Research On Fatigue Life Of Thin-wall Taper Sleeve On Macro-micro Cross-scale Behavior

Oil-film bearings are widely used in large-scale hydropower equipment, aerospace engineering, ocean engineering, nuclear power engineering, marine machinery, heavy machinery and other fields. Thin-wall taper sleeve, as a core bearing part of oil-film bearing, its life and running stability play a vital role in the oil-film bearing performance. Up to now, the analysis of sleeve operation behavior, the establishment of sleeve scrapped rules, and the collaborative optimization of sleeve structure size are still unsolved problems.The main research aim of this thesis is to reveal operation mechanics mechanism of thin-wall taper sleeve on across-scale, to solve macro-micro fluid-structure interaction mechanism of thin-wall taper sleeve, on these basis, to explore the tensile, creep, fatigue and other mechanical behavior of thin-walled taper sleeve. And then, fatigue life prediction of thin-wall taper sleeve was implemented, and the relationship between fatigue life and its influencing factors was established. At the same time, a multi-objective dynamic intelligent collaborative optimization design method was founded, and the optimized structure and the improved size were required. At last, the fatigue life was extended and the reliability was improved.In this thesis, the main research contents and conclusions are as follows:(1) Study on the operating mechanics mechanism of sleeve on macro-micro cross-scaleThe solid domain formed by sleeve and roll was discretized by three-dimensional electrostatic multi-pole method and the improved Generalized Minimal Residual Method(GMRES(m)) based on Krylov subspace methods was used to optimize and iterate the dense non-symmetric linear equations. Among them, the nonlinear mathematical programming based on Point-Surface model was used in the elastic friction contact domain, and non-matching grid number was used in the coupling interface. The micron grade oil-film was analyzed by elastic lubrication methods and was treated as no thickness. Then Lagrange interpolation function was introduced, and the operating mechanical model of sleeve was established on macro-micro cross-scale. The correctness of this method was verified by the test of the operating mechanics mechanism of the thin-wall taper sleeve.The results show that, the distribution of oil-film force field and contact stress field are three-dimensional dynamic and non-uniform during the process of the operation. And under complex alternating stress field, the high stress singularity of seal groove located at both ends of the sleeve is the mechanics cause of bond, fracture, etc. In the design stage, the rolling condition should be considered, and the fatigue damage can be reduced by the design of the appropriate amount of interference and the thickness of the sleeve.(2) Mechanical behavior analysis and fatigue life prediction of thin-wall taper sleeveTest materials, test equipment and test methods on mechanical behavior of thin-wall taper sleeve were expounded, and a method for room temperature creep test of thin-wall taper sleeve was introduced. Meanwhile, the performance of monotonic tensile, room temperature creep and fatigue were analyzed. Considering that the running load characteristics of thin-wall taper sleeve, a non-proportional loading model of thin-wall taper sleeve was established, with the fatigue life of different rolling force, interference and sleeve diameter were compared and analyzed.The results show that the creep of thin-wall taper sleeve is a typical two-stage low-temperature creep, and its creep behavior is the result of a single degree of freedom dislocation glide. And the general Graham fitting expression for thin-wall taper sleeve remains applicability at room temperature creep. When the load is less than the yield limit of material, the increase of rolling force, interference amount, and sleeve diameter will help to improve the fatigue life of thin-wall taper sleeve, and fatigue life and the amount of interference, taper sleeve diameter is approximately in a linear relationship.(3) Study on the multi-objective dynamic intelligent collaborative design of thin-wall taper sleeveThe influence of various factors on the contact pressure was analyzed, in which the dynamic relationship between multiple targets and multiple variables was synthetically considered. And the key factors of the taper sleeve interference connection design were determined combined with the actual situation. Sample data of key factors was obtained through the experimental design, and considering the targets such as the yield strength, torque and weight, the approximate model of the response surface was established by the universal Kriging. Then, a multi-objective dynamic adjustment design method for the interference fit connection of the conical surface was established by solving the NSGA-II-type improved algorithm.Examples analysis showed that, comparing with the traditional method, this method had a higher security reliability, and the accuracy of the method was 32 times higher than that of artificial neural networks. Finally, the correctness of the method was verified by experiments.