• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.53-68
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• 1998

Microstructural and rock structural analyses on the deformed Cheongsan granite characterized by abundant K-feldspar megacrysts have been carried out to understand the temperature condition for the ductile shear deformation. In K-feldspar, microkinks, microfractures and core-and-mantle structures without the development of subgrains in outer core-zone are the most common microstructures observed. Myrmekites and flame perthites are developed at the strain-localized areas along the microfractured K-feldspar. In plagioclase, microfractures, deformation twins and kink bands are predominant. The deformation twins cut across the igneous zonation of the plagioclase. Patterns of c-axis fabrics of dynamically recrystallized new quartz grains display single girdle and type II crossed girdle where prism slip system is predominant. These characteristic microstructures produced during the ductile shearing suggest that the ductile shear deformation in the Cheongsan granite occurred under epidote-amphibolite conditions($400-500^{\circ}C$). Three main shear zones are recognized at outcrop scale: discrete shear zone with anastomosing high-strain domain, shear zone with pervasive S-C structure and shear zone with homogeneously foliated domain. Geometric features of these shear zones produced during the ductile shear deformation are controlled by amount of strain under the $400-500^{\circ}C$ deformation temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.217-218
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.478-478
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• 2009

• 대한치주과학회:학술대회논문집
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• 2001.12a
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• pp.64-64
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• 2001

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.7-17
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• 2002

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.36-38
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• 2004

연연속 압연이란 1980년대에 열연제품의 생산성 향상을 위하여 도입된 개념으로서 조압연(rough rolling)이 끝난 판재를 서로 접합하여 연속적으로 사상압연(finish rolling)하는 방법을 말한다. (중략)

• Proceedings of the Materials Research Society of Korea Conference
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• 2005.05a
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• pp.274-274
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• 2005

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.343-352
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• 1992

The high temperature deformation behavior of microalloyed hot forging steels has been examined as a function of the temperature, the strain rate, and the alloying element by using high temperature compression test. The high temperature deformation mechanism, which was obtained by analyzing the flow stress-strain curve and microstructure, could be considered to dynamic recrystallization. The peak stress of Nb-V-Mo steel was more increased and the dynamic recrystallization of Nb-V-Mo steel was faster than those of Nb-V steel. The peak stress of 1.2Mn-0.09Nb steel was more increased and the dynamic recrystallization of 1.2Mn-0.09Nb was delayed a little bit than those of 1.0Mn-0.05Nb. The peak stress of C-Nb-V steel was more increased and the dynamic recrystallization of C-Nb-V steel was delayed than those of C-steel. The constitutive equation of high temperature deformation had a power law type. The grain size of dynamic recrystallization was refined as the Zener-Hollomon parameter was increased. The relation of the dynamic recrystallization grain size and Zener-Hollomon parameter could be quantified to power law.

• Korean Journal of Materials Research
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• v.6 no.1
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• pp.67-78
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• 1996

제 3원소가 첨가된 금속간 화합물 TiAI 금속간 화합물 분말을 PREP법(플라즈마 회전전극법)으로 제조하여, 통.방전 강압소결법에 의해 치밀한 소결체를 만들었다. 이에 대해 첨가 원소의 종류와 열처리에 따른 고온 및 상온 압축 특성의 변화를 조사하였다. 소결체의 미세조직은 ${\gamma}$/$\alpha$2 lamella로 이루어진 완전 변태구조였고, 결정립의 크기는 140-150$\mu\textrm{m}$였으며 계단형 결정립계를 나타내었다. 소결체를 ($\alpha$+${\gamma}$)구역인 130$0^{\circ}C$에서 2시간 동안 열처리한 결과, 모든 조성의 시편이 등축점 ${\gamma}$와 lamella로 이루어진 전형적인 duplexrn조로 변태하였다. 상온 압축 시험에서 시편은 파괴될 때까지 가공경화 현상이 나타났으며, Cr을 첨가한 시편이 가장 큰 파괴응력과 변형률을 나타내었다. 한편, 고온 압축 시험의 경우 온도상승 때문에 가공경화의 속도가 감소되었고, 80$0^{\circ}C$에서는 가공경화와 회복이 균형을 이루는 소위 정상 상태의 변형을 보였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.1933-1943
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• 2001

A micromechanical model is presented for superplasticity in which heterogeneous microstructures are coupled with deformation behavior. The effects of initial distributions of grain size, and their evolutions on the mechanical properties can be predicted by the model. Alternative stress rate models such as Jaumann rate and rotation incremental rate have been employed to analyze uniaxial loading and simple shear problems and the appropriate modeling was studied on the basis of hypoelasticity and elasto-viscoplasticity. The model has been implemented into finite element software so that full process simulation can be carried out. Tests have been conducted on Ti-6Al-4V alloy and the microstructural features such as grain size, distributions of grain size, and volume fraction of each phase were examined for the materials that were tested at different strain rates. The experimentally observed stress-strain behavior on a range of initial grain size distributions has been shown to be correctly predicted. In addition, the effect of volume fraction of the phases and concurrent grain growth were analyzed. The dependence of failure strain on strain rate has been explained in terms of the change in mechanism of grain growth that occurs with changing strain rate.