Study On Crack Detection Of CFRP-strengthened Steel Structure Based On Fiber Bragg Grating

Metal structural damage caused by crack initiation and expansion is a common type of failure to the crane.It has serious threat to production and life safety.Carbon Fiber Reinforced Polymers(CFRP)have high specific strength,specific stiffness and fatigue resistance.CFRP is an ideal reinforcement material to the damage structure,which can enhance the structural strength and avoid further expansion of the crack.As a result,the service life of mechanical equipment is extended.Fiber Bragg Grating(FBG)sensor has the properties of high sensitivity and strong anti-interference ability.It can measure the strain of the structure accurately.In this paper,the FBG strain transmission of CFRP reinforced steel structure is analyzed and simulated.This master thesis focuses on the structure of the cantilever beam strengthened by CFRP,and the structure crack is identified by FBG strain array.The main contents of this master thesis are as follows:1)The FBG strain transfer is carried out,and the transfer model of stress in each intermediate layer is established.The single-middle and multi-intermediate strain transfer formulas are carried out.The strain transfer ratio of steel structure strengthened by CFRP was calculated and simulated,and then compared.2)To vibration system,the calculation method of the strain frequency response function under the harmonic load is studied.For noise signal,the principle of the wavelet threshold noise reduction and the noise reduction process of experimental data are discussed.Then,the imaginary part of the strain frequency response function is used to calculate the damage identification index of the strain frequency response function.3)The finite element model of CFRP reinforced steel structure was established by ABAQUS.The structural strain distribution was analyzed by applying harmonic load,and the strain array was extracted.Then,the damage identification index of the strain frequency response function imaginary part which used to identify crack was calculated by strain array of each measurement point.Also,the damage identification analysis in different crack length and without CFRP was studied.4)The test platform was built through the test equipment and the test piece.The strain data of FBG sensor array was collected with the fiber grating sensing analyzer.And then the wavelet noise reduction and spectrum analysis are carried out by MATLAB.Finally,the strain matrix and the damage identification index of strain power spectrum frequency response function are introduced.The damage identification is carried out by the damage index.The result is verified to the simulation.By means of the research above,this paper testified the effectiveness of FBG strain array damage identification parameters to detect crack damage on CFRP reinforced steel structure.