Papers by Author: Jian Wang

Abstract: For understanding the dynamic behavior of open and closed foam subject to a shock wave, this paper through experiments, to gain a deeper understanding of the incidence, reflection and transmission of a shock wave when it interacted with cellular foam. Moreover, by analyzing the loss of the peak overpressure and positive impulse, we were able to respectively know the positive impulse of the incidence, reflection and transmission shock wave. The experimental results indicated that the attenuation capability for foam to the shock wave was caused by the internal friction and deformation of solid phase, which would absorb the energy of the shock wave. From the results we gain an understanding that the mechanical phenomenon of open foam to shock wave are not fully consistent with those of closed foam , while the attenuation of open foam to shock wave is more effective than that of closed foam.

Abstract: In view of the problems that traditional direct current control calculation is complex, that sensor precision requirements are high. This paper proposes a new control method of unit power factor power converter, which is easy to realize with simple control structure dispense with current sensor. Through the simulation and experimental verification, the control strategy can achieve unity power factor control, and the harmonic content is small and the operation is stable.

Abstract: This work addresses the dispersion of Love wave in an isotropic homogeneous elastic half-space covered with a functionally graded layer. First, the general dispersion equations are given. Then, the approximation analytical solutions of displacement, stress and the general dispersion relations of Love wave in both media are derived by the WKBJ approximation method. The solutions are checked against numerical calculations taking an example of functionally graded layer with exponentially varying shear modulus and density along the thickness direction. The dispersion curves obtained show that a cut-off frequency arises in the lowest order vibration model.

Abstract: Based on the principle of pore formation, geometric model to describe the closed-cell cellular materials is constructed. The model is tetrakaidecahedron shape with all thick edges. The dependence of relative density on microstructure of the model has been analyzed. By using finite elements method, the relative elastic modulus of the model is calculated. Wall-thickness and wall-face connective curvature radius are found to be the two independent factors affecting relative density. Nonlinearity which relative density produces on relative elastic modulus is obviously greater than one which wall thickness produces. For high and low porosity cellular materials, the materials added at the intersecting part of the wall-faces bring different influence on elastic modulus.

Abstract: Based on the pore formation principle, geometrical model to describe cellular materials was constructed. The model is closed-cell rhombus dodecahedron with thick edges. The dependence of relative density on microstructure parameters and the unitary relation have been obtained. By finite elements method, the relative elastic modulus was simulated, the influence of microstructure and relative density on elastic modulus was analyzed. The results show that the wall-face connective curvature radius is the primary affecting factor of relative density increment and the wall-thickness is less significant; the solid materials added at the intersecting part of the wall-faces produce same effect on elastic modulus. The conclusion can be applied in optimization design of cellular materials.

Abstract: For low prediction precision of online model for vertical rolling force in roughing trains of hot strip mill, the process of hot strip roughing trains was simulated by the FEM simulation software DEFORM. The cause of low prediction precision of rolling force during vertical rolling was analyzed. Then the new method for calculating deformation degree when edge rolling was presented by analysis of the FEM simulated results. The formula of external stress status modulus, which is fit for the vertical rolling force calculation, was obtained by analytic regression. Furthermore, a new formula about rolling force calculation was gained. It was approved that the prediction precision was obviously enhanced compared with the practical data for vertical rolling force.

Abstract: Improved methods to estimate the kinetics of dynamic and static recrystallization are proposed in this paper. The kinetics for dynamic and static recrystallization can be evaluated by inverse analysis of the flow curves obtained using the single-hit and double-hit hot compression tests carried out on Gleeble 3500. The dynamic and static recrystallization volume fractions can be seen as functions of plastic strain and time, respectively. The mathematical formulations between the recrystallization volume fractions and the dislocation density related to the flow stress are used in incremental forms in the study. The methods are applied to the hot compression tests of plain carbon steel and the kinetics of dynamic and static recrystallization are gained successfully for some conditions at elevated temperature. The results are clarified by comparing them with those reported in previous investigations. It is confirmed that the present methods can provide accurate kinetics for dynamic and static recrystallization with shorter time for experiment and computation.