Study of TBM cutterhead fatigue damage mechanisms based on a segmented comprehensive failure criterion. (December 2015) - Sun, Wei
Abstract: The cutterhead endures strong, multi-point distributed impact loads when the full face rock tunnel boring machine (TBM) tunnels, which leads to intense vibration and fatigue fracture. Accordingly the structure should meet the requirement of service life considering the fracture failure at weak locations. Hence, cutterhead damage mechanism is crucial to predict and analyze residual life of a operational cutterhead under impact loads. This paper combines with the characteristics of cutterhead life, Paris model and damage cumulative theory, proposes a new failure criterion for the long thick plate in complex stress states, and establishes a segmented crack propagation life prediction model, based on the existing multi-degree-of-freedom coupling dynamic TBM cutterhead model and fatigue crack propagation prediction method for large and complex structures. Meanwhile, a physical fatigue damage test of cutterhead specimens is carried out to validate the theoretical model. Then a TBM cutterhead in a water tunnel project is taken as an example, to calculate the fatigue crack propagation and analyze how different parameters affect fatigue life. The results of the analyses reveal that with fatigue crack propagation, life of actual cutterhead is 36.5 km, which gives a meaningful reference for cutterhead design. In addition, the cutterhead life decreases nearly 45.2% with the initial crack depth increasing from 0.5 mm to 2 mm, and it is inferred that the value of initial crack depth should be controlled below 1.6 mm, to ensure the service life. On the other side, the larger the crack shape ratio ( a / c ), the longer the fatigue life, and the cutterhead life with a round crack ( a / c = 1) is about 3 times with a narrow crack ( a / c = 0.1). Furthermore, the crack growth rate parameter m has greater influence on cutterhead life than parameter C, with C increasing 10%, the life decreases about 9%; however, the life decreases nearly 13% when m increases 1%. Then, the critical threshold values of cutterhead material parameters to meet life requirement are obtained. From the results of fatigue damage test, it can be showed that the specimens fracture quickly when the crack depth exceeds 50% of the panel thickness, and the crack shape ratio gradually increases with the loading cycles, which is consistent with the theoretical assumption, as well as the influence rules of parameters. Highlights: A segmented comprehensive failure criterion for a long thick plate in complex stress states is proposed. A segmented crack propagation life prediction model for TBM cutterhead under multi-point distributed impact loads is established. The effects of crack characteristics parameters and material parameters on cutterhead life are analyzed. A fatigue damage test of cutterhead specimens is carried out for validating the feasibility of the proposed method.