Fatigue crack state monitoring device and method for conformal steel structure

Abstract

The invention discloses a shape follow-up steel structure fatigue crack state monitoring device and method, and belongs to the technical field of steel structure fatigue crack monitoring. The monitoring device structurally comprises N optical fiber shape follow-up sensing films, a signal transmission optical fiber, a scattering enhancement optical fiber strain demodulator and an upper computer; the optical fiber conformal sensing film comprises a conformal flexible film, a scattering enhanced optical fiber strain sensing array and a temperature compensation optical fiber measuring point; the scattering-enhanced optical fiber strain sensing array is fixed on the shape-followed flexible film and comprises a plurality of scattering-enhanced optical fibers and arc-shaped connecting optical fibers connected with the scattering-enhanced optical fibers. According to the method, the spectral frequency offset is obtained by using the scattering enhancement optical fiber strain demodulator, the influence of the environment temperature is eliminated through the temperature compensation optical fiber measuring points, and the strain distribution and the crack width change of each measuring point are further inverted based on the spectral frequency offset, so that the crack state in the monitoring area is identified. According to the invention, high-precision and real-time automatic monitoring of the fatigue crack state of the complex area of the steel structure is realized.

Description

Technical Field

[0001] This invention belongs to the field of fatigue crack monitoring technology for steel structures, specifically relating to a device and method for monitoring the fatigue crack state of conformal steel structures. Background Technology

[0002] Steel structures are widely used in bridges, stadiums, high-rise buildings, and industrial facilities. During their service life, they are frequently subjected to cyclic loads, wind vibration, temperature changes, corrosion, and residual welding stress, making them highly susceptible to fatigue cracks in critical load-bearing areas. Fatigue cracks are characterized by their high degree of concealment and rapid propagation; if they are not detected and assessed in a timely manner, they will seriously endanger structural safety. Therefore, conducting long-term, continuous, and quantitative monitoring of surface cracks in steel structures is of significant engineering importance.

[0003] In actual steel structures, cracks often appear in welds, stiffening rib intersections, node connection plates, ear plates, weld toe areas, curved transition zones of components, and other locations with geometric abrupt changes. These areas typically have characteristics such as complex curvature, uneven surfaces, limited space, and significant stress concentration, posing a severe challenge to existing crack condition monitoring technologies. Traditional non-destructive testing methods such as ultrasonic, magnetic particle, and penetrant testing rely on manual operation and can only be performed on accessible and relatively flat surfaces, making real-time monitoring of complex areas impossible. Visual inspection and image recognition methods are easily affected by coatings, corrosion, or obstructions, limiting their quantitative crack detection capabilities (as seen in Chinese patent documents with publication numbers CN120891001A and CN113899746A, etc.). Point sensors and conventional fiber Bragg gratings (FBGs) are limited by fit and coverage, failing to effectively reflect the crack initiation and propagation state in complex morphological regions.

[0004] Chinese patent document CN116577406A discloses a real-time, high-precision ACFM crack condition monitoring method. This method performs analog signal processing on the rotating magnetic field distortion signal of the steel structure under test, and then amplifies and filters the weaker processed rotating magnetic field distortion signal to monitor surface crack defects in the steel structure. However, this invention mainly relies on a single physical field, limiting its monitoring range.

[0005] While distributed fiber optic sensing technology offers advantages in continuous strain measurement, ordinary optical fibers are difficult to conformally attach to irregular steel structure surfaces, leading to problems such as insufficient strain transfer, high signal noise, and easy installation damage. Furthermore, the limited backscattering intensity of ordinary single-mode fibers makes it difficult to accurately identify minute strain changes caused by cracks. Therefore, existing technologies still have significant shortcomings in terms of conformability, spatial resolution, and quantitative inversion of crack width in complex and detailed areas of steel structures.

[0006] To address the aforementioned issues, there is an urgent need to develop a novel monitoring solution that can adapt to complex steel structure surfaces, provide millimeter-level spatial resolution, possess high signal-to-noise ratio and temperature compensation capabilities, and enable quantitative identification of crack location and width. Summary of the Invention

[0007] This invention aims to solve the technical problem of fatigue crack monitoring in complex parts of steel structures in structural health monitoring, and provides a device and method for monitoring fatigue crack status of conformal steel structures, which can monitor the crack status of complex parts of steel structure surface.

[0008] The specific technical solution adopted is as follows: A fatigue crack monitoring device for conformal steel structures includes N conformal fiber sensing films, a signal transmission fiber, a scattering-enhanced fiber strain demodulator, and a host computer; N≥1; The conformal fiber sensing film includes: a conformal flexible film, a scattering-enhancing fiber strain sensing array, and temperature-compensating fiber measuring points; the scattering-enhancing fiber strain sensing array is fixed on the conformal flexible film, including multiple scattering-enhancing fibers and arc-shaped connecting fibers connecting the scattering-enhancing fibers; the conformal flexible film is used to fix the scattering-enhancing fiber strain sensing array to the surface of the steel structure under test in a conformal manner; the temperature-compensating fiber measuring points are used to compensate for the temperature effects on the scattering-enhancing fiber strain sensing array. The signal transmission fiber connects the fiber conformal sensing film and the scattering-enhanced fiber strain demodulator, and connects the scattering-enhanced fiber strain sensing arrays in N fiber conformal sensing films in series. The scattering-enhanced fiber strain demodulator is used to acquire the spectral frequency shift of the scattering-enhanced fiber strain sensing array and temperature-compensated fiber measuring points in each fiber conformal sensing film during the test time period, and transmit it to the host computer. The host computer uses the spectral frequency shift data to identify the crack state in the monitoring area of ​​each fiber conformal sensing film during the test time period.

[0009] Furthermore, the conformal flexible membrane includes a substrate layer and an adhesive layer. The substrate layer is used to fix the scattering-enhanced fiber strain sensing array, and the adhesive layer is used to bond it to the steel structure under test. The corresponding design can ensure high shear force transmission. The conformal flexible membrane as a whole has the characteristics of low bending stiffness, easy bonding with the surface of steel structure, and has fatigue resistance, corrosion resistance, and moisture resistance.

[0010] Furthermore, in the scattering-enhanced fiber strain sensor array, the scattering-enhanced fiber is an fiber in which the intensity of backscattered Rayleigh light is periodically modulated and enhanced within the fiber core using ultraviolet fiber writing technology. The arc-shaped connecting fiber is not subjected to scattering enhancement and is embedded within the conformal flexible membrane. The positions of the scattering-enhanced fiber and the arc-shaped connecting fiber in the scattering-enhanced fiber strain sensor array can be distinguished based on the signal-to-noise ratio on the scattering-enhanced fiber strain demodulator.

[0011] Furthermore, the scattering-enhanced fiber strain sensing array is embedded inside the conformal flexible membrane with an optimized topology, and the scattering-enhanced fiber strain sensing array is designed to be serpentine or S-shaped.

[0012] The monitoring device of this invention combines scattering-enhanced fiber strain demodulation technology with fiber conformal sensing film. It uses a demodulator to obtain the spectral frequency shift of the scattering-enhanced fiber in each film, and eliminates the influence of ambient temperature by temperature-compensated fiber measuring points. Furthermore, it inverts the strain distribution and crack width changes of each measuring point based on the spectral frequency shift, thereby identifying the initiation, propagation and direction of cracks in the monitoring area, and realizing high-precision, real-time automatic monitoring of fatigue crack state in complex areas of steel structures.

[0013] This invention also provides a method for monitoring the fatigue crack state of steel structures, utilizing the aforementioned conformal steel structure fatigue crack state monitoring device, the specific steps of which include: N cascaded conformal fiber sensing films are attached to the surface of the steel structure under test in a conformal manner. A scattering-enhanced fiber strain demodulator is used to collect the spectral frequency shift Δ at each measuring point of the scattering-enhanced fiber strain sensing array and temperature-compensated fiber within the conformal fiber sensing film during the test time period. v With △ v T The crack state of each fiber conformal sensing film monitoring area within the measured time period is identified by using spectral frequency offset data.

[0014] Furthermore, the crack width at each measuring point on the scattering-enhanced fiber strain sensing array is calculated using the following formula:

[0015] in, W ci For the scattering enhancement fiber strain sensing array i Crack width at the measuring point SR The spatial resolution set in the scattering-enhanced fiber strain demodulator. The center scanning wavelength of the scattering-enhanced fiber strain demodulator. c It's the speed of light. K ε Δ is the strain coefficient. vIt is the spectral frequency shift caused by both strain and temperature, measured by a scattering-enhanced fiber optic strain sensing array, Δ v T The spectral frequency shift caused by temperature is measured at the temperature-compensated fiber optic measuring point.

[0016] Furthermore, the crack width on each scattering-enhancing fiber in the scattering-enhancing fiber strain sensing array. W c and the location of the crack P ci It can be represented as:

[0017] in, W ci The first scattering-enhanced fiber strain sensing array i Crack width at the measuring point L The length of each scattering-enhancing fiber in the scattering-enhancing fiber strain sensor array. n This represents the number of segments in each scattering-enhancing fiber.

[0018] Furthermore, based on the geometry of the fiber optic conformal sensing film attached to the surface of the steel structure under test, the direction, length, and width of cracks on the steel structure surface are characterized.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention achieves millimeter-level spatial resolution strain monitoring by embedding a scattering-enhanced fiber strain sensing array within a conformal flexible membrane and employing enhanced Rayleigh scattering and a demodulator for high-precision spectral offset measurement. This enables timely and accurate identification of the generation and propagation of microcracks (crack initiation, width changes, etc.).

[0020] 2) The conformal flexible membrane has low bending stiffness and can be closely fitted to the complex geometric parts of the steel structure (such as welds, nodes, stiffening ribs, curved surfaces, etc.) to achieve coverage monitoring of key structural detail areas. It overcomes the problem that traditional rigid or point sensors are difficult to install. The conformal steel structure fatigue crack state monitoring device of the present invention can monitor the crack state of complex parts of the steel structure surface. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fatigue crack condition monitoring device for conformal steel structures.

[0022] Figure 2 This is a schematic diagram showing the deployment of the fatigue crack monitoring device for conformal steel structures in a complex configuration area of ​​a steel structure.

[0023] Figure 3This is a schematic diagram of the fatigue crack state of a steel structure obtained by the steel structure fatigue crack state monitoring method of the present invention.

[0024] Figure descriptions: 1. Conformal flexible membrane, 2. Scattering-enhanced fiber strain sensor array, 3. Temperature-compensated fiber optic measuring point, 4. Arc-shaped connecting fiber optic cable, 5. Signal transmission fiber optic cable, 6. Scattering-enhanced fiber optic strain demodulator, 7. Conformal fiber optic sensing film. Detailed Implementation

[0025] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0026] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0027] Example 1 This embodiment provides a fatigue crack monitoring device for conformal steel structures, which includes N conformal fiber sensing films, a signal transmission fiber 5, a scattering-enhanced fiber strain demodulator 6, and a host computer, where N is a positive integer greater than or equal to 1. Each conformal fiber sensing film comprises: a conformal flexible film 1, a scattering-enhanced fiber strain sensing array 2, and temperature-compensated fiber measuring points 3. The conformal flexible film 1 includes a substrate layer and an adhesive layer. The substrate layer is used to fix the scattering-enhanced fiber strain sensing array, and the adhesive layer is used to bond it to the steel structure under test. The conformal flexible film 1 is used to fix the scattering-enhanced fiber strain sensing array 2 to the surface of the steel structure under test in a conformal manner. The scattering-enhanced fiber strain sensing array 2 is embedded in the conformal flexible film 1 with an optimized topology (preferably serpentine or S-shaped) for monitoring fatigue cracks on the steel structure surface. The temperature-compensated fiber measuring points 3 are used to compensate for the temperature effects on the scattering-enhanced fiber strain sensing array 2. The scattering-enhanced fiber strain sensing array 2 includes multiple scattering-enhancing fibers and arc-shaped connecting fibers 4 connecting the scattering-enhancing fibers. The arc-shaped connecting fibers 4 are embedded in the conformal flexible film 1 to connect the scattering-enhancing fibers to form the scattering-enhanced fiber strain sensing array 2 and to distinguish the signals of each scattering-enhancing fiber.

[0028] In the scattering-enhanced fiber strain sensing array 2, the scattering-enhanced fiber is an optical fiber in which the intensity of backscattered Rayleigh light is enhanced by periodic modulation inside the fiber core using ultraviolet fiber writing technology, while the arc-shaped connecting fiber 4 is not subjected to scattering enhancement.

[0029] One end of the signal transmission fiber 5 is connected to the scattering-enhanced fiber strain demodulator 6, and the other end of the signal transmission fiber 5 is connected in sequence to N fiber conformal sensing films, so that the scattering-enhanced fiber strain sensing array 2 in the N fiber conformal sensing films is connected in series.

[0030] Because scattering-enhanced optical fibers can significantly improve the signal-to-noise ratio of Rayleigh scattering signals in optical fibers, they can achieve strain measurement along the line with millimeter-level spatial resolution and a sensing distance of several kilometers. In practical applications, multiple conformal fiber sensing films can be connected in series at certain intervals on complex surface configurations of different parts of steel structures to achieve highly sensitive monitoring of crack initiation and propagation states (initiation and propagation).

[0031] The host computer acquires the spectral frequency shift of the scattering-enhanced fiber strain sensor array 2 and the temperature-compensated fiber measuring point 3 in each fiber conformal sensing film obtained by the scattering-enhanced fiber strain demodulator 6 during the measured time period, and uses the spectral frequency shift to calculate the strain and temperature information of the scattering-enhanced fiber strain sensor array 2 and the temperature-compensated fiber measuring point 3 during the measured time period to identify the crack state in the monitoring area.

[0032] Specifically, when the state of the crack in the steel structure at the monitoring location changes (initiation or propagation), it will cause the fiber conformal sensing film to deform, which in turn causes the scattering-enhanced fiber strain sensing array 2 on the fiber conformal sensing film to generate strain, resulting in a change in the spectral frequency shift of the Rayleigh scattered light propagating in the fiber.

[0033] Specifically, the scattering-enhanced fiber strain sensor array 2 can be encapsulated into a deformation-sensing fiber conformal sensing film. Multiple fiber conformal sensing films can be connected in series to monitor the surface crack state of complex configurations in different parts of the steel structure. When the crack state in the area covered by the fiber conformal sensing film remains unchanged, the Rayleigh scattering spectral frequency in the scattering-enhanced fiber strain sensor array 2 does not change or changes slightly under noise. When the crack state in the area covered by the fiber conformal sensing film changes (initiation or propagation), the deformation of the fiber conformal sensing film caused by the change in crack state will lead to a shift in the Rayleigh scattering spectral frequency in the scattering-enhanced fiber strain sensor array 2. By demodulating the signal using a scattering-enhanced fiber strain demodulator 6, the monitoring of the surface crack state of complex configurations in different parts of the steel structure can be achieved.

[0034] The method for monitoring the fatigue crack state of steel structures using the aforementioned conformal steel structure fatigue crack state monitoring device is as follows: N cascaded conformal fiber sensing films are attached to the surface of the steel structure under test in a conformal manner. A scattering-enhanced fiber strain demodulator 6 is used to collect the spectral frequency shift Δ of the scattering-enhanced fiber strain sensing array 2 and the temperature-compensated fiber measuring point 3 within each conformal fiber sensing film during the test time period. v With △ v T The width of the crack passing through each scattering-enhancing fiber is calculated by using the spectral frequency shift at each measuring point of each scattering-enhancing fiber in each conformal sensing film and the spectral frequency shift at measuring point 3 in the temperature-compensated fiber. W c .

[0035] The relationship between the crack width at each measuring point on the scattering-enhanced fiber strain sensor array 2 and the spectral frequency shift measured by the scattering-enhanced fiber strain demodulator 6 is as follows:

[0036] in, W ci For the scattering-enhanced fiber strain sensing array 2 i Crack width at the measuring point SR The spatial resolution set in the scattering-enhanced fiber strain demodulator 6 The center scanning wavelength of the scattering-enhanced fiber strain demodulator 6. c It's the speed of light. K ε Δ is the strain coefficient. v It is the spectral frequency shift caused by both strain and temperature, measured by the scattering-enhanced fiber strain sensor array 2, Δ v T The spectral frequency shift caused by temperature is measured at point 3 of the temperature-compensated fiber optic cable.

[0037] Crack width on each scattering-enhancing fiber in the scattering-enhancing fiber strain sensing array 2 W c and the location of the crack P ci It can be represented as:

[0038] in, W ci For the scattering-enhanced fiber strain sensing array 2 i Crack width at the measuring point L The length of each scattering-enhancing fiber in the scattering-enhancing fiber strain sensing array 2 is given. n This represents the number of segments in each scattering-enhancing fiber.

[0039] The direction, length, and width of cracks on the surface of a steel structure can be characterized based on the geometry of the fiber optic conformal sensing film attached to the surface of the steel structure.

[0040] In practical applications, such as Figure 2 As shown, a series of conformal fiber optic sensing films 7 are fixed in a conformal manner to the surface of a complex steel structure requiring crack monitoring. The series-connected array of conformal fiber optic sensing films is then connected to a scattering-enhanced fiber optic strain demodulator and a host computer. The spectral frequency shift information of the scattering-enhanced fiber optic strain sensing array within the coverage area of ​​each conformal fiber optic sensing film 7 can be obtained through the scattering-enhanced fiber optic strain demodulator and the host computer, thereby achieving the purpose of monitoring cracks on the surface of the complex steel structure.

[0041] Figure 3 For application on the surface of a complex steel structure, the crack state information monitored by the fiber optic conformal sensing film can be obtained through the method of this invention, including crack direction, maximum width, and length.

[0042] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fatigue crack monitoring device for conformal steel structures, characterized in that, The structure includes N conformal fiber sensing films, signal transmission optical fibers, a scattering-enhanced fiber strain demodulator, and a host computer; The conformal fiber sensing film includes: a conformal flexible film, a scattering-enhancing fiber strain sensing array, and temperature-compensating fiber measuring points; the scattering-enhancing fiber strain sensing array is fixed on the conformal flexible film, including multiple scattering-enhancing fibers and arc-shaped connecting fibers connecting the scattering-enhancing fibers; the conformal flexible film is used to fix the scattering-enhancing fiber strain sensing array to the surface of the steel structure under test in a conformal manner; the temperature-compensating fiber measuring points are used to compensate for the temperature effects on the scattering-enhancing fiber strain sensing array. The signal transmission fiber connects the fiber conformal sensing film and the scattering-enhanced fiber strain demodulator, and connects the scattering-enhanced fiber strain sensing arrays in N fiber conformal sensing films in series. The scattering-enhanced fiber strain demodulator is used to acquire the spectral frequency shift of the scattering-enhanced fiber strain sensing array and temperature-compensated fiber measuring points in each fiber conformal sensing film during the test time period, and transmit it to the host computer. The host computer uses the spectral frequency shift data to identify the crack state in the monitoring area of ​​each fiber conformal sensing film during the test time period.

2. The fatigue crack condition monitoring device for conformal steel structures according to claim 1, characterized in that, The conformal flexible membrane includes a substrate layer and an adhesive layer. The substrate layer is used to fix the scattering-enhanced fiber strain sensing array, and the adhesive layer is used to bond it to the steel structure under test.

3. The fatigue crack condition monitoring device for conformal steel structures according to claim 1, characterized in that, In the scattering-enhanced fiber strain sensing array, the scattering-enhanced fiber is an optical fiber in which the intensity of backscattered Rayleigh light is enhanced by periodic modulation inside the fiber core using ultraviolet fiber writing technology, while the arc-shaped connecting fiber is not subjected to scattering enhancement.

4. The fatigue crack condition monitoring device for conformal steel structures according to claim 1, characterized in that, The scattering-enhanced fiber strain sensing array is designed in a serpentine or S-shape.

5. A method for monitoring fatigue crack condition in steel structures, characterized in that, The specific steps of using the fatigue crack condition monitoring device for conformal steel structures according to any one of claims 1-4 include: N cascaded conformal fiber sensing films are attached to the surface of the steel structure under test in a conformal manner. A scattering-enhanced fiber strain demodulator is used to collect the spectral frequency shift of the scattering-enhanced fiber strain sensing array and temperature-compensated fiber measuring points in each conformal fiber sensing film during the test period. The crack state in the monitoring area of ​​each conformal fiber sensing film during the test period is identified using the spectral frequency shift data.

6. The method for monitoring fatigue crack condition of steel structures according to claim 5, characterized in that, The crack width at each measuring point on the scattering-enhanced fiber strain sensing array is calculated using the following formula: ； in, W ci For the scattering enhancement fiber strain sensing array i Crack width at the measuring point SR The spatial resolution set in the scattering-enhanced fiber strain demodulator. The center scanning wavelength of the scattering-enhanced fiber strain demodulator. c It's the speed of light. K ε Let Δ be the strain coefficient. v It is the spectral frequency shift caused by both strain and temperature, measured by a scattering-enhanced fiber optic strain sensing array, Δ v T The spectral frequency shift caused by temperature is measured at the temperature-compensated fiber optic measuring point.

7. The method for monitoring fatigue crack condition of steel structures according to claim 6, characterized in that, Crack width on each scattering-enhancing fiber in the scattering-enhancing fiber strain sensing array W c and the location of the crack P ci It can be represented as: ； in, W ci The first scattering-enhanced fiber strain sensing array i Crack width at the measuring point L The length of each scattering-enhancing fiber in the scattering-enhancing fiber strain sensor array. n This represents the number of segments in each scattering-enhancing fiber.

8. The method for monitoring fatigue crack condition of steel structures according to claim 5, characterized in that, Based on the geometry of the fiber optic conformal sensing film attached to the surface of the steel structure under test, the direction, length and width of cracks on the steel structure surface are characterized.

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