Research On Magneto-mechanical Effect And Magnetic Flux Leakage Monitor Of Fatigue Damage For Wire Rope

Combined with the research project of the Advanced Performance of Wire Rope in the Port Cranes, a key technological problem of the Ministry ofCommunications, this dissertation investigated the stress-effect on the magnetic flux leakage (MFL) of wire ropes and the law of the MFL signal changes during wire rope fatigue testing by experiments and modern signal processing methods based on the ferromagnetic theory, being aimed at the present problems of current wire rope testing technology. The characteristic parameters and quantitative descriptive specifications for wire rope defective signal were analyzed in detail. This dissertation present a novel method of quantitatively evaluating locate faults (LF).Based on the energy theory of domain structure movement, for the first time this dissertation inquired into the stress-effect of the wire ropes axial MFL theoretically and experimentally. The results showed that the magnitude and shape of MFL vary with the change of wire rope tension. With the stress increment, the peak to peak values of broken wires reduce obviously and the total strength of MFL signal becomes weak and the ripple of MFL signal curve appears. This dissertation indicated the tensile loads of wire rope should be considered when quantitatively evaluating the defect by means of MFL.Through the wire rope fatigue test, for the first time this dissertation investigated the law of the axial MFL changes of wire rope. The results showed the axial magnetic permeability of the reciprocating and rectilinear part of wire rope gradually increases and its distribution tends evenness. But that of the glide wheel bending part gradually decreases and its distribution tends to unevenness. The results indicated that the monitoring wire rope fatigue damage by using MFL is potentially worthwhile to develop.The circumference MFL of the wire rope has a broad space-frequency range along the axial of rope. The MFL signal was analyzed by using the multi-resolution analysis and wavelet packet analysis. The MFL signal of different frequency ranges was analyzed in detail. This dissertation put forward a method of eliminating noise and reconstituting broken wires signal and inquired the space-frequency range of the signal ripple resulted from tensile stress on the MFL signal curve. The law ofpermeability changes of different frequency range was studied during the wire rope fatigue test.Based on the review of the factors of affecting the distribution of MFL on the ferromagnetic material, this dissertation described the wire rope defects characters from MFL signal and put emphasis on the analysis of the MFL character of mass broken wires in a strand. This dissertation indicated the peak value and width and sharpness of the MFL signal, which together provided information about mass broken wires.This dissertation analyzed the quantitative evaluation problem of LMA and LF and inquired into the importance of axial testing resolution in the field of the wire rope defects quantitative evaluation. This dissertation put forward a novel method of the LF quantitative evaluation based on the radial basis function network. This method connects the input and output of the neural network with mechanical sizes of the wire rope and the tester and increased the axial testing resolution. This method was proved to be available by a few examples.