CN-122015680-A - Device and method for monitoring fatigue crack state of conformal steel structure

Abstract

The invention discloses a monitoring device and a monitoring method for fatigue crack states of a conformal steel structure, which belong to the technical field of monitoring of fatigue cracks of steel structures, wherein the monitoring device structurally comprises N optical fiber conformal sensing films, signal transmission optical fibers, a scattering enhancement optical fiber strain demodulator and an upper computer; the optical fiber conformal sensing film comprises a conformal flexible film, a scattering enhancement optical fiber strain sensing array and a temperature compensation optical fiber measuring point, wherein the scattering enhancement optical fiber strain sensing array is fixed on the conformal flexible film and comprises a plurality of scattering enhancement optical fibers and arc-shaped connecting optical fibers connected with the scattering enhancement optical fibers. According to the invention, the scattering enhancement fiber strain demodulator is used for obtaining the spectral frequency offset, the influence of the ambient temperature is eliminated through the temperature compensation fiber measuring point, 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. The invention realizes high-precision real-time automatic monitoring of the fatigue crack state of the complex area of the steel structure.

Inventors

• LIU WEIKANG
• LI HEDONG
• SHEN YANBIN
• LUO YAOZHI

Assignees

• 浙江大学长三角智慧绿洲创新中心

Dates

Publication Date

20260512

Application Date

20251230

Claims (8)

1. 1. The device for monitoring the fatigue crack state of the conformal steel structure is characterized by comprising N optical fiber conformal sensing films, signal transmission optical fibers, a scattering enhancement optical fiber strain demodulator and an upper computer; The optical fiber conformal sensing film comprises a conformal flexible film, a scattering enhancement optical fiber strain sensing array and a temperature compensation optical fiber measuring point, wherein the scattering enhancement optical fiber strain sensing array is fixed on the conformal flexible film and comprises a plurality of scattering enhancement optical fibers and arc-shaped connecting optical fibers for connecting the scattering enhancement optical fibers; The signal transmission optical fiber is connected with the optical fiber conformal sensing film and the scattering enhancement optical fiber strain demodulator, and the scattering enhancement optical fiber strain sensing arrays in the N optical fiber conformal sensing films are connected in series; The scattering enhancement optical fiber strain demodulator is used for acquiring the spectral frequency offset of the scattering enhancement optical fiber strain sensing array and the temperature compensation optical fiber measuring point in each optical fiber conformal sensing film in the measured time period, and transmitting the spectral frequency offset to the upper computer, and the upper computer identifies the crack state in the monitoring area of each optical fiber conformal sensing film in the measured time period by utilizing the spectral frequency offset data.
2. 2. The device for monitoring fatigue crack state of conformal steel structure according to claim 1, wherein the conformal flexible film comprises a substrate layer and an adhesive layer, the substrate layer is used for fixing the scattering enhanced optical fiber strain sensing array, and the adhesive layer is used for being adhered to the steel structure to be tested.
3. 3. The device for monitoring fatigue crack state of conformal steel structure according to claim 1, wherein in the scattering enhancement optical fiber strain sensing array, the scattering enhancement optical fiber is an optical fiber which adopts ultraviolet light fiber inscription technology to periodically modulate and enhance the intensity of backward Rayleigh scattered light in the optical fiber core, and the circular arc-shaped connecting optical fiber does not perform scattering enhancement.
4. 4. The conformal steel structure fatigue crack status monitoring device according to claim 1, wherein the scatter-enhanced optical fiber strain sensing array is designed as a serpentine or S-shape.
5. 5. A method for monitoring fatigue crack state of a steel structure, which is characterized by using the conformal steel structure fatigue crack state monitoring device according to any one of claims 1-4, and specifically comprising the following steps: And attaching N optical fiber conformal sensing films connected in series on the surface of a detected steel structure in a conformal manner, collecting the spectral frequency offset of a scattering enhancement optical fiber strain sensing array and a temperature compensation optical fiber measuring point in each optical fiber conformal sensing film in a detected time period by using a scattering enhancement optical fiber strain demodulator, and identifying the crack state in a monitoring area of each optical fiber conformal sensing film in the detected time period by using the spectral frequency offset data.
6. 6. The method for monitoring fatigue crack state of steel structure according to claim 5, wherein the crack width at each measuring point on the scattering-enhanced fiber strain sensing array is calculated by the following formula: ; wherein W ci is the width of a crack at the ith measuring point of the scattering-enhanced optical fiber strain sensing array, SR is the spatial resolution arranged in the scattering-enhanced optical fiber strain demodulator, For the center scan wavelength of the scattering enhancement fiber strain demodulator, c is the speed of light, K ε is the strain coefficient, deltav is the spectral frequency shift due to both strain and temperature, as measured by the scattering enhancement fiber strain sensing array, deltav T is the spectral frequency shift due to temperature, as measured by the temperature compensating fiber measurement point.
7. 7. The method of claim 6, wherein the crack width W c and the crack position P ci of each of the respective diffusion enhancing fibers on the diffusion enhancing fiber strain sensing array are expressed as: ; Wherein W ci is the width of a crack at the ith measuring point of the scattering-enhancement optical fiber strain sensing array, L is the length of each scattering-enhancement optical fiber in the scattering-enhancement optical fiber strain sensing array, and n is the number of segments of each scattering-enhancement optical fiber.
8. 8. The method for monitoring the fatigue crack state of the steel structure according to claim 5, wherein the crack trend, the length and the width of the steel structure surface are characterized according to the geometric form of the optical fiber conformal sensing film attached to the steel structure surface to be tested.

Description

Device and method for monitoring fatigue crack state of conformal steel structure Technical Field The invention belongs to the technical field of steel structure fatigue crack monitoring, and particularly relates to a follow-up steel structure fatigue crack state monitoring device and method. Background The steel structure is widely applied to bridges, stadiums, super high-rise buildings and industrial facilities, is often influenced by factors such as cyclic load, wind vibration, temperature change, corrosion, welding residual stress and the like in the service process, and is extremely easy to generate fatigue cracks at key stress positions. The fatigue crack has the characteristics of strong concealment, high expansion speed and the like, and if the fatigue crack cannot be found and evaluated in time, the structural safety is seriously endangered. Therefore, the development of long-term, continuous and quantitative monitoring of the surface cracks of the steel structure has important engineering significance. In an actual steel structure, cracks often appear in welding seams, stiffening rib intersections, joint connection plates, lug plates, toe areas, component curved surface transition areas and other geometric abrupt change parts, and the areas generally have the characteristics of complex curvature, uneven surfaces, limited space, obvious stress concentration and the like, so that the existing crack state monitoring technology forms a serious challenge. The traditional nondestructive detection methods such as ultrasonic, magnetic powder, permeation and the like rely on manual operation, can only be implemented on a contactable and flatter surface, cannot realize real-time monitoring of complex parts, are susceptible to coating, rust or shielding by visual detection and image recognition methods, have limited crack quantification capability (Chinese patent document with publication number of CN120891001A, CN113899746A and the like), and the point sensor and the conventional fiber Bragg grating FBG are limited in laminating property and coverage range, and cannot effectively reflect crack generation and expansion states of complex morphology areas. The Chinese patent document with publication number CN116577406A discloses a real-time high-precision ACFM crack state monitoring method, which processes the rotating magnetic field distortion signal of the steel structure to be detected by analog signals, amplifies the processed weaker rotating magnetic field distortion signal by amplifying and filtering, and thus completes the monitoring of the crack defect on the surface of the steel structure to be detected. However, the invention mainly relies on a single physical field, and the monitoring range is limited. Although the distributed optical fiber sensing technology has advantages in the aspect of continuous strain measurement, common optical fibers are difficult to attach to the surface of an irregular steel structure along with the shape, and the problems of insufficient strain transmission, high signal noise, easy installation and the like are easy to occur. Meanwhile, the backscattering strength of the common single mode fiber is limited, so that tiny strain change caused by cracks is not easy to accurately identify. Therefore, the prior art still has obvious defects in the aspects of the conformality, the spatial resolution and the quantitative inversion of the crack width of the complex detail part of the steel structure. In view of the above problems, there is a need to develop a novel monitoring scheme that can adapt to the surface of a complex steel structure, provide millimeter-sized spatial resolution, have high signal-to-noise ratio and temperature compensation capability, and can realize quantitative recognition of crack positions and widths. Disclosure of Invention The invention aims to solve the technical problem of fatigue crack monitoring of a complex part of a steel structure in structural health monitoring, and provides a follow-up steel structure fatigue crack state monitoring device and method, which can monitor the crack state of the complex part of the surface configuration of the steel structure. The technical scheme adopted is as follows: the device for monitoring fatigue crack state of conformal steel structure structurally comprises N optical fiber conformal sensing films, signal transmission optical fibers, a scattering enhancement optical fiber strain demodulator and an upper computer, wherein N is more than or equal to 1; The optical fiber conformal sensing film comprises a conformal flexible film, a scattering enhancement optical fiber strain sensing array and a temperature compensation optical fiber measuring point, wherein the scattering enhancement optical fiber strain sensing array is fixed on the conformal flexible film and comprises a plurality of scattering enhancement optical fibers and arc-shaped connecting optical fibers for connecting the scattering enhancement op