• Proceedings of the Materials Research Society of Korea Conference
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• 2008.05a
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• pp.13.2-13.2
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• 2008

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.75-86
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• 1998

Eighteen oriented samples from the Jeongsun limestone of the Joseon Supergroup are collected. The orientations of C-axis of calcite and e twin plane, the average thickness, numbers of twins and the widths of calcite grains in 10 samples are measured. Then, the twin strain, mean width, intensity of twin and relative magnitude and orientations of principal stresses are calculated using Calcite Strain Gauge program. Twin strain, mean width and intensitv rainge between 0.801%~10.927%, $0.43{\mu\textrm{m}}~2.03{\mu\textrm{m}}$, and 33.5~113.4twim/mm, respectively. Metamorphic temperatures calculated from twin show below $70^{\circ}C$, indicating that twins were developed within 2.3km depth. In five samples, two events with different orientations of principal stress produced calcite twins, while only one event produced calcite twins in five samples. The direction of the maximum stress is almost horizontal and the minimum is almost vertical, indicating that the stress regirne is identical with thrust fault. E-W and NW-SE are the most dominant directions of comressive stress and N-S and NE-SW directions are also shown. Comparision between paleostress orientations measured in the study and others indicates that the maximum horizontal stress oriented to E-W may represent the paleostress of period either from the Silurian to the Triassic or from the Silulian to the Permian. Paleostress oriented to NW-SE may be the major direction of stress during the Daeho orogeny.

• The Journal of Engineering Geology
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• v.32 no.1
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• pp.13-26
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• 2022

Calcite twins were analyzed in six oriented samples of the Pungchon limestone, Joseon Supergroup, to reconstruct the paleostress field. The orientations of c-axis of calcite and e twin plane were measured along with the average thickness and numbers of twins, and the widths of calcite grains. Twin strain, mean width, and intensity of twinning, and the relative magnitude and orientations of principal stresses were calculated using Calcite Strain Gauge program. Twin strain, mean width, and intensity of twinning showed ranges of 1.09-15.36%, 0.53-3.72 ㎛ and 21.0-53.1 twim/mm, respectively. Metamorphic temperatures calculated from the twins were 170-200℃, indicating that the twins developed after the Pungchon limestone was uplifted to at least half of the maximum burial depth. Results for five of the samples indicate that the calcite twins formed during two events with principal stress axes of different orientations, while the remaining sample recorded only one event that produced calcite twins. The axis of maximum compressive stress was oriented mainly WNW-ESE to ENE-WSW, and to a lesser degree NW-SE and NE-SW. Comparison of paleostress orientations measured here and in other studies indicates that most twins were produced during the Songrim orogeny. However, the Daebo orogeny and the Bulguksa orogeny also produced calcite twins in the Punchon limestone.

• Economic and Environmental Geology
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• v.40 no.4
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• pp.461-471
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• 2007

A temperature of deformation and the state and direction of paleostress at that time when twins in calcite grains had been produced were observed, using analysis of calcite twins as indicators of paleostress history. The study was performed with the target of carbonate rocks distributed randomly small size in the southern area of south Korea. Considering the appearance of twins (thin or thick straight twins with one or two twin sets), average twin strain (1.235-7.453%), thickness ($0.77-1.94{\mu}m$) and intensity (25.26-41.99 twins/mm) from the results of calculated calcite twins, it is estimated that calcite twins were produced under temperatures lower than approximately $150-200^{\circ}C$. In the magnitudes and directions of principal strains, the maximum shortening strain axis ($e_3\leftrightarrow{\sigma}_1$) is approximately N-S direction in the GS-1 area in the southern Gyeongsang Basin as well as in the BS-1 area in the southern Yongnam Massif, whereas E-W direction in the NR-1 area in the southwestern Ogcheon Fold Belt. In case of the maximum extension strain axis ($e_1\leftrightarrow{\sigma}_3$), it is oriented in NW-SE and NE-SW directions in the GS-1 and BS-1 area, respectively, and in N-S direction in the NR-1 area. That is, it is suggested that the paleostress which produced the calcite twins may be applied at least more than two times in the study area.

• The Journal of the Petrological Society of Korea
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• v.24 no.2
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• pp.125-139
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• 2015

Rock structural and microstructural analyses on the deformed Cheongsan granite, which is characterized by abundant feldspar megacrystals, have been carried out to understand the microstructural change during the mylonitization by ductile shear deformation. In K-feldspars, the characteristic microstructures are recognized as microkinks, microfractures, myrmekites, flame perthites, and core-and-mantle structures without the development of subgrains in outer core-zone. Microkinks are observed in both the microfractured and unmicrofractured K-feldspars and the directions of their axes are generally extended across the adjacent K-feldspar fragments bounded by microfractures. Myrmekites and flame perthites are found on the strain-localized boundaries of the microfractured K-feldspars. In plagiclases, microfractures, deformation twins and kink bands are predominant. Grain size reduction of plagioclase megacrysts also occurs by microfracturing but the core-and-mantle structures like the case of K-feldspars are uncommon in the microfractured plagioclases. The deformation twins, which overlap the igneous zoning structures, are often found in less deformed rocks. The twin lamellae in more deformed rocks generally bisect the obtuse angles of conjugate kink-band boundaries, and are microfractured or microfaulted and randomly oriented. From such characteristic microstructures, thus, it can be suggested that the micostructures during the mylonitzation of Cheongsan granite was developed as follows: production of microkinks in the K-feldspar megacrysts and of deformation twins and kink bands in the plagioclase megacrysts, and then grain-size reduction of the feldspar megacrysts through microfracturing, and then production of core-and-mantle structures (grain-size reduction of the microfractured K-feldspars through grain boundary migration), myrmekites and flame perthites in the microfractured K-feldspars.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.234.1-234.1
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• 2005

• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.228-234
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• 1996

It is very important to understand the domain structures of ferroelectric BaTiO3 in the poling process. Especially because {111} twinning is frequently observed in most BaTiO3 ceramics it is required to know the relations between the ferroelectric domains and the structural twin. In this study the domain structures of a {111} twinned crystal sample were observed under a polarizing microscope. and the relation between the {111} twin and the domain configurations could be classified into two types of 'V'-shape and linear shape penetrating perpendicular to the twin boundary. Domain formation obeys the symmetry of the {111} twining when a new domain structure is developed by heat treatment and surface deformation due to domain formation is also occured symmetrically between the both sides of the{111} twin boundary. This symmetrical behavior of the domains could be interpreted with the "head-to-tall" orientation of the domains across the {111} twin boundary.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.247-250
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• 2009

본 연구에서는 반복하중을 받는 구리 나노와이어에서 나타나는 초탄성 거동을 분자동역학 전산모사를 통해 해석하였다. 나노스케일에서는 표면적 대 부피비가 매우 크기 때문에 표면효과가 지배적으로 나타난다. 이로 인해 벌크상태에서는 보이지 않던 새로운 성질들이 나노크기에서 나타나는데, 이러한 효과로 인해 나노와이어의 경우에는 초탄성 거동을 보인다. 초탄성 거동은 나노와이어의 결정학적 방향의 재배열에 의한 것으로써, 하중을 받는 동안 나노와이어의 결정 구조는 변하지 않으며, 쌍정의 발생 및 쌍정계면의 전파에 의해 결정학적 방향이 재배열된다. 재배열에 의해 부분적으로 변형되었던 나노와이어는 하중을 제거하거나 하중의 방향이 바뀜에 따라 원래의 상태를 회복하는 거동을 보이게 된다. 본 연구에서는 분자 동역학 전산 모사를 통해 <100>/{100} 구리 나노와이어가 반복적인 압축-인장 거동 하에서 초탄성을 보이게 됨을 확인하였으며, 반복 하중 싸이클을 증가시키는 전산모사를 통해 나노와이어의 초탄성이 영구적으로 유지됨을 확인하였다.

• Journal of the Mineralogical Society of Korea
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• v.16 no.1
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• pp.91-106
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• 2003

XRD results on annealing studies of Na-feldspars (Amelia albite) show rapid changes in the lattice parameters of the $1073^{\circ}C$-heated samples owing to disordering of Al and Si as well as lattice distortions upon quenching of the heated specimens. While a low albite transformed to a high albite by 7-days annealing at $1073^{\circ}C$, it remains as an early intermediate albite even by 140-days annealing at $924^{\circ}C$ due to the slower Al-Si disordering rate. From the heated samples tweed structures of $100∼200\AA$ were typically observed by TEM, which showed different ways of development between the $1073^{\circ}C$ -heated one and the $923 ^{\circ}C$ -heated one. The former locally trans-farmed to rnicrostructures similar to albite twin, while the latter transformed to domain structures containing albite twin plane in the wider area. The origin of tweed structures is suggested to be formation of incipient twins (albite twin and pericline twin) to reduce the lattice instability which is increased by disordering of Al and Si as well as quenching.

• 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.