Papers by Author: Xiao Chao Cui

Abstract: The grain size evolvement of AZ31 magnesium alloy during high ratio extrusion (HRE) was investigated by experiment and numerical simulation. A Yada model was established according to the results of experimental study and trial calculation. Effects of the deformation temperature, extrusion ratio and extrusion velocity on the grain size were analyzed. The results showed that the microstructure of the AZ31 alloy was dramatically refined by high ratio extrusion. The deformation conditions exhibited obvious effects on the grain size, and the deformation conditions were interplaying and interacting with each other during the HRE process. Compared to the deformation temperature and extrusion velocity, the severe plastic deformation induced by the high ratio extrusion is a major cause of grain refinement. With the increasing of the extrusion velocity, the grains could be refined due to a shorter recrystallized grain growth time. At the same time, the deformation temperature increased with the increasing of the plastic strain rate, which results in faster recrystallized grain growth. Finally, recommended method is advised to further refine the grain size.

Abstract: In the paper, flow status and solidification status of molten steel in inner-outer couple cooling mold in the filling process are simulated by using fluid dynamics software Flow-3d, and obtain distributing diagrams of flow field and temperature field and free-surface shape diagrams in the filling process. Influences of flow field and temperature field of filling process on solidification are analyzed in the slab continuous casting. It is indicated that inner cooler can improve molten steel flow status, which is favorable to inclusion in molten steel floating up, quicken the solidification rate of molten steel in the mold.

Abstract: A new technology of high efficiency concasting based on inner-outer couple cooling of molten steel in a mould has been advanced, that is to set an inner cooling apparatus, U shape pipes, in a mould. The flow status of molten steel in mould with inner cooling apparatus is analyzed by using fluid dynamics analysis software FLUENT, and compared with that without inner cooling apparatus. It is found that the inner U-shape cooling apparatus can make molten steel flow with a lower impact depth which is favourable to inclusion in steel floating up.

Abstract: Mold filling and solidification of molten steel for 750mm×450mm×300mm continuous casting mold of single SEN and double SEN are simulated by using CFD commercial code Flow-3d. The distributing diagrams of velocity field and temperature field and the location and shape diagrams of free-surface during mold filling process are obtained. Influences of single SEN model and double SEN model on velocity field and solidification are analyzed. It is found that double SEN model can lighten circumfluence intensity at the upper of mold, quicken solidification speed of steel liquid in the mold, which is favorable to improving the quality of billet and enhancing pull speed.

Abstract: The numeric simulation of effect of X-shape submerged nozzle on flow of molten steel in a mold for 160mm×160mm concasting billet has been carried out by viscous fluid mechanics theory and CFD software Fluent. It was verified that during pouring with X-shape submerged nozzle, the vortex molten steel entering into mold by guide of vortex guidance channel which was formed with top and bottom surface of two semioval flow guidance plate and invert taper pipe to availably reduce impact depth, promote inclusion and gas bubble aggregating and floating off, and improve concasting efficiency.

Abstract: The cracks-tip field on collinear periodic cracks of infinite orthotropic fiber reinforcement composite plate subjected to anti-plane shear force is studied in this paper. With the introduction of the Westergaard stress function and application of complex function theory and undetermined coefficients method, mechanical problem is changed into partial differential boundary value problem. The undetermined coefficients and the stress function are obtained with the help of boundary conditions. Due to the distribution of periodic cracks, stress intensity factor depends on the shape factor. The results show that interaction happens between the collinear periodic cracks. When the ratio of crack length and crack spacing is less than 1/3, the interaction between the cracks is very small. When the ratio gradually increases to 1, strong interaction between the cracks will be found. Cracks-tip field has scale effect. When the ratio of crack length and the given reference crack length decreases, the displacement field is significantly smaller.

Abstract: The Stress field of collinear periodic cracks in an infinite orthotropic composite plate subjected to the concentrated force is studied. The mechanical problem is turned into partial differential boundary value problem. The solution of partial differential equations can be obtained by the complex function methods, which contains unknown coefficients. Using undetermined coefficients method and with the help of boundary conditions, the partial differential boundary value problem is solved. The expressions for stress and displacements near crack tip are derived. Since the distribution of periodic cracks, the stress intensity factor is related to crack shape. Finally, a numerical example shows that the stress changes with the polar angle.

Abstract: An inner-outer coupled cooling technology of molten steel for 1240×200mm slab continuous casting, that is to set an inner cooler—U shape pipes in the mold, is put forward in order to enhance the efficiency of transmitting heat and improve inner structure of billet. The flow status and solidification status of molten steel under coupling flow field and temperature field in inner-outer coupled cooling mold are simulated by using fluid dynamics software, and compare with those in traditional mold. It is found that setting inner cooler in the mold can make molten steel flow status even, which is favorable to floating up of the inclusion, quickening the solidification of steel liquid and improving the quality of billet.

Abstract: The cracks-tip field on ModeⅡperiodic cracks of infinite orthotropic fiber reinforcement composite plate subjected to the concentrated force was studied. With the introduction of the Westergaard stress function and application of complex function theory and undetermined coefficients method, mechanical problem is changed into partial differential boundary value problem. Owing to the distribution of periodic cracks, stress intensity factor(SIF) depends on the shape factor, which is greatly influenced by the crack spacing and the crack length. The results show that interaction happens between the periodic cracks, and that scale effect of the stress intensity factor in cracks-tip is obvious.

Abstract: Analysis of mechanical behaviors near crack tip for linear elastic anisotropic composite plate under bending loadings and twisting loadings was done. By introducing proper deflection function, the mechanical problem reduced to the boundary value problem of partial differential equation. The mixed mode stress intensity factor at the crack tip were presented under bending loadings and twisting loadings at infinity. By solving boundary value problem of partial differential equation and using a complex variable function method, the expressions for bending moments, strains and displacements near crack tip are derived. The obtained results are used to the theoretical research and experimental analysis of the fracture problems of composite plate.