Development Of The Tensile Stress Testing System For Steel Strands Based On The Villari Reversal Effect

As the important component of bridge cable,monitoring the tensile stress state of steel strand is of great significance to ensure the normal operation of the cable.The existing magnetic testing method of ferromagnetic components mostly determines the optimal stress to characterize the magnetic parameters by analyzing the magnetic parameters of each magnetized working point with the change of stress.The searching process is cumbersome and mostly relies on human judgment,and lacks theoretical guidance for rapid positioning.Therefore,this dissertation proposes a stress characterization model based on force-induced magnetic induction strength.According to the structural particularity of steel strands,the model is applied to the tensile stress testing of steel strands,and the development of steel strand tensile stress testing system is carried out.Firstly,a stress characterization model based on force-induced magnetic induction is established.The intersection point and the Villari reversal point are distinguished and explained from the two points of "variable magnetic field" and "variable stress field",and the stress characterization model based on force-induced magnetic induction is derived according to the characteristics of Villar reversal point.Then,according to the characteristic that the bias of the magnetic induction to the stress at the reversal point of Villari is zero,obtaining the relationship between the force-induced magnetic induction and the stress.Considering high stress,the stress reciprocal term in the model is omitted,and the force-induced magnetic induction intensity has a first-order linear relationship with the stress.Secondly,the steel strand tensile stress testing system was completed.The finite element analysis of the leakage magnetic field distribution on the surface of the strand under constant magnetic excitation was carried out by the ANSYS software.The orthogonal distributed magnetic sensor and the array constant magnetic sensor were designed to obtain the axial and normal magnetic induction of the strand surface.Then,the multi-channel testing instrument based on the FPGA(Field Programmable Gate Array)was developed according to the signal characteristics of the array sensor.In addition,the modular layout method is adopted to reduce the layout area of the circuit and improve the fault tolerance and interchangeability of the circuit.The performance test results show that the hardware acquisition system meets the signal acquisition requirements.Finally,the development of the steel strand tensile stress constant magnetic testing software system was completed,and the system experimental test platform was built,including the steel strand force loading device,the steel strand tensile stress constant magnetic sensor system,the pressure sensor and the PC,etc.The results show that the relative error of the tensile stress testing of the system is less than 7%.