Research On Fretting Fatigue Life Of Surface To Surface Contact Considering Plasticity

In the industrial field,the key structure of the major equipment under the complex service conditions is subject to the action of alternating load,vibration load and so on,resulting in micro sliding or rolling,which is referred to as fretting,causing fretting damage to reduce the life of structure seriously,and resulting in certain economic losses and security risks.Take aeroengine turbine as an example,it bears the severe conditions such as high power,high temperature?up to 1900??and high speed?30-60 thousand r/min?under the service.There is a small relative displacement and high contact pressure between the two contact surfaces of dovetail tenon at the connection of blade and disc,easy to cause serious fretting fatigue and then lead to major safety accidents of machine damage and human death.Therefore,accurate prediction of fretting fatigue life of structure has attracted the attention of scholars and engineers at home and abroad.At present,the main problem in the prediction of fretting fatigue life is that the influence of plasticity of structure under alternating load is not fully considered,which makes the prediction of fretting fatigue life more conservative.Therefore,fully considering plasticity on fretting fatigue has certain theoretical significance for improving the accuracy of fretting fatigue life prediction.Taking the standard model,which is surface to surface contact,and dovetail joint model as research objects,combined its service environment,and analyzing the fretting damage mechanism to predict the fretting fatigue life in this paper.The specific research contents are as follows:1)Establishment and verification of the prediction model of fretting fatigue life considering plasticity:to accurately predict fretting fatigue life of structure,the first problem lies in solution of t maximum contact pressure caused by the high stress gradient at the edge of the contact area,which was solved by the contact theory of Oxford University.Secondly,aiming at the macroscopic appearance of crack initiation and rapid fracture after slow propagation to a certain extent under the load,the critical damage parameter D_crit and maximum plastic strain????_p were determined accurately by analyzing the change of elastic modulus under the cyclic load.Combined with the fretting fatigue test data of standard specimens under different loads,the unknown parameters in the model were determined by MATLAB,and the prediction model of fretting fatigue life considering plasticity was established.Another two groups of fretting fatigue tests of standard specimens under different loads were carried out.And the test data were compared with the prediction data of the new theoretical model,and the error is within 15%.The accuracy of the model was verified.2)Fretting fatigue life prediction model of dovetail:to study the applicability of complex dovetail structure,the fretting fatigue test data of the dovetail specimen under different loads were compared with the theoretical prediction,and the error was within 12%.According to the comparison,the prediction model based on the standard specimens was applicable to the dovetail.Furthermore,the similarities and differences between dovetail and standard specimen structure under fretting load were analyzed.It is found that the main factors affecting fretting fatigue life prediction are the same contact form under load and the local structure similarity of the trailing edge of the contact area.3)Considering the time,equipment and difficulty of fretting fatigue test,and the current situation that the established fretting fatigue life prediction model does not cover all the influencing factors,the influencing factors of fretting fatigue of standard specimens and the sensitivity of dovetail fretting fatigue to the change of contact area parameters were analyzed with the aid of ABAQUS,in this paper.Finally,the dovetail structure was improved to minimize the fretting stress?_fretting.