Research On The Quantitative Relation Between Stress And Damage Of Magnetic Memory Signal Of Steel Wire Rope

Wire rope is widely used in mining,construction,bridge and other engineering fields.After long-terrm high frequency operation,the steel wire rope will have some defects such as wear,wire breakage,strength decline,rust and so on.If it can not be detected or replaced in time,it will cause serious accidents once the wire rope breaks.As a new nondestructive testing technology,metal magnetic memory testing can locate the stress concentration and defect location of wire rope,but the quantitative relationship between stress state and damage degree is insufficient.For wire rope stress state and damage degree of quantitative relationship problems,based on the theory of magnetic mechanical effect,by means of experiment and numerical simulation technology,through the experimental research method of'wire-strand-rope,space form from simple to complex,this paper conducts the deep research of different stress state and damage degree of magnetic memory signal of wire rope.What's more,the theory of magnetic mechanical effect,the theory of magnetic coupling and the theory of magnetic dipole model are proved.And the discriminant characteristic variables of magnetic memory signal are proposed corresponding to the states of 'wire','strand'and 'rope',which provides an important theoretical basis for the magnetic memory detection of wire,rope.For the relationship between the strength of magnetic memory signal and stress state of single wire under different defect parameters and different stress states,tension test,bending and torsion test of single wire under different defect parameters(defect width b=1mm,2mm,3mm,defect depth h=0.1d,0.2d,0.3d)were caried out,and the stress of each cross section of single wire under different defect parameters and different stress states were obtained.At the same time,th,e magnetic memory eddy current tester is used to monitor the whole process of the magnetic memory signal change with the increase of the load.In this way,the normal leakage magnetic field intensity and magnetic memory characteristic of each cross section ofthe single wire can be obtained.Through the systematic analysis of the characteristic variables of magnetic memory signals under different defect parameters and different stress states,it can be concluded that the peak and zero-crossing phenomena can distinguish the defect position of the specimen,and the change of defect depth has a great influence on the amplitude of the magnetic signal;the zero-crossing position combined with the extreme position of the gradient curve can accurately locate the defect position of the specimen;and the abrupt extreme point phenomenon of magnetic memory signal in curved state can be used to judge the position of dangerous section under the asymmetric bending;the abrupt extreme point of magnetic memory signal curve in plastic torsion stage can judge the damage position;the incremental mean square deviation curve of magnetic memory signal can divide the dangerous section of single wire plastic torsion stage,and the minimum point of curve can be used as the early warning point before single wire torsion failure.For the problem of distinguishing characteristic quantity of magnetic memory signal and damage of strand under different defect conditions of single strand wire rope,the tensile test of strand specimens under different defect depths was carried out to monitor the change of magnetic memory signal of surface defect and smooth position of specimens under different load levels,and the corresponding relationship between the overall magnetic memory signal of specimens and load was obtained.It is found that the zero-crossing phenomenon of magnetic memory signal curve can not be used to accurately identify the defect location of wire rope.The gradient curve extremum method has a higher accuracy in the initial state and has no obvious discrimination effect in the loading stage.The incremental analysis method is used to draw the magnetic memory signal curves under various loads,to define the incremental amplitude threshold of components,to reveal the intrinsic relationship between the incremental amplitude threshold and the working status of components.Based on the incremental amplitude threshold,the method for judging the safety state of the bearing capacity of damaged strands is established.For the evolution law of the tension stress and magnetic memory signal strength of the whole rope under different wire breaking conditions,the tension test of the whole rope without wire breaking and under different wire breaking conditions was carried out,and the change of magnetic memory signal of the wire rope under different load levels was monitored.Through the comparison and analysis within the magnetic memory signal curves of the wire rope without wire breaking and broken wire rope,it was found that the number of broken wires has a significant effect on the magnetic memory signal.The damage location of the whole rope is identified by the maximum extremum of the magnetic memory signal curve and the gradient curve,and the stress state of the rope is defined by drawing the incremental variance curve.The evolution law of the tensile stress and the magnetic memory signal strength of the rope under different working conditions is clarified,and the early warning of the rope is completed.The damage location of the whole rope can be judged by the maximum extremum of the magnetic memory signal curve and gradient curve,and the stress state of the rope can be judged by drawing the incremental mean square deviation curve.The evolution law between the tension stress and the magnetic memory signal strength of the rope under different working conditions can be confirmed,which can be used as the basis for early warning of the rope.Based on the theory of magnetic mechanical effect and force-magnetic coupling,the identification of wire rope damage induced by defects and broken wires is considered as the problem of magnetic memory signal change caused by stress change of wire rope.Considering the different rules of magnetic characteristic parameters(permeability and coercivity)varying with the stress of ferromagnetic components in elastic and plastic stages,a modified model of force-magnetic coupling considering the influence of permeability and coercivity is proposed innovatively.Compared with the experimental results,it is found that the results of the improved model can better analyze the coupling simulation of the torsional steel wire through the calculation of numerical program compiled by APDL language.