specifically calculate the share ratio of each fastener. Further, in the case where the fastening body transmits the shearing force by using the frictional force between the members generated by the axial load, the load transmitted by the frictional force is focused on the relationship between the load and the axial distortion. And the load transmitted by the surface pressure contact between the member and the fastening body can be separated. Furthermore, by paying attention to the change in the relationship between the load and the axial strain, it is possible to detect the initial stage of plastic deformation and damage of the member in the vicinity of the fastening portion of the member fastened by the fastener, and the durability of the thin plate structure can be detected. It can contribute to the evaluation of gender and the formulation of repair time. This measurement of the shear load of the fastener is applicable not only to aircraft and spacecraft but also to general structures, and is widely applicable to online monitoring of actual loads, optimal design of fastener arrangement, and detection of damage at the fastener.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of strain measurement in a method for measuring a shear load of a fastener according to the present invention.
FIG. 2 is an enlarged view showing a relationship between a compressive stress field generated inside a fastening body and a strain gauge in the conceptual diagram of strain measurement shown in FIG.
FIG. 3 is a diagram illustrating an example of a load calibration method in the method for measuring a shear load of a fastener according to the present invention.
FIG. 4 is a diagram showing an application example of the method for measuring the shear load of the fastener according to the present invention to the measurement of load sharing of a multipoint (two-point) fastening structure.
FIG. 5 is a view showing load transmission by contact friction between members in the method for measuring a shear load of a fastener according to the present invention.
FIG. 6 is a graph showing a relationship between an external load and a strain gauge when a load is transmitted by contact friction between members in the method for measuring a shear load of a fastener according to the present invention.
FIG. 7 is a diagram showing a relationship between an axial load and an external load when plastic yielding or damage occurs in a member near a fastening portion in the method for measuring a shear load of a fastener according to the present invention.
FIG. 8 is a diagram showing a change in the amount of axial strain due to plastic yielding and damage in the vicinity of a fastening portion in the method for measuring a shear load of a fastener according to the present invention.
FIG. 9 is a diagram showing axial strain (vertical axis) at a depth position (horizontal axis) along the central axis c of the bolt using the load as a parameter in the method for measuring the shear load of a fastener according to the present invention.
FIG. 10 is a diagram showing the influence of Poisson's ratio on the axial strain distribution in the method for measuring the shear load of a fastener according to the present invention.
[Explanation of symbols]
1, 2 member 3 fastener
4 Bolt 4a Bolt head 4b Screw 4c Center axis
5 Nut 6 Washer 7 Solid shaft part 7a Outer peripheral surface
8 Measurement hole 8a Bottom 9 Strain sensor
10, 11 Fastening holes 10a, 11a Inner peripheral surface
12 Lead wire 13 Measuring equipment
15, 16 contact part 17 plane 18 fastening part
20 Fastened specimen
23 Calibration fastener 24 Bolt 25 Nut
P Tensile force Pa Compressive force Pf Friction force Pc Shear load

Claims (7)

Inside the solid shaft portion of the fastener having a solid shaft portion, a strain sensor for detecting the axial strain amount of the solid shaft portion is embedded, and the axial strain amount and the Poisson effect detected by the strain sensor. Measuring the shear load acting on the solid shaft portion based on the following formula. The method of measuring a shear load of a fastener according to claim 1, further comprising performing a strain-load calibration that associates the amount of the axial strain detected by the strain sensor with the shear load. When transmitting the load by the shear load acting on the solid shaft portion, between the plurality of members that are fastened in a state where the fastener is engaged with the solid shaft portion at different positions in the axial direction, The method for measuring the shear load of a fastener according to claim 1, wherein the method is applied to the measurement of a shear load. 4. The fastener of claim 3 wherein said member is applied individually to each fastener to ascertain the distribution of said shear load acting on each fastener when said members are joined by a plurality of said fasteners. Method for measuring the shear load of tools. In a case where the fastener causes a surface pressure between the members due to an axial tension, the shear load when the axial strain starts to be generated in the relationship between the axial strain and the shear load. The method according to claim 1, further comprising calculating a load transmitted by a frictional force generated between the members based on the surface pressure among loads acting on the member based on the shear force. Based on a change in the amount of axial strain with respect to the shear load in which the amount of axial strain sharply increases in the relationship between the amount of axial strain and the shear load, the contact pressure between the solid shaft portion of the fastener and the member is reduced The method for measuring a shear load of a fastener according to claim 1, comprising detecting a non-linear behavior such as plastic yielding, damage, or the like of the member caused near the fastening portion due to the non-linear behavior. The strain sensor is a resistance wire strain gauge or an optical fiber sensor fixed in a measurement hole formed in the solid shaft portion of the fastening body, and a lead wire from the strain sensor extends through an opening of the measurement hole. The method for measuring a shear load of a fastener according to claim 1, wherein the shear load is connected to the measuring device by a force.

Images