Materials Science Forum Vols. 675-677

Abstract: In this paper, a comprehensive three dimensional mathematical model is built to investigate the effect of electromagnetic stirring (EMS) on continuous casting process of copper round billet. The electromagnetic field is simulated by ANSYS software and the thermal-flow field is simulated by FLUENT software. The coupling between electromagnetic field and thermal-flow field is implemented by user-defined subroutines. The simulation results have good agreement with the experiment ones. The results show that electromagnetic frequency and current intensity have significant influence on the fluid velocity, temperature gradient and sump depth. The optimum current intensity and frequency are found to be 40A and 10Hz respectively.

Abstract: Self-compacting concrete (SCC) is employed to construct a new CFT column-CFT beam frame structure in this research. In order to further assess filling result of SCC in the long steel tube to ensure good compaction rate, a 1/4 scale column-beam subassembly made of acrylics tube and concrete visual model, in which fresh concrete is simulated through mortar phase and coarse aggregate phase, are adopted to do the simulation experiment work. The experiment result shows that good filling result is able to be obtained inside the subassembly which indicates that the new CFT column-CFT beam frame structure is possible to be constructed in the real building.

Abstract: The mechanisms of low-temperature deformation around a crack tip in a hexagonally closed-packed (hcp) magnesium single crystal have been studied by molecular dynamics simulations. In our simulation a {1010} < 12 10 > model I (opening model) crack is selected. The results indicate that slip on the basal plane is activated due to the shear stress at the crack tip. Thus shear banding caused by a successive slip of the basal planes is the main deformation way for this type of crack.

Abstract: Diamond-like carbon films have been extensively studied over the past decades due to their unique combination of properties, in particular, Si-DLC films are of significant interest for tribological effects. They possess the potential to improve wear performance in humid atmospheres and at higher temperatures. MD simulations were carried out to generate Si-DLC films at different silicon contents from 0 to 50%, in order to theoretically investigate the influence of silicon contents on microstructures and tribological properties between Si-DLC films. The results show that the sp3/sp2 ratio in Si-DLC films increases with the increasing silicon content. The MD simulation results suggest that the friction force increases with addition of silicon to DLC films. The bond numbers of interfilms have showed that the silicon addition promotes the bonding of interfilms forming, which results in the friction force increased.

Abstract: The process on rheocasting-rolling of semi-solid AZ91D magnesium alloy was investigated by the finite element method from the aspect of fluid mechanics .The mathematical model of the casting-rolling zone was built based on the analysis on the heat transfer mode and boundary conditions of the casting-rolling zone. The numerical simulations were carried out by different casting-rolling parameters to observe the full solidification point and find the best pouring temperature. The numerical simulation results showed that when the semi-solid slurry temperature was 584°C, magnesium strips with good structure and performance could be obtained by rheocasting-rolling. This simulation provided a valid evidence to determine the optimal process parameters.

Abstract: The Thermo-Calc and DICTRA software/database/programming-interface packages, through many successful applications in the fields of Computational Thermodynamics and Kinetics, have tremendously contributed to quantitative conceptual design and processing of various advanced materials. Materials scientists and engineers can efficiently apply such unique and comprehensive tools in calculating material properties, predicting material structures and simulating material processes, which are of wide-ranging industrial and academic importance.

Abstract: During the inertia friction welding (IFW) process of superalloy GH4169, the main mechanism for microstructural evolution is dynamic recrystallization (DRX). In order to investigate the microstructural evolution during the process, a finite element (FE) model coupled with the DRX model of the alloy was developed on the platform of MSC.Marc. Equivalent strain was introduced into the DRX model to improve the computational precision. As a result, the IFW process with microstructural evolution was simulated. Simulated results reveal that DRX region is very small. Fully recrystallized region and fine grains appear near the weld line. Dynamically recrystallized fraction (DRXF) decreases and grain size increases with the increase of the distance from the weld line. Predicted results of microstructural distribution agree well with experimental ones.

Abstract: A plate containing a central crack and subjected to biaxial stresses has been studied by a finite element method using ANSYS. The stress intensity factor was calculated using displacement extrapolation method and Dugdal model. From the results, it was found that the stress intensity factors increased with the increasing load ratio. There was good agreement between experimental and theoretical results.

Abstract: A model, which can be used to illustrate the process of nucleation of hydrogen induced cracking (HIC) in steels during sour service, was developed with the aid of Gibbs theory. A set of criteria for crack nucleation were then derived from the model. Metallurgical parameters influencing the criteria and thusly the susceptibility of the material to HIC, which are measurable and controllable in industrial processing, were also advanced in the present article.

Abstract: In this paper, the flow, heat transfer and stress during solidification process of the machine tool bed weighed about 2.5ton that has been optimized by structural topologymethod, was calculated with ProCAST software, and the causes of the crack forming in the casting of the machine tool bed was analysed. According to the calculation results, the structural design of the local part where cracks tends to form has been improved, and the heat transfer and the stress are calculated again. By comparing the temperature field with filling of molten cast iron and without filling, it has been found that there was little effect of filling on the results of temperature distribution of the cast, therefore the effect of filling can be ignored in the following temperature field calculation to save computation time. The model has been simplified in the stress field calculation with considering the complexity of the machine tool bed and the cost of computation. Then, the merits and demerits of the original design and the improved design are compared and analyzed depending on the calculated temperature and stress results. It is suggested that the improved one could get a more uniform temperature distribution and then the trend of the crack occurring can be greatly reduced. These results could provide a guide for the actual casting production, achieving the scientific control of the production of castings, ensuring the quality of the castings.