Method and system for measuring multi-staple structured fastener load

Abstract

The invention provides a method and a system for measuring the load of a multi-nail structure fastener. The method comprises the steps that a compensation light source is provided for the multi-nail structure fastener; capturing a deformation image of the multi-nail structured fastener; analyzing image data based on the deformed image to obtain a change in a monitored position of the multi-staple structured fastener; calculating a load according to one or more algorithms based on a change in the monitored position; and displaying the calculated load. The load algorithm comprises one or more of the following steps: measuring relative displacement of two side points of each nail, and respectively calculating nail load and nail load proportion; nail deformation is represented through the stretching direction line segment elongation difference value, the nail load and the nail load proportion are calculated respectively, and the stretching direction line segment elongation difference value comprises at least two calculation methods.

Description

Technical Field

[0001] The present invention relates to the technical field of structural mechanics and material fatigue monitoring, and in particular to a method and system for measuring the load of a multi-nail structure fastener. Background Art

[0002] Multi-nail lap joints are a common structural form in aircraft metal structures. Fatigue cracks are prone to occur at the nail holes due to stress concentration. Traditional methods estimate load distribution by attaching strain gauges to measure the average strain across the cross-section between the nails. However, this method suffers from low accuracy due to uneven stress distribution, strain gauge placement, and structural loading. Extensometers, while capable of measuring displacement, are limited in their implementation and cannot dynamically monitor full-field displacement.

[0003] Therefore, there is an urgent need for a high-precision, real-time nail load distribution measurement method and system. Summary of the Invention

[0004] To address the above technical issues, the present invention provides a solution for measuring the load of fasteners in multi-nail structures. By combining optical digital speckle technology with a compensating light source to optimize the light field, the deformation image of the test piece is captured in real time, and the nail load and distribution ratio are calculated based on three displacement methods.

[0005] According to one aspect of the present invention, a system for measuring the load of a multi-nail structural fastener is provided, the system comprising: a compensating light source device for providing a compensating light source of adjustable intensity to the multi-nail structural fastener; an imaging device for capturing a deformed image of the multi-nail structural fastener; and a processor configured to: receive the captured deformed image from the imaging device; analyze image data based on the received deformed image to obtain a change in a monitored position of the multi-nail structural fastener; and calculate a load according to one or more algorithms based on the change in the monitored position; and a display device for displaying the calculated load.

[0006] In one embodiment, the compensation light source device includes: a compensation light source emitter for emitting a light source beam to a multi-nail structure fastener; and a light intensity sensor for receiving the light source beam reflected from the multi-nail structure fastener and feeding back a light intensity signal to the compensation light source emitter to adjust the emission power of the compensation light source emitter.

[0007] In another embodiment, monitoring a change in position includes monitoring at least one of a change in length and a change in displacement of the position.

[0008] In another embodiment, the one or more algorithms include at least one of the following:

[0009] Measure the relative displacement of the points on both sides of each nail, and calculate the nail load and nail load ratio as follows:

[0010]

[0011] where R i is the load of the i-th nail, Δ b olt,i is the deformation displacement of the i-th nail, N is the number of nails, and P is the total load; or

[0012] The nail deformation is characterized by the difference in elongation of the line segment in the tensile direction, and the nail load and nail load ratio are calculated as follows:

[0013]

[0014] where R i is the load of the i-th nail, Δ b olt,i is the difference in elongation of the line segment in the tensile direction of the i-th nail, N is the number of nails, and P is the total load.

[0015] In another embodiment, the elongation difference Δ of the stretching direction line segment of the i-th nail bolt,i =Δ AD -Δ AC , where Δ AC is the elongation of the line segment between point C on one side of the nail and point A on the same side in the tensile direction, Δ AD The elongation of the line segment between point D on the other side of the nail and point A in the stretching direction; or Among them L AC is the length between AC, E1 is the elastic modulus of the plate, W is the plate width, and t1 is the plate thickness.

[0016] According to another aspect of the present invention, a method for measuring the load of a multi-nail structural fastener is provided, the method comprising providing a compensating light source to the multi-nail structural fastener; capturing a deformed image of the multi-nail structural fastener; analyzing image data based on the deformed image to obtain a change in a monitored position of the multi-nail structural fastener; calculating a load according to one or more algorithms based on the change in the monitored position; and displaying the calculated load.

[0017] In one embodiment, providing a compensating light source to a multi-nail structural fastener includes: emitting a light source beam to the multi-nail structural fastener; receiving a light source beam reflected from the multi-nail structural fastener; and feeding back a light intensity signal based on the received reflected light source beam to adjust the intensity of the compensating light source.

[0018] In another embodiment, monitoring a change in position includes monitoring at least one of a change in length and a change in displacement of the position.

[0019] In another embodiment, the one or more algorithms include at least one of the following:

[0020] Measure the relative displacement of the points on both sides of each nail, and calculate the nail load and nail load ratio as follows:

[0021]

[0022] where R i is the load of the i-th nail, Δ b olt,i is the deformation displacement of the i-th nail, N is the number of nails, and P is the total load; or

[0023] The nail deformation is characterized by the difference in elongation of the line segment in the tensile direction, and the nail load and nail load ratio are calculated as follows:

[0024]

[0025] where R i is the load of the i-th nail, Δ b olt,i is the difference in elongation of the line segment in the tensile direction of the i-th nail, N is the number of nails, and P is the total load.

[0026] In another embodiment, the elongation difference Δ of the stretching direction line segment of the i-th nail bolt,i =Δ AD -Δ AC , where Δ AC is the elongation of the line segment between point C on one side of the nail and point A on the same side in the tensile direction, Δ AD The elongation of the line segment between point D on the other side of the nail and point A in the stretching direction; or Among them L AC is the length between AC, E1 is the elastic modulus of the plate, W is the plate width, and t1 is the plate thickness.

[0027] Compared with the prior art, the solution for measuring the load of multi-nail structural fasteners provided by the present invention has at least the following advantages:

[0028] 1. The light intensity sensor works in conjunction with the compensation light source to eliminate ambient light interference and improve measurement accuracy;

[0029] 2. Provide three calculation methods to adapt to different test scenarios and accuracy requirements;

[0030] 3. Based on digital speckle technology, it avoids the measurement error of traditional strain gauges and is more convenient to implement;

[0031] 4. The computer system processes data synchronously and displays the nail load distribution ratio and load value in real time.

[0032] These and other features and advantages will become apparent from reading the following detailed description and referring to the associated drawings.It should be understood that the foregoing general description and the following detailed description are only illustrative and are not restrictive of the aspects claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. 4 is a schematic block diagram of a system for measuring loads of multi-nail structural fasteners according to an embodiment of the present invention.

[0034] Figure 2 FIG. 4 is a schematic structural diagram of a system for measuring the load of a multi-nail structural fastener according to an embodiment of the present invention.

[0035] Figure 3A and Figure 3B Schematic diagrams of multi-nail overlap test pieces including two nails and three nails respectively according to embodiments of the present invention.

[0036] Figure 4 The figure is a flow chart of a method for measuring the load of a multi-nail structure fastener according to an embodiment of the present invention.

[0037] Figure 5A and Figure 5B 1 is a side view of a test piece subjected to speckle spraying according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below with reference to the accompanying drawings, and the features of the present invention will be further apparent in the following detailed description. In the following detailed description, many specific details are set forth to provide a thorough understanding of the described exemplary embodiments. However, it will be apparent to those skilled in the art that the described embodiments can be practiced without some or all of these specific details. In other exemplary embodiments, well-known structures or processing steps are not described in detail to avoid unnecessarily obscuring the concepts of the present disclosure.

[0039] In this specification, unless otherwise specified, the term "A or B" used in this specification refers to "A and B" and "A or B", and does not mean excluding A and B. Similarly, the term "A and / or B" used in this specification refers to "A and B" and "A or B".

[0040] In aircraft metal structures, fatigue-sensitive and crack-prone locations generally occur at the points of maximum local stress concentration. Multi-nail lap joints are the most common connection structure in aircraft, and their connecting nail holes are extremely prone to fatigue. The points of maximum local stress concentration generally occur at the nail holes of the connecting fasteners, especially the first nail hole. Therefore, measuring the nail load at the fasteners and its proportion in the total load is the basis for aircraft fatigue and damage tolerance assessment.

[0041] Because the structure contains two or more plates made of different materials or with different geometries, the load share at each fastener will also change. When conducting a nail load distribution test, the tester usually needs to attach a strain gauge to the surface of the test piece. By measuring the strain at a representative point, the average strain on the cross section between the nails is estimated, and the load at the first fastener and its share of the total load are calculated. However, due to the uneven stress distribution at the nail connection, the nail load distribution calculated by using the above method to estimate the average strain on the cross section between the nails is not very accurate and is greatly affected by factors such as the structure, the load type, and the location of the strain gauge attachment.

[0042] To more accurately determine the load on overlapping structural fasteners and their contribution to the total load, the present invention provides a method and system for measuring the load of multi-nail structural fasteners to address the aforementioned issues. This method provides a displacement-based method for calculating nail loads and introduces a digital speckle displacement measurement device with optical compensation.

[0043] Figure 1 FIG. 1 is a schematic block diagram illustrating a system 100 for measuring the load of a multi-nail structural fastener according to an embodiment of the present invention. Figure 1 The blocks in FIG. 1 are illustrated as distinct components, but the functions described above with respect to these blocks may be implemented using a single hardware, software, or combined component or a combination of various components.

[0044] In some aspects, the system 100 may include: a compensating light source device 110 for providing a compensating light source with adjustable intensity to the multi-nail structural fastener. In one example, the compensating light source device 110 has a brightness adjustment function, which can emit a light source beam to the multi-nail structural fastener, and adjust the emission power based on the light source beam reflected from the multi-nail structural fastener to achieve the most ideal state (for example, so that the camera device 120 described below can capture it), thereby improving the measurement accuracy. In another example, the multi-nail structural fastener can be a multi-nail overlap test piece, the side of which is speckle sprayed. In some aspects, such a compensating light source device 110 may include a combination of Figure 2 One or more components of the system 200 for measuring multi-nail structural fastener loads, such as a compensated light source emitter 230, a light intensity sensor 240, and the like, are described.

[0045] In some aspects, the system 100 may include: a camera 120 for capturing a deformed image of a multi-nail structural fastener. In one example, the camera 120 may be a camera that is combined with a Figure 2 The high-definition high-speed camera 250 described can maintain a 90° angle with the side assessment area of ​​the multi-nail test piece and capture the deformation of the test piece in real time.

[0046] In some aspects, the system 100 may include a processor 130 configured to: receive a captured deformation image from the camera 120; analyze image data based on the received deformation image to obtain changes in monitored positions of a multi-nail structural fastener; and calculate loads based on these changes in monitored positions according to one or more algorithms (e.g., one or more of the three algorithms described below). In one example, the processor 130 may be a computer including a graphics processor to analyze image data based on the deformation image.

[0047] In some aspects, the system 100 may include a display device 140 for displaying the calculated load.

[0048] Figure 2 FIG. 2 is a schematic structural diagram illustrating a system 200 for measuring the load of a multi-nail structural fastener according to an embodiment of the present invention. Figure 2 As shown in , the multi-nail structural fastener may be a multi-nail overlap test piece 210 , the side of which is speckle-sprayed and clamped by a test fixture 220 .

[0049] In some aspects, the system 200 may include a compensating light source emitter 230 for emitting a light source beam toward the multi-nail overlap test piece 210 .

[0050] In some aspects, the system 200 may include: a light intensity sensor 240 for receiving a light source beam reflected from the multi-nail overlap test piece 210, and feeding back a light intensity signal to the compensation light source emitter 230 based on the received light source reflected beam to adjust the emission power of the compensation light source emitter 230.

[0051] In some aspects, the system 200 may include: a high-definition high-speed camera 250, which may be set to be 90 degrees (eg, Figure 2 ), for capturing deformation images of the multi-nail overlap test piece 210 during a tensile test.

[0052] In some aspects, the system 200 may include: a computer 260 for performing image processing on the deformation images captured by the high-definition high-speed camera 250 to obtain changes in the monitoring positions of the multi-nail lap joint test piece 210; and calculating the load based on the changes in these monitoring positions according to one or more algorithms (for example, one or more of the three algorithms described below).

[0053] Figure 3A and Figure 3B The schematic diagrams of displacement measurement points for a two-nail structure and a three-nail structure are explained separately. As non-limiting examples, three methods for calculating nail loads and nail load ratios using the displacement method are given here:

[0054] a) Method 1

[0055] for Figure 3A For the test piece, the nail deformation at nail 1 is the relative displacement at points C and D, i.e.

[0056] Δ bolt,1 =Δ CD (1)

[0057] The nail deformation at nail 2 is the relative displacement at points E and F, that is,

[0058] Δ bolt,2 =Δ EF (2)

[0059] Using the above-mentioned device (e.g. Figure 1 The compensation light source device 110, the camera device 120 and the processor 130 shown in FIG, or Figure 2 , a compensation light source emitter 230, a light intensity sensor 240, a high-definition high-speed camera 250, and a computer 260 are shown in FIG. CD and Δ EF .

[0060] The flexibility of nail 1 and nail 2 is the same, that is,

[0061]

[0062] Among them, R1 and R2 are the nail loads at nail 1 and nail 2.

[0063] It can be deduced that the load ratio of nail 1 is:

[0064]

[0065] The nail load at nail 1 is:

[0066]

[0067] Where P is the total load transferred by the structure (external load).

[0068] Similarly, the nail load ratio at nail 2 is:

[0069]

[0070] The nail load at nail 2 is:

[0071]

[0072] for Figure 3B For the test piece, the nail deformation at nail 1 is the relative displacement at points C and D, i.e.

[0073] Δ bolt,1 =Δ CD (8)

[0074] The nail deformation at nail 2 is the relative displacement at points E and F, that is,

[0075] Δ bolt,2 =Δ EF (9)

[0076] The nail deformation at nail 2 is the relative displacement at points I and J, that is,

[0077] Δ bolt,3 =Δ IJ (10)

[0078] The flexibility of nail 1, nail 2 and nail 3 is the same, that is,

[0079]

[0080] Among them, R1, R2 and R3 are the nail loads at nail 1, nail 2 and nail 3 respectively.

[0081] It can be deduced that the load ratio of nail 1 is:

[0082]

[0083] The nail load at nail 1 is:

[0084]

[0085] Where P is the total load transferred by the structure (external load).

[0086] Similarly, the nail load ratio at nail 2 is:

[0087]

[0088] The nail load at nail 2 is:

[0089]

[0090] The load ratio of nail 3 is:

[0091]

[0092] The nail load at 3 locations is:

[0093]

[0094] b) Method 2

[0095] for Figure 3A For the test piece, since the relative displacement between C and D is small, the deformation of nail 1 can be characterized by the elongation at AD along the tensile direction minus the elongation at AC, that is,

[0096] Δ bolt，1 =Δ AD -ΔAC (18)

[0097] Since the displacement between E and F is small, the deformation of nail 2 can be characterized by the elongation along the tensile direction of EH minus the elongation at FH, that is,

[0098] Δ bolt,2 =Δ EH -Δ FH (19)

[0099] Using the above-mentioned device (e.g. Figure 1 The compensation light source device 110, the camera device 120 and the processor 130 shown in FIG, or Figure 2 , a compensation light source emitter 230, a light intensity sensor 240, a high-definition high-speed camera 250, and a computer 260 are shown in FIG. AD , Δ AC , Δ EH and Δ FH .

[0100] Substituting equations (18) and (19) into equation (3), the nail load and nail load ratio at nail 1 and nail 2 can be obtained in the same way.

[0101] c) Method 3

[0102] for Figure 3A For the test piece, since the displacement between C and D is small, the deformation of nail 1 can be characterized by subtracting the elongation at AC from the elongation at AD along the tensile direction. In this method, the elongation at AC is:

[0103]

[0104] Among them, L AC is the length between AC, E1 is the elastic modulus of plate 1, W is the width of the plate, and t1 is the thickness of plate 1.

[0105] Substituting formula (20) into formula (18), the nail load and nail load ratio at nail 1 can be calculated.

[0106] for Figure 3A For the test piece, since the displacement between E and F is small, the deformation of nail 2 can be characterized by the elongation along the tensile direction of EH minus the elongation at FG. In this method, the elongation at FH is:

[0107]

[0108] Substituting formula (21) into formula (19), the nail load and nail load ratio at nail 2 can be calculated.

[0109] By analogy, when the multi-nail lap joint test piece contains N nails, the nail load and nail load ratio of each nail can be calculated separately.

[0110] In some aspects, the relative displacement of points on both sides of each nail can be measured, and the nail load and nail load ratio can be calculated as follows:

[0111]

[0112] where R i is the load of the i-th nail, Δ b olt,i is the deformation displacement of the i-th nail, N is the number of nails, and P is the total load.

[0113] In some aspects, the nail deformation can be characterized by the difference in elongation of the line segment in the tensile direction, and the nail load and nail load ratio can be calculated as follows:

[0114]

[0115] where R i is the load of the i-th nail, Δ b olt,i is the difference in elongation of the line segment in the tensile direction of the i-th nail, N is the number of nails, and P is the total load.

[0116] In some aspects, the elongation difference Δ of the stretching direction segment of the i-th nail bolt,i =Δ AD -Δ AC , where Δ AC is the elongation of the line segment between point C on one side of the nail and point A on the same side in the tensile direction, Δ AD The elongation of the line segment between point D on the other side of the nail and point A in the stretching direction; or , where L AC is the length between AC, E1 is the elastic modulus of the plate, W is the plate width, and t1 is the plate thickness.

[0117] Figure 4 Flowchart illustrating a method 400 for measuring the load of a multi-nail structural fastener. The method 400 is a system (e.g., Figure 1 The system 100 for measuring the load of a multi-nail structural fastener is depicted in Figure 2 An example of a method for measuring the load of a multi-nail structural fastener is performed by the system 200 for measuring the load of a multi-nail structural fastener depicted in FIG.

[0118] like Figure 4As shown in , in some aspects, method 400 may include providing a compensating light source to a multi-nail structural fastener (block 410). For example, system 100 (e.g., using compensating light source device 110, camera device 120, processor 130, display device 140) or system 200 (e.g., using compensating light source emitter 230, light intensity sensor 240, high-definition high-speed camera 250, computer 260) may provide a compensating light source to a multi-nail structural fastener, as described above.

[0119] like Figure 4 As further shown in FIG4 , in some aspects, method 400 may include capturing a deformed image of a multi-pin structural fastener (block 420). For example, system 100 (e.g., using the compensated light source device 110, the camera device 120, the processor 130, and the display device 140) or system 200 (e.g., using the compensated light source emitter 230, the light intensity sensor 240, the high-definition high-speed camera 250, and the computer 260) may capture a deformed image of a multi-pin structural fastener, as described above.

[0120] like Figure 4 As further shown in FIG4 , in some aspects, method 400 may include analyzing image data based on the deformed image to obtain changes in the monitored positions of the multi-nail structural fasteners (block 430). For example, system 100 (e.g., using the compensating light source device 110, the camera device 120, the processor 130, and the display device 140) or system 200 (e.g., using the compensating light source emitter 230, the light intensity sensor 240, the high-definition high-speed camera 250, and the computer 260) may analyze image data based on the deformed image to obtain changes in the monitored positions of the multi-nail structural fasteners, as described above.

[0121] like Figure 4 As further shown in FIG4 , in some aspects, method 400 may include calculating a load according to one or more algorithms based on the change in monitored position (block 440). For example, system 100 (e.g., using the compensated light source device 110, the camera device 120, the processor 130, and the display device 140) or system 200 (e.g., using the compensated light source emitter 230, the light intensity sensor 240, the high-definition high-speed camera 250, and the computer 260) may analyze image data based on the deformed image to obtain the change in monitored position of the multi-nail structural fastener, as described above.

[0122] like Figure 4As further shown in FIG4 , in some aspects, method 400 may include displaying the calculated load (block 450). For example, system 100 (e.g., using compensated light source device 110, camera device 120, processor 130, display device 140) or system 200 (e.g., using compensated light source emitter 230, light intensity sensor 240, high-definition high-speed camera 250, computer 260) may display the calculated load, as described above.

[0123] Figure 5A and Figure 5B The side view of the test piece after speckle spraying is explained separately. In the multi-nail overlap test, the side of the test piece is speckle sprayed. After completion, the side of the test piece is as follows Figure 5A and Figure 5B shown.

[0124] The various steps and modules of the methods, devices, and systems described above can be implemented in hardware, software, or a combination thereof. If implemented in hardware, the various illustrative steps, modules, and circuits described in conjunction with the present disclosure can be implemented or executed using a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic components, hardware components, or any combination thereof. The general-purpose processor can be a processor, a microprocessor, a controller, a microcontroller, or a state machine, etc. If implemented in software, the various illustrative steps and modules described in conjunction with the present disclosure can be stored or transmitted as one or more instructions or codes on a computer-readable medium. The software modules that implement the various operations of the present disclosure can reside in a storage medium, such as RAM, flash memory, ROM, EPROM, EEPROM, registers, hard disk, removable disk, CD-ROM, cloud storage, etc. The storage medium can be coupled to a processor so that the processor can read and write information from / to the storage medium and execute the corresponding program modules to implement the various steps of the present disclosure. Moreover, software-based embodiments can be uploaded, downloaded, or remotely accessed through appropriate communication means. Such appropriate communication means include, for example, the Internet, the World Wide Web, an intranet, software applications, cable (including fiber optic cables), magnetic communication, electromagnetic communication (including RF, microwave and infrared communication), electronic communication or other such communication means.

[0125] The numerical values ​​given in the various embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, as a whole, the technical solution may include other components or steps not listed in the claims or the specification. Furthermore, a single name for a component does not preclude the use of other names for that component.

[0126] It should also be noted that these embodiments may be described as processes depicted as flow charts, flow diagrams, structure diagrams, or block diagrams. Although a flow chart may describe the operations as sequential processes, many of these operations can be performed in parallel or concurrently. In addition, the order of these operations can be rearranged.

[0127] The disclosed methods, devices, and systems should not be limited in any way. On the contrary, the present disclosure covers all novel and non-obvious features and aspects of the various disclosed embodiments (alone and in various combinations and subcombinations with each other). The disclosed methods, devices, and systems are not limited to any specific aspect or feature or combination thereof, nor do any disclosed embodiments require any one or more specific advantages or solutions to specific or all technical problems.

[0128] The present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many forms without departing from the scope of protection of the present invention and the claims. These all fall within the scope of protection of the present invention.

Claims

1. A system for measuring the load of multi-nail structural fasteners, characterized in that: include: A compensating light source device for providing a compensating light source with adjustable intensity to a multi-nail structural fastener; a camera device for capturing a deformed image of the multi-nail structural fastener; as well as A processor configured to: receiving the captured deformed image from the camera device; analyzing image data based on the received deformed image to obtain a change in a monitored position of the multi-nail structural fastener; as well as calculating a load according to one or more algorithms based on the change in the monitored position; and a display device for displaying the calculated load.

2. The system according to claim 1, wherein The compensation light source device comprises: a compensation light source emitter, configured to emit a light source beam toward the multi-nail structural fastener; and The light intensity sensor is used to receive the light source beam reflected from the multi-nail structure fastener and feed back a light intensity signal to the compensation light source transmitter to adjust the emission power of the compensation light source transmitter.

3. The system according to claim 1, wherein: The change in the monitoring position includes at least one of a length change and a displacement change of the monitoring position.

4. The system according to claim 1, wherein: The algorithm includes at least one of the following: Measure the relative displacement of the points on both sides of each nail, and calculate the nail load and nail load ratio as follows: where R i is the load of the i-th nail, Δ b olt,i is the deformation displacement of the i-th nail, N is the number of nails, and P is the total load; or The nail deformation is characterized by the difference in elongation of the line segment in the tensile direction, and the nail load and nail load ratio are calculated as follows: where R i is the load of the i-th nail, Δ b olt,i is the difference in elongation of the line segment in the tensile direction of the i-th nail, N is the number of nails, and P is the total load.

5. The system according to claim 4, wherein: The elongation difference Δ of the line segment in the tensile direction of the i-th nail bolt,i =Δ AD -Δ AC , where Δ AC is the elongation of the line segment between point C on one side of the nail and point A on the same side in the tensile direction, Δ AD The elongation of the line segment between point D on the other side of the nail and point A in the stretching direction; or Among them L AC is the length between AC, E1 is the elastic modulus of the plate, W is the plate width, and t1 is the plate thickness.

6. A method for measuring the load of a multi-nail structural fastener, characterized in that: include: Providing a compensating light source to a multi-nail structural fastener; capturing a deformed image of the multi-nail structural fastener; analyzing image data based on the deformed image to obtain a change in a monitored position of the multi-nail structural fastener; calculating a load according to one or more algorithms based on the change in the monitored position; as well as Displays the calculated loads.

7. The method according to claim 6, wherein Providing a compensating light source to a multi-nail structural fastener includes: emitting a light beam from a light source toward the multi-nail structural fastener; receiving a light source beam reflected from the multi-nail structural fastener; and A light intensity signal is fed back based on the received reflected light source light beam to adjust the compensation light source intensity.

8. The method according to claim 6, wherein The change in the monitoring position includes at least one of a length change and a displacement change of the monitoring position.

9. The method according to claim 6, wherein The algorithm includes at least one of the following: Measure the relative displacement of the points on both sides of each nail, and calculate the nail load and nail load ratio as follows: where R i is the load of the i-th nail, Δ b olt,i is the deformation displacement of the i-th nail, N is the number of nails, and P is the total load; or The nail deformation is characterized by the difference in elongation of the line segment in the tensile direction, and the nail load and nail load ratio are calculated as follows: where R i is the load of the i-th nail, Δ b olt,i is the difference in elongation of the line segment in the tensile direction of the i-th nail, N is the number of nails, and P is the total load.

10. The method according to claim 9, wherein The elongation difference Δ of the line segment in the tensile direction of the i-th nail bolt,i =Δ AD -Δ AC , where Δ AC is the elongation of the line segment between point C on one side of the nail and point A on the same side in the tensile direction, Δ AD The elongation of the line segment between point D on the other side of the nail and point A in the stretching direction; or Among them L AC is the length between AC, E1 is the elastic modulus of the plate, W is the plate width, and t1 is the plate thickness.

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