• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.57-60
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• 2008

The studies for internal void closure have been conducted experimentally and numerically for open die forging. The FEM analysis is performed to investigate the deformation behavior of some internal voids in cast ingots during two upsetting stages. The calculated results of void closure behavior are compared with the measured results before and after upsetting. The shapes and sizes of each internal void are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the void closure can be investigated by the types of void. Closed voids could be compressed and eliminated after forging when the applied deformation amounts were larger than the critical effective strains. On the other hand, open voids could not be compressed and removed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.288-292
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• 2008

Plastics is commonly used in consumer electronics because of it is high strength per unit mass and good productivity. But plastic parts are usually distorted after injection molding due to the residual stress after filling, packing, cooling process, and etc. And plastic material is to be deteriorated according to various temperature conditions and operating time, which can be characterized by stress relaxation and creep. The viscoelastic behaviour of plastic materials in time domain can be expressed by the Prony series of the commercial code, ABAQUS. In the paper, the process to predict the post deformation under cyclic thermal loadings was suggested. The process was applied to the real panel, and the deformation predicted by the analysis was compared with that of real test, which showed the possibility of applying the suggested process to predict the post deformation of plastic product under thermal loadings.

• Transactions of Materials Processing
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• v.6 no.2
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• pp.118-135
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• 1997

In order to analyze the deformation and residual curvature of steel sheets in the strip processing lines, a program for calculating curvature and work hardening of sheet was developed. Strip deformation caused by repeated bending under tension in the process lines was analyzed on the basis of the incremental-plasticity theory with the mixed hardenting model for the purpose of predicting the strip shape and the yield stress change. The developed calculation program was applied to predict curl and gutter of sheets within a 10% difference. The yield stress increment was also predicted with the similar accuracy. Application of the model to tension legvelling process showed that gutter could be controlled by intermesh and elongation. The yield stress increment in the electro-galvanizing line calculated by the developed program was found to be dependent on the yield strength, the applied tension and the diameter of the smallest roll.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.06a
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• pp.86-86
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• 2006

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.499-499
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.395-395
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• 2008

• Transactions of Materials Processing
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• v.8 no.6
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• pp.576-582
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• 1999

The high temperature behavior of Al 6061 alloy was characterized by the hot torsion test in the temperature ranges of 400∼550℃ and the strain rate ranges of 0.05∼5/sec. To decide optimum deformation condition, three types of deformation maps were individually made from the critical strain (εc). deformation resistance(σp) and deformation efficiency (η). The critical strain(εc) for dynamic recrystallization (DRX) which was decided from the inflection point of strain hardening rate(θ) - effective stress (σ) curve was about 0.65 times of peak strain (εp). The relationship among deformation resistance (peak stress, σp), strain rate (ε), and temperature (T) could be expressed by ε=2.9×1013[sinh(0.0256σp]7.3exp (-216,000/RT). The deformation efficiency (η)which was calculated on the basis of the dynamic materials model (DMM) showed high values at the condition of 500∼550℃, 5/sec for 100% strain. The results from three deformation maps were compared with microstructures. The best condition of plastic deformation could be determined as 500℃ and 5/sec.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.424-424
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• 2009

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.368-368
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• 2009

• Korean Journal of Metals and Materials
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• v.48 no.8
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• pp.699-704
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• 2010

We investigated the cryogenic temperature plasticity of a bulk amorphous alloy. Experiments showed that as temperature decreases, the plasticity of the alloy increases, such that the alloy exhibited ~20% of plastic strain when tested at $-196^{\circ}C$. This enhancement in the plasticity at cryogenic temperatures was associated with the formation of abundant shear bands distributed uniformly over the entire surface of the sample. Nonetheless, the serrations, the characteristic feature of the plastic deformation of amorphous alloys, were unclear at $-196^{\circ}C$. In this study, both the enhanced plasticity and the unclear serrations exhibited by the amorphous alloy at cryogenic temperatures were clarified by exploring shear banding behaviors in the context of the velocity and the viscosity of a propagating shear band.