Papers by Author: Hong Tao Zhu

Abstract: Hot strip rolling process is one of the most promising industrial processes to fabricate finished or semi-finished bulk products. Numerical analysis on the temperature and thermal stress distributions in a high speed steel work roll during hot rolling has been conducted based on a transient thermo-mechanical model. Influence of initial work roll body temperature on temperature and thermal stress has been discussed in detail by assuming different rolling stages. Compared to the work roll surface, stress is much smaller at depth of 2.1 mm and 5.0 mm, respectively. Results showed similar maximum circumferential thermal stress at both depths of 2.1 mm and 5.0 mm when the roll has initial temperature of 25 °C and 100 °C, but they are about 3 times and 8 times larger than at depth of 2.1 mm and 5.0 mm, respectively, when the initial temperature is 200 °C.

Abstract: A large-scale molecular dynamics simulation was used to investigate the propagation of cracks in three dimensional samples of nanocrystalline copper, with average grain sizes ranging from 5.34 to 14.8 nm and temperatures ranging from 1K to 500 K. It was shown that intragranular fracture can proceed inside the grain at low temperature, and plastic deformation around the tip of the crack is accommodated by dislocation nucleation/emission; indeed, both fully extended dislocation and deformation twinning were visible around the tip of the crack during fracture. In addition, due to a higher concentration of stress in front of the crack at a relative lower temperature, it was found that twinning deformation is easier to nucleate from the tip of the crack. These results also showed that the decreasing grain size below a critical value exhibits a reverse Hall-Petch relationship due to the enhancing grain boundary mediation, and high temperature is better for propagating ductile cracks.

Abstract: In this paper, a new technique to set up non-sinusoidal oscillations of the mold in continuous casting is presented. The waveform functions of this non-sinusoidal oscillation technique and operational parameters are analyzed and the design to realize the non-sinusoidal oscillation of mold is presented. It is anticipated that this technique will be widely applied as it has many advantages such as lower investment and maintenance cost, simple equipment which is easy to manufacture and maintain.

Abstract: The slab edge rolling has been widely used in the roughing stand of hot strip mill to control the width of the slab. However, the slab edge rolling and consequent horizontal rolling will cause a significant width change in the head part and tail part of the slab, which have to be trimmed before the finishing stands. The short stroke control (SSC) technology has been developed to overcome this problem. In this paper, the finite element method (FEM) has been used to simulate the unsteady edge rolling process. Three SSC control curves have been compared in order to obtain the best width control result. The optimized SSC control curve has been applied to the industrial rolling mill.

Abstract: There are many defects on the surface of continuous casting slab, such as corner cracks, longitudinal cracks etc. To analyze the cracks and determine their locations, two-dimensional heat transfer mathematical model and thermal elasto-plastic stress model of slab casting were established in this paper. The process of solidification, temperature field, and thermal stress distribution on slab surface were analyzed using finite element method. The effect of thermal stress on the cracks on the slab surface was discussed. The location of the cracks caused by thermal stress can be predicted. This is useful for finding approaches to overcome these defects.

Abstract: The defects in crystalline materials significantly affect the fracture behaviors. In this paper molecular dynamics (MD) model using a potential of embedded atom method (EAM) has been developed to investigate the effect of the major crystalline defects, stacking fault and edge dislocation, on the crack propagation in Fe crystal. Six cases with different locations of stacking fault and edge dislocation have been studied. The strain distribution in lattice aggregate was heterogeneous. The dislocations were observed slipping along directions [100] and [-100] on the plane (100). Simulation results showed that the location of the stacking fault and edge dislocation significantly influenced the crack propagation speed.

Abstract: Asymmetric rolling of thin strip has become important due to a significant decrease of rolling force, which contributes to obtain the extremely thin strip, to reduce the rolling passes, and to save the energy by a decrease of anneal treatment. In asymmetric rolling of thin strip, edges of work rolls may contact and deform when no or small work roll bending force is applied. Work roll edge contact forms a new deformation feature. In this paper, the effects of initial thickness of strip and friction coefficient on the rolling pressure, roll edge contact length and strip crown during asymmetric rolling of thin strip with work roll edge contact effect has been discussed, and the calculated rolling force with work roll edge contact is compared with the measured value.

Abstract: Asymmetric rolling is used to produce thinner strip, which can reduce rolling force significantly. When a thinner strip is rolled on a rolling mill, work roll edge may contact each other, which affects the mechanics of this special asymmetric rolling and the crown of the rolled strip. In this paper, the authors developed a numerical model to simulate this special rolling and obtained the rolling force, intermediate force, roll edge contact force, the crown of the rolled strip and the edge contact length. The effects of the initial thickness of strip and the friction variation at upper and lower work rolls on the rolling force and crown of the rolled strip are also discussed.

Abstract: The variation of the friction in the roll bite is of great importance in cold strip rolling. The main interest of the paper is to model the friction coefficient in the roll bite during cold rolling. The deformation resistance of the rolled products and friction coefficient in the roll bite were determined simultaneously by minimizing the error of the measured and calculated rolling forces based on nonlinear least squares optimization algorithm. The neural network was introduced to further improve the accuracy of friction coefficient calculation in cold strip rolling. The results already obtained shows that friction decreases with roll wear, and the lower the rolling speed, the higher is the friction.