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The Study Of The Deformation Characteristics Of Welded Cracks And Cantilever Beams Based On Fiber Bragg Grating

Posted on:2021-02-18Degree:MasterType:Thesis
Country:ChinaCandidate:Y K LiuFull Text:PDF
GTID:2381330620478629Subject:Engineering
Abstract/Summary:PDF Full Text Request
Steel is widely used in manufacturing,construction,machinery,marine,aerospace and other fields as well as plays an irreplaceable role in these fields.In addition,cantilever beam structures and welded structures are frequently applied to large steel structures.Welded cantilever beam structures are quite common in jack-up drilling platforms,tower cranes and large buildings.Due to the instability of welded structure and the influence of various loads,bending moments and torques on cantilever beam structure,deformation and cracks are easy to occur,thus causing the instability of the whole structure and the occurrence of accidents.Therefore,it is particularly important to detect cracks and cantilever beam deformation.Common methods for crack detection and displacement change detection at the free end of cantilever beam include direct observation method,strain gauge detection method,electromagnetic sensor detection method,etc.However,all these traditional methods mentioned above have some problems,such as the sensor is affected by human measurement errors and electromagnetic signals.As a result,the detection effect is not ideal in most cases.The fiber grating sensor has the advantages of small volume,little electromagnetic interference,stable chemical performance,large transmission capacity,distributed measurement and the like,which can better realize the detection of micro cracks and deformation.Therefore,this paper proposes to detect and analyze prefabricated cracked steel plates and cantilever beam structures on the basis of fiber bragg grating.The main research contents and achievements of this paper are as follows:(1)On the basis of the coupled mode theory,the fundamental theory and sensing characteristics of fiber gratings are analyzed,and various fiber gratings are simulated and analyzed map by using Matlab;(2)The ANSYS finite element analysis method is adopted to establish the model the analysis of which is carried out on the prefabricated crack steel plate and cantilever beam structure in order to draw the equivalent effect diagram,equivalentstrain diagram and displacement change diagram,and then use those diagrams to do the corresponding analysis and research.It is found that the crack tip has a tendency to expand when the crack tip continues to be subjected to the force,and the force on the free end of the cantilever beam structure will cause the deformation of the whole structure.(3)The experimental system of Welding the steel plate and cantilever beam structure is to be built on the basis of fiber grating.The relationship between fiber grating center wavelength and cracks direction of change as well as width is studied through the change of fiber grating center wavelength amplitude.The stress point displacement change at the free end of cantilever beam structure is measured.The application of fiber grating sensor to the detection of small displacement change at the free end of cantilever beam structure is fully studied through theoretical analysis and experimental measurement.Through the above two experiments,it can be concluded that the FBG sensor can well detect the crack direction,width and micro-displacement of the free end of the cantilever beam.
Keywords/Search Tags:Fiber Bragg Grating, Sensing, Cantilever beam, Steel plate crack, ANSYS finite element analysis
PDF Full Text Request
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