Papers by Author: Jing Tao Han

Abstract: Brazing of commercially pure titanium to low carbon steel by using the Ag72Cu28 interlayer at different conditions was carried out in the present work in order to investigate the tensile-shear strength, microstructure and the fracture morphology of brazed joint. The results show that different intermetallic compounds such as CuTi,CuTi₂,Cu₄Ti₃ and FeTi were formed at the bonding area. It was observed that the microstructure of joint has a considerable effect on tensile-shear strength of the brazed samples and the maximum tensile-shear strength was achieved at “750°C-10min→850°C-5min”.All the fracture paths after tensile-shear tests occurred in the interface between titanium and silver-based interlayer in spite of the different fracture morphology.

Abstract: The friction is a key factor that influences the surface quality in metal forming. To figure out the relationship between the friction and the surface roughening, a finite element model is employed in the commercial finite element software ABAQUS to simulate the surface roughness of top side of Al plate during uniaxial planar compression. With the change of friction conditions, the surface roughening varies. The average surface roughness (Ra) shows a relationship with the friction coefficient. During the surface roughening process, the grain slip takes place in the “soft orientation”, and the “hard orientations” become the barrier of the slip.

Abstract: In this paper, the extrusion process of bimetallic tubes is discussed, and the extrusion pressure is calculated based on the method of energy conservation, according to the three categories of metal flow that may occur during the process. A number of parameters, geometry of bimetallic tube, mechanical properties of material components and friction conditions, are highlighted in this analytical method. Compared with the data of TP304l/20G bimetallic tubes which were extruded at 1100-1200 °C, the calculated results show a good agreement with the industrial results, with the error less than 10 %. It also proves that the friction between the two layers play an important role in the process.

Abstract: With the technology advancement, crystal plasticity finite element modeling becomes more and more popular in the simulation of metal forming process. In order to obtain a better understanding of the difference between the Taylor model and finite element model during the simulation of metal forming process, an implicit time-integration procedure with the two polycrystal models is applied in the commercial finite element code ABAQUS to simulate the plane strain compression separately. FCC metal is used in this study. The simulation shows that the two polycrystal models both can predict the compression process approximately. The two modelling results of surface roughness show an agreement with that of the experimental results. However, the side profile calculated by the Taylor polycrystal model is much steeper and straighter than that of finite element polycrystal model. The experimental surface roughness curve shows a high frequency fluctuation. It is much steeper than those of the two models. The simulation results also show that the von Mises stress from the Taylor model is much higher than that of the finite element model.

Abstract: Taylor-type and finite element polycrstal models have been embedded into the commercial finite element code ABAQUS to carry out the crystal plasticity finite element modelling of BCC deformation texture based on rate dependent crystal constitutive equations. Initial orientations measured by EBSD were directly used in crystal plasticity finite element model to simulate the development of rolling texture of IF steel under various reductions. The calculated results are in good agreement with the experimental values. The predicted and measured textures tend to sharper with an increase of reduction, and the texture obtained from the Taylor-type model is much stronger than that by finite element model. The rolling textures calculated with 48 {110}<110>, {112}<111> and {123}<111> slip systems are close to the EBSD results.

Abstract: Two polycrystal models are implemented into the finite element code to model texture development for pure Al under uniaxial tensile deformation and cold rolling deformation with EBSD data. Both models predictions in tensile deformation are reasonable agreement with the experimental data. Texture development under cold rolling predicted by the finite element model is more approximate to the measurement than Taylor-type model. Some other ideal orientations are failed to be predicted.

Abstract: In diffusion-rolling bonding, bonding temperature is a key parameter influencing interface bonding strength. In this case, lab experiments were carried out in a vacuum furnace to simulate the diffusion-rolling bonding of steel sheet of polycrystal structures under different temperatures. Bonding strength and interlayer film thickness were measured. The relationship between bonding strength and “diffused interlayer” thickness
λ was investigated. The effect of temperature on diffusion-rolling bonding was investigated. Diffusion mechanism was qualitatively discussed. Based on above diffusion mechanism, the transformation in phase structure and its effect on the diffusion coefficient under different temperature was also analyzed and compared with the experimental results.