Bolt connection structure hole edge damage monitoring method based on far-field eddy current

Abstract

The invention relates to the technical field of hole edge damage monitoring, in particular to a bolt connection structure hole edge damage monitoring method based on far-field eddy current, which comprises the following steps: providing a far-field eddy current sensing film, the far-field eddy current sensing film comprises a plurality of exciting coils and receiving coils, and the exciting coils and the receiving coils are arranged on the surface of a bolt rod; the far-field eddy current sensing film is connected to a multiplexing switch, the excitation coils are connected to a signal generator, and the signal generator outputs sine alternating voltage to control the excitation coils to generate a magnetic field; the excitation coils are switched through the multiplexing switch, so that the different excitation coils are alternately electrified, induced voltage signals are measured in the corresponding far-field receiving coils, and the amplitude difference and the phase difference are calculated based on the induced voltage amplitude and phase change of the receiving coils, so that the position where the damage occurs is obtained. Therefore, the bolt hole edge damage can be effectively identified, and the early detection of the hole edge crack and the prediction of the expansion trend of the hole edge crack can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of hole edge damage monitoring, and in particular to a method for monitoring hole edge damage of a bolt connection structure based on far-field eddy current. Background Art

[0002] Bolted connection structures are widely used in aerospace, bridges, automobiles and marine engineering, and their safety and reliability are directly related to the service life of the overall structure. However, cracks and other damages often occur around bolt holes due to stress concentration or fatigue loads. If they are not discovered and repaired in time, catastrophic consequences may occur.

[0003] At present, near-field eddy current testing has the following problems in bolt hole edge detection: the higher excitation frequency causes the eddy current to concentrate on the surface of the plate being tested, resulting in limited detection depth and difficulty in identifying hidden defects inside the hole edge.

[0004] It should be noted that the information disclosed in this background technology section is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes prior art already known to a person skilled in the art. Summary of the invention

[0005] In order to solve the difficulties of the prior art, the present invention is based on the advantages of far-field eddy current detection technology, which has low excitation frequency, large penetration depth, and is not significantly affected by the electrical conductivity of the material. It is applied to bolted connection structures in limited spaces, thereby forming a new monitoring method based on far-field eddy currents, which monitors longer hole edge cracks and evaluates their expansion trends in real time.

[0006] The present invention provides a method for monitoring hole edge damage of a bolt connection structure based on far-field eddy current, which comprises the following steps: A far-field eddy current sensing film is provided, wherein the far-field eddy current sensing film comprises a plurality of excitation coils and receiving coils, wherein the excitation coils and the receiving coils are wound and arranged on the surface of the bolt rod; The far-field eddy current sensing film is connected to a multiplex switch, and the excitation coil is connected to a signal generator, and the signal generator outputs a sinusoidal AC voltage to control each of the excitation coils to generate a magnetic field; The excitation coils are switched by the multiplexer switch so that different excitation coils are energized alternately, and the induced voltage signal is measured in the corresponding far-field receiving coil. Based on the induced voltage amplitude and phase changes of the receiving coil, the amplitude difference and the phase difference are calculated to obtain the location of the damage. The calculation formula is as follows:

[0007]

[0008] Among them, VCn-Cm and P Cn-Cm are the induced voltage amplitude and phase of the nth receiving coil under the action of the mth exciting coil, Cn-Cm and P Cn-Cm are the amplitude difference and phase difference under the damaged state, V Cn-Cm0 is the reference value of the induced voltage amplitude under lossless state, P Cn-Cm0 is the reference value of the phase in the lossless state; After determining the damage location, further obtain the specific length of the overlap plate hole edge damage, select the corresponding coil pair for excitation and reception, and obtain the receiving coil induced voltage amplitude V under different damage lengths. Dn With the phase value P Dn , and the relationship between the damage length d and the induced voltage amplitude and phase is fitted based on the following calculation formula:

[0009]

[0010] Among them, k1 is the linear coefficient; k2 is the quadratic coefficient; λ controls the rate of phase change; δ reflects the maximum amplitude of phase change; V0 and P0 are the reference amplitude and phase in the lossless state respectively.

[0011] Furthermore, the induced voltage of the nth receiving coil V Coil-n The following relationship is satisfied: , N is the number of turns of the receiving coil; A is the equivalent area of ​​the receiving coil, A = bolt circumference * number of coil layers; B eff is the effective magnetic induction intensity induced by the receiving coil; is the excitation voltage angular frequency; is the phase angle.

[0012] Furthermore, the excitation coil and the receiving coil are arranged at intervals along the axial direction of the bolt rod.

[0013] Furthermore, the distance between two adjacent excitation coils and receiving coils is greater than or equal to twice the diameter of the bolt.

[0014] Furthermore, the bolt hole edge damage monitoring method also includes the following steps: the receiving coil is first connected to a preamplifier to amplify weak signals, then connected to a low-pass filter to filter out noise, and finally connected to a phase-locked amplifier to collect far-field eddy current signals obtained by several receiving coils.

[0015] The present invention also provides a bolt hole edge damage monitoring system based on far-field eddy current, which adopts a bolt connection structure hole edge damage monitoring method based on far-field eddy current.

[0016] Furthermore, the material of the bolts and the lap plates includes metal or carbon fiber composite materials.

[0017] Furthermore, when the bolt hole edge damage monitoring method is applied to bolts made of metal materials, the excitation frequency range used is 200Hz to 15kHz, and when the bolt hole edge damage monitoring method is applied to bolts made of carbon fiber composite materials, the excitation frequency range used is 200kHz to 1MHz.

[0018] Furthermore, the signal generator is used to provide a sinusoidal AC voltage to the excitation coil to generate far-field eddy currents; the receiving coil inputs the sensed signal into the data acquisition device after pre-amplification, filtering, and phase-locked amplification.

[0019] Furthermore, the data acquisition equipment includes a digital oscilloscope and a signal analysis device, and combines the FFT algorithm to extract the signal frequency domain characteristics; through the time domain and frequency domain analysis of the far-field eddy current signal, the identification of the hole edge damage of the bolted connection structure and the prediction of the expansion trend are realized.

[0020] The present invention provides a method for monitoring hole edge damage of a bolted connection structure based on far-field eddy currents. Based on the far-field eddy currents, the effective monitoring range and monitoring accuracy of the hole edge damage length are improved, overcoming the shortcomings of the traditional near-field eddy current technology. By analyzing the signal characteristics in real time and comparing them with the damage database, the present invention can achieve early detection of hole edge cracks and prediction of their expansion trends, avoiding the lag in damage judgment in traditional technologies. Moreover, with the help of the special structure of the bolt connection, the far-field eddy current phenomenon can be directly generated inside. In addition, the method is not limited by the detection environment, can flexibly adapt to the damage monitoring of bolted connection structures under various working conditions, and is widely used in aerospace, railways, bridges and other fields.

[0021] Other features and beneficial effects of the present invention will be described in the following description, and some of the technical features and beneficial effects can be obviously derived from the description or understood by implementing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 is a schematic diagram of a bolt hole edge damage monitoring method provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of assembling a bolt and a flexible eddy current sensor film provided by an embodiment of the present invention; Figure 3 is a schematic diagram of coil arrangement on a bolt provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of far-field eddy current detection of bolt hole edge damage provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be understood that the terms "center", "lateral", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In addition, the term "including" and any variation thereof all mean "at least including".

[0026] See also Figures 1 to 4 As shown in the figure, a method for monitoring hole edge damage of a bolted connection structure based on far-field eddy current is provided in one embodiment of the present invention, which comprises the following steps: S100: Provide a far-field eddy current sensing film, the far-field eddy current sensing film includes a plurality of excitation coils and receiving coils, the excitation coils and the receiving coils are wound and arranged on the surface of the bolt rod. Optionally, the number of turns of the excitation coil is at least 40, the number of layers is at least 2, each layer is 20 copper traces that are parallel to each other, the line width and line spacing is 0.2mm, and the length is the circumference of the bolt rod. After winding, the tail of the first trace is welded to the head of the second trace, and then welded to the last trace in turn and led out to form a spiral coil wound on the bolt rod. The number of turns of the receiving coil is at least 60, the number of layers is at least 3, and the traces of each layer are consistent with the excitation coil.

[0027] S200: connecting the far-field eddy current sensing film to a multiplex switch, connecting the excitation coil to a signal generator, and controlling each of the excitation coils to generate a magnetic field by outputting a sinusoidal AC voltage through the signal generator; S300: The excitation coils are switched by the multiplexing switch so that different excitation coils are energized alternately, and the induced voltage signal is measured in the corresponding far-field receiving coil, and the amplitude difference and the phase difference are calculated based on the induced voltage amplitude and phase changes of the receiving coil, so as to know the location where the damage occurs, and the calculation formula is as follows:

[0028]

[0029] Among them, V Cn-Cm and P Cn-Cm are the induced voltage amplitude and phase of the nth receiving coil under the action of the mth exciting coil, Cn-Cm and P Cn-Cm are the amplitude difference and phase difference under the damaged state, V Cn-Cm0 is the reference value of the induced voltage amplitude under lossless state, P Cn-Cm0 is the reference value of the phase in the lossless state; S400: After determining the damage position, further obtain the specific length of the damage on the edge of the overlap plate hole, select the corresponding coil pair for excitation and reception, and obtain the induced voltage amplitude V of the receiving coil under different damage lengths Dn With the phase value P Dn , and the relationship between the damage length d and the induced voltage amplitude and phase is fitted based on the following calculation formula:

[0030]

[0031] Among them, k1 is the linear coefficient; k2 is the quadratic coefficient; λ controls the rate of phase change; δ reflects the maximum amplitude of phase change; V0 and P0 are the reference amplitude and phase in the lossless state, respectively. This describes the evolution trend of the far-field eddy current signal as the damage expands and improves the quantitative prediction ability of damage.

[0032] In some embodiments, to ensure effective propagation of far-field eddy current signals, the induced voltage of the nth receiving coil is V Coil-n The following relationship is satisfied: , N is the number of turns of the receiving coil; A is the equivalent area of ​​the receiving coil, A = bolt circumference * number of coil layers; B eff is the effective magnetic induction intensity induced by the receiving coil; is the excitation voltage angular frequency; is the phase angle.

[0033] In some embodiments, the excitation coil and the receiving coil are spaced apart from each other along the axial direction of the bolt rod.

[0034] In some embodiments, the distance between two adjacent excitation coils and receiving coils is greater than or equal to 2 times the bolt diameter. In addition, an oscilloscope can be used to collect the receiving coil signal waveforms at different damages, and Fourier transform can be used to extract the instantaneous amplitude, phase and other characteristics of the signal for time domain signal analysis to identify the dynamic changes when the damage occurs; according to the changes in eddy current signals under different damage states, combined with the law of damage expansion, the damage expansion of the bolt connection structure hole edge can be located and monitored in real time, effectively and accurately.

[0035] In some embodiments, the bolt hole edge damage monitoring method also includes the following steps: the receiving coil is first connected to a preamplifier to amplify weak signals, then connected to a low-pass filter to filter out noise, and finally connected to a phase-locked amplifier to collect far-field eddy current signals obtained by several receiving coils.

[0036] For example, the number of coil turns and the coil spacing are designed according to the length of the bolt rod: taking a bolt with a diameter of 10mm and a rod length of 60mm as an example, 3 excitation coils and 3 receiving coils can be designed, and the width of each coil is 10mm, ensuring that the spacing between the excitation coil and the receiving coil is ≥ 2 times the bolt diameter. Starting from the bolt head, there are coils C1, C2, C3, C4, C5, and C6, among which C1 and C4 form the excitation receiving coil group 1, C2 and C5 form the excitation receiving coil group 2, and C3 and C6 form the excitation receiving coil group 3. When C1, C2, and C3 are respectively used as excitation coils, C4, C5, and C6 are the corresponding far-field eddy current receiving coils; conversely, when C4, C5, and C6 are respectively used as excitation coils, C1, C2, and C3 are the corresponding far-field eddy current receiving coils, thereby realizing full-section monitoring of the entire bolt rod lap plate.

[0037] The present invention also provides a bolt hole edge damage monitoring system based on far-field eddy current, which adopts the above-mentioned bolt hole edge damage monitoring method for monitoring.

[0038] In some embodiments, the material of the bolts and the lap plate includes metal or carbon fiber composite material.

[0039] In some embodiments, when the bolt hole edge damage monitoring method is applied to bolts made of metal materials, the excitation frequency range used is 200Hz to 15kHz. When the bolt hole edge damage monitoring method is applied to bolts made of carbon fiber composite materials, the excitation frequency range used is 200kHz to 1MHz, thereby satisfying the generation of far-field eddy currents and taking into account detection sensitivity.

[0040] In some embodiments, the signal generator is used to provide a sinusoidal AC voltage to the excitation coil to generate far-field eddy currents; the receiving coil inputs the induced signal into the data acquisition device after preamplification, filtering, and phase-locked amplification in sequence. The preamplifier is used to amplify the weak signal of the receiving coil; the phase-locked amplifier is used to extract information such as the amplitude and phase of the induced voltage of the receiving coil.

[0041] In some embodiments, the data acquisition device includes a digital oscilloscope and a signal analysis device, and extracts the signal frequency domain characteristics in combination with the FFT algorithm; through the time domain and frequency domain analysis of the far-field eddy current signal, the identification of the hole edge damage of the bolt connection structure and the prediction of the expansion trend are realized. The oscilloscope is used to extract the time domain waveform of the induced voltage of the receiving coil.

[0042] This application uses the special structure of bolt connection and the excitation / receiving coils installed at intervals on the bolt rod, without the need to set a shielding layer, to directly generate far-field eddy current phenomena in the structure. Considering that the main reason for the generation of far-field eddy currents is that the indirect coupling between the excitation coil and the receiving coil is greater than the direct coupling, indirect coupling plays a major role. In the bolt connection structure, since the spacing between the excitation coil and the receiving coil is large (such as greater than or equal to 2 times the bolt diameter), the direct coupling energy between the coils is very weak at this time; in addition, the bolts and lap plates are usually made of conductive materials (such as metals), and their conductivity makes the eddy currents mainly propagate inside the structure of the bolt connection area, rather than directly forming a strong coupling path between the excitation and receiving coils, thereby enhancing the indirect coupling effect.

[0043] In summary, the present invention provides a method for monitoring hole edge damage of bolted connection structures based on far-field eddy currents. Based on far-field eddy currents, the effective monitoring range and monitoring accuracy of hole edge damage length are improved, overcoming the shortcomings of traditional near-field eddy current technology. By analyzing signal characteristics in real time and comparing them with the damage database, the present invention can achieve early detection of hole edge cracks and prediction of their expansion trends, avoiding the lag in damage judgment in traditional technologies. In addition, the method is not limited by the detection environment, can flexibly adapt to the monitoring of bolted connection structure damage under various working conditions, and is widely used in aerospace, railways, bridges and other fields.

[0044] In addition, those skilled in the art should understand that, although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, without having to solve all the technical problems listed in the prior art or background technology at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be used as a limitation on the claim.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for monitoring hole edge damage of bolted connection structure based on far-field eddy current, characterized in that: The bolt hole edge damage monitoring method based on remote field eddy current comprises the following steps: A far-field eddy current sensing film is provided, wherein the far-field eddy current sensing film comprises a plurality of excitation coils and receiving coils, wherein the excitation coils and the receiving coils are wound and arranged on the surface of the bolt rod; The far-field eddy current sensing film is connected to a multiplex switch, and the excitation coil is connected to a signal generator, and the signal generator outputs a sinusoidal AC voltage to control each of the excitation coils to generate a magnetic field; The excitation coils are switched by the multiplexer switch so that different excitation coils are energized alternately, and the induced voltage signal is measured in the corresponding far-field receiving coil. Based on the induced voltage amplitude and phase changes of the receiving coil, the amplitude difference and the phase difference are calculated to obtain the location of the damage. The calculation formula is as follows: Among them, V Cn-Cm and P Cn-Cm are the induced voltage amplitude and phase of the nth receiving coil under the action of the mth exciting coil, V Cn-Cm and P Cn-Cm are the amplitude difference and phase difference under the damaged state, V Cn-Cm0 is the reference value of the induced voltage amplitude under lossless state, P Cn-Cm0 is the reference value of the phase in the lossless state; After determining the damage location, further obtain the specific length of the overlap plate hole edge damage, select the corresponding coil pair for excitation and reception, and obtain the receiving coil induced voltage amplitude V under different damage lengths. Dn With the phase value P Dn , and the relationship between the damage length d and the induced voltage amplitude and phase is fitted based on the following calculation formula: Among them, k1 is the linear coefficient; k2 is the quadratic coefficient; λ controls the rate of phase change; δ reflects the maximum amplitude of phase change; V0 and P0 are the reference amplitude and phase in the lossless state respectively.

2. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 1, characterized in that: The induced voltage of the nth receiving coil V Coil-n The following relationship is satisfied: , N is the number of turns of the receiving coil; A is the equivalent area of ​​the receiving coil, A = bolt circumference * number of coil layers; B eff is the effective magnetic induction intensity induced by the receiving coil; is the excitation voltage angular frequency; is the phase angle.

3. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 1 is characterized by: The excitation coil and the receiving coil are arranged with a spacing along the axial direction of the bolt rod.

4. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 3 is characterized by: The distance between two adjacent excitation coils and receiving coils is greater than or equal to twice the diameter of the bolt.

5. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 1, characterized in that: The bolt hole edge damage monitoring method also includes the following steps: the receiving coil is first connected to a preamplifier to amplify weak signals, then connected to a low-pass filter to filter out noise, and finally connected to a phase-locked amplifier to collect far-field eddy current signals obtained by a number of receiving coils.

6. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 1, characterized in that: The bolt connection structure hole edge damage monitoring method is applied to a bolt hole edge damage monitoring system.

7. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 6, characterized in that: The materials of the bolts and the lap plates include metal or carbon fiber composite materials.

8. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 7, characterized in that: When the bolt hole edge damage monitoring method is applied to bolts made of metal materials, the excitation frequency range used is 200Hz to 15kHz. When the bolt hole edge damage monitoring method is applied to bolts made of carbon fiber composite materials, the excitation frequency range used is 200kHz to 1MHz.

9. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 6, characterized in that: The signal generator is used to provide a sinusoidal AC voltage to the excitation coil to generate far-field eddy currents; the receiving coil inputs the sensed signal into the data acquisition device after pre-amplification, filtering, and phase-locked amplification.

10. The method for monitoring hole edge damage of bolted connection structure based on far-field eddy current according to claim 9, characterized in that: The data acquisition equipment includes a digital oscilloscope and a signal analysis device, and extracts the signal frequency domain characteristics in combination with the FFT algorithm; through the time domain and frequency domain analysis of the far-field eddy current signal, the identification of the hole edge damage of the bolt connection structure and the prediction of the expansion trend are realized.

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