Mechanical Analysis And Structural Optimization Of The Cutterhead Of An EPB Shield

As the most important tunneling tool of underground tunnel in recent years,shield machines are playing an irreplaceable role in the engineering construction of railway,highway and subway of our country.Due to the tunneling efficiency of shield machine influenced greatly by the cutter head structure,the mechanical analyses and optimization design for the cutter head of shield machine has very important significance.The cutter head structure of an EPB shield machine used in Lanzhou Metro Line construction taken as research object,its mechanical performance were analyzed such as static strength,rigidity,fatigue strength and natural frequency in normal working conditions,maximum thrust conditions and static starting-breakout conditions,and the proposal for its structural improvement and optimization was putted forward.In this paper,firstly,the mechanical performance of the cutter head structure in normal working conditions was analyzed with the application of ANSYS Workbench.In terms of obtained contours of equivalent stress,total deformation and nominal fatigue life,it can be decided that the weakest positions of static and fatigue strength in the cutter head of studied shield machine appear at the outer corner of corbels near its interface with the back of faceplates,while the poorest positions of stiffness are in the outer edge of two faceplates without muck outlet.Secondly,improved design schemes are presented aiming at the shortages of the cutter head structure.It can be seen from analysis,in the case that the head aperture ratio changes from 35 % to 37 %,the static strength and nominal fatigue life in the weakest positions of the improved cutter head in normal working conditions can respectively be increased by 71 % and 221 %;while the deformation at the outer edge of faceplates be decreased by about 15 %.Thirdly,the dynamic analyses of the cutter head structure have been carried out on the basis of static analyses,and the vibration mode contours,the first six natural frequencies,the frequency as well as the maximum amplitude at the positions of maximum amplitude are obtained.The calculation shows that,after improvement,the lower natural frequency of the cutter head increases from 35.58 Hz to 36.89 Hz,while the amplitude in the direction of Z axis is reduced from 47.93 mm to 46.05 mm.Finally,the multi-objective design method was used for the optimization design of the improved cutter head.By taking the maximum equivalent stress σi max and the total deformation emax in the cutter head as well as the mass m of the cutter head as objective functions,the thicknesses t2,t3,t4,t5 of the second to the fifth rib plates on the panel and the inner hole radius r of the elliptical corbels as design variables,the dimension of improved cutter head was optimized by use of Design Explorer in ANSYS Workbench,and both the static strength and the nominal fatigue life at the weakest position of the optimized cutter head in normal working conditions have been furtherly promoted.These research results provide a reference for the optimizing design of the cutter head of the EPB shield machine used in Lanzhou Metro Line construction.