Research On Prediction And Analysis Of Fatigue Life Of Combined Bearing

As the key supporting parts of the tool spindle,the combined bearing of the wellbore trajectory control tool has a direct impact on the working performance of the tool because of its fatigue life.In this paper,two pairs of self-aligning thrust roller bearing and one pair of self-aligning roller bearing are taken as the research object.The contact loads of roller and raceway under different loads were studied by static and dynamic analysis respectively.The influence of load and structure factors on the life of combined bearing is analyzed,and the life of combined bearing obtained by two methods is compared and analyzed.The contents of the research are as follows:The function of the combined bearing in the tool is analyzed.The non-critical dimension is neglected,the geometric model of combined bearing is established by combining with the material object of combined bearing in the principle prototype.In the process of static analysis,considering the influence of disc spring on both sides of combined bearing,the relationship between axial force and pre-compression value of disc spring is analyzed,and the physical model of combined bearing is established.By using the Stribeck maximum rolling load estimation formula and the Palmgren bearing displacement estimation formula,the load of each bearing in the combined bearing is studied,and the mathematical model of combined bearing is established.Based on the assumption that the radial displacement of each bearing is the same in the combined bearing,the displacement coordination condition of the combined bearing is established,and the relationship between the axial displacement and the radial displacement is discussed.The single variable method is used to calculate the relationship between the internal loads of combined bearing by Matlab,and the influence of structural parameters(the type of disc spring,the pre-compression value of disc spring and radial clearance of self-aligning roller bearing)on internal loads is studied,which lays a foundation for the calculation and analysis of fatigue life.According to the actual working state of the combined bearing,the dynamic analysis model of combined bearing is established by using the D'Alembert's principle,and the dynamic equations of each bearing are established.By using ADMAS software,the dynamic simulation analysis of the whole bearing is carried out.The load distribution diagram of the rolling body is obtained by setting the inner and outer ring of the bearing as a rigid body,and the influence of external load and rotational speed on the load of the bearing roller is studied.The load distribution law of each bearing inside combined bearing is studied by using quantitative analysis method.The results show that there is a certain fluctuation of the load on each bearing in the combined bearing,but the whole load tends to be stable,which is in good agreement with the actual moving force state.Based on the Weibull distribution of the life of combined bearing and the standard calculation method of the fatigue life of the bearing,the fatigue life calculation model of combined bearing is established by using multiplication theorem of probability.At the same time,the fatigue life of combined bearing is discussed based on static analysis and dynamic analysis.When the fatigue life of combined bearing is studied by statics analysis,the effects of pre-compression value and radial clearance on the fatigue life of bearing are studied,and the optimum pre-compression value and radial clearance are obtained.The effect of actual working state and variable load on combined bearing is simulated.The fatigue life of combined bearing is studied by dynamic analysis,the variable trend of fatigue life under variable load and the influence of load and rotational speed on fatigue life are studied.Finally,the fatigue life of combined bearing obtained by static and dynamic analysis is compared and analyzed.The results show that the fatigue life of combined bearing obtained by statics method is higher,the fatigue life of combined bearing obtained by dynamic method is more practical because of the influence of centrifugal force and vibration shock.The research results in this paper can be used in the design,analysis and simulation of combined bearing in the wellbore trajectory control tool.The fatigue life prediction method of combined bearing based on dynamics can be used to predict and analyze the fatigue life of combined bearing,which has strong practical significance in engineering.