Study On Fatigue Life Prediction Of Excavator Stick Based On Load Spectrum

The fatigue failure of domestic excavator working device is a key factor that restricts the domestic excavators to improve quality.This paper is combined with the project supported by the National Science and Technology Support Program "Research and application of key technologies for energy-saving and emission reduction of construction machinery"(No.2015BAF07B00).An excavator stick is taken as the research object,based on the operating characteristics of the excavator,a load spectrum test program for the excavator stick is proposed.The major operation condition of the excavator was tested for two different job object,and the time history curve of the pressure and displacement of each hydraulic cylinder was obtained.Basing signal processing theory,using MATLAB and nCode software to achieve preprocessing of measured load signals such as filtering and denoising,removing trend terms,etc.On this basis,using theoretical mechanics to calculated the hinge point forces of the stick and determined the bench test loading force.According to the obvious segmented working characteristics of the excavator,a method for processing the stick load according to the operation segment was proposed.The random stationarity test was performed on the load signals of each operation segment,and it was concluded that the stick load signal with the operation segment as the basic unit is a stochastic stationary process.Rain-flow counting was performed on the load data of each operation segment,and then the load frequency non-parametric extrapolation based on each rain-flow matrix.Finally,the extrapolation matrix of each operation segment is superimposed to composed the multi-workload synthetic load spectrum.In order to facilitate the implementation of the fatigue test,the "dig-continuation-dig" 8-grade program load spectrum of stick was compiled based on fluctuation center method.The finite element analysis of the stick is performed using ANSYS Workbench.Combining with the stick S-N curve that obtained from the material characteristics,structural characteristics and manufacturing process of the stick,the fatigue life of the stick is predicted using stress fatigue analysis method in the software nCode DesignLife.The fatigue life of the stick with different loads was analyzed and explained,and the acceleration spectrum of the stick fatigue test was formed.Through the research work of the dissertation,preliminary established excavator stick load spectrum test,compilation and fatigue life estimation method.This provides a reference for the anti-fatigue design of the excavator stick.