The missing nut defect in concrete fasteners directly affects its load-bearing capacity.In order to ensure the safety of engineering structures,it is proposed to use the detection surface magnetic field intensity distribution characteristics to identify missing nut defects in screw fasteners.Firstly,the magnetic field strength at three sets of positioning detection points is calculated using finite element software to accurately locate the screw axis.Secondly,on the basis of completing the screw positioning,the change law and characteristics of the magnetic field strength on the screw axis were simulated and calculated to determine whether there were nut missing defects on the screw.Finally,a stable magnetic field emission and Gaussian meter detection test platform was built to measure the waveform of magnetic field strength with the magnetic field emission position with or without nuts,which verified the rationality of the detection method and simulation calculation results.The results show that compared with fasteners without nuts,when nuts are present in M30 screws,the magnetic field strength at the nut will have a sudden change of up to 0.23 mT,and the mutation amount can distinguish whether there is a nut on the screw and the relative position of the nut,which has high sensitivity and reliability,and provides method support for non-destructive testing of nut missing defects in concrete structural fasteners.
concrete fastenersmissing nut defectsteady magnetic fieldnon-destructive testing
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