3D Crack Propagation Mechanism And Anti-damage Design Of TBM Cutterhead

Full face rock tunnel boring machine(TBM)is a typical large complex equipment in the field of tunnel excavation.Cutter head is the core component of TBM,whose service life is directly equivalent to the life of TBM.Due to the harsh driving environment,the parts such as tool holder and hob appear different degrees of damage before reaching the expected life,resulting in huge economic losses,during the tunneling process.After statistics of actual working conditions,it is known that cracks are the main causes of damage of TBM cutterhead.The fundamental cause of fatigue failure of the cutter head is the lack of research on the fatigue performance of the TBM cutterhead,so there is no specific design scheme and evaluation method for fatigue performance.Therefore,researching on the fatigue failure mechanism of the TBM cutterhead,the anti-damage design scheme of the TBM cutter head under spatial multi-point load and the corresponding evaluation criteria have great theoretical value and engineering significance for prolonging the service life of the TBM cutterhead and reducing the economic losses.In order to solve the above problems effectively,the failure mechanism,damage resistance design scheme and fatigue performance evaluation of cutter head are deeply studied and discussed in this paper.The main research contents are as follows:(1)The total-cycle crack growth rate model of TBM cutter head:In view of the serious cracking problem of the TBM cutterhead in service,the main failure mode of the TBM cutter head was studied according to the failure sample,combined with the main factors affecting the crack propagation and the structure of the cutterhead,a folly-cycle crack growth rate model suitable for the TBM cutterhead was established,and the fatigue tensile test was carried out to determine the relevant parameters.The experimental results were compared to verify the crack growth rate model,which provides a theoretical model for the calculation of fatigue life of TBM cutterhead.(2)Numerical simulation of three-dimensional crack growth under random loading:The complex structure and random load of the cutterhead lead to the difficulty of calculating the relevant parameters in the process of crack propagation.For this problem,the finite element software Zencrack is used as the platform to configure the crack-tip mesh,based on the theory of linear elastic fracture mechanics.And the stress intensity factor and the crack propagation path of the three dimensional crack tip under random loading are calculated by the displacement interpolation method and the maximum energy release method.Fatigue tensile tests of multiple cracks and single crack were carried out to verify the accuracy of three dimensional crack growth simulation.Based on it,the failure rules of various multi-crack propagation failure modes are summarized,which provides a basis for fatigue life calculation of TBM cutterhead.(3)The fatigue damage resistance design of TBM cutter head:According to the structure of TBM cutterhead,the influence of ribbed slab on crack growth rate is analyzed by three-dimensional crack propagation simulation,and the method of predicting the initial crack location of TBM cutterhead is proposed.The initial crack propagation path of the cutterhead under actual working conditions is simulated.Combining the effect of ribbed slab on crack growth rate and the structure of cutter head,the design scheme of damage resistance of TBM cutterhead is formulated to to reduce the fatigue failure of the TBM cutterhead.(4)Fatigue performance evaluation of TBM cutterhead:In order to test the influence of local structure improvement on the fatigue performance of the cutter head,a fatigue performance evaluation method of the TBM cutterhead is proposed.For this method,the dangerous region of TBM cutterhead is divided according to the structure of TBM cutterhead and the stress response of different regions,and the evaluation system of fatigue performance of TBM cutterhead is established with each dangerous region as the secondary index.Based on the cumulative damage theory,the calculation model of the fatigue performance evaluation index of the TBM cutterhead is established based on the critical crack length.Considering the uncertainty of the parameters in the model,the Monter-Claro method is used to calculate the evaluation results of each region,and the overall fatigue performance of the TBM cutterhead is evaluated by using the linear superposition method and the weight between the indexes.(5)Anti damage design and fatigue performance evaluation of TBM cutterhead in Jilin diversion project:Taking the cutter head of Jilin diversion project as an example,in order to further verify the validity and practicability of the model and method proposed in this paper,the initial crack location of the cutter head is predicted.Combined with the prediction of the structure of the TBM cutter head and the path of crack propagation,the improvement scheme of the cutterhead damage resistance structure is proposed,and the uncertainties affecting the crack propagation parameters of the TBM cutter head are analyzed and calculated.The results of fatigue performance evaluation before and after improvement are calculated,and the practicality of the proposed method was verified by comparison of the results.