Papers by Author: Zong Xi Cai

Abstract: A new algorithm is presented for the finite element analysis of fracture mechanics. The algorithm allows crack propagation in any direction, and guarantees the crack path smoothly. This is achieved by tracking the path of the crack tip and by introducing a new remeshing method. Examples show that this algorithm is efficient for 2D problems.

Abstract: In this paper a method for evaluating the slip speed in rolling contact is introduced from the contact mechanics viewpoint. Based on the analysis of the wear factors of the disc cutter, a theoretical model which includes disc cutter structural parameters and boring parameters is proposed to estimate the wear of the disc cutter in normal wear conditions. This theoretical model provides a basis for estimating the wear of the disc cutter and determining the replacing time of the disc cutter.

Abstract: In order to determine the normal force acting on the TBM disc cutter, a 3-D FEM model is established to simulate the cutting process, with the failure effect of the rock. Afterwards, by using this model, a series of numerical simulations are performed. Based on the numerical simulation results, via modifying Evans formula, an improved formula is given. The modified formula indicates the relationship between the normal force acting on a single disc cutter and the penetration depth, and contains the influence of formation stress and wear.

Abstract: Based on the analytical solution for the stress field around an inclined borehole in an anisotropic medium, a computer program was developed and a serial parametric study was conducted. The effects of parameters such as degree of anisotropy, borehole inclination, bedding plane inclination and in-situ stress conditions on the stress distribution around a borehole were evaluated. The results showed that medium anisotropy has little effect on borehole fracture analysis at low borehole inclinations, but its influence becomes significant for highly inclined boreholes. As the degree of anisotropy varies the maximum shear stress changes remarkably. This indicates that the degree of anisotropy plays a role in the collapse failure of a borehole. The information generated in these studies can be used in predicting the fracture or collapse-initiating pressures.

Abstract: Based on the theory of elasticity and taken the casing-cement sheath as a totally contacted composite cylinder subjected to arbitrarily distributed loading on inner and outer surfaces, an analytical solution in Fourier serial form was obtained for stresses and displacements. A computer program was developed to evaluate the stress and displacement in the combined cylinder. The results are in good agreement with those from the finite element method (FEM). With these solutions we can investigate the interaction between casing and the cement sheath. This is of importance in improving the design of casing.

Abstract: In order to determine the loads acting on the cutterhead of a compound shield, this paper aims at the large-scale and fully coupled system of the excavation face. Firstly, a new model is proposed to calculate the loads acting on a single cutter, in which the earth pressure of the chamber is taken into consideration. Then, by transforming the large-scale nonlinear contact problem into a smaller one, we set up the governing equations only including the penetration depth of cutters in the approach of the sub-structure condensation, to calculate the loads acting on the cutterhead. Finally, the relationship between the penetration per revolution and the total thrust and total torque acting on the cutters of the cutterhead of a compound shield is investigated.