Research On Fatigue Life Prediction Of Steel Wire Rope Based On Grey Theory Under Small Sample Condiction

Steel wire rope plays an important role in the field of engineering application,its reliability and fatigue life prediction are always important academic subject.However,it is difficult to predict the fatigue life of the wire rope,due to the large amount of experiment sample required,many uncertain factors and the complex geometric and mechanical model of the wire rope.Based on the small sample fatigue life data of steel wire rope,this paper takes 40 6×31SW FC type steel wire rope as the research object,and its fatigue life under different tension forces is predicted through the fatigue life prediction method based on the grey theory.Compared with conventional methods,this method has the following advantages: needing less sample data,higher prediction accuracy,and simpler prediction model.Moreover,this method has certain innovation and engineering significance.The main content of this paper includes the following four aspects:First of all,reliability life prediction sequence of the wire rope is obtained based on the grey prediction model.The fatigue test data is obtained by small sample bending fatigue test on the wire rope bending fatigue test bench.After that,in order to determine the reliability life of wire rope under different tension forces when the reliability is 0.9999,the test data of small sample is processed,and the mathematical model of wire rope reliability is established based on Weibull distribution curve.According to the distribution characteristics of wire rope reliability life,an improved grey GM(1,1)model is constructed to realize the simulation prediction of wire rope reliability life under different tension forces,and obtain reliability life prediction sequence.Next,the dangerous part of the wire rope and its mechanical model are determined.The mathematical equations of the space spiral of wire rope in straight section and bending section are determined according to the actual structure of 40 6×31SW FC type wire rope.Then the three-dimensional model of wire rope is constructed.On this basis,the mechanical model of straight and curved sections of wire rope is established.Furthermore,the dangerous parts and their stress of wire rope are determined.Then,the stress-life curve of the dangerous part of the wire rope is determined.In order to determine the equivalent stress-time history curve of the dangerous part,this paper carrys out dynamic simulation of the wire rope under different tension forces according to the actual bending fatigue test process,and combining with the mechanical model of the dangerous part of the wire rope and the multi-axis fatigue theory.After that,the equivalent stress-time history curve of the dangerous part of the wire rope is processed by rain-flow counting method,and the equivalent stress spectrum is obtained,which is converted into the alternating stress with the same life span by Goodman method.Following this,this paper uses support vector regression machine method to fit the equivalent alternating stress and the reliability fatigue life sequence,and then determine the stress-life curve of dangerous parts of steel wire rope.Finally,the fatigue life prediction of wire rope under different loading conditions is realized.Based on the stress-life curve and the fatigue damage accumulation theory,this paper has established the fatigue life prediction model,and realized the fatigue life prediction of the wire rope under different loading conditions.Moreover,the accuracy and scientificity of the fatigue life prediction method based on grey theory is proved by comparing with the conventional method and the test results.