Papers by Author: Xue Mei Yu

Abstract: The deformation of dynamic damage in a pressure-sensitivity media was investigated by means of spherical cavity expansion model. By constructing a three region model of spherical cavity, dynamic solutions with damage and elastic area was investigated when distortion was so small that no plastic area arisen (cavity expansion rate is generally less than 0.4). Firstly, by elastic and damage mechanics, the continuous conditions in the damage region were given. Secondly, the governing equations and analytical solutions of the damage region were deduced. Finally, numerical solutions were obtained by shooting method. The result shows that some material parameters such as damage index and Poisson ratio have significant effects on the range and field quantities of damage region.

Abstract: Porous materials have been successfully used in an aerostatic bearing. In this paper, the dynamic stiffness and damping of partial porous aerostatic thrust bearings are analyzed by numerical calculation method. Firstly, the pressure distribution function of the bearing is divided into the static and dynamic pressure distribution functions through minor perturbation method. Then, the static and dynamic pressure distribution functions are calculated by FEM. Finally, the dynamic stiffness and damping coefficients of the bearing are solved. The result indicates that the dynamic stiffness increases obviously with the increment of supply pressure and first increases then decreases with the increment of frequency, and that there is negative damping in the low frequency band and the supply pressure has a great impact on the stability of the bearing.

Abstract: Investigation on mechanical properties of rock, soil and powder metallurgy is an important subject in study of damage constitutive models. These materials contain micro-voids (such as defects, inclusions and cracks) and perform pressure sensitivity. Unlike metal materials, hydrostatic pressure can influence plastic yield of these materials. Following the modified Gurson model in meso-mechanics and considering the meso-compressibility, this paper focuses on plastic limit analysis of micro-deformation mechanism of these materials. The two-independent-parameters criterion is taken as matrix yield function and spherical voids as the represent unit cell. The macroscopic stress and strain rate related to micro structure parameters are derived via upper-bound theorem. Then the macroscopic yield function (containing micro structure parameters) is established. Finally, the properties of macroscopic yield surfaces are studied by setting different values of these micro parameters. This paper provides theory foundations for materials damage and design.

Abstract: Based on the theories of fracture mechanics and composite materials mechanics, fibrous composite model that interacted on stratum, cement loop and casing was firstly established. Boundary conditions that the repaired force acted in fibrous composite model were also given. The influences of interface damage evolution and fracture process of fiber and matrix on the cement loop mechanical properties were studied as well. Meanwhile the distributions of stress and displacement fields were obtained. Finally, the debonded length and variation of the optimum repaired force were also determined, which can restrict the cement damage length to the lowest scale. The results given here can provide a reliable design references for improving the technology of repairing casing damage well.