| Fretting fatigue is one of the most common failure modes in mechanical structures,which leads to the rapid propagation of fatigue cracks between contact surfaces and greatly decreases the life of components.In practical engineering,the safety and stability of mechanical equipment operation is often affected by fretting fatigue,which leads to greater safety accidents,so it needs to be studied systematically.The experimental method can effectively carry out research on fretting fatigue.Previously,scholars mostly carried out experimental research on uniaxial loading or biaxial loading under fixed normal load,considering relatively simple working conditions.In practical engineering,many components of mechanical equipment often work in complex working conditions,so the study of fretting fatigue under complex working conditions is particularly important.Therefore,this paper takes the actual engineering background as the entry point to carry out the research on the complex working condition that the aluminum alloy specimen is subjected to alternating load in the normal direction and has phase difference with the axial load.According to this research,the stress field distribution of the contact area between the specimen and the fretting pad under typical and complex working conditions was discussed by finite element analysis.The fatigue test under complex working conditions was carried out by using the independently designed testing machine which could apply the alternating normal load.The main research contents of this paper are as follows:(1)By referring to the traditional fretting fatigue model,test principle and the existing fatigue testing machine,a set of testing machine system is designed which can carry out the fatigue test under complex conditions,and the loading device and the test fixture are designed.In order to ensure the accuracy of testing machine loading,Abaqus software was used as a tool to analyze the errors involved.According to the analysis results,these errors have little impact on the loading of the testing machine is accurate.(2)Creo and Abaqus software were used to establish the three-dimensional finite element model of the contact between the specimen and the fretting pad.The distribution of stress field in contact area under typical and complex working conditions is discussed respectively.The influence of axial load,normal load and stiffness on the distribution of stress field is explored under typical working conditions,and it is known that the normal load has the greatest influence on the distribution of stress field in the contact area,which needs to be further studied.It is proved that the study of alternating normal load involved in this paper is valuable.The influence of different phase difference on stress field distribution is investigated under complex working conditions.The results show that: with the increase of phase difference,the adhesive region of the contact area tends to decrease.(3)The self-designed biaxial loading fretting fatigue testing machine is used to carry out tests under complex working conditions.According to the test results,the influence of different phase differences on the fatigue life of specimens under the action of alternating normal load and the causes of this phenomenon are explored.The micromorphology of fracture and contact surface was observed by scanning electron microscope,and the fretting fatigue mechanism was studied.According to the results,with the increase of phase difference,the operation mechanism of the contact zone changes from partial slip to gross slip,which affects the fatigue life of the specimen.At the same time,it also explains the reason why the stress field distribution in the contact area and the decrease trend in the adhesive area under different phase differences.Through the research of this paper,the fretting fatigue behavior under the action of alternating normal load is preliminarily revealed,and the research content of fretting fatigue is expanded,which can provide better theoretical guidance for the research of practical engineering fretting problems. |
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