Study of TBM cutterhead fatigue crack propagation life based on multi-degree of freedom coupling system dynamics. (May 2015) - Ling, Jingxiu
Abstract : Graphical abstract: This paper first proposes a method of fatigue crack propagation life prediction for the kind of complex assembly, such as TBM cutterhead. For the purpose of illustrating the proposed method, the TBM cutterhead of an actual project is taken as an example, to predict the fatigue crack propagation life of cutterhead piece and analyze the influences of plate thicknesses on fatigue life. At first, the load distributions of cutterhead piece are analyzed based on the coupling dynamics model of cutterhead system proposed. Next, a finite element model of cutterhead piece which contained a surface crack is established, and the stress intensity factors (SIFs) along crack front are calculated based on the submodeling technique. Then the function between SIF at the deepest crack point and crack deep is fitted through polynomial, further to predict the fatigue crack propagation life of cutterhead. Finally, the influences of plate thicknesses on the fatigue life are present, to provide technical support for evaluating the cutterhead structure. A schematic showing the overall technical route is illustrated in the following figure. Highlights: A method of crack propagation life prediction for complex structures is proposed. The stress intensity factors of TBM cutterhead are calculated based on FEM. A collaborative simulation technology is employed to solve the fatigue life of TBM cutterhead. We propose a new structure modified scheme of cutterhead with 8.08% weight decrease. Abstract: Cutterhead is the core component of TBM tunneling equipment, which endures strong, multi-point distributed impact loads when the TBM tunnels, owing to the extreme surrounding rock environment of high hardness, high temperature and high quartz content. For this reason, the cutterhead works in an extremely severe vibration environment, which leads to engineering fault by a large area crack damage before the service life. Hence, the study on life prediction of TBM cutterhead under the impact loads is a core part of cutterhead design. This paper combines with the technology of system dynamics, linear elastic fracture mechanics and cumulative theory of fatigue damage, for the first time, proposes a method of fatigue crack propagation life prediction for the large and complex structures. In this paper, the TBM cutterhead of an actual project is taken as an example, to predict the fatigue crack propagation life of cutterhead piece and analyze the influences of plate thicknesses on fatigue life, then a new improved scheme of cutterhead structure is presented. The results show that the fatigue crack propagation life of actual cutterhead is 26.6 km, which is able to meet the requirement of 20 km service life. Moreover, the upper cover plate thickness has the greatest influence on cutterhead fatigue crack propagation life, with the thickness increasing 10%, the life increases nearly by 1.24 times. Then, the other influencing factors are as follows: thickness of the main support plate, thickness of the annular support plate and thickness of the support plate, whereas the influence of the lower cover plate thickness on fatigue life is minimal. Furthermore, the plate thickness limit sizes meeting the life requirement are obtained, and a new structure modified scheme of cutterhead is proposed. Compared with the original scheme, the new cutterhead scheme meets the requirements of structural strength and service life with 8.08% weight decrease, which achieves life determination design and lightweight design. The proposed method of fatigue crack propagation life prediction is feasible in the design and application stage of TBM cutterhead, besides, it is flexible enough and can also be applied in damage strength assessment, dynamic parameters optimization and establishment of nondestructive inspection cycle for the other large and complex structure, and takes on stronger project value and generality.