Crack Initiation-Propagation Whole Fatigue Lifetime Prediction Of TBM Cutterhead Under Multi-impact Loads

With economics and society transformation, urbanization has come into critical period. The development and utilization of underspace is of profound impact on relieving the stress of short of surface space and improving infrastructure construction. China has become into the nation in maximum demand of Tunnel Boring Machines (TBM). Cutterhead is the key part of TBM influencing rock-breaking efficiency, but existing designs considered fatigue lifetime less. Under severe vibrating conditions, however, crack initiation and propagation in cutterhead will extremely lower construction efficiency and even bring about potential safety risks. Therefore, research on cutterhead whole fatigue lifetime prediction has great significance to safety service of TBM.Under the premise of deep understanding the theory and method of fatigue crack initiation and propagation duration prediction, relevant research has been carried out through theoretical calculation, numerical simulation and experiment. Details are as follows,(1) Based on the force analysis of cutterhead, a modified quasi-static method taken accuracy and efficiency into consideration for computing dynamic stress has been proposed. Using this method, dynamic stresses of danger points and the test point have been computed. A wireless testing system has been set up and cutterhead strain has been measured during excavation. Comparing the computed results to the test data, the error of mean value is only 3.2% but the error of range is 9.8%, which shows that this quasi-static method is capable of calculating cutterhead stress history.(2) According to rainflow counting process, stress amplitude and mean value histograms have been obtained through statistical counting of stress history. The amplitude distribution functions have been fitted based on statistical theory and stress spectrums have been compiled. Combined with material S-N curve and damage accumulative rule, crack initiation duration has been predicted. It has also been explored that the effect of Miner rule and Chaboche rule on prediction results, and that the influence of stress-interaction on initiation lifetime, which shows that Chaboche rule is more conservative than Miner rule and lifetime tends to be longer under low-high stress spectrum.(3) As for the complex structure of cutterhead to compute stress intensity factors, which is under random stress. a small time scale model has been utilized to predict the propagation duration. A stable crack growth experiment under low-constrain condition has been launched to decide the crack tip opening angle (CTOA) of Q345D material. In order to verify this model, a substructure has been extracted from the whole cuttehead, in addition a specimen and pre-crack have been designed as per certain scale. Moreover, some fatigue experiments have been carried out. Finally, this crack propagation model has been used to predict the lifetime of a certain project.