• 한국전기전자재료학회논문지
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• 제17권8호
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• pp.888-892
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• 2004

It is necessary to develop soft magnetic layer with high saturation magnetization 4 $\pi{M}_s$ and in-plane magnetic anisotropy field Hk for soft magnetic underlayer of perpendicular magnetic recording media with high signal to noise ratio. Fe-Co-B layer with high 4 $\pi$Ms of about 23 kG deposited on Ni-Fe and Ni-Fe/Si seedlayer exhibited very high in-plane magnetic anisotropy filed Hk of about 280 and 380 Oe, respectively, In-plane XRD studies clarified that the lattice spacing of planes along the easy axis direction was longer than that along the hard axis direction in the Fe-Co-B layers with high Hk. These results indicate that high Hk of Fe-Co-B/Ni-Fe and Fe-Co-B/［Ni-Fe/si］ layers were resulted from magnetoelastic anisotropy owing to a residual stress. Moreover, the high Hk in the Fe-Co-B/Ni-Fe layer was maintained until 30$0^{\circ}C$ annealing temperature.

• 대한기계학회논문집B
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• 제22권3호
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• pp.280-293
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• 1998

Numerical study on turbulent and mean structures of a turbulent boundary layer with longitudinal and spanwise pressure gradient is carried out by using Reynolds-stress-model (RSM). The existence of pressure gradient in a turbulent boundary layer causes the skewing or divergence of rates of strain, which contributes to production of turbulent kinetic energy. Also, this augmentation of production due to extra rates of strain can increase the turbulent mixing and cause the anisotropy of turbulent intensities in the outer layer. This paper uses the Reynolds Stress Model to capture anisotropy of turbulent structures effectively and is devoted to compare the results computed by using RSM and the standard k-.epsilon. model with experimental data. It is concluded that the RSM can produce the more accurate predictions for capturing the anisotropy of turbulent structure than the standard k-.epsilon. model.

• Geomechanics and Engineering
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• 제7권4호
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• pp.403-430
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• 2014

Shale gas formations exhibit strong mechanical and strength anisotropies. Thus, it is necessary to study the effect of anisotropy on the hydraulic fracture initiation pressure. The calculation model for the in-situ stress of the bedding formation is improved according to the effective stress theory. An analytical model of the stresses around wellbore in shale gas reservoirs, in consideration of stratum dip direction, dip angle, and in-situ stress azimuth, has been built. Besides, this work established a calculation model for the stress around the perforation holes. In combination with the tensile failure criterion, a prediction model for the hydraulic fracture initiation pressure in the shale gas reservoirs is put forward. The error between the prediction result and the measured value for the shale gas reservoir in the southern Sichuan Province is only 3.5%. Specifically, effects of factors including elasticity modulus, Poisson's ratio, in-situ stress ratio, tensile strength, perforation angle (the angle between perforation direction and the maximum principal stress) of anisotropic formations on hydraulic fracture initiation pressure have been investigated. The perforation angle has the largest effect on the fracture initiation pressure, followed by the in-situ stress ratio, ratio of tensile strength to pore pressure, and the anisotropy ratio of elasticity moduli as the last. The effect of the anisotropy ratio of the Poisson's ratio on the fracture initiation pressure can be ignored. This study provides a reference for the hydraulic fracturing design in shale gas wells.

• 자원환경지질
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• 제30권4호
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• pp.353-362
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• 1997

P wave velocities of core samples from the Pocheon granite were measured before and after applications of cyclic loading. Then. distribution of the pre-existing microcracks and microcracks developed due to the cyclic loading was investigated by analyzing P wave velocity anisotropies and microscopic observations from thin sections. Anisotropy constants were calculated with three different ways: (1) $C_A$ between the maximum and the minimum velocities, (2) $C_AI$ between velocities measured along the axial direction and the average of six velocities measured in the planes perpendicular to the loading axis (rift plane) and (3) $C_AII$ between the maximum and the minimum velocities measured in the plane perpendicular to the loading axis. Among anisotropy constants. $C_AI$ was the most effective anisotropy constant to identify the rift plane whose orientation is parallel to the pre-existing microcracks as well as the distribution of stress induced microcracks. $C_AI$ decreased after cyclic loading and the relationship between $C_AI$ and number of cycles shows comparatively coherent negative trends. indicating that stress induced microcracks are aligned perpendicular to the orientation of pre-existing microcracks and that the amounts are proportional to the number of loading cycles. The difference of anisotropy constants before and after cyclic loading was effective in delineating the level of cracks and we called it Induced Crack Index. Velocity measurements and microscopic observations show that anisotropy was caused mainly due to microcracks aligned to a particular direction.

• 암석학회지
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• 제21권2호
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• pp.249-261
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• 2012

감람석은 맨틀 상부의 주요 광물이고, 탄성적으로 매우 비균질하다. 맨틀암석이 고압고온에서 변형될 때, 이러한 감람석이 배열되어 격자선호방향(LPO, Lattice Preferred Orientation)이 형성된다. 감람석의 격자선호방향은 압력, 응력, 그리고 감람석 내부의 물(OH)의 양에 따라 크게 영향을 받을 수 있다. 이 논문에서는 물, 응력, 그리고 압력이 어떻게 감람석의 격자선호방향(LPO)의 형성에 영향을 주는지에 대해 그동안 발표된 논문들을 리뷰했고, 자연 맨틀암석에서 발견된 감람석의 격자선호방향들을 요약했으며, 감람석의 격자선호방향과 맨틀상부에서 나타나는 지진파의 비등방성과의 연계성에 대해 토의하였다. 그리고 최근에 맨틀암석에서 발견된 사방휘석의 네 가지 격자선호방향들을 기술하였다.

• 한국지반공학회논문집
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• 제19권3호
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• pp.15-22
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• 2003

지반의 실제 거동을 보다 정확하게 표현하기 위한, 응력의 비등방성 및 시간의존적(time-dependent) 거동의 적절한 묘사는 특히 점성토의 응력-변형률 관계를 나타내는 구성관계식에 있어서 중요한 관심사이다. 본 연구에서는 적은 모델정수로 응력의 비등방성을 묘사할 수 있는 소성 구성관계식과, 대표적 시간의존적 거동인 변형률 속도 효과를 간편하게 표현할 수 있는 변형률속도 의존적 구성관계식을 일반 점성이론에 입각하여 조합하였다. 결론적으로 제안된 하나의 비등방성 변형률속도 의존적 구성관계식은 비교적 모델정수가 적고, 변형률속도가 바뀔 때마다 모델정수 값을 다시 결정할 필요가 없다는 장점이 있다. 제안된 구성모델은 인위적으로 제작된 균질한 시료를 이용한 실내시험을 통하여 검증되었으며, 상세 거동 및 문제점을 고찰하였다.

• Geomechanics and Engineering
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• 제25권4호
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• pp.303-315
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• 2021

A rigorous and generic similarity solution is developed for assessment of the undrained expansion responses of a cylindrical cavity expansion in K₀-consolidated anisotropic soils. A K₀-consolidated anisotropic modified Cam-clay (K₀-AMCC) model that can represent the initial stress anisotropy and the effects of stress-induced anisotropy is used to model the soil behaviors during cavity expansion. All the seven basic unknowns, the three stress components, the pore water pressure, the particle velocity, the specific volume and the hardening parameter, are reduced to the functions of a dimensionless radial coordinate and are taken as coupled variables to formulate the problem. The governing equations are formulated by making use of the equilibrium equation, the constitutive equation, the consistency condition, the continuity condition and the undrained condition, which are then solved as an initial value problem. The proposed rigorous similarity solution is compared with some well-documented rigorous solutions to validate the solution and to highlight the special expansion responses in anisotropic soils. The results reveal that the present solution can yield more predictions for cavity expansion problems in soils with initial anisotropic stresses.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1508-1516
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• 2003

In numerical analysis for hydroforming process, the stress calculation is effected by flow stress which is general obtained by stress-strain relationship from uni-axial tension test, so the result of the analysis, especially in tube hydroforming, has limitation of accuracy, tubes are made in roll-forming process and become work-hardened. Then roll forming process causes material properties between rolling direction and circumstantial direction of the tube to be different. So it is difficult to predict material behavior in the process condition of bi-axial stress state. In this study, the flow stress of the tube is determined by inverse engineering approach and bulge test that is widely used for formability test in the condition of bi-axial stress. And Hill's quadratic yield function and flow rule are used to consider the anisotropy of the tube in the roll forming process.

• 한국지반공학회논문집
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• 제18권6호
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• pp.33-42
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• 2002

지반 굴착시 지반의 변위특성과 지보재의 설치시기에 대한 중요한 정보를 제공하는 지반반응곡선(Ground reaction curve)을 구하는 방법은 일반적으로 원형단면이고 측압계수 K＝1.0인 상태를 가정한 closed from solution을 통해서 구해지지만, 실제 현장에서는 주로 마제형 굴착단면이 사용되며 $K\neq$1.0인 경우 대부분이다. 지반 굴착시 측압계수와 굴착 형상에 따라 측벽에서의 초기탄성변위 및 임계지보압이 변화하는 경향을 알아보기 위하여 측압계수 값을 0.5～3.0 사이에서 변화시키고, 각 측압계수마다 초기연직응력을 5～30MPa 사이에서 변화시켜가면서 원형단면과 마제형 단면인 경우를 구분하여 수치해석을 통해 지반반응곡선을 얻었다. Closed form solution에 의해 얻어진 지반반응곡선은 측압계수와 굴착단면의 형상을 고려하지 못하기 때문에 $K\neq$1.0인 실제 지반에 대한 변위거동과 지반의 자립성을 평가하는 데 큰 오차를 유발할 수 있는 것으로 나타났다. 따라서, Closed from solution에 의해 지보재의 설치시기를 예측하는 것은 많은 오차를 수반하는 과정이므로, 수치해석을 통한 지보설치 시기와 자립성에 대한 검토를 수행하는 것이 바람직 할 것으로 판단된다.

• Elastomers and Composites
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• 제36권1호
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• pp.30-36
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• 2001

이 연구의 목적은 카본블랙이 충전된 천연고무에서 비 등방성 발생에 영향을 주는 인자를 조사하기 위함이다. 고분자 사슬의 방향성은 인장특성에 영향을 준다. Pre-strained 방향의 parallel 시편은 등방성 혹은 perpendicular 시편에 비하여 낮은 인장영역에서 낮은 강도를 보이지만 높은 신장영역에서 높은 강도를 보인다. 고 인장 영역에서 parallel한 천연고무 시편은 비결정성인 SBR에 비하여 높은 강도를 보여주고 있다. 이것은 parallel 시편의 방향성에 영향을 받는 것으로, 시편의 방향성은 2차 인장시 결정화를 위한 핵으로 작용하여 결정화도를 증가시키는 것으로 보인다.