Fatigue Life Prediction And Reliability Analysis Of Cutterhead For TBM

With the development and utilization of underground space,TBM has become the first choice of hard rock tunnel equipment due to its characteristics of high efficiency,economy,safety and environmental protection.As the key component of TBM which directly interacts with rocks,the cutterhead is subjected to severe vibration and impact.These loadings will result in inevitable cracks.The cracks mainly initiate and grow on the cutterhead faceplate and the cutter saddle,and the fatigue failure most easily occurs on the weld joint of the cutter saddle.This paper takes TBM cutterhead structure and typical structure-cutter saddle weld as the research object respectively.We analyze fatigue life and reliability by the finite element simulation and reliability modeling.Then the influence of different parameters on the structure failure probability is also investigated to provide the reference for cutterhead structure design,manufacturing and safety construction.The main work and conclusions are as follows:(1)Finite element modeling and static analysis are carried out on the research object to obtain the danger point position.The stress time history of the danger point is obtained by quasi-static method.The rain-flow counting method and distribution fitting are carried out to deal with them.The results obtained above will be utilized in following fatigue reliability analysis.Then a cutterhead fatigue life prediction system is established through MATLAB GUI design function to calculate the fatigue life of the dangerous points in the cutterhead faceplate using the nominal stress method calculation process.(2)Fatigue failure probability of the structure under different conditions are analyzed by PDS module of ANSYS with the fatigue limit.The statistical characteristics,sensitivity,and correlation of the function are analyzed based on the established model.It is proved that the load of hobs which are installed densely are sensitivity factors of structure reliability.It is also discussed how the cutterhead failure probability change with USC and hob penetration.Results show that the fatigue reliability of the cutterhead decreases with the increase of USC value and penetration,and when the total load increases to a certain extent,the fatigue reliability probability of the cutterhead decreases rapidly.(3)Fatigue life of the positive weld of cutter saddle is predicted using the Verity module of fatigue analysis software FE-SAFE on the base of hob loads obtained by experiment.The study reveals that the life of center hob weld is bigger than that of positive hob.The fatigue life increases with rise of crack depth.And the increase amplitude of center hob is larger than that of positive hob.However,the increase tendencies of positive hob's fatigue life are the same.The influence of each unidirectional force on the weld fatigue life is also analyzed,which is determined by both the crack growth direction and load.(4)Fatigue propagation reliability model is established with taking fatigue life as the basic variable.Fatigue reliability of weld under different hob loads are calculated by JC method programming.Results show that failure probability of cutter saddle weld in center hob is smaller than that of positive hob.The failure probability of positive hob decreases with hob installation radius increasing,which is consistent with the hob stress analysis made by cutterhead structure and construction characteristics.And we also investigate the impact of different crack parameters(initial crack depth,the critical crack depth,crack shape ratio)on the cutter saddle failure probability.The results show that the failure probability of cutter saddle weld increases dramatically with the initial crack depth.And the crack shape ratio increases,the failure probability of cutter saddle weld decreases.However,the change of the failure probability with critical crack depth is not obvious.As a result,we should pay close attention to crack depth and shape during the construction and take timely measures to remedy if necessary.The results obtained in this paper will help to further understanding of fatigue of the TBM cutterhead.They are also useful for the TBM design and tunneling construction to predict the fatigue failure of cutterhead and improve the safety of tunneling process.