Fabrication Of A Kind Of Buried Fissure Water Pressure Fiber Bragg Grating Sensor

Crack seepage can cause unexpected accidents in civil engineering and geotechnical engineering.Therefore,there is a need for a sensor and system for real-time monitoring of fractured water pressure.The fiber grating sensor has the advantages of small volume,small influence on the mechanical properties of the tested structure,high sensitivity,corrosion resistance,easy fabrication,easy networking,and distribution measurement.It has good application value in pressure detection.This paper combined with the province of mine disaster prevention and control of construction of state key laboratory breeding base of open fund "mine pore permeability(water)pressure of fiber Bragg grating sensor and network" and the civil engineering college of hydrostatic test for rock mass joint project,a theoretical and experimental study of a self-designed buried fissure water pressure fiber grating sensor has been carried out.The main contents include:1.The structure of fiber grating stress(strain)sensor and its application development in engineering are discussed.According to the different sensor package structure,the current status of the development of the existing fiber grating infiltration(water)pressure sensor structure and various sensors is summarized.2.Research on Fiber Grating Stress Model Theory.Based on the coupling mode theory of fiber gratings,the theoretical research on the strain-sensing principle of axial strain,radial strain and arbitrary direction of the fiber grating is carried out respectively.and theoretical models of stress fiber grating sensing in various directions were obtained.3.A buried fissure water pressure fiber grating sensor structure was proposed,and the finite element simulation analysis of the force condition of the fiber is carried out.The results are used to guide the sensor size and the design of force transmission material parameters.4.The proposed buried fissure water pressure fiber grating sensor uses polyurethane as a cylindrical structure with a length of 25mm and a diameter of 5mm.The fiber Bragg grating(FBG)is encapsulated in the middle of the cylinder.The outlets are respectively arranged at both ends and the water pressure passes through.The polyurethane material of the elastomer material is transmitted to the fiber grating to drive the FBG to realize the sensing of the water pressure.5.Experimental research on sensor sensing characteristics and fabrication of sensors.The sensor is repeatedly packaged,and its spectral characteristics,pressure and wavelength drift correlation tests are experimentally studied to further optimize the sensor packaging scheme.The experimental results show that the structure sensor has a high sensitivity to external pressure,and the maximum value can be achieved at 12.135nm/MPa in the experiment,and has a good linearity and so on.6.Research on Simulation Test of Cracked Water Pressure Similar Material.Three sensors with different center wavelengths are selected to construct a small sensor network,buried in a similar material to be modeled,and the sensing model is installed on a fracture hydraulic pressure tester.The water pressure in the input fracture is controlled to simulate the seepage of the fracture.In the case of rock and soil deformation,in the experiment,with the change of the control input water pressure,the drift of the Bragg wavelength of the sensor is very obvious,and the distribution curve of the water pressure distribution at different positions at the inlet end of the seepage water is obtained.