Bolt pre-tightening force method and device for fixed axial force construction device

Abstract

The invention provides a bolt pre-tightening force loading method and device of a fixed axial force construction device, and relates to the technical field of bolt assembling.According to the bolt pre-tightening force loading method and device, the sound wave propagation time of a bolt is measured through an ultrasonic sensor in the state that stress is not applied, and standard propagation time and related physical parameters are established. And a target pre-tightening force is set, and an initial pre-tightening force is generated according to the target pre-tightening force, so that the bolt is preliminarily fastened. The sound wave propagation time is measured again at the real-time temperature, and the bolt length and the Young modulus are corrected based on the temperature deviation to calculate the real-time stress; and comparing the real-time stress with the target stress to generate a stress deviation index and an adjustment strategy, adjusting the pre-tightening force through the adjustment strategy and an adjustment threshold value, calculating the stress deviation index again for the adjusted pre-tightening force, and ensuring that the adjusted stress deviation index meets the requirement of slightly adjusting the threshold value. According to the method, dynamic monitoring and self-adaptive adjustment of the bolt pre-tightening force are achieved, and the safety of a fixed axial force construction device is improved.

Description

Technical Field

[0001] The invention relates to the technical field of bolt assembly, and in particular to a method and a device for loading bolt pre-tightening force of a fixed-axis force construction device. Background Art

[0002] Bolts are a common connection method in mechanical mechanisms, and accurate control of their preload is crucial to the safety and reliability of the connection. Traditional bolt preload loading methods usually rely on manual operation and work experience, making it difficult to monitor changes in preload in real time. The control of preload is not accurate, and it is not adaptable enough to factors such as temperature and material properties. This method may not only lead to insufficient preload or over-tightening, but may also cause connection failure due to environmental changes, posing a safety hazard. Therefore, it is urgent to develop a solution that can monitor and adjust bolt preload in real time to improve the reliability and safety of the connection.

[0003] In existing calculations, publication number CN114707375A discloses a method, device, medium, and electronic equipment for loading bolt preload, including: obtaining a target preload for a component to be assembled, calculating a temperature change amplitude that can drive the bolt to deform based on the target preload, establishing a finite element simulation model including a component model corresponding to the component to be assembled and a bolt model corresponding to the assembly bolt, loading the temperature change amplitude onto the bolt model in the finite element simulation model, and simulating the assembly bolt loading the target preload on the component to be assembled.

[0004] The main problems with the above method are: preload control through finite element simulation model requires a long calculation time and more computing resources, which may not meet the requirements of dynamic control of bolt preload. In addition, this method relies on equivalent temperature difference to drive bolt deformation. The accuracy of preload control is too dependent on temperature data. When a harsh environment causes uneven or rapid temperature changes, the preload cannot be truly reflected.

[0005] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute the prior art that is already known to one of ordinary skill in the art. Summary of the invention

[0006] The object of the present invention is to provide a method and device for loading the bolt preload force of a fixed-axis force construction device, so as to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for loading bolt preload force of a fixed-axis force construction device, the specific steps comprising:

[0009] Step 1: Place an ultrasonic sensor on the top of the bolt. Before applying the preload, send a calibration signal through the ultrasonic sensor to measure the sound wave propagation time of the bolt in the unstressed state, record it as the standard propagation time, and collect the length and Young's modulus of the bolt at the standard temperature, where the standard temperature is 25°C.

[0010] Step 2: Set a target preload force for the bolt that meets the requirements, generate an initial preload force based on the target preload force, the effective area of ​​the bolt and the connector, and the elastic modulus of the bolt and the connector, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state;

[0011] Step 3: The ultrasonic sensor on the top of the bolt emits a sound wave signal, receives the sound wave signal reflected from the other end of the bolt, collects the current ambient temperature, and corrects the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. The real-time propagation time of the sound wave signal is generated according to the physical properties of the bolt material and the corrected bolt length, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time.

[0012] Step 4: Generate a target stress of the bolt according to the target preload of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold;

[0013] Step 5: After the preload is adjusted according to the adjustment strategy, the ultrasonic sensor re-emits the acoustic wave signal, calculates the adjusted bolt stress, and generates an adjusted stress deviation index based on the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload is loaded.

[0014] Furthermore, the formula for generating the initial preload is:

[0015]

[0016] Where F0 represents the initial preload force, F T represents the target preload, k represents the relaxation coefficient, and 0≤k≤1, S1 represents the cross-sectional area of ​​the bolt, S2 represents the contact area between the bolt and the fastener, A1 represents the elastic modulus of the bolt material, and A2 represents the elastic modulus of the fastener material.

[0017] Furthermore, the principle for generating the real-time stress of the bolt is based on:

[0018] The corrected bolt length is generated based on the formula:

[0019] L(T)=L0·(1+α(T-T0))

[0020] Wherein, L(T) represents the bolt length after correction according to the current ambient temperature, L0 represents the bolt length at the standard temperature, and α represents the linear thermal expansion coefficient of the bolt material;

[0021] The real-time propagation time of the sound wave signal is:

[0022] E(T)=E0·(1-β(T-T0))

[0023]

[0024]

[0025] Wherein, E(T) represents the Young's modulus of the bolt material at the current ambient temperature, T represents the current ambient temperature, E0 represents the Young's modulus of the bolt material at the standard temperature, T0 represents the standard temperature, β represents the sensitivity of the Young's modulus of the material to temperature, ρ represents the density of the bolt material, t represents the real-time propagation time of the acoustic wave signal, and v represents the propagation speed of the acoustic wave in the bolt;

[0026] The formula used to generate the real-time stress in the bolt is:

[0027]

[0028] Where σ represents the real-time stress of the bolt and t0 represents the standard propagation time.

[0029] Furthermore, the principle on which the stress deviation index is generated is:

[0030] The formula for generating the target stress of the bolt based on the target preload of the bolt is:

[0031]

[0032] Among them, σ T represents the target stress of the bolt, F T represents the target preload, S1 represents the cross-sectional area of ​​the bolt;

[0033] The formula used to generate the stress deviation index is:

[0034]

[0035] Where G represents the stress deviation index.

[0036] Furthermore, the principle on which the adjustment threshold is set and the corresponding preload adjustment strategy is generated according to the magnitude relationship between the stress deviation index and the adjustment threshold is:

[0037] Slightly adjust the threshold to: Y1 = 0.05;

[0038] The moderate adjustment threshold is: Y2 = 0.15;

[0039] The drastic adjustment threshold is: Y3 = 0.25;

[0040] The preload adjustment strategy is:

[0041] When 0≤G≤Y1, no adjustment is made to the bolt preload;

[0042] When Y1<G≤Y2, increase or decrease the bolt preload by 5% to 15%;

[0043] When Y2<G≤Y3, increase or decrease the bolt preload by 15% to 25%;

[0044] When G>Y3, increase or decrease the bolt preload by more than 25%.

[0045] The present invention also provides a bolt preload force loading device for a fixed-axis force construction device, and the device is used to implement the bolt preload force loading method for the fixed-axis force construction device, which specifically includes:

[0046] The data acquisition module is used to place an ultrasonic sensor on the top of the bolt. Before the preload is applied, the ultrasonic sensor emits a calibration signal to measure the sound wave propagation time of the bolt in a state where no stress is applied, which is recorded as the standard propagation time, and collect the length and Young's modulus of the bolt at a standard temperature, where the standard temperature is 25°C.

[0047] The initialization module is used to set the target preload force of the bolt that meets the requirements, generate the initial preload force according to the target preload force, the effective area of ​​the bolt and the connecting part, and the elastic modulus of the bolt and the connecting part, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state;

[0048] A real-time calculation module is used to transmit a sound wave signal through an ultrasonic sensor on the top of the bolt, receive the sound wave signal reflected from the other end of the bolt, collect the current ambient temperature, and correct the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. According to the physical properties of the bolt material and the corrected bolt length, the real-time propagation time of the sound wave signal is generated, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time;

[0049] A strategy adjustment module is used to generate a target stress of the bolt according to the target preload force of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold;

[0050] The feedback optimization module is used to adjust the preload force according to the adjustment strategy, re-emit the acoustic wave signal through the ultrasonic sensor, calculate the adjusted bolt stress, and generate the adjusted stress deviation index according to the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload force loading is completed.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The present invention detects the sound wave propagation time of the bolt before the preload is loaded according to the ultrasonic sensor, and collects the physical properties of the bolt at the standard temperature, thereby reducing the influence of temperature change on the sound wave propagation rate, helping to reduce the error caused by temperature through temperature compensation, and the propagation time of the sound wave can be quickly obtained through ultrasonic detection; and the target preload is set based on the physical properties of the bolt, and the initial preload is generated according to the effective area and elastic modulus, ensuring that the bolt is in a reasonable preload state when the preload is initially applied, reducing the risk caused by over-tightening and over-loosening, and being more accurate than the initial preload manually adjusted based on experience. In actual work, the bolt length and Young's modulus are corrected based on the temperature difference between the real-time temperature and the standard temperature, and the preload of the bolt is converted into the stress received by the bolt. The ultrasonic wave can be effectively identified and calculated, providing a more accurate real-time stress evaluation, and minimizing the calculation error caused by temperature change.

[0053] The present invention also calculates the target stress according to the target preload through the relationship between stress and preload, and generates a stress deviation index based on the target stress. The stress deviation index reflects the adjustment range of the preload, and determines whether to make adjustments based on the size relationship between the stress deviation index and the preset adjustment threshold, which can prevent excessive or frequent adjustments and help extend the service life of the bolt. For bolts that do not meet the requirements, the preload is adjusted and repeated detection is performed to generate a new stress deviation index for further judgment until the stress deviation index is within the slight adjustment threshold range, ensuring that each bolt is in the best preload state. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of a method flow chart of an embodiment of the present invention;

[0055] Figure 2 Schematic diagram of a device module according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0057] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0058] Example:

[0059] See also Figure 1 , the present invention provides a technical solution:

[0060] A method for loading bolt preload force of a fixed-axis force construction device, the specific steps comprising:

[0061] Step 1: Place an ultrasonic sensor on the top of the bolt. Before applying the preload, send a calibration signal through the ultrasonic sensor to measure the sound wave propagation time of the bolt in the unstressed state, record it as the standard propagation time, and collect the length and Young's modulus of the bolt at the standard temperature, where the standard temperature is 25°C.

[0062] Step 2: Set a target preload force for the bolt that meets the requirements, generate an initial preload force based on the target preload force, the effective area of ​​the bolt and the connector, and the elastic modulus of the bolt and the connector, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state;

[0063] In this embodiment, the formula for generating the initial preload force is:

[0064]

[0065] Where F0 represents the initial preload force, F T represents the target preload, k represents the relaxation coefficient, and 0≤k≤1, S1 represents the cross-sectional area of ​​the bolt, S2 represents the contact area between the bolt and the fastener, A1 represents the elastic modulus of the bolt material, and A2 represents the elastic modulus of the fastener material.

[0066] The initial preload refers to the preload that needs to be applied when the bolt is initially fixed to the connection part, where: It represents the relationship between the elastic restoring force of bolts and connectors. The elastic modulus and effective area of ​​bolts and connectors determine how the load is shared between bolts and connectors during the application of preload. Under continuous load, the preload gradually decreases over time and a relaxation effect occurs, causing the actual preload to be lower than the initial set value. Therefore, the relaxation coefficient is used to correct the preload loss caused by the relaxation effect, thereby ensuring that after the relaxation effect occurs, the actual preload in the system can reach or approach the target preload. When calculating the initial preload, the relaxation and elastic recovery phenomena that may occur in bolts and connectors during the tensioning process and subsequent use are comprehensively considered, thereby ensuring that the bolt connection can maintain the required preload level. The size of the initial preload is proportional to the size of the target preload and to the relationship between the elastic restoring force of the bolt and connector.

[0067] Step 3: The ultrasonic sensor on the top of the bolt emits a sound wave signal, receives the sound wave signal reflected from the other end of the bolt, collects the current ambient temperature, and corrects the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. The real-time propagation time of the sound wave signal is generated according to the physical properties of the bolt material and the corrected bolt length, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time.

[0068] In this embodiment, the principle for generating the real-time stress of the bolt is:

[0069] The corrected bolt length is generated based on the formula:

[0070] L(T)=L0·(1+α(T-T0))

[0071] Wherein, L(T) represents the bolt length after correction according to the current ambient temperature, L0 represents the bolt length at the standard temperature, and α represents the linear thermal expansion coefficient of the bolt material;

[0072] The above correction formula is based on the principle of thermal expansion. When the temperature of the material rises, the average distance between its internal atoms increases, so the overall size of the material will increase, and the thermal expansion can be approximately considered to be linear. Therefore, the linear thermal expansion coefficient α is used to reflect the change of the bolt length with temperature. Different materials have different linear thermal expansion coefficients, which can be determined experimentally or found through instructions and other materials. The bolt length after temperature correction is proportional to the bolt length at standard temperature, the linear thermal expansion coefficient of the bolt material, and the temperature difference between the current ambient temperature and the standard temperature.

[0073] The real-time propagation time of the sound wave signal is:

[0074] E(T)=E0·(1-β(T-T0))

[0075]

[0076]

[0077] Wherein, E(T) represents the Young's modulus of the bolt material at the current ambient temperature, T represents the current ambient temperature, E0 represents the Young's modulus of the bolt material at the standard temperature, T0 represents the standard temperature, β represents the sensitivity of the Young's modulus of the material to temperature, ρ represents the density of the bolt material, t represents the real-time propagation time of the acoustic wave signal, and v represents the propagation speed of the acoustic wave in the bolt;

[0078] Generally speaking, as the temperature rises, the atomic vibration amplitude in the material increases, causing the Young's modulus of the material to decrease. When the temperature change range is not large, the Young's modulus decreases with increasing temperature. The sensitivity of the Young's modulus to temperature, β, reflects the sensitivity of the Young's modulus to temperature, and is used to indicate the decrease in the Young's modulus with each degree Celsius increase in temperature. When calculating the propagation speed of sound waves, it is calculated based on the physical principle of longitudinal wave propagation in solid materials, based on the elastic and inertial properties of the material. The elastic property is expressed as Young's modulus, and the inertial property is expressed as density. By solving the wave equation, the speed expression of the sound wave in the solid is obtained. The propagation time of the sound wave is the ratio of the round trip distance in the bolt to the propagation speed, and the propagation time is proportional to the bolt length at the current ambient temperature, and inversely proportional to the propagation speed of the sound wave in the bolt.

[0079] The formula used to generate the real-time stress in the bolt is:

[0080]

[0081] Where σ represents the real-time stress of the bolt and t0 represents the standard propagation time.

[0082] The real-time stress of the bolt reflects the load intensity currently borne by the bolt. It is calculated by the propagation delay of the sound wave. The real-time stress of the bolt is proportional to the Young's modulus of the bolt at the current ambient temperature and the propagation delay of the sound wave in the stressed and unstressed states, and inversely proportional to the length of the bolt.

[0083] In this embodiment, the principle for generating the stress deviation index is:

[0084] The formula for generating the target stress of the bolt based on the target preload of the bolt is:

[0085]

[0086] Among them, σ T represents the target stress of the bolt, F Y represents the target preload, S1 represents the cross-sectional area of ​​the bolt;

[0087] For a bolt, the target stress is determined based on the required preload force of the bolt and the characteristics of the bolt material. It represents the size of the preload force applied to the unit effective area. The effective area of ​​the bolt is the cross-sectional area of ​​the bolt. The preload force of the bolt represents the force required to tightly connect the bolt and the connecting piece. It can be determined based on the preload force between bolts and connecting pieces of the same type in historical data. The target stress of the bolt is proportional to the target preload force and inversely proportional to the cross-sectional area of ​​the bolt.

[0088] The formula used to generate the stress deviation index is:

[0089]

[0090] Where G represents the stress deviation index.

[0091] The stress deviation index is the difference between the ratio of the target stress of the bolt to the real-time stress of the bolt and 1, which reflects the difference between the real-time stress and the target stress. According to the stress calculation formula, the cross-sectional area of ​​the bolt remains unchanged, and the stress of the bolt is only related to the preload. Therefore, the stress deviation index also reflects the deviation of the preload. When , it means that the target stress is greater than the real-time stress, and the real-time stress needs to be increased. The increase is the value of the stress deviation index at this time; when , it means that the real-time stress is greater than the target stress and the real-time stress needs to be reduced. The reduction amplitude is the value of the stress deviation index at this time.

[0092] Step 4: Generate a target stress of the bolt according to the target preload of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold;

[0093] In this embodiment, the principle on which the adjustment threshold is set and the corresponding preload adjustment strategy is generated according to the magnitude relationship between the stress deviation index and the adjustment threshold is:

[0094] Slightly adjust the threshold to: Y1 = 0.05;

[0095] Slight adjustment of the threshold is considered acceptable, with a deviation range of 0-5%, which will not affect key tasks and structures and can be considered within the system error range;

[0096] The moderate adjustment threshold is: Y2 = 0.15;

[0097] The deviation range of the moderate adjustment threshold is 5% to 25%, which may cause problems in some sensitive situations and require timely adjustment of the preload applied to the bolts;

[0098] The drastic adjustment threshold is: Y3 = 0.25;

[0099] Deviations above 25% from the drastic adjustment threshold may have a significant impact on the integrity of the structure and require immediate and drastic adjustments;

[0100] The preload adjustment strategy is:

[0101] When 0≤G≤Y1, no adjustment is made to the bolt preload;

[0102] When Y1<G≤Y2, increase or decrease the bolt preload by 5% to 15%;

[0103] When Y2<G≤Y3, increase or decrease the bolt preload by 15% to 25%;

[0104] When G>Y3, increase or decrease the bolt preload by more than 25%.

[0105] The stress deviation index can reflect the bolt preload deviation. The value of the stress deviation index indicates the adjustment range of the preload force applied to the bolt. When the target stress is greater than the real-time stress, the preload force of the bolt is increased. When the target stress is less than the real-time stress, the preload force of the bolt is reduced.

[0106] Step 5: After the preload is adjusted according to the adjustment strategy, the ultrasonic sensor re-emits the acoustic wave signal, calculates the adjusted bolt stress, and generates an adjusted stress deviation index based on the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload is loaded.

[0107] In this embodiment, the initial preload force of the bolt is adjusted according to the preload force adjustment strategy, which mainly involves increasing the force applied to the bolt. The specific adjustment range is determined by the adjustment strategy. After adjusting the preload force, steps 3 and 4 are repeated to calculate the stress deviation index after adjustment. When the stress deviation index is within the light adjustment threshold range, the preload force loading of the bolt is completed, otherwise the preload force adjustment strategy is regenerated.

[0108] See also Figure 2 The present invention also provides a bolt preload force loading system for a fixed-axis force construction device, the system is used to implement the bolt preload force loading method for the fixed-axis force construction device, specifically comprising:

[0109] The data acquisition module is used to place an ultrasonic sensor on the top of the bolt. Before the preload is applied, the ultrasonic sensor emits a calibration signal to measure the sound wave propagation time of the bolt in a state where no stress is applied, which is recorded as the standard propagation time, and collect the length and Young's modulus of the bolt at a standard temperature, where the standard temperature is 25°C.

[0110] The initialization module is used to set the target preload force of the bolt that meets the requirements, generate the initial preload force according to the target preload force, the effective area of ​​the bolt and the connecting part, and the elastic modulus of the bolt and the connecting part, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state;

[0111] A real-time calculation module is used to transmit a sound wave signal through an ultrasonic sensor on the top of the bolt, receive the sound wave signal reflected from the other end of the bolt, collect the current ambient temperature, and correct the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. According to the physical properties of the bolt material and the corrected bolt length, the real-time propagation time of the sound wave signal is generated, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time;

[0112] A strategy adjustment module is used to generate a target stress of the bolt according to the target preload force of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold;

[0113] The feedback optimization module is used to adjust the preload force according to the adjustment strategy, re-emit the acoustic wave signal through the ultrasonic sensor, calculate the adjusted bolt stress, and generate the adjusted stress deviation index according to the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload force loading is completed.

[0114] The above formulas are all dimensionless and numerical calculations. The formula is a formula for the most recent real situation obtained by collecting a large amount of data and performing software simulation. The preset parameters in the formula are set by technicians in this field according to actual conditions.

[0115] The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination thereof. When implemented by software, the above embodiments may be implemented in whole or in part in the form of a computer program product. Those skilled in the art may appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein may be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed by hardware or software methods depends on the specific application and design constraints of the technical solution.

[0116] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, and may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0117] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application.

Claims

1. A method for loading bolt preload force of a fixed-axis force construction device, characterized in that: The specific steps include: Step 1: Place an ultrasonic sensor on the top of the bolt. Before applying the preload, send a calibration signal through the ultrasonic sensor to measure the sound wave propagation time of the bolt in the unstressed state, record it as the standard propagation time, and collect the length and Young's modulus of the bolt at the standard temperature, where the standard temperature is 25°C. Step 2: Set a target preload force for the bolt that meets the requirements, generate an initial preload force based on the target preload force, the effective area of ​​the bolt and the connector, and the elastic modulus of the bolt and the connector, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state; Step 3: The ultrasonic sensor on the top of the bolt emits a sound wave signal, receives the sound wave signal reflected from the other end of the bolt, collects the current ambient temperature, and corrects the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. The real-time propagation time of the sound wave signal is generated according to the physical properties of the bolt material and the corrected bolt length, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time. Step 4: Generate a target stress of the bolt according to the target preload of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold; Step 5: After the preload is adjusted according to the adjustment strategy, the ultrasonic sensor re-emits the acoustic wave signal, calculates the adjusted bolt stress, and generates an adjusted stress deviation index based on the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload is loaded.

2. The bolt preload force loading method of the fixed axial force construction device according to claim 1 is characterized in that: The formula for generating the initial preload in step 2 is: Where F0 represents the initial preload force, F T represents the target preload, k represents the relaxation coefficient, and 0≤k≤1, S1 represents the cross-sectional area of ​​the bolt, S2 represents the contact area between the bolt and the fastener, A1 represents the elastic modulus of the bolt material, and A2 represents the elastic modulus of the fastener material.

3. The bolt preload force loading method of the fixed axis force construction device according to claim 1 is characterized in that: The principle for generating the real-time stress of the bolt in step 3 is: The corrected bolt length is generated based on the formula: L(T)=L0·(1+α(T-T0)) Wherein, L(T) represents the bolt length after correction according to the current ambient temperature, L0 represents the bolt length at the standard temperature, and α represents the linear thermal expansion coefficient of the bolt material; The real-time propagation time of the sound wave signal is: E(T)=E0·(1-β(T-T0)) Wherein, E(T) represents the Young's modulus of the bolt material at the current ambient temperature, T represents the current ambient temperature, E0 represents the Young's modulus of the bolt material at the standard temperature, T0 represents the standard temperature, β represents the sensitivity of the Young's modulus of the material to temperature, ρ represents the density of the bolt material, t represents the real-time propagation time of the acoustic wave signal, and v represents the propagation speed of the acoustic wave in the bolt; The formula used to generate the real-time stress in the bolt is: Where σ represents the real-time stress of the bolt and t0 represents the standard propagation time.

4. The bolt preload force loading method of the fixed axial force construction device according to claim 1 is characterized in that: The principle for generating the stress deviation index in step 4 is: The formula for generating the target stress of the bolt based on the target preload of the bolt is: Among them, σ T represents the target stress of the bolt, F T represents the target preload, S1 represents the cross-sectional area of ​​the bolt; The formula used to generate the stress deviation index is: Where G represents the stress deviation index.

5. The bolt preload force loading method of the fixed axial force construction device according to claim 1 is characterized in that: The principle for setting the adjustment threshold in step 4 and generating the corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold is as follows: Slightly adjust the threshold to: Y1 = 0.05; The moderate adjustment threshold is: Y2 = 0.15; The drastic adjustment threshold is: Y3 = 0.25; The preload adjustment strategy is: When 0≤G≤Y1, no adjustment is made to the bolt preload; When Y1<G≤Y2, increase or decrease the bolt preload by 5% to 15%; When Y2<G≤Y3, increase or decrease the bolt preload by 15% to 25%; When G>Y3, increase or decrease the bolt preload by more than 25%.

6. A bolt preload force loading device for a fixed axial force construction device, characterized in that: The device is used to implement the bolt preload force loading method of the fixed axial force construction device according to any one of claims 1 to 5, specifically comprising: The data acquisition module is used to place an ultrasonic sensor on the top of the bolt. Before the preload is applied, the ultrasonic sensor emits a calibration signal to measure the sound wave propagation time of the bolt in a state where no stress is applied, which is recorded as the standard propagation time, and collect the length and Young's modulus of the bolt at a standard temperature, where the standard temperature is 25°C. The initialization module is used to set the target preload force of the bolt that meets the requirements, generate the initial preload force according to the target preload force, the effective area of ​​the bolt and the connecting part, and the elastic modulus of the bolt and the connecting part, and apply the initial preload force to the bolt to put the bolt in a preliminary tightening state; A real-time calculation module is used to transmit a sound wave signal through an ultrasonic sensor on the top of the bolt, receive the sound wave signal reflected from the other end of the bolt, collect the current ambient temperature, and correct the bolt length at the current ambient temperature based on the temperature difference between the current ambient temperature and the standard temperature. According to the physical properties of the bolt material and the corrected bolt length, the real-time propagation time of the sound wave signal is generated, and the real-time stress of the bolt is generated based on the real-time propagation time of the sound wave signal and the standard propagation time; A strategy adjustment module is used to generate a target stress of the bolt according to the target preload force of the bolt, generate a stress deviation index according to the target stress and the real-time stress, set an adjustment threshold, and generate a corresponding preload adjustment strategy according to the magnitude relationship between the stress deviation index and the adjustment threshold; The feedback optimization module is used to adjust the preload force according to the adjustment strategy, re-emit the acoustic wave signal through the ultrasonic sensor, calculate the adjusted bolt stress, and generate the adjusted stress deviation index according to the adjusted bolt stress and the target stress. When the adjusted stress deviation index is less than the slight adjustment threshold, the preload force loading is completed.

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