• 한국지반환경공학회 논문집
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• 제18권5호
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• pp.17-26
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• 2017

절리가 형성된 암반지층에서의 터널굴착은 터널굴착 선을 따라 변위를 유발시키며 이러한 변위값의 산정은 터널의 안정성과 소요공간을 확보하는 것과 관련하여 매우 중요한 사항이다. 터널변위는 지반의 변형계수와 직접적으로 관련되므로 이를 파악하는 것이 무엇보다도 중요하다. 그렇지만, 터널이 건설되는 대부분의 암반지층은 일반적으로 절리가 형성되어 있어서 단순히 균질한 등가탄성매질에 근거하여 절리형성 암반지층의 변형계수를 파악할 수는 없다. 왜냐하면 절리형성 암반지층의 변형계수는 암석의 종류뿐만 아니라 절리조건에 의해서 큰 영향을 받기 때문이다. 따라서 본 연구에서는 터널굴착 조건에서 다양한 절리 및 암석조건을 고려한 암반지층의 변형계수 변화를 조사하였으며 이를 위하여 수치해석적 매개변수연구를 수행하였다. 이를 통한 본 연구의 결과는 기존의 경험적인 방법들과 상호 비교되었으며, 또한 다양한 절리암반을 고려한 변형계수 변화표의 형태로서 제시되었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.105-106
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• 2007

Microstructure and hardness of metallic powder of Cu was studied after high pressure torsion (HPT) with 10 torsions and high pressure of 6 GPa. The size Cu grain decreases drastically after HPT and reaches the nano size range. During HPT, Cu powder increases hardness and Hall-Petch hardening, due to the decreasing grain size. In this study, effect of HPT on the hardness of Cu powders and consolidation with Nanocrystalline of the work reported here. The results indicated that Cu powder has a beneficial effect on homogeneous deformation, reducing grain size.

• Steel and Composite Structures
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• 제18권1호
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• pp.91-120
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• 2015

A refined higher-order shear deformation theory for bending, vibration and buckling analysis of functionally graded sandwich plates is presented in this paper. It contains only four unknowns, accounts for a hyperbolic distribution of transverse shear stress and satisfies the traction free boundary conditions. Equations of motion are derived from Hamilton's principle. The Navier-type and finite element solutions are derived for plate with simply-supported and various boundary conditions, respectively. Numerical examples are presented for functionally graded sandwich plates with homogeneous hardcore and softcore to verify the validity of the developed theory. It is observed that the present theory with four unknowns predicts the response accurately and efficiently.

• 기계와재료
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• 제23권3호
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• pp.16-29
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• 2011

결정 합금 대비 비정질 합금은 높은 경도를 갖기 때문에 마모 저항성도 좋고 내부 식성 등 환경에 대한 저항성도 월등하며, 또한 과냉된 액상 상태까지 재가열하게 되면 낮은 점성도를 갖게 되므로 복잡한 3차원적인 형상을 가지는 부품을 환경에 대한 저항성, 피로 저항성, 강도 및 경도 등을 모두 고려하여 높은 정밀도를 가지고 제조하는 것이 가능하므로 우수한 물성을 갖는 구조 및 기능성 재료로의 다양한 응용이 타진되고 있다. 이러한 비정질 합금의 변형 거동에 대한 연구는 대부분 유리 천이 온도 이하에서의 전단 및 파단에 이르는 이른바 불균일 변형(Inhomogeneous Deformation) 거동에 대한 이해를 위한 실험 및 해석적 연구에 집중되어 왔다. 반면 상업화의 기반이 되는 고상 기반 2차 정형 성형은 과냉 액상 영역에서의 구조 완화 및 결정화롤 대표되는 미세 구조 제어 균일 변형(Homogeneous Deformation)에 대한 이해 없이는 불가능하므로, 이러한 관점에서 비정질 합금 특유의 점성 유동 특성을 이용한 균일 변형 응용 예시 및 미세구조 변화 연계 해석 기술의 현황을 소개하고자 한다.

• Steel and Composite Structures
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• 제15권2호
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• pp.221-245
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• 2013

This paper presents an analytical solution to the thermomechanical bending analysis of functionally graded sandwich plates by using a new hyperbolic shear deformation theory in which the stretching effect is included. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are investigated.

• Structural Engineering and Mechanics
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• 제34권3호
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• pp.285-300
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• 2010

The two-dimensional deformation of a homogeneous, isotropic thermoelastic half-space with voids with variable modulus of elasticity and thermal conductivity subjected to thermomechanical boundary conditions has been investigated. The formulation is applied to the coupled theory(CT) as well as generalized theories: Lord and Shulman theory with one relaxation time(LS), Green and Lindsay theory with two relaxation times(GL) Chandrasekharaiah and Tzou theory with dual phase lag(C-T) of thermoelasticity. The Laplace and Fourier transforms techniques are used to solve the problem. As an application, concentrated/uniformly distributed mechanical or thermal sources have been considered to illustrate the utility of the approach. The integral transforms have been inverted by using a numerical inversion technique to obtain the components of displacement, stress, changes in volume fraction field and temperature distribution in the physical domain. The effect of dependence of modulus of elasticity on the components of stress, changes in volume fraction field and temperature distribution are illustrated graphically for a specific model. Different special cases are also deduced.

• Steel and Composite Structures
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• 제24권1호
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• pp.79-91
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• 2017

Free vibrations of steel-concrete composite beams are analyzed by using the dynamic stiffness approach. The coupled equations of motion of the composite beams are derived with help of the Hamilton's principle. The effects of the shear deformation and rotary inertia of the two beams as well as the transverse and axial deformations of the stud connectors are included in the formulation. The dynamic stiffness matrix is developed on the basis of the exact general solutions of the homogeneous governing differential equations of the composite beams. The use of the dynamic stiffness method to determine the natural frequencies and mode shapes of a particular steel-concrete composite beam with various boundary conditions is demonstrated. The accuracy and effectiveness of the present model and formulation are validated by comparison of the present results with the available solutions in literature.

• Steel and Composite Structures
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• 제28권4호
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• pp.495-508
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• 2018

In this paper, the effect of matrix cracks on the buckling of a hybrid laminated plate is investigated. The plate is composed of carbon nanotube reinforced functionally graded (CNTR-FG) layers and conventional fiber reinforced composite (FRC) layers. Different distributions of single walled carbon nanotubes (SWCNTs) through the thickness of layers are considered. The cracks are modeled as aligned slit cracks across the ply thickness and transverse to the laminate plane, and the distribution of cracks is assumed statistically homogeneous corresponding to an average crack density. The first-order shear deformation theory (FSDT) is employed to incorporate the effects of rotary inertia and transverse shear deformation, and the meshless kp-Ritz method is used to obtain the buckling solutions. Detailed parametric studies are conducted to investigate the effects of matrix crack density, CNTs distributions, CNT volume fraction, plate aspect ratio and plate length-to-thickness ratio, boundary conditions and number of layers on buckling behaviors of hybrid laminated plates containing CNTR-FG layers.

• 소성∙가공
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• 제7권4호
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• pp.364-374
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• 1998

It is the objective of this study to analyze the effect of various process variables on the quality of extruded product and extrusion force for semi-solid extrusion of Al2024 with solid phase structure of globular type by the finite element method. Process variables are initial solid fraction, ram speed, semi-angle of die, and reduction in area. The results of experiment are compared with those of simulation in order to verify the usefulness of the developed finite element program. The flow and deformation of semi-solid alloy are analyzed by coupling by coupling the deformation of porous skeleton and the flow of liquid phase. It is also assumed that initial solid fraction is homogeneous.

• 소성∙가공
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• 제16권5호통권95호
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• pp.360-363
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• 2007

Microstructure and microhardness of metallic powders of pure copper were studied after high pressure torsion(HPT) processing with 10 turns of die rotation and high pressure of 6 GPa. The grain size of copper decreases drastically after HPT and reaches nanometer size ranges. During HPT, the hardness of consolidates of copper powders increases with increasing the temperature of HPT processing. Examinations of the fracture surfaces indicated evidence of ductile fracture. The results proved that HPT of copper powders has a beneficial effect for homogeneous deformation with reducing grain size.