Papers by Author: Cheng Lu

Abstract: In this study, texture evolution during high pressure torsion (HPT) of aluminum single crystal is predicted by the crystal plasticity finite element method (CPFEM) model integrating the crystal plasticity constitutive theory with Bassani & Wu hardening model. It has been found by the simulation that, during the HPT process, the lattice rotates mainly around the radial direction of the sample. With increasing HPT deformation, the initial cube orientation rotates progressively to the rotated cube orientation, and then to the C component of ideal torsion texture which could be remained over a wide strain range. Further HPT deformation leads to the orientation towards to the ideal texture component.

Abstract: Refinement of the grain diameter of the micro structure of Aluminium foil with a thickness of 300μm has been done through the ARB process up to fourth cycles with 72 layers that are proven to increase formability in micro forming a cup. Grain size was measured from the full annealed condition, of the ARB process, and the results of ARB process followed by stress relieved. Formability of the formation of a cup which is expressed as the LDR has increased from 1.87 for the material conditions of full annealed to 2.00 for the ARB process followed by stress relieved in a single step process. In addition to improved formability obtained in a cup formation, grain refinement in the microstructure can also reduce cup earing and wrinkle on the cup wall.

Abstract: Twin-roll strip casting is a concerned technology for economically producing magnesium alloys sheets. In this paper, numerical simulation of the twin-roll strip casting of an AZ61 magnesium alloy was carried out and the optimal process parameters were obtained. Then, under the conditions obtained through simulation, AZ61 strips of good surface quality were successfully manufactured. The microstructure of the alloy by twin-rolled strip casting is obvious refined compared with that by conventional casting.

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: The crystalline orientation significantly affects the fracture behavior of crystals. However, the orientation-dependent failure criterion is still lacking up to now. In this paper the failure criteria for different crystalline planes of aluminum have been developed. The critical normal stresses to separate two parallel crystallographic planes have been calculated based on Morse potential. The critical stresses on four different planes ({100}, {111}, {110} and {120}) were obtained. It has been found that plane {120} had the minimum critical normal stress. The developed failure criteria have been applied in the crystal plasticity finite element method (CPFEM) model to simulate the uniaxial tensile deformation of single crystal aluminum with a notch. The lattice orientation evolution during deformation has been predicted by the CPFEM model. Elements at notch tip reaching predefined orientation-dependent failure criterion were removed from the mesh so that the crack growing could be determined explicitly without any path assumption.

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: In this paper, molecular dynamics method has been employed to model mode I crack propagation in body center cubic (BCC) single iron crystal. To maximize the simulation efficiency the parallel computing was performed. Six cases with different lattice orientations have been simulated to investigate the crack propagation behaviors at atomic level. The strain distributions have been calculated to indicate the density of dislocation. It has been found that the lattice orientation significantly affects the propagation behaviors. The crack in BCC iron propagates more readily along the direction <111> on the plane {1-10}.

Abstract: It was impossible to obtain the transverse friction along the strip width in most previous studies of cold strip rolling because the surface roughness lays were assumed to be vertical to the rolling direction. In this study, several types of oblique roughness textures were manufactured on aluminum samples and compression tests were carried out to obtain the effect of different textures on the deformation behavior of surface asperity. Different surface textures resulted in very different peak value of stress. It was found that stress was high and changed dramatically at the initial compression stage but tended to be stable when the total reduction increased. The asperity of which the top angle is 160° showed relatively high resistance to deformation.

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.

Abstract: In this paper, a 3D slab method model has been developed. Two differential equations governing the longitudinal and transverse force equilibriums coupled with the Von Mises yield criterion have been solved to obtain the rolling pressure distribution. The strip speed is calculated according to the volume constancy. The Coulomb friction law with different frictional coefficient and speeds were applied to the longitudinal and transverse direction. Coupled with the roll stack deformation model and thermal model, the developed 3D slab method model was used to predict the strip profile and edge drop. The effects of bending force, reduction and transverse friction on the strip profile and edge drop have been discussed in this paper. The calculated result predicted by the 3D slab method is in very good agreement with measured results. The results have shown that the large bending force, small reduction and small friction will improve the strip profile and reduce the edge drop.