• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.219-222
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• 1995

The objective of this study is to demonstrate the ability of a computer simulation of microstructural evolution in hot forging of C-Mn steels. The finite element method is applied to the prediction of the microstructural evolution, and it should be coupled with heat transfer analysis to consider the change of thermomechanical properties during the deformation. In this study, Yada's recrystallization model and rigid-thermoviscoplastic finite element method were employed in order to analyze microstructural evolution during hot forging process. To show the validity and effectveness of the proposed method, the experiment of hot compression process was accomplished and the results of experiment were compared with those of simulation. Consequently, this approach shows a good agreement with experimental results.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1025-1029
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• 2003

We studied the cross-sectional profiles of deformed thermoplastics in hot embossing process and compared with melt flow index for various embossing conditions such as embossing temperature, embossing pressure and initial thickness of the thermoplastics. The fastest embossing times for complete penetration of the cavities were obtained at temperature greater than $60^{\circ}C$ above glass transition temperature (Tg). When the melt flow index of polymer is low, the penetration ratio does not become large even if the embossing pressure increases. The complete occupation of the cavities was easier obtained with high melt flow index polymer than low melt flow index polymer at the same process condition. We believe these results can be very useful for optimizing nanostructured hot embossing also known nanoimprinting process conditions.

• Transactions of Materials Processing
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• v.8 no.6
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• pp.626-633
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• 1999

$Al_{85}Ni_{10}Y_5$ (at. %) amorphous alloy ribbons have been produced by rapidly solidification process and consolidated by the conventional powder metallurgy method. The grains with ∼90 nm were obtained in the Al85Ni10Y5 alloy extrudates by hot-pressing followed by hot-extusion. To investigate the effect of heat treatment on microstructural change of the extrudates, heat treatment was carried out from 200℃ to 400℃ at the step of 50℃. In addition, mechanical properties of the extrudates were analysed from torsion test at the temperature range or 400∼500℃ under a strain rates of 0.2, 0.5, and 1.0/sec. The extrudates showed a flow stress of ∼190 MPa and low elongation of ∼150% at 400℃, contributing to the enhancement of ductility and hardness for extrudates. Also, grain boundary sliding was occurred in the $Al_{85}Ni_{10}Y_5$ alloy during hot deformation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.417-420
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• 2009

The hot forming process of a CAM for vessel engine was designed by finite element (FE) simulation and experimental analysis. An aim of process design was to achieve the near-net shaped CAM forgings by hot forging process. Based on the compression test results of the low alloy steel, deformation processing map was generated using the superposition approach between the dynamic materials model (DMM) and flow stability and/or instability criteria. From the processing map, the initial heating temperature was determined as $1200^{\circ}C$. FE analysis was simulated to predict the formation of rolling defects and deformed shape with different forging designs. Optimum process design suggested in this work was made by comparing with the CAM for vessel engine manufactured by actual forging process.

• Journal of Magnetics
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• v.2 no.3
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• pp.67-71
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• 1997

A new hot-forming process has been studied to produce anisotropic Nd-Fe-B based magnets from melt-spun ribbons. The ribbon fragments were inserted in a Cu tube and hot-deformed together with one-stroke. At a height reduction ratio of 0.44, the melt-spun ribbons were densified into a magnet with a density of 7.14 g/cm3, and showed a (BH)max of 14.6 MGOe. With further deformation, the magnets were plastically deformed with Cu tubes in the lateral direction, and crystallographic anisotropy was introduced. The magnets with a height reduction ratio of 0.75 exhibited magnetic properties of (BH)max = 32.1 MGOe, Br = 11.7 kG, and iHc = 10.6 kOe. This process shows the possibility that the conventional hot-pressing and subsequent die-upsetting for anisotropic magnets can be simplified into a one-step process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.493-496
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• 2008

The residual stress generated in the boron steel blank formed via hot press forming process was predicted by JMatPro, a material property modeler, and Abaqus. The numerical predictions were compared by the experimental measurements obtained by the instrumented indentation. Both the predicted and measured principal stresses monitored at the outer surface of central bending position were qualitatively in good agreement. It was concluded that the residual stresses generated from hot forming process is not negligible as it has been generally assumed, although the spring back deformation is quite small. This should be specially considered from the part design stage since the tensile nature of the residual stress exhibited on the surface may lead to the stress corrosion cracking.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.47-54
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• 1994

The study is concerned with the coupled analysis of heat transfer and thermoelastoplastic deformation. The thermoelastoplastic model is very useful for the analysis of residual stress and the analysis of thermal stress as well as the analysis of metal forming. Heat of deformation, phase transformation and contact heat transfer boundary are considered. The contact heat transfer boundary is treated by the interpolation of shape function. The analysis of deformation and the analysis of heat transfer are carried out for the could upsetting and the hot rolling. The computed results are found to be in good agreement with the experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.70-73
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• 2006

In the present study, the flow-softening behavior occurring during high temperature deformation of AZ31 Mg alloy was investigated. Flow softening of AZ31 Mg alloy was attributed to (1) thermal softening by deformation heating and (2) microstructural softening by dynamic recrystallization. Artificial neural networks method was used to derive the accurate amounts of thermal softening by deformation heating. A series of mechanical tests (High temperature compression and load relaxation tests) was conducted at various temperatures ($250^{\circ}C{\sim}500^{\circ}C$) and strain rates ($10^{-4}/s{\sim}100/s$) to formulate the recrystallization kinetics and grain size relation. The effect of DRX kinetics on microstructure evolution (fraction of recrystallization) was evaluated by the unified SRX/DRX (static recrystallization/dynamic recrystallization) approaches

• Steel and Composite Structures
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• v.21 no.4
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• pp.949-962
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• 2016

The braking hose in the automotive hydraulic braking system exhibits the complicated anisotropic large deformation while its movable end is moving along the cyclic path according to the steering and bump/rebound motions of vehicle. The complicated large deformation may cause not only the interference with other adjacent automotive parts but also the durability problem resulting in the fatal microcraking. In this regard, the design of high-durable braking hose with the interference-free layout becomes a hot issue in the automotive industry. However, since it has been traditionally relied on the cost-/time-consuming trial and error experiments, the cost- and time-effective optimum design method that can replace the experiment is highly desirable. Meanwhile, the hose deformed configuration and fatigue life are different for different hose cyclic paths, so that their characteristic investigation becomes an important preliminary research subject. As a preliminary step for developing the optimum design methodology, we in this study investigate the hose deformed configuration and the fatigue life for four representative hose cyclic paths.

• Advances in materials Research
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• v.9 no.3
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• pp.171-187
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• 2020

The microstructural evolution of different compositions of Mg-Sn alloys (30%Sn-70%Mg, 40%Sn-60%Mg and 50%Sn-50%Mg) is studied at first to understand the changes observed with change in tin content and deformation conditions. The Mg₂Sn phase increases with increase in tin content and a significant substructure development is found in 50%Sn-50%Mg alloy. The above observation led to further deformation studies on Mg₂Sn based thermoelectric materials with higher tin percentage. The microstructure in terms of Electron backscatter diffraction (EBSD)measurements is studied in detail followed by the determination of thermoelectric properties i.e., Seebeck coefficient and electrical conductivity for both as cast and extruded Mg_(2+x)Sn-Ag alloys. The electrical conductivity of the extruded Mg_(2+x)Sn-.3wt%Ag {x =1} alloy was found to be more than its as cast counterpart while the Seebeck coefficient values remained almost the same.