• Steel and Composite Structures
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• v.46 no.4
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• pp.525-538
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• 2023

This paper focuses on the energy absorption of lattice core sandwich structures of different configurations. The diamond lattice unit cell, which has been extensively investigated for energy absorption applications, is the starting point for this research. The energy absorption behaviour of sandwich structures with an expanded metal sheet as the core is investigated at low-velocity impact loading. Numerical simulations were carried out using ABAQUS/EXPLICIT and the results were thoroughly compared with the experimental results, which indicated desirable accuracy. A parametric analysis, using a Box-Behnken design (BBD), as a method for the design of experiments (DOE), was performed. The samples fabricated in three levels of parameters include 0.081, 0.145, and 0.562 mm² Cell sizes, and 0, 45, and 90-degree cell orientation, which were investigated. It was observed from experimental data that the angle of cells orientation had the highest degree of influence on the specific energy absorption. The results showed that the angle of cells orientation has been the most influential parameter to increase the peak forces. The results from using the design expert software showed the optimal specific energy absorption and peak force to be 1786 J/kg and 26314.4 N, respectively. The obtained R2 values and normal probability plots indicated a good agreement between the experimental results and those predicted by the model.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.4
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• pp.145-150
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• 1997

A computer-aided process design system for axisymmetric deep drawing products has been developed. An approach to the system is based on the knowledge based system. The hypothesized process outline of the deep drawing operations is generated in the geometrical design module of the system. In this paper, the module has been expanded. The rules of process design sechems for complex cup drawings are formulated from handbooks, experimental results and empirical knowhow of the field experts. The input to the system is final sheet-metal objects geometry and the output from the system is process sequence with intermediate objects geometries and process parameters, such as drawing load, blank holding force, clearance and cup-drawing coefficient.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.5
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• pp.194-199
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• 2020

By controlling the composition of the metal-oxide nanosheet having a two-dimensional layered crystal structure, material properties and application can be extended. In this study, the composition of the nanosheet could be expanded from pure composition to doping composition by successfully synthesizing the TiO₂ nanosheet doped with Nb. Specifically, the doping composition was designed when synthesizing the layered metal oxide as a starting material (K_0.8Ti_1.73-xNb_xLi_0.27O₄, x = 0, 0.03, 0.07) and chemical exfoliation was performed. By doing this, it was possible to obtain the Nb-doped TiO_y ultrathin nanosheet. The size of the nano sheet was 2 ㎛ or less based on the long length in the x-y direction, and the thickness was about 1 nm. Nb-doping was confirmed by XRD and SEM-EDS analysis.

• Transactions of Materials Processing
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• v.30 no.6
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• pp.291-300
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• 2021

Currently, starting with electric vehicles, the application of ultra-high-strength steel sheets and light metals has expanded to improve mileage by reducing vehicle weight. At a time when internal combustion engine vehicles are rapidly changing to electric vehicles, the application of ultra-high-strength steel is expanding to satisfy both weight reductions and the performance safety of the chassis parts. There is an urgent need to improve the quality of parts without defects. It is particularly difficult to estimate the part formability through the finite element method (FEM) in the burring operation, so product design has been based on the hole expansion ratio (HER) and experience. In this study, design of experiment (DOE), analysis of variance (ANOVA), and regression analysis were combined to optimize the formability by adjusting the process variables affecting the burring formability of ultra-high-strength steel parts. The optimal variables were derived by analyzing the influence of variables and the correlation between the variables through FE analysis. Finally, the optimized process parameters were verified by comparing experiment with simulation. As for the main influence of each process variable, the initial hole diameter of the piercing process and the shape height of the preforming process had the greatest effects on burring formability, while the effect of a lower round of punching in the burring process was the least. Moreover, as the diameter of the initial hole increased, the thickness reduction rate in the burring part decreased, and the final burring height increased as the shape height during preforming increased.