Research On Some Key Issues In Anti-fatigue Design Of Large Flange Shaft

The turnover is a kind of heavy equipment used for the position and attitude adjustment of operating objects of different specifications.Flange type spindle is one of the most commonly used spindle forms for large turnover.The flange shaft is subjected to varying stresses when the turnover is working.Fatigue failure caused by alternating stress is one of the main failure forms of flange shaft.Therefore,it is necessary to study the fatigue of large flange shafts.The study of fatigue problems of large structural members generally needs a large number of tests to complete.However,due to the constraints of the test site,test conditions and other factors,the prototype test of large components can’t be realized in many cases,and then measure the S-N curve of large members,resulting in the anti-fatigue design of large structural members has become a major problem restricting the development of heavy equipment industry.In this paper,aiming at the fatigue life evaluation and anti-fatigue design of large flange shaft,a new fatigue life evaluation method of large structural members is explored and presented to guide the anti-fatigue design of large flange shaft.The main research contents are as follows:1.The size effect of large flange shaft is studied.The fatigue tests of geometrically similar flanged shafts were carried out.The results show that the size effect of notched specimens(or specimens with cross-section mutation)needs to consider the effect of stress gradient and high-stress volume at the notch.Therefore,the concepts of relative stress gradient G and notch characteristic size L are introduced,and the influence of which on size effect is represented L G.The fatigue test data of flange shaft are analyzed and studied,and the calculation formula of dimension coefficient of flange shaft is given to realize the quantitative evaluation of dimension effect of flange shaft.2.The fatigue comprehensive correction coefficient of large flange shaft is studied.Considering the influence of stress concentration,size effect and surface machining state,a new calculation model of fatigue comprehensive correction coefficient of large flange shaft is deduced and given.The rationality and reliability of the correction coefficient are verified by comparing with the existing correction coefficient and fatigue test of flange shaft.3.The fatigue life prediction method of large flange shaft is proposed.The S-N curve of large flange shaft is obtained by modifying the comprehensive correction coefficient.Combines with the cumulative damage theory and cycle counting method,the fatigue life prediction of flange shaft under arbitrary alternating stress is realized by APDL programming of finite element software ANSYS.The fatigue test of flange shaft is carried out,and the comparison between the finite element calculation results and the test results show that the fatigue life prediction method for large flange shaft presented in this paper has higher prediction accuracy.The difficulty and error of fatigue life prediction of large flange shaft causes by the failure of prototype test are solved.4.The crack propagation characteristics of flange shaft are studied.Based on fracture mechanics theory,a three-dimensional numerical simulation program is developed for the fatigue crack propagation of a cracked flange shaft.The crack propagation characteristics of the existing flange shaft are studied by numerical simulation and fatigue test.The results show whether the crack propagation is related to the initial crack angle of the flange shaft,and the fatigue crack propagation can be achieved only when the initial crack angle is in a certain effective interval.At the same time,the determination formula of the crack initiation of the existing flange shaft is obtained,which can be used as the criterion of whether the existing crack of the flange shaft expands,providing a basis for the repair,reinforcement and scrapping of the flange shaft in service.5.Research on anti-fatigue optimization design of large flange shaft is carried out.To optimize the structure with the lightest weight and the maximum fatigue life,the author analyzed the design factors of the large flange shaft structure,combined with the large flange shaft fatigue life research method proposed in this paper,the flange shaft is optimized.The detailed design of flange shaft structure is explored,and several effective structural design and improvement schemes are putted forward.The finite element method is used to analyze the fatigue life of the improved flange shaft.The results show that the design method proposes in this paper is effective,which provides a reference for the anti-fatigue design of similar large structural members.