Research On Fatigue Life Prediction Of Wire Rope Based On Improved Field Strength Method

The precursory characteristics of steel wire rope are not obvious when fatigue fracture occurs,which makes it have some hidden trouble in engineering application.It is of great theoretical value and practical significance to analyze and study the fatigue failure process of steel wire rope and to explore a scientific and reasonable method for predicting the life of steel wire rope.The research object of this paper is 6 × 31WS+FC wire rope.When it is subjected to load,its mechanical characteristics are analyzed and calculated.On this basis,the field strength method is improved.The fatigue life of steel wire rope is estimated by using the improved field strength method,and the predictive power of the improved field strength method is verified and evaluated by relevant tests.This paper mainly completed the following work:Firstly,the three-dimensional solid modeling of steel wire rope is established and the geometric characteristics of steel wire are analyzed.The space helical equation of wire rope in straight state and bending state is obtained by coordinate transformation principle.The three-dimensional geometric model of steel wire rope was established in NX UG,and the geometric characteristics of each wire in the strand are calculated and analyzed by using MATLAB.Next,analyze and calculate the mechanical properties of steel wire ropes under load.The mechanical model of 6 × 31WS+FC wire rope is established based on Costello's theory of elastic wire rope mechanics,and the internal stress of the wire rope is analyzed and calculated.The results show that the dangerous part of the wire rope in the course of operation is between the two strands of the wire rope,and calculated the fourth strength theoretical equivalent stress of the dangerous point.The correctness of wire rope mechanics analysis is proved by ANSYS finite element simulation.Then,the improved field strength method is used to estimate the wire rope life.Based on the original field strength method,the three-dimension damage area and the three-dimension damage function with practical physical significance were redefined,and the McDiarmid and Brown criteria were used as new destruction functions to consider the impact of the wire rope to withstand multi-axis non-proportional loads during operation process.The fatigue life of wire rope is estimated by the improved field strength method.Finally,the ability to improve the field strength method to predict the life of wire rope is evaluated.The real life of steel wire rope is obtained by fatigue test of steel wire rope.The nominal stress method and local stress strain method are used to estimate the life of wire rope under high cycle fatigue and low cycle fatigue respectively.The estimated results of the nominal stress method,local stress-strain method,original field strength method,and improved field strength method were compared with the experimental results for error statistical analysis.The results show that under high cycle fatigue,the average logarithmic lifetime error of the improved field strength method is 1.22%,5.61% lower than that of the nominal stress method and 1.55% lower than that of the original field strength method;Under low cycle fatigue,the mean logarithmic life error is 1.81%,3.73% lower than that of the local stress strain method,2.75% lower than the original strong method.Compared with other methods,the improved field strength method is the best method to predict the life of wire rope...