A flange bolt group loosening detection method and system based on joint surface gap change

Abstract

A flange bolt group loosening detection method and system based on the change of the gap between the joint surfaces, the method comprising the following steps: S1, constructing a finite element model of the bolt flange connection to obtain the gap distribution law; S2, performing cubic interpolation fitting on the discrete numerical value of the maximum gap obtained through simulation to construct a "pretightening force-gap" relationship curve; S3, obtaining the gap measurement value between adjacent bolts through a gap measurement device, performing feature extraction, and correcting the data to improve the "pretightening force-gap" relationship curve; S4, performing feature extraction on the gap value under the critical condition of bolt connection failure, obtaining the maximum value of the gap under the critical condition, and setting the value as the bolt connection effectiveness threshold according to the "pretightening force-gap" relationship curve; S5, if the maximum gap values obtained after feature extraction of the gap values of two continuous detection regions are less than the threshold, then the bolts between the two regions are determined as connection failure bolts.

Description

Technical Field

[0001] This invention relates to the field of computer-aided analysis technology, and in particular to a method and system for detecting loosening of flange bolt assemblies based on changes in the gap between mating surfaces. Background Technology

[0002] Bolted connections offer advantages such as convenient installation and easy maintenance, and are widely used in engineering fields such as machinery, aerospace, and civil engineering. However, due to improper preload during installation and the effects of various time-varying loads or other environmental factors during service, bolt loosening is one of the most common problems. Studies have shown that 70% to 90% of the failure modes of mechanical equipment are directly related to the failure modes of bolted connections. Therefore, ensuring that bolts do not fail during the connection process, thereby guaranteeing the normal and stable operation of mechanical equipment, structural safety, and preventing major safety accidents, has significant engineering value and importance.

[0003] Various methods have been developed for detecting bolt loosening, but all have certain limitations. Strain-based methods are difficult to implement on a large scale due to the challenge of strain gauge placement. Vibration analysis-based methods face technical difficulties because low-order vibration parameters of the overall structural dynamics are not highly sensitive to bolt loosening damage. Piezoelectric and ultrasonic technologies also struggle to effectively monitor bolt loosening due to expensive equipment and interference from complex environmental signals. Therefore, it is necessary to propose a technical solution to address the aforementioned problems of high cost, difficulty in detection, and susceptibility to interference in bolt loosening detection. Summary of the Invention

[0004] Based on the above problems, this invention proposes a method and system for detecting loosening of flange bolt assemblies by considering changes in surface clearance. The method includes the following steps:

[0005] S1. When flanges are connected using bolt sets, a preload is applied to the bolts. Under different preloads, the gap between the flange mating surfaces varies. By establishing a finite element model of the bolt connection, changing the preload of the bolt set, and calculating the gap under different preloads, the gap distribution pattern is obtained. Discrete data showing the maximum gap and the coordinates of the locations where the maximum gap occurs are acquired.

[0006] S2. Perform cubic interpolation fitting on the discrete values ​​of the maximum clearance data obtained in step S1 to construct the "preload-clearance" relationship curve;

[0007] S3. In the bolted connection structure of the flange, a gap detection area is set between every two bolts. The gap measurement value of the area is obtained by a gap measuring device, feature extraction is performed, the maximum gap value is obtained, the simulation data is corrected, and the "preload-gap" relationship curve is improved.

[0008] S4. Extract the feature value of the gap under the critical condition of bolt connection failure, obtain the maximum value of the gap under the critical condition, and set this value as the bolt connection effectiveness threshold according to the "preload-gap" relationship curve.

[0009] S5. Within the detection area of ​​all gaps, if the maximum gap value obtained after feature extraction of two consecutive detection areas is less than the threshold, then the bolt between the two areas is determined to be a bolt with connection failure.

[0010] Furthermore, step S1 includes:

[0011] S101. Using the torque T applied to the bolt as the input condition, the preload value of each bolt is obtained according to the relationship between torque and preload.

[0012] S102. Using finite element analysis software, set the inner side of the upper flange as a fixed constraint, apply the same preload to the bolt group, solve the gap distribution of the mating surface under different preloads, and obtain the discrete values ​​of the gap in the flange mating surface area under different preloads.

[0013] S103. Extract feature data from the discrete data of the flange mating surface area to obtain the maximum value of the mating surface gap.

[0014] Furthermore, in step S2, according to formula (1), cubic spline interpolation is performed on u(F) to construct the relationship curve between the bolt group preload and the maximum clearance.

[0015] u(F)=cubic[u(F)] (1)

[0016] Where u is the maximum gap value, and cubic represents cubic spline interpolation.

[0017] Furthermore, step S3 includes:

[0018] S301. In the flange structure, due to the symmetry of the structure, when the bolt group is subjected to an equal preload, the gap distribution between each pair of bolts is basically the same. Therefore, a gap measurement area is set in the area between each pair of bolts.

[0019] S302. Based on the maximum gap location obtained from the finite element simulation analysis results, gap measurement points are arranged at this location. The gap value of the area is measured by the gap measurement device. The gap value is different under different preload conditions, and discrete gap values ​​are obtained.

[0020] S303. Extract features from the obtained discrete gap values ​​to obtain the maximum gap value under different preloads, correct the computer simulation results, and improve the "preload-gap" relationship curve.

[0021] Furthermore, step S4 includes: based on the existence of a critical preload when the bolt connection fails, applying a critical preload to the bolt group, measuring the maximum value of the gap between the mating surfaces under the critical preload, and marking this value on the "preload-gap" curve to set this value as the threshold when the bolt loosens.

[0022] Furthermore, step S5 includes: when the bolt loosens, the value of the preload decreases accordingly, and the gap between the mating surfaces changes accordingly. Based on the "preload-gap" curve, if the maximum value of the discrete values ​​detected in two consecutive gap detection areas is extracted, and if it is less than the gap threshold, then the bolt between the two detection areas is determined to be an abnormal bolt that needs to be repaired.

[0023] The present invention also provides a flange bolt group loosening detection system based on the change of mating surface clearance, characterized in that the system comprises:

[0024] The finite element model construction module is used to construct a finite element model of the flange and bolt assembly. When the bolt assembly applies preload, a gap will be generated at the mating surface of the flange. With one end fixed and constrained, the flange generates different gaps under different bolt preloads, and discrete gap values ​​are obtained. Feature extraction is performed on the data to obtain multiple sets of maximum gap values ​​at different preloads. Based on the corresponding preload, cubic spline interpolation is performed on the discrete gap data to construct the "preload-gap" relationship curve.

[0025] The data correction module arranges gap measurement points in the area between every two bolts of the flange structure. The gap measurement device detects the actual value of the gap between the mating surfaces when the bolts are subjected to different preloads. The maximum gap value is also extracted to correct the limited data and improve the "preload-gap" curve.

[0026] The loose area determination module, when the flange structure measures the gap value of the detection area, performs feature extraction on the discrete gap value of each detection area to obtain the maximum value of the gap, and compares it with the "preload-gap" curve to determine whether the area is a bolt loose area;

[0027] The bolt failure location module determines the location of the bolt based on the loose bolt location area. If the gap value of two consecutive areas is abnormal, the bolt in the middle of the two areas is determined to be the faulty bolt, thus locating the position of the faulty bolt.

[0028] This invention provides a method and system for detecting loose bolts in flange bolt assemblies based on changes in the gap between mating surfaces. By measuring the gap between the mating surfaces, the specific loose bolts can be identified. The method is simple and easy to implement, avoids the possibility of missed detection, and reduces the cost of bolt loosening detection. Attached Figure Description

[0029] The following are specific embodiments of this application, described in conjunction with the accompanying drawings, to further illustrate the technical solutions of this application. However, this application is not limited to these embodiments. In the following description, specific details such as particular configurations and components are provided merely to aid in a comprehensive understanding of the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Furthermore, for clarity and brevity, descriptions of known functions and structures have been omitted.

[0030] Figure 1 Flowchart of a flange bolt loosening detection method based on finite element analysis:

[0031] Figure 2 This is a schematic diagram of the assembly of bolts and clearance measuring device on the flange.

[0032] Figure 3 The "preload-clearance" relationship curve

[0033] 1-First gap measuring area, 2-Second gap measuring area, 3-Third gap measuring area, 4-Fourth measuring area, 5-Fifth gap measuring area, 6-Sixth gap measuring area, 7-First bolt, 8-Second bolt, 9-Third bolt, 10-Fourth bolt, 11-Fifth bolt, 12-Sixth bolt, 13-Gap measuring device. Detailed Implementation

[0034] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content specified in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] like Figure 1 As shown, this invention provides a method for detecting loosening of flange bolt assemblies based on changes in the mating surface clearance. The method includes the following steps:

[0036] S1. When flanges are connected using bolted sets, a preload is applied to the bolts. The gap between the flange mating surfaces varies under different preloads. By establishing a finite element model of the bolted connection, changing the preload of the bolt set, and calculating the gap under different preloads, the gap distribution pattern is obtained. Discrete data showing the maximum gap value are acquired.

[0037] S2. Perform cubic interpolation fitting on the discrete values ​​of the maximum gap data obtained in step S1 to obtain the component's "preload-gap" relationship curve;

[0038] S3. In the bolted connection structure of the flange, a gap detection area is set between every two bolts. The gap measurement value of the area is obtained by a gap measuring device, feature extraction is performed, the maximum gap value is obtained, the simulation data is corrected, and the "preload-gap relationship" curve is improved.

[0039] S4. Extract the feature value of the gap under the critical condition of bolt connection failure, obtain the maximum value of the gap under the critical condition, and set this value as the bolt connection effectiveness threshold according to the "preload-gap" relationship curve.

[0040] S5. Within the detection area of ​​all gaps, if the maximum gap value obtained after feature extraction of two consecutive detection areas is less than the threshold, then the bolt between the two areas is determined to be a bolt with connection failure.

[0041] like Figure 2 The diagram shows the assembly of bolts and clearance measuring devices on the flange. For ease of explanation, six bolts are used in this embodiment, but this does not mean that the number of bolts is limited to six. Similarly, the clearance measuring area is not limited to six; the number of bolts can be more depending on the specific circumstances. The number of clearance measuring areas is the same as the number of bolts. Furthermore, the position of the clearance measuring device is not fixed. After measuring the clearance in the first measuring area, the clearance in the second measuring area is measured, and so on, until all areas are measured.

[0042] Step S1 includes:

[0043] S101. Using the torque T applied to the bolt as the input condition, the preload value of each bolt is obtained according to the relationship between torque and preload.

[0044] S102. Using finite element analysis software, set the inner side of the upper flange as a fixed constraint, apply the same preload to the bolt group, solve the gap distribution of the mating surface under different preloads, and obtain the discrete values ​​of the gap in the flange mating surface area under different preloads.

[0045] S103. Extract feature data from the discrete data of the flange mating surface area to obtain the maximum value of the mating surface gap.

[0046] Step S2: According to formula (1), perform cubic spline interpolation on u(F) to construct the relationship curve between bolt preload and maximum clearance.

[0047] u(F)=cubic[u(F)] (1)

[0048] Where u is the maximum gap value, and cubic represents cubic spline interpolation.

[0049] Step S3 includes:

[0050] S301. In the flange structure, due to the symmetry of the structure, when the bolt group is subjected to an equal preload, the gap distribution between each pair of bolts is basically the same. Therefore, a gap measurement area is set in the area between each pair of bolts.

[0051] S302. Based on the maximum gap location obtained from the finite element simulation analysis results, gap measurement points are arranged at this location. The gap value of the area is measured by the gap measurement device. The gap value is different under different preload conditions, and discrete gap values ​​are obtained.

[0052] S303. Extract features from the obtained discrete gap values ​​to obtain the maximum gap value under different preloads, correct the computer simulation results, and improve the "preload-gap" relationship curve.

[0053] The purpose of this step is to obtain improved accuracy of the preload-clearance relationship curve, focusing on accurately reflecting the relationship between bolt preload and clearance, thus making the detection of loose bolts reliable.

[0054] As an exemplary embodiment, the present invention does not specify any particular gap detection device or means when describing the gap detection device. It should be understood that any device capable of detecting gaps can be used, such as ultrasonic, laser, image monitoring, etc.

[0055] Feature extraction is performed on the gap value under the critical condition of bolt connection failure to obtain the maximum value of the gap under the critical condition. Based on the "preload-gap" relationship curve, this value is set as the bolt connection effectiveness threshold.

[0056] In this embodiment, the bolt damage threshold is obtained by measuring the critical value of the maximum gap when the bolt connection fails. The value of the maximum gap in the detection area can be compared with the threshold. When the value of the maximum gap at the mating surface of the detection area is less than the threshold, it is determined that the bolts near that area have failed.

[0057] In step S5, if the maximum gap value obtained after feature extraction for two consecutive detection areas within all gap detection areas is less than the threshold, then the bolt between the two areas is determined to be a bolt with connection failure.

[0058] Below, in conjunction with Figure 2 The feasibility of determining the exact location of the damaged bolt is explained in detail. It should be noted that this embodiment only illustrates the situation where one bolt fails in connection, and the method for determining the exact location of the failed bolt in this situation:

[0059] Suppose that for any bolt detection area, the first bolt becomes loose, and the two gap detection areas corresponding to the first bolt loosening detection area are the first gap detection area and the second gap detection area.

[0060] When the value of the first gap detection area is measured by the gap detection device, data feature extraction is performed to obtain the maximum value of the gap Δt1 in that area.

[0061] When the value of the second gap detection area is measured by the gap detection device, data feature extraction is performed to obtain the maximum value of the gap Δt2 in that area.

[0062] Depend on Figure 3 The "preload-clearance" relationship curve is used to find the corresponding preload value by comparing the values ​​of Δt1 and Δt2 with the threshold Δt.

[0063] Where Δt>Δt1, Δt>Δt2;

[0064] Therefore, by obtaining the relationship between the gaps, when the maximum value of the gap between the two gap detection areas is obtained, and when searching the "preload-gap" relationship curve, if both values ​​are less than the given threshold, it is determined that the bolt between the two areas has a loosening fault.

[0065] Similarly, if other bolts become loose, the corresponding mating surface gap detection area is also checked, and the maximum value of the gap in the area is extracted and compared. Figure 3 The "preload-clearance" relationship curve is used to determine whether the bolts are loose.

[0066] As can be seen from the above embodiments, when the bolt loosens, the value of the preload decreases accordingly, and the gap between the mating surfaces changes accordingly. According to the "preload-gap" curve, if the maximum value of the discrete values ​​detected in two consecutive gap detection areas is extracted, and if it is less than the gap threshold, then the bolt between the two detection areas is determined to be a loose bolt.

[0067] The present invention also provides a flange bolt group loosening detection system based on the change of mating surface clearance, characterized in that the system comprises:

[0068] The finite element model construction module is used to construct a finite element model of the flange and bolt assembly. When the bolt assembly applies preload, a gap will be generated at the mating surface of the flange. With one end fixed and constrained, the flange generates different gaps under different preloads of the bolt assembly, and discrete gap values ​​are obtained. Feature extraction is performed on the data to obtain multiple sets of maximum gap values ​​of the mating surface under different preloads. Based on the corresponding preload, cubic spline interpolation is performed on the discrete gap data to construct the "preload-gap" relationship curve.

[0069] The data correction module arranges gap measurement points in the area between every two bolts of the flange structure. The gap measurement device detects the actual value of the gap of the mating surface when the bolt group is subjected to different preloads. The maximum gap value is also extracted to correct the limited data and improve the "preload-gap" curve.

[0070] The loose area identification module, when the flange structure measures the gap value of the detection area, performs feature extraction on the discrete gap value of each detection area to obtain the maximum value of the gap, and compares it with the "preload-gap" curve to determine whether the area is a bolt loose area;

[0071] The bolt failure location module determines the location of the bolt based on the loose bolt location area. If the gap value of two consecutive areas is abnormal, the bolt in the middle of the two areas is determined to be the faulty bolt, thus locating the position of the faulty bolt.

[0072] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0073] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0074] The specific embodiments described herein are merely illustrative examples of the spirit of this application. Those skilled in the art to which this application pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this application or exceeding the scope defined by the appended claims.

Claims

1. A method and system for detecting loosening of flange bolt assemblies based on changes in mating surface clearance, characterized in that, The method includes the following steps; S1. When flanges are connected by bolt groups, a preload is applied to the bolts. Under different preloads, the gap between the flange mating surfaces is different. By establishing a finite element model of the bolt connection, changing the preload of the bolt group, the gap between the mating surfaces under different preloads is calculated to obtain the gap distribution law. Discrete data of the maximum gap and the coordinates of the maximum gap are obtained. S2. Perform cubic interpolation fitting on the discrete values ​​of the maximum clearance data obtained in step S1 to construct the "preload-clearance" relationship curve; S3. In the bolted connection structure of the flange, a gap detection area is set between every two bolts. The gap measurement value of the area is obtained by a gap measuring device, feature extraction is performed, the maximum gap value is obtained, the simulation data is corrected, and the "preload-gap" relationship curve is improved. S4. Extract the feature value of the gap under the critical condition of bolt connection failure, obtain the maximum value of the gap under the critical condition, and set this value as the bolt connection effectiveness threshold according to the "preload-gap" relationship curve. S5. Within the detection area of ​​all gaps, if the maximum gap value obtained after feature extraction of two consecutive detection areas is less than the threshold, then the bolt between the two areas is determined to be a bolt with connection failure.

2. The bolt loosening detection method based on the change in the gap between mating surfaces according to claim 1, characterized in that, Step S1 includes: S101. Using the torque T applied to the bolt as the input condition, the preload value of each bolt is obtained according to the relationship between torque and preload. S102. Using finite element analysis software, set the inner side of the upper flange as a fixed constraint, apply the same preload to the bolt group, solve the gap distribution of the mating surface under different preloads, and obtain the discrete values ​​of the gap in the flange mating surface area under different preloads. S103. Extract feature data from the discrete data of the obtained bonding surface region to obtain the maximum value of the bonding surface gap.

3. The method for detecting loosening of flange bolt assemblies based on the change in mating surface clearance according to claim 1, characterized in that, Step S2 includes: According to formula (1), cubic spline interpolation is performed on u(F) to construct the relationship curve between the preload of the bolt group and the maximum clearance. u(F)=cubic[u(F)] (1) Where u is the maximum gap value, and cubic represents cubic spline interpolation.

4. The method for detecting loosening of flange bolt assemblies based on the change in mating surface clearance as described in claim 1, characterized in that, Step S3 includes: S301. In the flange structure, due to the symmetry of the structure, when the bolt group is subjected to an equal preload, the gap distribution between each pair of bolts is basically the same. Therefore, a gap measurement area is set in the area between each pair of bolts. S302. Based on the maximum gap location obtained from the finite element simulation analysis results, gap measurement points are arranged at this location. The gap value of the area is measured by the gap measurement device. The gap value is different under different preload conditions, and discrete gap values ​​are obtained. S303. Extract features from the obtained discrete gap values ​​to obtain the maximum gap value under different preloads, correct the computer simulation results, and improve the "preload-gap" relationship curve.

5. The method for detecting loosening of flange bolt assemblies based on the change in mating surface clearance according to claim 1, characterized in that, Step S4 includes: Based on the existence of a critical preload when a bolt connection fails, a critical preload is applied to the bolt group, and the maximum value of the gap between the mating surfaces under this critical preload is measured. This value is marked on the "preload-gap" curve and set as the threshold value when the bolt loosens.

6. The method for detecting loosening of flange bolt assemblies based on the change in mating surface clearance according to claim 1, characterized in that, Step S5 includes: when the bolt loosens, the value of the preload decreases accordingly, and the gap between the mating surfaces changes accordingly. Based on the "preload-gap" curve, if the maximum value of the discrete values ​​detected in two consecutive gap detection areas is extracted, and if it is less than the gap threshold, then the bolt between the two detection areas is determined to be an abnormal bolt that needs to be repaired.

7. A method and system for detecting loosening of flange bolt assemblies based on changes in mating surface clearance, characterized in that, The system includes: The finite element model construction module is used to construct a finite element model of the flange and bolt assembly. When the bolt assembly applies preload, a gap will be generated at the mating surface of the flange. With one end fixed and constrained, the flange generates different gaps under different preloads of the bolt assembly, and discrete gap values ​​are obtained. Feature extraction is performed on the data to obtain multiple sets of maximum gap values ​​of the mating surface under different preloads. Based on the corresponding preload, cubic spline interpolation is performed on the discrete gap data to construct the "preload-gap" relationship curve. The data correction module arranges gap measurement points in the area between every two bolts of the flange structure. The gap measurement device detects the actual value of the gap between the mating surfaces when the bolt group is subjected to different preloads. The maximum gap value is also extracted to correct the limited data and improve the "preload-gap" curve. The loose area identification module, when the flange structure measures the gap value of the detection area, performs feature extraction on the discrete gap value of each detection area to obtain the maximum value of the gap, and compares it with the "preload-gap" curve to determine whether the area is a bolt loose area; The bolt failure location module determines the location of the bolt based on the loose bolt location area. If the gap value of two consecutive areas is abnormal, the bolt in the middle of the two areas is determined to be the faulty bolt, thus locating the position of the faulty bolt.

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