Materials Science Forum Vols. 561-565

Abstract: The grain boundary structure and its energy are necessary for the fundamental understanding of the physical properties of materials. In aluminum, three distinct atomic structures of a Σ9(221)[110] tilt grain boundary have been reported in previous studies using atomistic simulations and a high-resolution transmission electron microscopy (HRTEM). In this work, we studied the atomic structure and energy of the Σ9 tilt grain boundary in aluminum using first-principles calculations. A comparison of the grain boundary energies among the three distinct Σ9 tilt grain boundaries determined through first-principles calculations allowed us to identify the most stable atomic structure of Σ9 tilt grain boundary in aluminum.

Abstract: A method was presented for the indirect measurement of dynamic stress of casting in this paper. A stress sensor embedded in the sand mold close to the casting was used to reveal the pressure resulted by the shrinkage of casting which could figure out the dynamic stress of the frame-shaped casting indirectly. The numerical simulation was also carried out by FDM/FEM method. The results showed that the pressure grew up quickly in the rapid cooling period and then kept on a steady value. The experimental and calculated results were in good agreement.

Abstract: Commercial DEFORMTM three-dimensional finite element (FE) code is employed to examine the plastic deformation behavior of porous beams at the roll gap during the H-sectioned rolling process. The simulations assume that the rolls are fully rigid and that the change in temperature induced in the beams during rolling can be ignored. The simulations systematically examine the respective effects of the arc radius of the H-section flange region of the upper and lower rolls, the friction factor between the beam and the rolls, the density of the porous beams and the radii of the upper and lower rolls on the filling ratio at the roll gap, the thickness reduction of the rolled beam in the flange region, and the effective stress and strain distribution induced in the rolled product. The Taguchi method is then employed to optimize the processing parameters for the H-sectioned rolling of porous beams. Overall, the simulation results confirm the effectiveness of the Taguchi design methodology as a means of optimizing the H-sectioned rolling process conditions.

Abstract: The work hardening behavior of an Al-3Cu-0.05Sn (wt %) alloy was studied using tensile tests and Bauschinger tests. Emphasis is placed on the influence of the precipitation state (number density, size distribution and volume fraction) and separating the isotropic and kinematic components of the work hardening.

Abstract: The displacement profile in a shank and dedendum-addendum circle of helical gear made of through-hardened S45C carbon steel and carburized-hardened SCr420H low alloy steel by gas carburizing was measured and predicted using a finite element method of DEFORM-HT. Both gears were quenched into same oil quenchant. Heat Transfer Coefficient (HTC) was taken by measuring thermal history inside of firstly silver probe and secondly stainless steel SUS304 gear blank. Uniform HTC of silver probe was calculated by lumped heat capacity method, whereas zone-based HTC of SUS304 gear blank was calculated by iterative modification method. Transformation plasticity was included and excluded to predict the tendency of distortion. Simulation results were analyzed and compared to the experimental results to validate the influence of transformation plasticity on the prediction of distortion during the martensitic and bainitic/pearlitic transformation. However, more accurate distortion profiles require detailed HTC by taking thermal history on the surface of the tooth.

Abstract: Computer simulation can be utilized to predict the property and quality of heat-treated products. The prediction accuracy depends upon the thermal boundary condition and the thermal history from which surface heat transfer coefficient (HTC) is derived. Variables studied are thermal boundary and the surface HTC. Zone-based thermal boundary is set with and without edge effect. Lumped heat capacity method is used to predict HTC of silver probe (1st step), then iterative modification method is applied to the prediction of HTC of SUS304 cylinder (2nd step) and S45C cylinder itself (3rd step). Using FEM tool of DEFORM-HT combined with lumped heat program LUMPPROB, this research is intended to obtain the number of thermal boundary and iterative modification step. The higher accuracy is obtained by employing the edge effect of thermal boundary. The 2nd step significantly increases the prediction accuracy of radial distortion and residual stress distribution. However, 3rd step does not significantly increase the prediction accuracy.

Abstract: Surface energies of indium doped ZnO were calculated to explain the polarized growth of ZnO nanodisks due to indium doping. Calculation results show that the surface energy of ZnO (0001) surface is much larger than that of ZnO (10 1 0) surface, leading to a preferred growth direction of [0001] for pure ZnO. At a doping rate of 1/8, the surface energies of indium doped ZnO are greatly reduced, but the surface energy of (0001) surface is still larger than that of (10 1 0) surface. At a doping rate of 1/4, the surface energies are decreased further, and the surface energy of (0001) surface is lower than that of (10 1 0) surface. Hence, growth of ZnO along [10 1 0] direction is made possible by heavy indium doping.

Abstract: The dislocation 1/2[111](1-10) in iron is constructed. The motion behaviors of dislocation 1/2[111](1-10) in iron, as well as the dislocation with the Carbon located in dislocation core, are simulated by the molecular dynamics method with a modified analytic embedded atomic method (MAEAM). The carbon atoms are easy captured by the dislocation core and they can block the dislocation moving. After the carbon atoms are separated from the dislocation, the moving velocities of the dislocation are similar as the case of single dislocation.

Abstract: A hybrid global optimization method combining the Real-coded genetic algorithm and some classical local optimization methods is constructed and applied to develop a special program for parameter identification. Finally, the parameter identification for both 26Cr2Ni4MoV steel and AZ31D magnesium alloy is carried out by using the program. A comparison of deformation test and numerical simulation shows that the parameter identification and the obtained two sets of material parameters are all available.

Abstract: Non-stability factors affect stability of radial ring rolling process, and lead to fluctuating of ring position. This decreases rolling precision. Evaluating stability of the process is very important. A stability evaluating method is proposed. The stability can be measured with the mean square root of sequence of oscillation of ring geometrical centerline displacement. Using ABAQUS/Explicit, the stability is analyzed. It is showed that guide-roll position angle has the significant effect to the stability. If guide-roll is located at the tangential position to the ring’s fringe, the stability will vary with the angle between two planes. One passes through axes of guide roll and ring blank, and another passes through axes of drive roll and ring blank. The stability is highest when guide roll is situated at the position angle of 100˚to 130˚at exit side of ring rolling mill.