• 한국지반공학회논문집
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• 제24권8호
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• pp.53-60
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• 2008

본 연구에서는 균질 지반에 매설된 단독말뚝에 수평하중이 작용할 경우 말뚝 배면지반에서 발생되는 여러 가지 거동 특성, 즉 말뚝 배면지반의 변형영역, 파괴면의 경사각, 그리고 회전절점과 같은 거동 특성을 모형실험을 통하여 규명하고자 모형실험을 수행하였다. 이는 말뚝의 휨력에 대한 저항력 산정에 매우 중요한 사항이다. 그 결과 다음과 같은 결과를 얻을 수 있었다. 수평하중이 작용하는 단독말뚝 배면지반에서 쐐기 파괴면은 거의 선형적인 거동 특성을 나타내고, 말뚝과 파괴면이 이루는 경사각은 말뚝 길이, 말뚝 두부의 변위에 상관없이 지반의 상대밀도 증가에 따라 조금씩 증가하다 일정한 값으로 수렴하는 경향을 나타낸다.

• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.938-945
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• 2005

The microstructure evolution in hot forging process is composed of dynamic recrystallization during deformation as well as grain growth during dwell time. Therefore, the control of forging parameters such as strain, strain rate. temperature and holding time is important because the microstructure change in hot working affects the mechanical properties. Modeling equations are developed to represent the flow curve. grain size. recrystallized volume fraction and grain growth phenomena by various tests. The developed modeling equations were combined with thermo-viscoplastic finite element modeling to predict the microstructure change evolution during hot forging process. The large exhaust valve spindle (head diameter of 512mm) was simulated by closed die forging with hydraulic press and cooled in air after forging. The preform was heated to each 1080 and 1150$^{\circ}C$. Numerical calculation was performed by DEFORM-2D. a commercial finite element code. Heat transfer can be coupled with the deformation analysis in a non-isothermal deformation analysis. In order to obtain the fine and homogeneous microstructure and good mechanical properties in forging. the FEM would become a useful tool in the simulation of the microstructure development. In forging, appropriate temperature, strain and strain rate and rapid cooling are required to obtain the fine grain microstructure The optimal forging temperature and effective strain range of Nimonic 80A for large exhaust valve spindle are about 1080$\∼$l120$^{\circ}C$ and 150$\∼$200$\%$.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.353-368
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• 2018

In this work, a high order hyperbolic shear deformation theory with four variables is presented to study the vibratory behavior of functionally graduated plates. The field of displacement of the theory used in this work is introduced indeterminate integral variables. In addition, the effect of porosity is studied. It is assumed that the material characteristics of the porous FGM plate, varies continuously in the direction of thickness as a function of the power law model in terms of volume fractions of constituents taken into account the homogeneous distribution of porosity. The equations of motion are obtained using the principle of virtual work. An analytical solution of the Navier type for free vibration analysis is obtained for a FGM plate for simply supported boundary conditions. A comparison of the results obtained with those of the literature is made to verify the accuracy and efficiency of the present theory. It can be concluded from his results that the current theory is not only accurate but also simple for the presentation of the response of free vibration and the effect of porosity on the latter.

• Coupled systems mechanics
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• 제8권4호
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• pp.299-313
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• 2019

The paper represents computer modeling of the deformed state of physically nonlinear transversally isotropic bodies with hole. In order to describe the anisotropy of the mechanical properties of transversally-isotropic materials a structurally phenomenological model has been used. This model allows representing the initial material in the form of the coupled isotropic materials: the basic material (binder) considered from the positions of continuum mechanics and the fiber material oriented along the anisotropy direction of the original material. It is assumed that the fibers perceive only the axial tensile-compression forces and are deformed together with the base material. To solve the problems of the theory of plasticity, simplified theories of small elastoplastic deformation have been used for a transversely-isotropic body, developed by B.E. Pobedrya. A simplified theory allows applying the theory of small elastoplastic deformations to solve specific applied problems, since in this case the fibrous medium is replaced by an equivalent transversely isotropic medium with effective mechanical parameters. The essence of simplification is that with simple stretching of composite in direction of the transversal isotropy axis and in direction perpendicular to it, plastic deformations do not arise. As a result, the intensity of stresses and deformations both along the principal axis of the transversal isotropy and along the perpendicular plane of isotropy is determined separately. The representation of the fibrous composite in the form of a homogeneous anisotropic material with effective mechanical parameters allows for a sufficiently accurate calculation of stresses and strains. The calculation is carried out under different loading conditions, keeping in mind that both sizes characterizing the fibrous material fiber thickness and the gap between the fibers-are several orders smaller than the radius of the hole. Based on the simplified theory and the finite element method, a computer model of nonlinear deformation of fibrous composites is constructed. For carrying out computational experiments, a specialized software package was developed. The effect of hole configuration on the distribution of deformation and stress fields in the vicinity of concentrators was investigated.

• Computers and Concrete
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• 제33권1호
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• pp.27-39
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• 2024

In this study, the authors investigate the free vibration behavior of three-phases functionally graded sandwich plates using a novel nth-order shear deformation theory. These plates are composed of a homogeneous core and two face-sheet layers made of different functionally graded materials. This is the novel type of the sandwich structures that can be applied in many fields of mechanical engineering and industrial. The proposed theory only requires four unknown displacement functions, and the transverse displacement does not need to be separated into bending and shear parts, simplifying the theory. One noteworthy feature of the proposed theory is its ability to capture the parabolic distribution of transverse shear strains and stresses throughout the plate's thickness while ensuring zero values on the two free surfaces. By eliminating the need for shear correction factors, the theory further enhances computational efficiency. Equations of motion are established using Hamilton's principle and solved via Navier's solution. The accuracy and efficiency of the proposed theory are verified by comparing results with available solutions. The authors then use the proposed theory to investigate the free vibration characteristics of three-phases functionally graded sandwich plates, considering the effects of parameters such as aspect ratio, side-to-thickness ratio, skin-core-skin thicknesses, and power-law indexes. Through careful analysis of the free vibration behavior of three-phases functionally graded sandwich plates, the work highlighted the significant roles played by individual material ingredients in influencing their frequencies.

• 대한기계학회논문집A
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• 제32권4호
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• pp.319-326
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• 2008

In this study, we investigate the deformation behavior of F.C.C. single crystals containing micro- or submicron-sized voids by using three dimensional finite element methods. The locally homogeneous constitutive model for the rate-dependent crystal plasticity is integrated based on the backward Euler method and implemented into a finite element program (ABAQUS) by means of user-defined subroutine (UMAT). The unit cell analysis has been investigated to study the effect of stress triaxiality and crystallographic orientations on the growth and coalescence of voids in F.C.C. single crystals.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.197-198
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• 2002

In order to produce micromachined parts with a great dimensional accuracy, it is important to clarify the influence of heterogeneity and/or discontinuity of workpiece materials on the micromachining process, because almost all structural materials are composed of heterogeneous and/or homogeneous crystal grains at the micro scale. Experiments where JIS S25C steel had been scratched with a diamond triangular pyramid indenter were conducted under a field emission scanning electron microscope (FE-SEM). The difference of plastic deformation at a groove scratched between a pearlite zone and a proeutectoid ferrite zone was investigated through comparison with the groove scratched of a pearlite zone and a proeutectoid ferrite zone.

• Geomechanics and Engineering
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• 제21권5호
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• pp.461-469
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• 2020

The objective of this paper is to study the deformation in a homogeneous isotropic modified couple stress thermoelastic medium with and without energy dissipation and with two temperatures due to thermal source and mechanical force. Laplace and Fourier transform techniques are applied to obtain the solutions of the governing equations. The displacement components, stress components, conductive temperature and couple stress are obtained in the transformed domain. Isothermal boundary and insulated boundary conditions are used to investigate the problem.The effect of two temperature and GN theory of type-II and type-III has been depicted graphically on the various components. Numerical inversion technique has been used to obtain the solutions in the physical domain. Some special cases of interest are also deduced.

• Geomechanics and Engineering
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• 제22권2호
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• pp.109-117
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• 2020

The present article is concerned about the study of disturbances in a homogeneous nonlocal magneto-thermoelastic medium under the combined effects of hall current, rotation and two temperatures. The model under assumption has been subjected to normal force. Laplace and Fourier transform have been used for finding the solution to the field equations. The analytical expressions for conductive temperature, stress components, normal current density, transverse current density and displacement components have been obtained in the physical domain using a numerical inversion technique. The effects of hall current and nonlocal parameter on resulting quantities have been depicted graphically. Some particular cases have also been figured out from the current work. The results can be very important for the researchers working in the field of magneto-thermoelastic materials, nonlocal thermoelasticity, geophysics etc.

• 한국지반공학회논문집
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• 제17권6호
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• pp.85-98
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• 2001

Arbitrary Lagrangian-Eulerian(ALE) 기법에 의거하여 콘 관입문제를 해석하였다. 완전한 관입을 모의하기 위하여 ABAQUS/Explicit을 이용하여 지반의 상향 유동을 모델링하는 정상상태해석(steady state analysis)을 수행하였다. 단일 지층의 해석에서는 흙 입자의 유동 경로와 변형률이 strain path method와 일관된 결과를 나타내고 있음을 확인하였고 극한저항을 합리적으로 계산할 수 있었다. 상이한 지층에 콘을 관입하는 경우에 대해서도 콘 저항이 전이하는 경향을 해석할 수 있었다. 따라서 ALE 해법의 정상상태해석으로 층상 지층에 대한 완전한 관입을 해석할 수 있었다.