Study On Fatigue Reliability Of Shield Main Bearing Under Unsteady Load

As a key part of transmitting force and movement in shield construction,the working performance and fatigue life of the main drive bearing directly affect the service life of the shield machine.In this thesis,aiming at the problem that the main shield bearing is prone to fatigue failure when the load changes randomly,the mechanical analysis model of the main bearing is established,and the fatigue life of the main bearing under random load is calculated.The main research contents and conclusions of the thesis are as follows:(1)Aiming at the problem of compiling the load spectrum of the main bearing,the randomly varying collected data is first converted into the load data borne by the main bearing,and then the rainflow method is used for statistical processing,and the distribution law of the average load and amplitude is obtained,and the conversion of random load to two-dimensional load spectrum is realized;Finally,the wave center method is used to equivalently convert the two-dimensional load spectrum to the one-dimensional load spectrum.(2)According to the problem of static contact characteristic distribution of main bearing,the static balance equation of main bearing is established,the static load distribution characteristics of main bearing are obtained,and the influence of clearance and oil film thickness on the load distribution of main bearing is analyzed.The results show that the maximum value of contact load and deformation of the three rows of rollers increases monotonically with the increase of clearance,and decreases monotonically with the increase of minimum oil film thickness,but the influence degree of oil film thickness is not as significant as that of clearance.(3)Aiming at the load distribution of main bearings under dynamic conditions,the transient dynamic model of main bearings is established,the load distribution of main bearings under dynamic conditions is obtained,and the influence of axial force on load distribution is studied.The results show that the change law of the contact characteristic distribution of the main bearing under dynamic is consistent with that during static,but the contact load and deformation during dynamic time are greater.The maximum contact load and deformation of the main thrust rollers increased linearly with the increase of axial force,while the remaining two rows of rollers basically did not change.(4)Aiming at the fatigue life calculation problem of main bearings,the rolling element life calculation is introduced,combined with the load spectrum and L-P theory,the fatigue life of the main bearing under all working conditions is obtained,and the influence of the number of rolling elements,diameter and contact line length on the life of the main bearing is studied.The results show that when the number of rollers increases,the diameter increases or the length of the contact line increases,the life of the main bearing shows a monotonic increasing trend.Among the three rows of rollers,the main thrust rollers had a greater influence on the life of the main bearing,while the reverse thrust rollers and radial rollers had little influence.Among the three structural factors,the change of rolling element diameter has the greatest influence on the life of the main bearing,followed by the number of rolling elements,and the contact line length has the least effect.