Thermal control system and thermal control method of vibration and sound modulation signal of bolt connection and computer system

Abstract

The present invention discloses a thermal control system and method for the vibration and acoustic modulation signal of a bolted joint, and a computer system. The system comprises: a temperature monitoring module that monitors the temperature of the bolted joint; a thermal control module that heats the bolted joint to control the local temperature of the joint to a target value under different working conditions; a signal excitation module that transmits two continuous high- and low-frequency sinusoidal wave signals to an exciter and a piezoelectric ceramic actuator to generate high- and low-frequency acoustic waves; a signal receiving module that receives the vibration and acoustic modulation signal caused by the mixing of the two excitation signals; and a signal post-processing module that performs spectrum analysis and establishes a nonlinear index by comparing the amplitude of the modulated harmonics to the amplitude of the low-frequency fundamental wave and the amplitude of the high-frequency fundamental wave. The relative magnitude of the nonlinear index represents the degree of bolt loosening. The present invention has the advantage of regulating the characteristics of the vibration and acoustic modulation response signal by proposing a local temperature increase or decrease at the bolted joint, thereby changing the thermo-elasto-plastic contact conditions in the bolted joint area.

Description

Technical Field

[0001] The present invention relates to the fields of instrumentation technology, mechanical engineering technology, and construction engineering technology, and in particular to a thermal control system and method for vibration and sound modulation signals of a bolt connection, and a computer system. Background Art

[0002] The statements in this section merely provide background technology related to the present application and do not necessarily constitute prior art.

[0003] The vibration-acoustic modulation signal is a nonlinear acoustic measurement signal. The modulation and decoupling characteristics of this signal are used for non-destructive testing projects such as measuring structural stress changes and crack development. In the field of bolt loosening, this method generates two incident signals, a low-frequency vibration wave and a high-frequency detection wave, by exciting the bolt connection structure. The nonlinear acoustic modulation signal caused by these signals in the structure is then used to monitor and identify the residual preload of the bolt. When the bolt connection is loose, obvious modulated harmonics will be generated under the excitation of vibration-acoustic modulation. The amplitude ratio of the modulated harmonics to the fundamental wave (i.e., the nonlinear index) is usually used as an indicator to evaluate the degree of bolt loosening. In theory, the nonlinear index will show a downward trend as the bolt preload increases.

[0004] In 2018, Zhen Zhang, Menglong Liu, Yaozhong Liao, Zhongqing Su, and Yi Xiao published "Contact acoustic nonlinearity (CAN)-based continuous monitoring of bolt loosening: Hybrid use of high-order harmonics and spectral sidebands" (Mechanical Systems and Signal Processing, 2018, 103:280-294). They established a mechanical relationship between vibroacoustic modulation characteristics and bolt loosening based on elastic contact theory. The study showed that the nonlinear index increases monotonically with decreasing bolt residual torque. However, in the early stages of bolt loosening, due to the high residual torque, the nonlinear index of vibroacoustic modulation is relatively insensitive to changes.

[0005] In 2021, Jiang Mingshun, Qin Xiaoshu, Jia Lei, Zhang Lei, Zhang Faye, Sui Qingmei, and Lü Shanshan published a paper titled "Detecting Early Loosening of Carbon Fiber Composite Bolts Based on Nonlinear Acoustic Modulation" (CN202110192614.4). This paper selected the most suitable excitation frequency through frequency sweep testing, improving the nonlinear response strength and the effectiveness of early identification of bolt loosening. The study showed that the nonlinear characteristics of vibroacoustic modulation exhibit nonmonotonic variations at different bolt stress stages, making misjudgment during structural stress measurement more likely.

[0006] In 2024, Jianbin Li, Bo Wen, Zhen Zhang, Qian Li, Yi He, and Zhongqing Su published "Interface Behaviors of Elastic-plastic Waves and Its Impact on Uncertainties in Vibro-acoustic Modulation (VAM) for Structural Health Monitoring (SHM) of Bolt Loosening" (Mechanical Systems and Signal Processing, 2024, 212:111268). This paper proposed an elastic-plastic theoretical model for the early relaxation stage of bolts, explaining the nonmonotonic variation of the modulation signal during bolt loosening. The study showed that when the preload in a bolted connection exceeds a certain value, plastic deformation occurs at the microscopic contact surface, and the nonlinear response of the vibro-acoustic modulation is significantly enhanced at both high and low stress stages compared to the intermediate stress stage.

[0007] Currently, there is a lack of effective means to actively control the sensitivity drop caused by reduced intensity and monotonicity of the vibroacoustic modulation signal during bolt loosening monitoring. This paper proposes a thermal control system for vibroacoustic modulation signals to improve the active modulation signal intensity and monotonicity, thereby improving the sensitivity of bolt stress loosening measurements. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to propose a thermal control system, a thermal control method and a computer system for the vibration and acoustic modulation signal of a bolt connection. In order to solve the problem that the sensitivity of the vibration and acoustic modulation signal decreases during the early relaxation of the bolt, the contact acoustic thermal modulation effect is introduced to change the correlation curve between the nonlinear index of the vibration and acoustic modulation used as a damage indicator and the bolt preload, thereby improving the non-monotonic behavior of the vibration and acoustic modulation of bolt loosening and enhancing its sensitivity to monitoring residual torque changes.

[0009] In order to solve the above technical problems, the present invention proposes a thermal control system and method for the vibration and acoustic modulation signal of a bolted connection, and a computer system. The basic derivation of its theoretical basis includes:

[0010] Step 1: The residual torque N of the bolted joint and the normal contact pressure generated on the contact surface p Expressed as:

[0011] ;

[0012] in τ is the friction coefficient, d is the bolt diameter, S is the contact area;

[0013] Step 2: Assemble the contact pressure by introducing a thermal control system P In addition, thermal expansion also produces temperature stress P t , and its pressure change is P 0 : ;

[0014] Thermal elastic deformation of connected plates and bolts for: ;in, α 1 and α 2 are the coefficients of thermal expansion at two temperatures, T 1 and T 0 It's different temperatures, L is the thickness;

[0015] The resulting change in preload is p t : ;in: k 1 and k 2 is the material stiffness of the bolt and the connected plate;

[0016] Step 3: Establish a contact stiffness model: ;in: K 1 * is the linear contact stiffness, C is the proportionality constant, m 0 is the initial roughness coefficient, n is the roughness softening coefficient;

[0017] This model introduces the -np 0 " is used to describe the elastic-plastic softening effect of the interface under pressure growth. n = 0, it degenerates into the elastic Hertz contact model, that is: ;

[0018] Step 4: According to the definition of Taylor expansion, the linear contact stiffness K 1 * Taking the derivative yields the nonlinear contact stiffness: ;

[0019] Step 5: Substitute the above linear and nonlinear stiffness expressions into the governing equations of vibroacoustic modulation: ;in: M It's quality, x is the vibration displacement, is the acceleration, t It's time, φ is the perturbation parameter, ω 1 and ω 2 is the circular frequency of the two excitation signals, A 1 and A 2 is the excitation amplitude;

[0020] Step 6: The analytical solution of the signal is obtained by perturbation method:

[0021] ;

[0022] ;

[0023] ;

[0024] ;

[0025] in, X LF is the low-frequency fundamental displacement, X HF is the high-frequency fundamental wave displacement, and the two columns of signals belong to the linear component; X LS and X RS is the left and right sideband displacement, which is a nonlinear component; A LF is the low-frequency fundamental amplitude, A HF is the high-frequency fundamental wave amplitude, and the two columns of signals belong to the linear component; ALS and A RS are the left and right sideband amplitudes;

[0026] Step 7: Construct a nonlinear index by the ratio of the amplitude of the nonlinear component to the amplitude of the linear component β：

[0027] ;

[0028] Since the contact stiffness is also affected by the bolt preload N and temperature T By changing the temperature of the connection part, the nonlinear index β , enhance the preload monitoring effect.

[0029] The technical problem to be solved by the present invention is to provide a thermal control system for vibration and acoustic modulation signals of bolted joints, comprising:

[0030] Temperature monitoring module: Infrared thermal imager monitors the temperature of bolt connection parts;

[0031] Thermal control module: A heating resistor with a heating function is attached to the bolt connection or a hot air blower is used to heat the bolt connection part to control the local temperature of the connection part to the target value under different working conditions;

[0032] Signal excitation module: A dual-channel signal generator outputs two continuous high-frequency sine wave signals and a low-frequency sine wave signal. The low-frequency signal is transmitted through an amplifying circuit to an exciter bonded to the bolted object, causing low-frequency vibration of the bolted connection. The high-frequency signal is transmitted through a circuit to a piezoelectric ceramic actuator bonded to the bolted object, generating high-frequency sound waves.

[0033] Signal receiving module: The two excitation signals output by the signal excitation module are mixed in the bolted joint, and the vibration and sound modulation signals are received by the acceleration sensor attached to the surface of the bolted object.

[0034] Signal post-processing module: The signal received by the acceleration sensor is transmitted to the oscilloscope through the circuit for observation and storage, and is exported for spectrum analysis. The nonlinear index is established by modulating the harmonic amplitude ratio of the low-frequency fundamental wave and the high-frequency fundamental wave amplitude. β , using the nonlinear index β The relative size of the value represents the degree of loosening of the bolt.

[0035] The thermal control method of the thermal control system of the vibration and acoustic modulation signal of the bolt connection part comprises the following steps:

[0036] Step S1: completing the pre-tightening assembly of the bolt connection;

[0037] Step S11: adjusting the setting value of the torque wrench according to the preload target value of the engineering design, and putting the torque wrench on the bolt head;

[0038] Step S12: Connect the two metal / composite connectors with bolts, and evenly rotate the torque wrench clockwise until the set pre-tightening force target value is reached; check the bolts to ensure that the bolts have reached the predetermined tightening torque;

[0039] Step S2: changing the local ambient temperature of the bolt connection part to stimulate the thermal regulation effect of the connection interface;

[0040] Step S21: Install an infrared thermal imager within 1 to 3 meters of the bolt to clearly monitor the temperature of the bolt connection; adjust the focus and angle of the thermal imager to obtain the best temperature monitoring effect;

[0041] Step S22: Select a heating device according to the set control temperature to uniformly heat the bolt connection part; monitor the temperature reading of the infrared thermal imager in real time, and gradually adjust the power and heating time of the heating device to ensure that the local temperature reaches the set control temperature;

[0042] The heating device is a heating resistor or a hot air gun; the heating resistor is fixed to the bolt connection part to uniformly heat the bolt connection part, or a hot air gun is used to uniformly heat the bolt connection part;

[0043] Step S23: Continuously monitor the temperature of the bolted joint to ensure that the temperature is stable within the designed control range. If the temperature deviates from the target range, immediately adjust the heating equipment, recalibrate the temperature, record the temperature reading of the infrared thermal imager and the operating parameters of the heating equipment, and save all relevant data for subsequent analysis and verification.

[0044] Step S3: Conducting vibration and acoustic modulation signal monitoring under thermal control to complete health monitoring of the early loosening process of the bolt;

[0045] Step S31: The dual-channel signal generator outputs two continuous high-frequency sinusoidal wave signals and a low-frequency sinusoidal wave signal. The low-frequency signal is transmitted through an amplifying circuit to an exciter bonded to the metal / composite connector to induce low-frequency vibration of the bolt connector. The high-frequency signal is transmitted through the circuit to a piezoelectric ceramic actuator bonded to the metal / composite connector to generate high-frequency sound waves.

[0046] Step S32: The two continuous high-frequency sine wave signals and the low-frequency sine wave signals are mixed in the bolted joint and induce a vibration-acoustic modulation signal, which is then received by an acceleration sensor attached to the surface of the metal / composite joint;

[0047] Step S33: The signal received by the acceleration sensor is transmitted to the oscilloscope through the circuit for observation and storage, and is derived for spectrum analysis. The nonlinear index is calculated by the ratio of the measured modulation harmonic amplitude to the low-frequency fundamental wave and the high-frequency fundamental wave amplitude. β , the formula is as follows:

[0048] ;

[0049] Nonlinear index β It is a commonly used damage judgment index in nonlinear acoustics: theoretically, if the bolt connection is in good contact, its nonlinear stiffness K 2 * will infinitely approach 0, corresponding to β is approximately equal to 0; due to the exponential characteristics of the Hertz contact stiffness model, as the bolt loosens more or the material plasticity accumulates, β Increase exponentially.

[0050] However, since Hertz contact changes exponentially, when the temperature effect is not considered and only static contact is considered, β The same amplitude change does not occur during the process of equal change of bolt preload, resulting in a non-sensitive range in the damage monitoring results. In addition, high stress state is prone to cause plastic accumulation on the contact surface, making the bolt loosening process monotonically β The phenomenon of non-monotonic changes occurs, which interferes with the judgment of the detection personnel.

[0051] The present invention also provides a computer system comprising a memory, a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the thermal control method for regulating the vibration and acoustic modulation signal of a bolted connection.

[0052] Therefore, the present invention proposes a vibration-acoustic modulation theory that takes thermal effects into account and introduces the temperature T As a pair β The new influencing factors are to change the local temperature change of the connection interface by artificially controlling the connection interface. β The range of change, β In the specific torque change range, there are still large changes and no non-monotonic changes. Finally, the nonlinear index is used to β The relative size of the value represents the degree of loosening of the bolt.

[0053] The beneficial effects of the present invention are: by proposing to regulate the local temperature increase or decrease of the bolt connection, the thermo-elasto-plastic contact conditions of the bolt connection area are changed, thereby achieving the purpose of regulating the characteristics of the vibration-acoustic modulation response signal, specifically:

[0054] (1) Regulate the amplitude of the nonlinear signal sideband to make the nonlinear index in the specific torque range of the bolt at room temperatureβ The sensitivity change increases by 2 to 3 times, thereby improving the monitoring accuracy and detectability of bolt loosening;

[0055] (2) Enhance or suppress the contribution ratio of the nonlinear sound source to the nonlinear modulation behavior, so that the nonlinear index in the specific torque range of the bolt at room temperature is β The value only increases or decreases as the bolts loosen, suppressing non-monotonic fluctuations.

[0056] (3) Used to construct a signal control system to enhance the sensitivity of vibration-acoustic modulation signals in the measurement of structural bolt stress in civil engineering, construction, machinery, aviation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 Schematic diagram of the equipment layout of the bolt connection in the thermal control vibration and sound modulation system in a specific embodiment of the present invention;

[0058] Figure 2 This is an image of the local ambient temperature of a bolt connection under monitoring by an infrared thermal imager according to a specific embodiment of the present invention;

[0059] Figure 3 This is a spectrum diagram obtained by vibration and sound modulation at 20°C when the bolt torque is 15 N·M according to a specific embodiment of the present invention;

[0060] Figure 4 This is a spectrum diagram obtained by vibration and sound modulation at 30°C when the bolt torque is 15 N·M according to a specific embodiment of the present invention;

[0061] Figure 5 This is a graph showing the change of nonlinear index during bolt loosening measured by vibration and acoustic modulation under different bolt torques and temperature controls according to a specific embodiment of the present invention;

[0062] Description of the marks in the figure:

[0063] 1—Metal / composite connector; 2—bolt;

[0064] 3—heating resistor; 4—infrared thermal imager;

[0065] 5—Signal generator; 6—Amplifier;

[0066] 7—piezoelectric ceramic actuator; 8—vibrator;

[0067] 9—Acceleration sensor; 10—Oscilloscope. DETAILED DESCRIPTION

[0068] The specific embodiment of the present invention is described in detail by taking a carbon fiber composite material (CFRP) bolt as an example.

[0069] It should be noted that the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0070] The present invention provides a thermal control method and computer system for a thermal control system of a vibration-acoustic modulation signal of a bolted connection, comprising the following steps:

[0071] Step S1: Figure 1 As shown, the pre-tightening assembly of the metal / composite connector 1 is completed, and the infrared thermal imager 4 is installed within 1 to 3 meters of the bolt 2. The infrared thermal imager 4 clearly monitors the temperature of the connection part of the bolt 2; the heating resistor 3 or the hot air blower is used to heat the connection part of the bolt 2. Figure 2 As shown, the brightness of the bolt 2 connection part corresponds to the temperature scale on the far right of the monitoring screen, and the local temperature value of the bolt connection part is read out. The heating resistor 3 or the hot air blower is adjusted to control the local temperature to the target value under different working conditions.

[0072] Step S2: A dual-channel signal generator 5 is used to output two continuous high-frequency and low-frequency sinusoidal wave signals, which are amplified by an amplifier 6. The low-frequency signal is transmitted to an exciter 8 bonded to one metal / composite connector 1 to induce low-frequency vibration at the connection portion of the bolt 2. The high-frequency signal is transmitted through a circuit to a piezoelectric ceramic actuator 7 bonded to another metal / composite connector 1 to generate high-frequency sound waves.

[0073] Step S3: The two excitation signals are mixed at the connection part of the bolt 2 and induce a vibration-acoustic modulation signal which is then received by the acceleration sensor 9 attached to the surface of the metal / composite connector 1;

[0074] Step S4: The signal received by the acceleration sensor 9 is transmitted to the oscilloscope 10 through the circuit for observation and storage, and is derived for spectrum analysis. The nonlinear index is established by the ratio of the amplitude of the modulated harmonics to the amplitude of the low-frequency fundamental wave and the high-frequency fundamental wave. β ;

[0075] Step S5: Within the working temperature range of the bolt 2, adjust the temperature of the heating resistor 3 in step S1 to different values, repeat the vibration and sound modulation measurement process from step S2 to step S4, and adjust the characteristic intensity of the vibration and sound modulation signal under the same pre-tightening torque. Figure 3 is the amplitude of the vibration sound modulation spectrum measured at 20 degrees and 15N·m, Figure 4 It is the amplitude of the vibration sound modulation spectrum measured at 30 degrees and 15 N·m;

[0076] Step 6: Finally, draw and obtain the nonlinear parameter change curve of bolt 2 under different local ambient temperature control of 10℃~60℃, such as Figure 5 At 20℃, the bolt torque increase corresponds to β Monotonically decreases, and as the temperature increases, the bolt torque increases correspondingly β A "V"-shaped non-monotonic change gradually appears, and finally increases monotonically at 60℃, and it is in the high stress stage of the bolt, that is, the early loosening stage. β The change amplitude is the largest and the damage identification sensitivity is stronger, that is, the control goal of the nonlinear index in the process of bolt loosening is achieved.

Claims

1. A thermal control system for vibration and acoustic modulation signals of bolted joints, characterized by: include: Temperature monitoring module: Infrared thermal imager monitors the temperature of bolt connection parts; Thermal control module: A heating component with a heating function is attached to the bolt connection or a heating device is used to heat the bolt connection part to control the local temperature of the connection part to the target value under different working conditions; Signal excitation module: A dual-channel signal generator outputs two continuous high-frequency sine wave signals and a low-frequency sine wave signal. The low-frequency signal is transmitted through an amplifying circuit to an exciter bonded to the bolted object, causing low-frequency vibration of the bolted connection. The high-frequency signal is transmitted through a circuit to a piezoelectric ceramic actuator bonded to the bolted object, generating high-frequency sound waves. Signal receiving module: The two excitation signals output by the signal excitation module are mixed in the bolted joint, and the vibration and sound modulation signals are received by the acceleration sensor attached to the surface of the bolted object. Signal post-processing module: The signal received by the acceleration sensor is transmitted to the oscilloscope through the circuit for observation and storage, and is exported for spectrum analysis. The nonlinear index is established by modulating the harmonic amplitude ratio of the low-frequency fundamental wave and the high-frequency fundamental wave amplitude. β , according to the nonlinear index β The relative size of the value represents the degree of loosening of the bolt.

2. The thermal control method of the thermal control system of the vibration and acoustic modulation signal of the bolted connection according to claim 1, comprising the following steps: Step S1: completing the pre-tightening assembly of the bolt connection; Step S2: changing the local ambient temperature of the bolt connection part to stimulate the thermal regulation effect of the connection interface; Step S21: Install an infrared thermal imager within 1 to 3 meters of the bolt to clearly monitor the temperature of the bolt connection; adjust the focus and angle of the thermal imager to obtain the best temperature monitoring effect; Step S22: Select a heating device according to the set control temperature to uniformly heat the bolt connection part; monitor the temperature reading of the infrared thermal imager in real time, and gradually adjust the power and heating time of the heating device to ensure that the local temperature reaches the set control temperature; Step S3: Conducting vibration and acoustic modulation signal monitoring under thermal control to complete health monitoring of the early loosening process of the bolt; Step S31: The dual-channel signal generator outputs two columns of continuous high-frequency sine wave signals and low-frequency sine wave signals; wherein, The low-frequency signal is transmitted through the amplifying circuit to the exciter bonded to the metal / composite connector to induce low-frequency vibration of the bolt connector. The high-frequency signal is transmitted through the circuit to the piezoelectric ceramic actuator bonded to the metal / composite connector to generate high-frequency sound waves. Step S32: The two continuous high-frequency sine wave signals and the low-frequency sine wave signals are mixed in the bolted joint and induce a vibration-acoustic modulation signal, which is then received by an acceleration sensor attached to the surface of the metal / composite joint; Step S33: The signal received by the acceleration sensor is transmitted to the oscilloscope through the circuit for observation and storage, and is derived for spectrum analysis. The nonlinear index is calculated by the ratio of the measured modulation harmonic amplitude to the low-frequency fundamental wave and the high-frequency fundamental wave amplitude. β , the formula is as follows: ； Where: M It's quality, N is the preload torque, T It's the temperature, ω 1 and ω 2 is the circular frequency of the two excitation signals; For the contact stiffness based model: ,in: C is the proportionality constant, m 0 is the initial roughness coefficient, n is the roughness softening coefficient; A LF is the low-frequency fundamental amplitude, A HF is the high-frequency fundamental wave amplitude, and the two columns of signals belong to the linear component; A LS and A RS are the left and right sideband amplitudes; Pressure changes P 0 for: ;in: P is the normal contact pressure ，P t is the change of preload force; Normal contact pressure P for: ,in: τ is the friction coefficient, d is the bolt diameter, S is the contact area, N is the residual torque; Preload change for: , among which: k 1 and k 2 is the material stiffness of the bolt and the connected plate, is the thermoelastic deformation of the connected plates and bolts: ,in: α 1 and α 2 are the coefficients of thermal expansion at two temperatures, T 1 and T 0 It's different temperatures, L is the thickness; Linear contact stiffness Taking the derivative to get the nonlinear contact stiffness : , according to the nonlinear index β The relative size of the value represents the degree of loosening of the bolt.

3. The thermal control method of the thermal control system of the vibration and acoustic modulation signal of the bolted connection according to claim 2, characterized in that: The step S1 includes the following specific steps: Step S11: adjusting the setting value of the torque wrench according to the preload target value designed for the project, and putting the torque wrench on the bolt head; Step S12: Connect the two metal / composite connectors with bolts, and rotate the torque wrench clockwise evenly until the set pre-tightening force target value is reached; check the bolts to ensure that the bolts have reached the predetermined tightening torque.

4. The thermal control method of the thermal control system of the vibration and acoustic modulation signal of the bolted connection according to claim 2, characterized in that: The step S2 further includes: continuously monitoring the temperature of the bolt connection part to ensure that the temperature is stable within the designed control range; if it is found that the temperature deviates from the target range, immediately adjusting the heating equipment, recalibrating the temperature, recording the temperature reading of the infrared thermal imager and the operating parameters of the heating equipment, and saving all relevant data for subsequent analysis and verification.

5. A computer system comprising a memory, a processor, and a computer program stored in the memory, wherein: The processor executes the computer program to implement the steps of the thermal control method of the thermal control system of the vibration and acoustic modulation signal of the bolted connection according to any one of claims 2 to 4.

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