Dae-Suk Kim

Determination of the initial billet geometry for a forged product using neural networks

Abstract In the paper, the authors propose a new technique to determine the initial billet geometry for the forged products using a function approximation in neural networks. A three-layer neural network is used and the back-propagation algorithm is employed to train the network. The billet geometry is determined by applying the ability of the function approximation of neural networks to determine an optimal billet which, satisfies the forming limitations; minimises incomplete filling in the die cavity, load, energy; and also secures a more uniform distribution of effective strain. The neural networks are applied to find the optimal initial billet size for a plane-strain rib-web product in cold forging and for an axisymmetric rib-web product in hot forging. The neural networks may reduce the number of finite-element simulation for the determination of the optimal die geometry of forging products and, further, they can be usefully applied in the physical modeling of the forging design.

Fine Structure Effect of PdCo electrocatalyst for Oxygen Reduction Reaction Activity: Based on X-ray Absorption Spectroscopy Studies with Synchrotron Beam

In this study, we have demonstrated the fine structure effect of PdCo electrocatalyst on oxygen reduction reaction activity with different alloy composition and heat-treatment time. In order to identify the intrinsic factors for the electrocatalytic activity, various X-ray analyses were used, including inductively coupled plasma-atomic emission spectrometer, transmission electron microscopy, X-ray diffractometer, and X-ray Absorption Spectroscopy technique. In particular, extended X-ray absorption fine structure was employed to extract the structural parameters required for understanding the atomic distribution and alloying extent, and to identify the corresponding simulated structures by using FEFF8 code and IFEFFIT software. The electrocatalytic activity of PdCo alloy nanoparticles for the oxygen reduction reaction was evaluated by using rotating disk electrode technique and correlated to the change in structural parameters. We have found that Pd-rich surface was formed on the Co core with increasing heating time over 5 hours. Such core shell structure of PdCo/C showed that a superior oxygen reduction reaction activity than pure Pd/C or alloy phase of PdCo/C electrocatalysts, because the adsorption energy of adsorbates was apparently reduced by lowering the dband center of the Pd skin due to a combination of the compressive strain effect and ligand effect.