A bolt pre-tightening force measuring system and method based on laser electromagnetic ultrasonic

Abstract

This application proposes a bolt preload measurement system and method based on laser-electromagnetic ultrasound, relating to the field of bolt nondestructive testing. The measurement system includes a laser source, an ultrasonic probe, a signal conditioning module, a temperature module, a loading module, and a data processing module. The laser source generates pulsed laser light. The ultrasonic probe includes a long-axis housing and an electromagnetic ultrasonic transducer unit. The housing contains an incident light path and an outgoing light path. The electromagnetic ultrasonic transducer unit is located inside the housing near the end of the outgoing light path. The signal conditioning module preprocesses the ultrasonic waves received by the electromagnetic ultrasonic transducer unit. The temperature module acquires the bolt temperature in real time. The loading module applies an axial tensile load to the bolt when it is at thermal equilibrium temperature. The data processing module calculates the bolt preload based on the flight time of the preprocessed ultrasonic waves and the tensile load. This application enables non-contact, high-precision measurement of the preload of small-diameter bolts under extreme conditions.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing of bolts, and in particular to a bolt preload measurement system and method based on laser electromagnetic ultrasound. Background Technology

[0002] Bolted connections are the core connection method for load transfer and sealing in aerospace, energy equipment, pressure vessels, and major mechanical structures. Bolt preload is a key parameter for controlling connection stiffness, sealing performance, and fatigue life. Its accurate measurement and effective management are the core technical prerequisites for ensuring the safe and reliable service of equipment structures. Especially in extreme conditions such as high temperature, high pressure, strong vibration, and confined space in aircraft engines, artillery barrels, and nuclear power pipelines, high-precision in-situ detection of preload of small-diameter high-temperature alloy and titanium alloy bolts has become an important research direction in the field of non-destructive testing of major equipment.

[0003] Currently, the technical approach of combining single-wave or dual-wave acoustic time measurement with finite element simulation is often adopted. The finite element model is used to screen weak stress areas, establish the calibration relationship between acoustic time difference and axial force, and combine temperature compensation and neural networks to realize axial force calculation, risk assessment and health warning.

[0004] However, axial force calculation methods based on finite element analysis rely on the complete space and conventional dimensions of the bolt, making it difficult to model small-diameter bolts in extremely confined installation spaces and resulting in insufficient simulation accuracy. This makes it impossible to accurately identify the effective stress area and reliably extract the acoustic signal. Moreover, traditional ultrasonic testing uses a separate excitation and reception layout, resulting in large probes, high installation requirements, and extremely poor spatial adaptability. This makes it impossible to achieve single-sided, non-disassembly, in-situ testing within compact structures such as aircraft engines and artillery barrels. Furthermore, conventional ultrasonic testing methods suffer from low signal excitation efficiency and poor signal-to-noise ratio in highly attenuating materials such as high-temperature alloys and titanium alloys. They also lack an integrated non-contact testing structure and signal enhancement mechanism, making it difficult to balance adaptability to confined spaces, high-temperature stability, and measurement accuracy. Consequently, they cannot achieve high-precision non-destructive assessment of the preload of small-diameter bolts under extreme conditions. Summary of the Invention

[0005] This summary section is provided to briefly introduce the concepts, which will be described in detail in the detailed description section below. This summary section is not intended to identify key or essential features of the claimed technical solution, nor is it intended to limit the scope of the claimed technical solution.

[0006] In a first aspect, this disclosure provides a bolt preload measurement system based on laser electromagnetic ultrasound, comprising a laser source, an ultrasonic probe, a signal conditioning module, a temperature module, a loading module, and a data processing module. The laser source generates a pulsed laser with preset output parameters. The pulsed laser is used to excite the bolt to generate ultrasonic waves via a thermoelastic mechanism. The ultrasonic probe includes a long-axis-shaped housing and an electromagnetic ultrasonic transducer unit. The housing contains an incident light path and an exit light path. The incident light path receives the pulsed laser light incident from the side of the housing along its axial direction. The exit light path extends parallel to the axial direction of the housing. The electromagnetic ultrasonic transducer unit... The signal conditioning module is located inside the housing and at the end of the emitted light path, which passes through the central hollow area of ​​the electromagnetic ultrasonic transducer. The signal conditioning module is used to preprocess the ultrasonic waves received by the electromagnetic ultrasonic transducer. The preprocessing includes at least amplification and filtering. The temperature module is used to acquire the bolt temperature of the bolt under test in real time. The loading module is used to apply an axial tensile load to the bolt under test when it is at thermal equilibrium temperature. The data processing module is used to acquire the flight time of the preprocessed ultrasonic waves and the tensile load, and calculate the preload of the bolt based on the flight time and the tensile load.

[0007] Secondly, this disclosure provides a method for measuring bolt preload, implemented using the aforementioned bolt preload measurement system based on laser electromagnetic ultrasound. The ultrasonic probe is fixed to the nut side of the bolt to be tested, and the outlet of the emitted optical path faces the end face of the nut side of the bolt to be tested. The laser source emits a pulsed laser with preset output parameters to the laser action area on the end face of the nut side of the bolt to be tested. The method includes: Obtain the temperature of the bolt to be tested; Determine whether the temperature of the bolt to be tested has reached the thermal equilibrium temperature; If so, ultrasonic signals are acquired in real time through the electromagnetic ultrasonic transducer unit; wherein, the ultrasonic signals include a first longitudinal wave signal formed when the bolt is in a stress-free state, and a second longitudinal wave signal and a first transverse wave signal formed when the bolt to be tested is subjected to axial tensile loads in stages. Obtain the type information of the bolt to be tested, and determine the type of the bolt to be tested based on the type information; If the bolt is in the assembly stage, then based on the obtained first longitudinal wave signal and second longitudinal wave signal, the longitudinal wave reference flight time of the bolt in the stress-free state and the first longitudinal wave flight time under each level of tensile load are obtained respectively. Calculate the first flight time difference between the first longitudinal wave flight time and the longitudinal wave reference flight time, and fit a first linear regression model between the first flight time difference and the preload under the corresponding tensile load based on the first flight time difference; Obtain the second longitudinal wave flight time of the longitudinal wave signal corresponding to the bolt assembly, and calculate the second flight time difference between the second longitudinal wave flight time and the longitudinal wave reference flight time; The preload of bolts during the assembly stage is obtained based on the first linear regression model and the second time-of-flight difference. If the bolt is already tightened and in service, then based on the obtained second longitudinal wave signal and first transverse wave signal, the flight time of the third longitudinal wave and the flight time of the first transverse wave of the bolt under each level of tensile load are obtained respectively. Calculate the first flight time ratio of the first transverse wave flight time to the third longitudinal wave flight time, and fit a second linear regression model between the first flight time ratio and the preload under the corresponding tensile load based on the first flight time ratio; Obtain the fourth longitudinal wave flight time of the longitudinal wave signal corresponding to the tightened in-service bolt and the second transverse wave flight time of the corresponding transverse wave signal, and calculate the second flight time ratio of the second transverse wave flight time to the fourth longitudinal wave flight time. The preload of the tightened bolts in service is obtained based on the second linear regression model and the second flight time ratio.

[0008] Thirdly, this disclosure provides a computer-readable medium having a computer program stored thereon, which, when executed by a processing device, implements the steps of the method described in the second aspect.

[0009] Fourthly, this disclosure provides an electronic device, comprising: A storage device on which computer programs are stored; A processing device for executing the computer program in the storage device to implement the steps of the method described in the second aspect.

[0010] The aforementioned technical solution employs an integrated ultrasonic probe structure combining axial side-incidence and coaxial side-incidence. Its slender shape allows it to penetrate narrow, enclosed, and deep-hole structures, enabling single-end-face detection and solving the problem of traditional probes being unable to fit into compact spaces such as those found in aircraft engines and artillery barrels. Simultaneously, it utilizes laser thermoelastic excitation and non-contact reception via an electromagnetic ultrasonic transducer unit, eliminating the need for coupling agents and minimizing susceptibility to high temperatures, vibrations, and electromagnetic interference. This makes it stably applicable to extreme conditions and difficult-to-test materials such as high-temperature alloys and titanium alloys. Furthermore, it supports bolt preload testing during assembly and in-service stages, covering the entire lifecycle testing needs of bolts.

[0011] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0012] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the originals and elements are not necessarily drawn to scale. In the drawings: Figure 1 This is a block diagram of a bolt preload measurement system based on laser electromagnetic ultrasound according to one embodiment of the present disclosure; Figure 2 This is a schematic diagram of the structure of an ultrasonic probe according to one embodiment of the present disclosure; Figure 3 This is a schematic diagram of the mechanism of laser-ultrasonic interaction between an ultrasonic probe and a bolt to be tested, according to one embodiment of the present disclosure. Figure 4 This is a schematic diagram of the mechanism of laser-ultrasonic interaction between an ultrasonic probe and a silver silicone grease coating on a bolt to be tested, according to one embodiment of the present disclosure. Figure 5 This is a flowchart of a bolt preload measurement method according to one embodiment of the present disclosure; Figure 6 A schematic diagram of the structure of an electronic device suitable for implementing embodiments of the present disclosure is shown. Detailed Implementation

[0013] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0014] It should be understood that the steps described in the method embodiments of this disclosure may be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of this disclosure is not limited in this respect.

[0015] The term "comprising" and its variations as used herein are open-ended inclusions, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Definitions of other terms will be given in the description below.

[0016] It should be noted that the concepts of "first" and "second" mentioned in this disclosure are used only to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies.

[0017] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0018] The names of messages or information exchanged between multiple devices in the embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of such messages or information.

[0019] It is understood that before using the technical solutions disclosed in the various embodiments of this disclosure, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in this disclosure in an appropriate manner in accordance with relevant laws and regulations, and user authorization should be obtained.

[0020] For example, upon receiving a user's active request, a prompt message is sent to the user to explicitly inform them that the requested operation will require the acquisition and use of the user's personal information. This allows the user to independently choose whether to provide personal information to the software or hardware, such as the electronic device, application, server, or storage medium performing the operations of this disclosed technical solution, based on the prompt message.

[0021] As an optional but non-limiting implementation, in response to a user's active request, sending a prompt message to the user can be done via a pop-up window, where the prompt message can be presented in text format. Furthermore, the pop-up window can also include a selection control allowing the user to choose "agree" or "disagree" to provide personal information to the electronic device.

[0022] It is understood that the above notification and user authorization process are merely illustrative and do not constitute a limitation on the implementation of this disclosure. Other methods that comply with relevant laws and regulations may also be applied to the implementation of this disclosure.

[0023] Meanwhile, it is understood that the data involved in this technical solution (including but not limited to the data itself, the acquisition or use of the data) shall comply with the requirements of relevant laws, regulations and related provisions.

[0024] refer to Figure 1 The present application provides a bolt preload measurement system based on laser electromagnetic ultrasound, which includes a laser source, an ultrasonic probe, a signal conditioning module, a temperature module, a loading module, and a data processing module.

[0025] Specifically, the laser source is used to generate a pulsed laser that satisfies the preset output parameters of the thermoelastic excitation mechanism. After the pulsed laser is incident perpendicularly on the end face of the bolt to be tested, it excites ultrasonic waves inside the bolt through the transient thermal expansion effect. The excited ultrasonic waves include transverse waves and longitudinal waves. At the same time, the laser power density is always lower than the surface damage threshold of the metal material of the bolt to be tested, so as to avoid irreversible ablation damage to the bolt to be tested.

[0026] The ultrasonic probe is the core integrated unit of the measurement system, reference Figure 2 The ultrasonic probe includes a housing 100 and an electromagnetic ultrasonic transducer unit 200. To accommodate the end face dimensions of small-diameter bolts such as M8 and M10, and to perform inspections within confined installation spaces such as turbine connections in aircraft engines and gun barrel bearings, the housing 100 is designed as an elongated shaft. For example, the housing 100 can be designed as a cylindrical structure and machined from aerospace-grade aluminum. Furthermore, to adapt to inspections under extreme conditions, such as high temperature, high pressure, and strong vibration, the housing 100 needs to be made of materials with high temperature resistance, high pressure resistance, and high structural strength, such as titanium alloy.

[0027] The housing 100 contains an incident light path 110 and an exit light path 120, which are refracted and shaped for focusing by built-in optical components. The incident light path 110 receives pulsed laser light from a laser source from the side of the housing 100 along its axial direction. The axial end of the housing 100 is the detection end face. The exit light path 120 extends parallel to the axial direction of the housing 100 and extends to the detection end face. During detection, the detection end face is parallel to and opposite to the end face of the bolt / nut side to be tested, maintaining a certain distance. Simultaneously, the pulsed laser light is incident perpendicularly to the center area of ​​the end face of the bolt to be tested, avoiding large measurement errors caused by oblique incidence of the pulsed laser light.

[0028] The electromagnetic ultrasonic transducer unit 200 is fixed inside the housing 100 and located near the end of the outgoing light path 120. After assembly, the electromagnetic ultrasonic transducer unit 200 is close to the detection end face of the housing 100 and maintains a certain distance. The electromagnetic ultrasonic transducer unit 200 has a hollowed-out middle section, which allows the outgoing light path 120 to completely pass through the hollowed-out area in the middle of the electromagnetic ultrasonic transducer unit 200, ensuring that the laser is incident on the end face of the bolt and nut to be tested without obstruction.

[0029] The temperature module collects the temperature of the bolt under test in real time, and it also works in real time with the data processing module. Collecting the bolt temperature helps determine whether the bolt has reached thermal equilibrium temperature after laser treatment, thus eliminating interference from temperature fluctuations. The temperature module can use a thermocouple temperature sensor, which can be attached to the shank of the bolt under test using a high-temperature adhesive.

[0030] It should be noted that the thermal equilibrium temperature is the steady-state temperature reached when the temperature of the bolt under test no longer continues to rise over time after being continuously excited by a pulsed laser.

[0031] The loading module applies a precise axial tensile load after the bolt under test reaches its thermal equilibrium temperature, and the loading module works in real time with the data processing module. Specifically, the loading module provides a precise axial stress reference for the calibration and modeling of the bolt's preload.

[0032] refer to Figure 3 During testing, the laser source outputs pulsed lasers with preset parameters. The pulsed lasers are transmitted to the ultrasonic probe via optical fiber. The ultrasonic probe converts the incident pulsed lasers into a focused beam that exits axially, exciting ultrasonic waves inside the bolt under test through a thermoelastic mechanism. Simultaneously, the probe receives the ultrasonic signals returned from inside the bolt through its integrated electromagnetic ultrasonic transducer 200. The electromagnetic ultrasonic transducer 200 converts the ultrasonic signals into weak electrical signals and sends them to the signal conditioning module for amplification, filtering, and other preprocessing before transmitting them to the data processing module. The data processing module simultaneously acquires the preprocessed electrical signals and real-time tensile load, extracts the time of flight (TOF) of the ultrasonic waves, and combines acoustoelastic theory with a pre-calibrated model to complete the quantitative calculation and output of the bolt preload.

[0033] It should be noted that the electromagnetic ultrasonic transducer unit 200 is only used to passively receive the ultrasonic waves generated by the pulsed laser acting on the bolt under test, and does not undertake the excitation function.

[0034] In some embodiments of the present invention, reference is made to... Figure 1 and Figure 2 The electromagnetic ultrasonic transducer unit 200 includes a ring-shaped permanent magnet 210 and a PCB coil 220, which are coaxially nested. The center of the electromagnetic ultrasonic transducer unit 200 forms a hollow area that matches the output light path 120. The aperture of the hollow area is slightly larger than the diameter of the collimated laser beam to ensure that the laser passes through without obstruction. The permanent magnet 210 can form a stable static magnetic field region.

[0035] In some embodiments of the present invention, the permanent magnet 210 may be made of high energy product permanent magnet materials such as N58 neodymium iron boron. Such permanent magnet materials can form a high magnetic flux density in the laser action area on the end face of the bolt and nut side of the bolt to be tested, which meets the detection requirements of low conductivity and small diameter bolts. At the same time, such permanent magnet materials can withstand high temperature environment, which can reduce the performance decay caused by high temperature demagnetization, thereby achieving the purpose of improving the magnetoacoustic conversion efficiency and receiving sensitivity of the electromagnetic ultrasonic transducer unit 200.

[0036] In some embodiments of the present invention, the PCB coil 220 has a multi-turn hollow spiral structure and is manufactured using a double-layer PCB process. The central aperture of the PCB coil 220 is aligned with the inner aperture of the permanent magnet 210, together forming the central hollow area of ​​the electromagnetic ultrasonic transducer unit 200. During operation, the PCB coil 220 can form a highly efficient coupling with the eddy current field on the surface of the bolt under test, receiving the induced electromotive force signal generated by ultrasonic vibration.

[0037] In some embodiments of the present invention, the electromagnetic ultrasonic transducer 200 is detachably connected to the housing 100, so that the permanent magnet 210 and the PCB coil 220 can be flexibly replaced according to the material properties (such as conductivity and attenuation coefficient) and size parameters of the object being tested, thus taking into account the needs of strong attenuation material testing and multiple application scenarios.

[0038] In some embodiments of the present invention, the signal conditioning module includes a differential gain amplifier circuit and a filter circuit. Specifically, the differential gain amplifier circuit can linearly amplify the weak electrical signal output by the electromagnetic ultrasonic transducer unit 200, while effectively suppressing common-mode electromagnetic interference generated by laser excitation and environmental power frequency interference. The filter circuit can filter out invalid signals such as laser impact noise, high-frequency electromagnetic clutter, and low-frequency vibration interference, retaining only the effective signal passbands of longitudinal and transverse waves propagating inside the bolt under test, thereby improving the signal-to-noise ratio.

[0039] In some embodiments of the present invention, the loading module may employ a hydraulic tensioning machine, which can achieve precise application and stable maintenance of gradient loads. Furthermore, during calibration, the preload can be acquired using an axial force sensor mounted on the hydraulic tensioning machine.

[0040] To maintain a consistent effective stress area, the hydraulic tensile testing machine can be equipped with coaxial clamping fixtures. These fixtures are designed according to the specifications of the bolts being tested; for example, a 30mm clamping fixture is used for an M10 Inconel 718 bolt (50mm long, 10mm diameter), and a 15mm clamping fixture is used for an M8 titanium alloy bolt (34mm long, 8mm diameter). Simultaneously, a dial indicator can be used to adjust the coaxiality of the hydraulic tensile testing machine to prevent the bolt from experiencing additional bending moments when tensile loads are applied, which could lead to uneven stress distribution and affect the fitting accuracy of the acoustoelastic model.

[0041] It should be noted that the axial load applied by the hydraulic tensioning machine needs to be set with reference to the actual service conditions of the bolts in the target structure. For example, the measurement load range set for M10 Inconel 718 bolts is 0~25kN, and the measurement load range set for M8 Inconel 718 bolts (50mm in length, 8mm in diameter) and M8 titanium alloy bolts is 0~15kN. Furthermore, the load points are set at predetermined small intervals (e.g., 1kN). At the same time, to meet the measurement accuracy requirements, it is necessary to ensure high load application accuracy, for example, controlling the load error within ±0.01kN.

[0042] In some embodiments of the present invention, the data processing module includes a high-speed data acquisition card and a control computer. Specifically, the high-speed data acquisition card can synchronously acquire the electrical signals output by the signal conditioning module to accurately acquire longitudinal wave signals and transverse wave signals, while the control computer can calculate the time of flight (TOF) of these two wave signals.

[0043] Reference Figure 2 In some embodiments of the present invention, the built-in optical component includes a reflector 300, which is located within the housing 100, and the incident light path 110 and the outgoing light path 120 intersect on the reflector surface of the reflector 300. For example, the reflector 300 is arranged such that the incident light path 110 and the outgoing light path 120 are perpendicular to each other.

[0044] During testing, the reflecting mirror can precisely refract the pulsed laser incident from the side of the housing 100 along the axial direction into an outgoing beam that propagates forward along the axial direction of the housing 100. The outgoing beam passes precisely through the hollowed-out area in the middle of the electromagnetic ultrasonic transducer unit 200 and then enters the center of the end face of the bolt and nut to be tested perpendicularly.

[0045] In this embodiment, the pulsed laser is incident radially from the side wall of the housing 100, so that there are no optical components at the tail of the ultrasonic probe, which can shorten the axial length of the ultrasonic probe and adapt to the limited depth and unavoidable installation constraints inside the equipment.

[0046] Reference Figure 2 In some embodiments of the present invention, the built-in optical components further include an optical fiber collimator 400, which is disposed within the incident optical path 110. Specifically, a radially arranged incident optical hole can be opened on the side wall of the housing 100, and a mounting base for fixing the optical fiber collimator 400 is provided in the incident optical hole. The mounting base is a coaxial positioning structure, which can ensure that the optical axis of the optical fiber collimator 400 is strictly coaxial with the optical axis of the incident optical path 110.

[0047] In this embodiment, the fiber collimator 400 can shape the divergent laser beam input from the fiber optic interface into a parallel beam that meets the measurement requirements and stably transmit it to the reflector surface of the reflector 300.

[0048] In some embodiments of the present invention, the pulsed laser has a wavelength of 532 nm, a pulse width of 8.3 ns, a beam diameter of 4 mm, a single pulse energy of 5.5 mJ, a repetition frequency of 100 Hz, and a beam diameter of 1.5 mm to 2 mm after being collimated by an optical fiber collimator 400.

[0049] Reference Figure 2 In some embodiments of the present invention, the built-in optical components also include a GRIN lens 500, which is disposed within the outgoing light path 120 and located between the reflector 300 and the electromagnetic ultrasonic transducer 200. The optical axis of the GRIN lens 500 is strictly coaxial with the outgoing light path 120.

[0050] In this embodiment, the parallel laser beam, after being deflected by the reflector 300, first enters the GRIN lens 500 for close-range focusing, and then passes through the central hollow area of ​​the electromagnetic ultrasonic transducer unit 200. It is then vertically incident on the end face of the bolt and nut side under test with a small spot and high energy density, which enhances the excitation intensity of thermoelastic ultrasonic waves, thereby enabling efficient excitation of ultrasonic waves under the thermoelastic mechanism.

[0051] refer to Figure 4 In some embodiments of the present invention, a silver grease coating 130 of a predetermined thickness is coated on the laser-acting area.

[0052] In this embodiment, the silver grease coating 130 has both good thermal conductivity and surface adhesion, and exhibits stable properties such as non-volatility, non-excessive oxidation, and non-corrosion of the bolt surface at high temperatures. When subjected to transient laser heating, the thermal expansion of the silver grease coating 130 can apply additional normal constraint pressure to the laser action area, thereby changing the boundary conditions of the bolt surface and concentrating the laser-induced thermoelastic deformation within a limited area, thus improving the excitation efficiency of the ultrasonic longitudinal wave.

[0053] Since a thin silver grease coating 130 has poor surface constraint effect, while a thick silver grease coating 130 will excessively absorb laser energy and cause signal attenuation, the thickness of the silver grease coating 130 is preferably 0.1~0.3mm to effectively balance the constraint effect and energy utilization rate, thereby improving the longitudinal wave amplitude and signal-to-noise ratio of bolts made of difficult-to-measure materials such as high-temperature alloys and titanium alloys, and laying a signal foundation for subsequent quantitative measurement.

[0054] refer to Figure 5This application provides a bolt preload measurement method, implemented using the aforementioned bolt preload measurement system based on laser electromagnetic ultrasound. The ultrasonic probe is fixed to the nut side of the bolt to be measured, and the outlet of the output optical path 120 faces the end face of the nut side of the bolt. The laser source emits a pulsed laser with preset output parameters to the laser action area on the end face of the nut side of the bolt. The measurement method includes steps S100 to S500: Step S100: Obtain the temperature of the bolt to be tested; Specifically, the temperature of the bolt under test is collected in real time by the temperature module, and the temperature data is uploaded to the data processing module in real time.

[0055] Step S200: The data processing module compares the real-time bolt temperature with the thermal equilibrium temperature to determine whether the temperature of the bolt under test has reached the thermal equilibrium temperature. If so, the ultrasonic signal is acquired in real time through the electromagnetic ultrasonic transducer 200; wherein, the ultrasonic signal includes the first longitudinal wave signal formed when the bolt is in a stress-free state, and the second longitudinal wave signal and the first transverse wave signal formed when the bolt to be tested is subjected to axial tensile load in stages. If the temperature of the bolt to be tested has not reached the thermal equilibrium temperature, continue to wait until the temperature of the bolt to be tested reaches the thermal equilibrium temperature.

[0056] In this step, the thermal equilibrium temperature is the steady-state temperature reached when the temperature of the bolt under test no longer rises over time after continuous pulsed laser excitation. Before reaching this thermal equilibrium temperature, the local heat generated by laser irradiation has not yet fully dissipated, resulting in a temperature gradient inside the bolt. This causes uneven changes in the ultrasonic wave propagation speed, leading to significant drift and errors in the time-of-flight (TOF) measurement. Therefore, the thermal equilibrium temperature is set as the trigger condition for data acquisition. The system only begins to acquire ultrasonic signals when the bolt temperature stabilizes at the thermal equilibrium temperature and remains in thermal equilibrium. This effectively eliminates the interference caused by temperature changes and temperature gradients on the TOF measurement, improving the accuracy, stability, and repeatability of the preload calculation results. This allows the measurement method to be stably adapted to extreme operating conditions with high temperature, variable temperature, and large temperature fluctuations, such as those found in aircraft engines and artillery barrels.

[0057] Step S300: Obtain the type information of the bolt to be tested, and determine the type of the bolt to be tested based on the type information; In this step, the data processing module can obtain the type information of the bolt to be tested based on pre-input (e.g., user input) or automatic identification (e.g., through image recognition). The type information includes: bolts in the assembly stage (bolts not yet in service, which can be subjected to stress-free reference and graded loads) and bolts already fastened in service (bolts that have been assembled into the equipment structure, cannot be disassembled, and cannot provide stress-free reference).

[0058] Step S400: If it is a bolt in the assembly stage, then based on the obtained first longitudinal wave signal and second longitudinal wave signal, the longitudinal wave reference flight time when the bolt is under no preload and the first longitudinal wave flight time under each level of tensile load are obtained respectively. Calculate the time difference between the first P-wave flight time and the P-wave reference flight time; A first linear regression model between the first flight time difference and the preload under the corresponding tensile load is fitted based on the first flight time difference and the preload. The first linear regression model is fitted using the following formula:

[0059] Where σ is the preload force borne by the bolt under the corresponding tensile load. The ultrasonic flight time is the time of flight of the ultrasonic waves generated when the bolt under test is subjected to a preload σ. The ultrasonic flight time is the time of flight of the ultrasonic waves generated by the bolt under test when there is no preload. The effective clamping length is the length of the bolt under test when it is subjected to a preload force σ. This is the effective clamping length of the bolt under test when there is no preload. Let be the Young's modulus of the material used to manufacture the bolt to be tested. The acoustoelastic coefficient of the bolt under test to ultrasonic waves; It should be noted that the acoustoelastic coefficient is a material parameter, and it needs to be recalibrated when the material grade, structural dimensions, and clamping length change. Specifically, The stress calibration coefficient of the bolt under test is obtained by fitting different preloads σ and their corresponding first flight time differences.

[0060] Obtain the second longitudinal wave flight time of the longitudinal wave signal corresponding to the bolt assembly, and calculate the second flight time difference between the second longitudinal wave flight time and the longitudinal wave reference flight time; The preload of bolts in the assembly stage is obtained based on the first linear regression model and the difference between the second flight time. Specifically, the difference between the second flight time and the first linear regression model are substituted into the first model to directly calculate and output the preload of bolts in the current assembly stage.

[0061] Step S500: If the bolt is already tightened and in service, then based on the obtained second longitudinal wave signal and first transverse wave signal, the third longitudinal wave flight time and the first transverse wave flight time of the bolt under each level of tensile load are obtained respectively. Calculate the ratio of the first flight time of the first transverse wave to the first flight time of the third longitudinal wave; A second linear regression model between the first flight time ratio and the preload under the corresponding tensile load is fitted: The second linear regression model is fitted using the following formula:

[0062] in, The reference flight time of the transverse wave formed by the bolt under test without preload is given. The reference flight time of the longitudinal wave formed by the bolt under test without preload is given. The transverse wave flight time is the transverse wave formed by the bolt under test when it is subjected to a preload σ. Let be the flight time of the longitudinal wave formed by the bolt under test when it is subjected to a preload σ. Let be the acoustoelastic coefficient of the bolt under test with respect to longitudinal waves. is the acoustoelastic coefficient of the bolt under test to the transverse wave; It should be noted that the slope and intercept All of these are calibration coefficients to be determined, obtained by fitting different preload σ and the ratio of their corresponding longitudinal wave flight time to transverse wave flight time.

[0063] Obtain the fourth longitudinal wave flight time of the longitudinal wave signal corresponding to the tightened in-service bolt and the second transverse wave flight time of the corresponding transverse wave signal, and calculate the second flight time ratio of the second transverse wave flight time to the fourth longitudinal wave flight time. The preload of bolts already tightened in service is obtained based on the second linear regression model and the ratio of the second flight time. Specifically, the second flight time ratio is substituted into the second linear regression model to directly calculate and output the preload of bolts currently tightened in service.

[0064] In some embodiments of the present invention, the flight time of the first longitudinal wave, the flight time of the third longitudinal wave, and the flight time of the first transverse wave under each axial tensile load are measured repeatedly multiple times, and then the average value of the multiple measurements is taken. This can improve the fitting accuracy of the first linear regression model and the second linear regression model.

[0065] refer to Figure 6 The diagram illustrates a structural schematic of an electronic device 600 (e.g., a terminal device or a server) suitable for implementing embodiments of the present disclosure. The terminal device in the embodiments of the present disclosure may include, but is not limited to, mobile terminals such as mobile phones, laptops, digital broadcast receivers, PDAs (personal digital assistants), PADs (tablet computers), PMPs (portable multimedia players), and in-vehicle terminals (e.g., in-vehicle navigation terminals), as well as fixed terminals such as digital TVs and desktop computers. Figure 6The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of the embodiments disclosed herein.

[0066] like Figure 6 As shown, electronic device 600 may include a processing unit (e.g., a central processing unit, a graphics processing unit, etc.) that can perform various appropriate actions and processes according to a program stored in ROM or a program loaded into RAM from a storage device. The RAM also stores various programs and data required for the operation of electronic device 600. The processing unit, ROM, and RAM are interconnected via bus 604, and I / O interfaces are also connected to bus 604.

[0067] Typically, the following devices can be connected to an I / O interface: input devices such as touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices such as liquid crystal displays (LCDs), speakers, vibrators, etc.; storage devices such as magnetic tapes, hard drives, etc.; and communication devices. Communication devices allow electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 6 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown. More or fewer devices may be implemented or have alternatively.

[0068] In particular, according to embodiments of this disclosure, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this disclosure include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program including instructions for performing the processes. Figure 5 The program code for the method shown. In such an embodiment, the computer program can be downloaded and installed from a network via a communication device, or installed from a storage device, or installed from a ROM. When the computer program is executed by a processing device, it performs the functions defined in the method of this disclosure embodiment.

[0069] It should be noted that the computer-readable medium described in this disclosure can be a computer-readable signal medium or a computer-readable storage medium, or any combination thereof. A computer-readable storage medium can be, for example,—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of a computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, RAM, ROM, an erasable programmable read-only memory, an optical fiber, a portable compact disk read-only memory, an optical storage device, a magnetic storage device, or any suitable combination thereof. In this disclosure, a computer-readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. In this disclosure, a computer-readable signal medium can include a data signal propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium other than a computer-readable storage medium, which can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the computer-readable medium can be transmitted using any suitable medium, including but not limited to: wires, optical fibers, radio frequencies, or any suitable combination thereof.

[0070] In some implementations, clients and servers can communicate using any currently known or future-developed network protocol such as HTTP (Hypertext Transfer Protocol), and can interconnect with digital data communication (e.g., communication networks) of any form or medium. Examples of communication networks include local area networks (LANs), wide area networks (WANs), the Internet, and peer-to-peer networks, as well as any currently known or future-developed networks.

[0071] The aforementioned computer-readable medium may be included in the aforementioned electronic device; or it may exist independently and not assembled into the electronic device.

[0072] The aforementioned computer-readable medium carries one or more programs that, when executed by the electronic device, cause the electronic device to: Obtain the temperature of the bolt to be tested; Determine whether the temperature of the bolt to be tested has reached the thermal equilibrium temperature; If so, ultrasonic signals are acquired in real time through the electromagnetic ultrasonic transducer unit; wherein, the ultrasonic signals include a first longitudinal wave signal formed when the bolt is in a stress-free state, and a second longitudinal wave signal and a first transverse wave signal formed when the bolt to be tested is subjected to axial tensile loads in stages. Obtain the type information of the bolt to be tested, and determine the type of the bolt to be tested based on the type information; If the bolt is in the assembly stage, then based on the obtained first longitudinal wave signal and second longitudinal wave signal, the longitudinal wave reference flight time of the bolt in the stress-free state and the first longitudinal wave flight time under each level of tensile load are obtained respectively. Calculate the first flight time difference between the first longitudinal wave flight time and the longitudinal wave reference flight time, and fit a first linear regression model between the first flight time difference and the preload under the corresponding tensile load based on the first flight time difference; Obtain the second longitudinal wave flight time of the longitudinal wave signal corresponding to the bolt assembly, and calculate the second flight time difference between the second longitudinal wave flight time and the longitudinal wave reference flight time; The preload of bolts during the assembly stage is obtained based on the first linear regression model and the second time-of-flight difference. If the bolt is already tightened and in service, then based on the obtained second longitudinal wave signal and first transverse wave signal, the flight time of the third longitudinal wave and the flight time of the first transverse wave of the bolt under each level of tensile load are obtained respectively. Calculate the first flight time ratio of the first transverse wave flight time to the third longitudinal wave flight time, and fit a second linear regression model between the first flight time ratio and the preload under the corresponding tensile load based on the first flight time ratio; Obtain the fourth longitudinal wave flight time of the longitudinal wave signal corresponding to the tightened in-service bolt and the second transverse wave flight time of the corresponding transverse wave signal, and calculate the second flight time ratio of the second transverse wave flight time to the fourth longitudinal wave flight time. The preload of the tightened bolts in service is obtained based on the second linear regression model and the second flight time ratio.

[0073] Computer program code for performing the operations of this disclosure can be written in one or more programming languages ​​or a combination thereof, including but not limited to object-oriented programming languages ​​such as Java, Smalltalk, and C++, as well as conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including local area networks (LANs) or wide area networks (WANs), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0074] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0075] The functions described above in this document can be performed at least in part by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), system-on-a-chip (SoCs), complex programmable logic devices (CPLDs), etc.

[0076] In the context of this disclosure, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, RAM, ROM, erasable programmable read-only memory, optical fibers, portable compact disk read-only memory, optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0077] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

[0078] Furthermore, while the operations are described in a specific order, this should not be construed as requiring these operations to be performed in the specific order shown or in a sequential order. In certain environments, multitasking and parallel processing may be advantageous. Similarly, while several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of this disclosure. Certain features described in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments.

[0079] Although the subject matter has been described using language specific to structural features and / or methodological logic, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are merely illustrative forms of implementing the claims. Regarding the apparatus in the above embodiments, the specific manner in which the various modules perform their operations has been described in detail in the embodiments relating to the method, and will not be elaborated upon here.

Claims

1. A laser electromagnetic acoustic pulse based bolt pre-load measurement system, characterized in that, include: A laser source capable of generating pulsed laser with preset output parameters, the pulsed laser being used to excite the bolt to generate ultrasonic waves using a thermoelastic mechanism; An ultrasonic probe includes a long-axis shaped housing and an electromagnetic ultrasonic transducer unit. The housing has an incident light path and an exit light path. The incident light path is used to receive pulsed laser light incident from the side of the housing in the axial direction. The exit light path extends parallel to the axial direction of the housing. The electromagnetic ultrasonic transducer unit is disposed in the housing and near the end of the exit light path. The exit light path passes through the hollow area in the middle of the electromagnetic ultrasonic transducer unit. The signal conditioning module is used to preprocess the ultrasonic waves received by the electromagnetic ultrasonic transducer unit, and the preprocessing includes at least amplification processing and filtering processing. Temperature module, used to acquire the bolt temperature of the bolt under test in real time; The loading module is used to apply an axial tensile load to the bolt under test when the bolt is at thermal equilibrium temperature. The data processing module is used to acquire the flight time of the preprocessed ultrasonic wave and the tensile load, and to calculate the preload of the bolt under test based on the flight time and the tensile load.

2. The laser electromagnetic acoustic based bolt pre-load measurement system of claim 1, wherein, The ultrasonic probe also includes a reflector, which is located inside the housing, and the incident light path and the outgoing light path intersect on the reflector surface.

3. The laser electromagnetic acoustic based bolt pre-load measurement system of claim 1, wherein, The ultrasonic probe also includes an optical fiber collimator, which is located within the incident optical path.

4. The laser electromagnetic acoustic based bolt pre-load measurement system of claim 1, wherein, The ultrasonic probe also includes a GRIN lens, which is disposed within the outgoing optical path.

5. The bolt preload measurement system based on laser electromagnetic ultrasound according to claim 3, characterized in that, The pulsed laser has a wavelength of 532nm, a pulse width of 8.3ns, a beam diameter of 4mm, a single pulse energy of 5.5mJ, a repetition frequency of 100Hz, and a beam diameter of 1.5mm~2mm after being collimated by the fiber collimator.

6. A method for measuring bolt preload, characterized in that, The bolt preload measurement system based on laser electromagnetic ultrasound as described in any one of claims 1 to 5 is used, wherein the ultrasonic probe is fixed to the nut side of the bolt to be tested, and the outlet of the emitted optical path is directly facing the end face of the nut side of the bolt to be tested; the laser source emits a pulsed laser with preset output parameters to the laser action area on the end face of the nut side of the bolt to be tested; the method includes: Obtain the temperature of the bolt to be tested; Determine whether the temperature of the bolt to be tested has reached the thermal equilibrium temperature; If so, ultrasonic signals are acquired in real time through the electromagnetic ultrasonic transducer unit; wherein, the ultrasonic signals include a first longitudinal wave signal formed when the bolt is in a stress-free state, and a second longitudinal wave signal and a first transverse wave signal formed when the bolt to be tested is subjected to axial tensile loads in stages. Obtain the type information of the bolt to be tested, and determine the type of the bolt to be tested based on the type information; If the bolt is in the assembly stage, then based on the obtained first longitudinal wave signal and second longitudinal wave signal, the longitudinal wave reference flight time of the bolt in the stress-free state and the first longitudinal wave flight time under each level of tensile load are obtained respectively. Calculate the first flight time difference between the first longitudinal wave flight time and the longitudinal wave reference flight time, and fit a first linear regression model between the first flight time difference and the preload under the corresponding tensile load based on the first flight time difference; Obtain the second longitudinal wave flight time of the longitudinal wave signal corresponding to the bolt assembly, and calculate the second flight time difference between the second longitudinal wave flight time and the longitudinal wave reference flight time; The preload of bolts during the assembly stage is obtained based on the first linear regression model and the second time-of-flight difference. If the bolt is already tightened and in service, then based on the obtained second longitudinal wave signal and first transverse wave signal, the flight time of the third longitudinal wave and the flight time of the first transverse wave of the bolt under each level of tensile load are obtained respectively. Calculate the first flight time ratio of the first transverse wave flight time to the third longitudinal wave flight time, and fit a second linear regression model between the first flight time ratio and the preload under the corresponding tensile load based on the first flight time ratio; Obtain the fourth longitudinal wave flight time of the longitudinal wave signal corresponding to the tightened in-service bolt and the second transverse wave flight time of the corresponding transverse wave signal, and calculate the second flight time ratio of the second transverse wave flight time to the fourth longitudinal wave flight time. The preload of the tightened bolts in service is obtained based on the second linear regression model and the second flight time ratio.

7. The bolt preload measurement method according to claim 6, characterized in that, The first linear regression model is fitted using the following formula: Where σ is the preload force borne by the bolt under the corresponding tensile load. The ultrasonic flight time is the time of flight of the ultrasonic waves generated when the bolt under test is subjected to a preload σ. The ultrasonic flight time is the time of flight of the ultrasonic waves generated by the bolt under test when there is no preload. The effective clamping length is the length of the bolt under test when it is subjected to a preload force σ. This is the effective clamping length of the bolt under test when there is no preload. Let be the Young's modulus of the material used to manufacture the bolt to be tested. is the acoustoelastic coefficient of the bolt under test to ultrasonic waves.

8. The bolt preload measurement method according to claim 6, characterized in that, The second linear regression model is fitted using the following formula: in, The reference flight time of the transverse wave formed by the bolt under test without preload is given. The reference flight time of the longitudinal wave formed by the bolt under test without preload is given. The transverse wave flight time is the transverse wave formed by the bolt under test when it is subjected to a preload σ. Let be the flight time of the longitudinal wave formed by the bolt under test when it is subjected to a preload σ. Let be the acoustoelastic coefficient of the bolt under test with respect to longitudinal waves. is the acoustoelastic coefficient of the bolt under test to the transverse wave.

9. A computer-readable medium having a computer program stored thereon, characterized in that, When the program is executed by the processing device, it implements the steps of the method as described in any one of claims 6 to 8.

10. An electronic device, characterized in that, include: A storage device on which computer programs are stored; A processing device for executing the computer program in the storage device to implement the steps of the method as claimed in any one of claims 6 to 8.

Images