混凝土紧固件螺母缺失电磁无损检测

Research on electromagnetic non-destructive testing of missing concrete fastener nuts

混凝土紧固件螺母缺失缺陷直接影响其承载能力,为了保障工程结构安全,提出了利用检测面磁场强度分布特征辨别螺杆螺母缺失缺陷。首先,利用有限元软件计算三组定位检测点的磁场强度,准确定位螺杆轴线;其次,在完成螺杆定位的基础上,仿真计算螺杆轴线上磁场强度的变化规律和特征,用以判断螺杆上是否存在螺母缺失缺陷;最后,搭建稳恒磁场发射与高斯计检测试验平台,测量有无螺母时磁场强度随检测点位置变化的波形,验证了检测方法和仿真计算结果的合理性。研究结果表明,对比无螺母存在的紧固件,M30型螺杆存在螺母时,螺母处磁场强度会发生最大0.23 mT的突变,突变量可以分辨螺杆上有无螺母以及螺母所处相对位置,具有较高的灵敏度和可靠性,对无损检测混凝土结构紧固件中有无螺母缺失缺陷提供了方法支持。

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.