Materials Science Forum Vols. 561-565

Abstract: The parameters of atomizer were obtained from the experiment. Based on the obtained parameters, a mathematical model was proposed to simulate the growing profile of billet during spray forming. The model included some process parameters which relate to the shape profile such as nozzle data, eccentric distance, rotation speed, withdraw speed and so on. After being compared with the billet shape of experiment, we got good consistent results between the simulation and experiment, it was found that the results of the simulation is in good consistent with that of the experiment.

Abstract: This paper presents the prediction results of the temperature change during the solidification process of the cylinder head made of the AC2A aluminum alloy. Prediction results have been obtained by using the FDM solidification analysis based on two different solidification models were investigated. Here, the solidification model means functional relationship between the Temperature and the Fraction Solid. The first model is a simple Linear function and the second model is estimated from DSC measurement. The comparison between the simulated and measured temperatures of the aluminum cylinder head revealed that the selection of solidification models significantly reflects the prediction results. The DSC model gives higher prediction accuracy of the temperature change than the Linear model. The solidification models estimated by using Thermo- Calc and UMSA [3] were also investigated.

Abstract: To clarify the origin of a characteristic fine grain structure formed under the high burn-up of the nuclear fuel, the comprehensive first-principles calculations for UO2 containing various types of point defect have been performed by the PAW-GGA+U with lattice relaxation for supercells containing 1, 2 and 8 unit cells of UO2. The electronic structure, the atomic displacement and the defect formation energies of defective systems are obtained, and the effects of supercell size on these properties are discussed. Based on this relatively high precise self-consistent formation energies dataset, thermodynamic properties of various types of point defects in UO2 are further investigated in the framework of the point defects model.

Abstract: For a given sheet metal forming process, an accurate determination of the contact pressure distribution experienced is an essential step towards the estimation of tool life. This investigation utilizes finite element (FE) analysis to determine the evolution and distribution of contact pressure over the die radius, throughout the duration of a channel forming process. It was found that a typical two-peak steady-state contact pressure response exists for the majority of the process. However, this was preceded by a transient response, which produced extremely large and localized contact pressures. Notably, it was found that the peak transient contact pressure was more than double the steady-state peak. These contact pressure results may have a significant influence on the tool wear response and therefore impact current wear testing and prediction techniques. Hence, an investigation into the validity of the predicted contact pressure was conducted.

Abstract: A numerical analysis of orientation stability is conducted for equal channel angular extrusion (ECAE) of hexagonal close-packed (hcp) materials based on lattice rotations from rate-sensitive crystal plasticity simulations. The relatively stable orientations associated with five slip modes are identified and then applied to interpret the characteristics of texture evolution in ECAE-processed titanium. The results indicate that during ECAE deformation, the slip plane and slip direction tend to rotate respectively towards the macroscopic simple shear plane and shear direction.

Abstract: The relationship between grain subdivision mechanisms of a crystalline metal and the strain gradient under severe plastic deformation is studied by using molecular dynamics simulations in quasi two dimensions. Two problems are simulated for single crystal models: (a) uniaxial tensile and compressive deformation and (b) localized shear deformation. In the case of uniaxial deformation, a large number of dislocation pairs with opposite Burgers vectors are generated under deformation, but most dislocations are vanished due to pair annihilation under relaxation. Therefore, no dislocation boundary can be formed. On the other hand, in case of localized shear deformation with large strain gradient, dislocation boundaries are formed between undeformed and deformed regions. These dislocations can be regarded as geometrically necessary dislocations. Consequently, the importance of the strain gradient to make grain boundaries under plastic deformation can be confirmed by atomic simulations.

Abstract: The incident energy flux impinged on the free surface of liquid layer was considered to be balanced with the latent heat in evaporation and the heat in directional conduction but neglecting convective heat transfer due to a small Peclet number at the cavity base. The quasi-steady state model was developed in this study to analyze the effect of the energy density during the penetration process and an exponential expression for penetration velocity as a function of liquid-thickness and temperature was also derived. The penetration velocity versus energy density calculated by the present model showed good agreements with the experimental data for drilling copper, which the relative errors between the calculated and the experimental data are less than 15%. By the setup of non-uniform grids distribution in numerical method, this work had successfully predicted the variation of the penetration velocity with energy density distribution. The effects of the energy density on flow rate, thickness of liquid layer, base temperature of fusion zone had also been discussed in this study.

Abstract: A numerical model has been developed to simulate the distribution of polygonal grain size in a sprayed microstructure formed from an alloy droplet spray containing a large number of solid, mushy and liquid droplets. The model takes into account the effects of: (1) the droplet size distribution; (2) its corresponding distribution of solid, mushy and liquid droplets at the instant of deposition; (3) the overall thermal condition of the spray formed preform during final solidification. The model has been validated against experiments of the spray forming of Ni superalloy rings, with modelled grain size distributions giving good agreement with measurements obtained by electron backscatter diffraction.

Abstract: In order to solve the problem existed in the numerical simulation of sheet metal forming for its use the strain-based forming limit diagram as criterion, which has the flaw of dependence on the strain paths, this paper develops the finite element analysis program based on the stress forming limit criterion applicable to the blank plastic forming technique, which follows the stress-strain transformation relationship when the sheet metal is undergoing plastic deformation, chooses Hill’s quadratic normal anisotropic criterion as computational model and selects the commercial finite element code Dynaform as its development environment. Also it be analyzed the finite element numerical simulation results of two deep drawing parts by the developed program module and realizes the prediction of sheet metal forming limit adopting the FLSD as criterion. The stress-based forming limit criterion for the developed program provides a new means to analyze the forming limit for the multistage sheet metal forming.

Abstract: Cooling channel design is important in mould designs to achieve shorter cycles, dimensional stability and reduced part stresses. Traditionally, cooling channels have been machined into mould components to avoid interference with the ejection system, coring, cavity and other mould details. Over the years straight drilled cooling channels have given away, in part, to conformal cooling technique often using free form fabrication techniques. This paper presents a study of optimised mould design with conformal cooling channel using finite element analysis. Various configurations of conformal cooling channels have been developed. The part cooling time using the conformal cooling channels and the straight cooling channels in the mould are computed using the Pro/Mechanica Thermal FEA software. Results are presented based on temperature distribution and cooling time using steady state and transient analysis conditions. The results show a reduction in cycle time for the plastic part with conformal cooling channel design.