• 열처리공학회지
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• 제9권3호
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• pp.161-168
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• 1996

The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.354-357
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• 2005

When Ti-6Al-4V is used in long steam turbine blades, the main issues are how to improve the fatigue strength as a problem of internal quality and how to forge the thinnest possible blades as problem of dimensional precision. To assure an excellent fatigue strength, it is important to make the two phase fine and equiaxial structure by providing enough plastic deformation in the two phase$(\alpha\;phase/\beta\;phase)$ temperature region. Accordingly, it needs to predict that forging temperature, preform design and forging velocity in forging process. To achieve this end, the two steps forging process was suggested to forge the thin and twisted blades with a precision hammer considering die forces and metal flow. Two steps forging process consists of the flattening forging process and finishing forging process. Process in forging of a 1016mm long steam turbine blade is designed by the finite element method. This study attempts to derive systematic design procedures for process design in the forging. Forging parameters was analyzed in two-dimensional plane-strain simulation and two steps forging process carried out in three-dimensional simulation. Consequently, optimal forging process parameters of long steam turbine blades in Ti-6Al-4V with a high dimensional precision are selected in the hammer die forging.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.87-90
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• 2005

The drawbead is used to control the material flow into the die and increase the forming quality during the binder wrap process and the stamping process in the sheet metal forming. Drawbead restraining force (DBRF) is controlled by geometrical parameters and influenced by process parameters such as friction coefficient and blank thickness. In order to inspect the effect of process parameters, parameter studies are performed with the variation of parameters using finite element model of drawbead which is utilized reliably for the calculation of the drawbead restraining force. Drawbead analysis is carried out with 2-D plane-strain element and 3-D shell element. After the verification of the accuracy of the drawbead model with 3-D shell element, it is utilized to the prediction and the investigation of the effect of process parameters. The result of parameter studies can be utilized to the die design in the tryout stage.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 Proceedings of 2004 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.169-175
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• 2004

The characteristics of flow around a rotating propeller were investigated using PIV technique. For each of four different blade phases of $0^{\circ},\;18^{\circ},\;36^{\circ}\;and\;54^{\circ}$four hundred instantaneous velocity fields were ensemble averaged to investigate the spatial evolution of the flow around a propeller. The phase-averaged mean velocity fields show that the viscous wake formed by the boundary layers developed on the blade surfaces and the slipstream contraction in the near-wake region. The out-of-plane velocity component and strain rate had large values at the locations of the tip and trailing vortices. The boundary layer developed along the ship hull bottom surface of the ship stern provides a strong turbulent shear layer, affecting the vortex structure in the propeller near-wake. As the flow develops in the downstream direction, the trailing vortices formed behind the propeller hub move upward slightly due to the presence of the hull wake and free surface. The turbulence intensity has large values around the tip and trailing vortices. As the wake moves downstream, the strength of the vorticity diminishes and the turbulence intensity increases due to turbulent diffusion and active mixing between the tip vortices and adjacent wake flow.

• Journal of Welding and Joining
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• 제28권1호
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• pp.86-91
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• 2010

In the present study, two-dimensional plane deformation thermo elasto-plastic analysis has been carried out, in order to investigate the thermal and mechanical behaviour (residual stress, plastic strain, magnitude of stress and their distribution and production mechanism) on multi-pass FCA butt weldment of high strength EH36-TMCP ultra thick plate. Moreover, this study can be considered as a basis for analysing the fracture toughness, KIC, and its effect on welding residual stress redistribution with notch on multi-pass FCA butt weldment, in future. The results of welding residual stress obtained from thermo elasto-plastic analysis has been compared and verified with the results measured by XRD.

• 한국농공학회지
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• 제40권5호
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.

• Smart Structures and Systems
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• 제18권1호
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• pp.155-181
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• 2016

In the present paper we discuss the stability and the post-buckling behaviour of thin piezoelastic plates. The first part of the paper is concerned with the modelling of such plates. We discuss the constitutive modelling, starting with the three-dimensional constitutive relations within Voigt's linearized theory of piezoelasticity. Assuming a plane state of stress and a linear distribution of the strains with respect to the thickness of the thin plate, two-dimensional constitutive relations are obtained. The specific form of the linear thickness distribution of the strain is first derived within a fully geometrically nonlinear formulation, for which a Finite Element implementation is introduced. Then, a simplified theory based on the von Karman and Tsien kinematic assumption and the Berger approximation is introduced for simply supported plates with polygonal planform. The governing equations of this theory are solved using a Galerkin procedure and cast into a non-dimensional formulation. In the second part of the paper we discuss the stability and the post-buckling behaviour for single term and multi term solutions of the non-dimensional equations. Finally, numerical results are presented using the Finite Element implementation for the fully geometrically nonlinear theory. The results from the simplified von Karman and Tsien theory are then verified by a comparison with the numerical solutions.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 박판성형기술의 진보
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• pp.147-162
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• 1994

Generally, the forming process of sheet metal is very complex and difficult process because of many variables such as tool geometry, material properties and lubrication. In this view point, the numerical analysis of sheet metal forming process is very difficult. High speed computer is used to model complex sheet metal forming process on a reasonable time scale. The design and development of sheet metal parts in the automotive industry and the need for improved sheet forming process and reduced part development cost have led to the use of computer simulation in tool/die design of sheet metal pressing. HMC(Hyundai Mator Company) has invested to develop programs for analysis of sheet metal forming process with connection of Universities. As a result, several programs were developed. Recently, the commercial software, PAM-STAMP of ESI was installed and is being tried to application of it to the real automotive panels. This article reviews the ongoing activities on development and application of analytical modeling of sheet metal forming at HMC.

• 한국전산구조공학회논문집
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• 제18권3호
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• pp.321-332
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• 2005

본 논문에서는 축대칭 형상의 점탄성 구조물이 정적 하중을 받을 때에 대한 시간영역에서의 유한요소해법의 정식화 과정을 제시한다. 또한, 여러 가지 경계조건을 갖는 점탄성 중공구나 원통 문제들의 변위나 응력 이론해들을 탄성-점탄성 상응원리를 이용하여 유도하고 제시한다. 이때 점탄성 재료는 부피변형이 탄성적이고 전단변형은 3요소로 구성된 표준선형 고체처럼 거동한다고 가정한다. 구대칭, 축대칭 및 평면변형률 유한요소모텔을 이용한 수치결과들을 유도된 이론해들과 비교하여 제시된 유한요소해법과 이론해들의 타당성과 정확성을 보인다.

• Structural Engineering and Mechanics
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• 제56권6호
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• pp.917-938
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• 2015

The nonlinear numerical analysis of the impact response of reinforced concrete/mortar beam incorporated with the updated Lagrangian method, namely the Smoothed Particle Hydrodynamics (SPH) is carried out in this study. The analysis includes the simulation of the effects of high mass low velocity impact load falling on beam structures. Three material models to describe the localized failure of structural elements are: (1) linear pressure-sensitive yield criteria (Drucker-Prager type) in the pre-peak regime for the concrete/mortar meanwhile, the shear strain energy criterion (Von Mises) is applied for the steel reinforcement (2) nonlinear hardening law by means of modified linear Drucker-Prager envelope by employing the plane cap surface to simulate the irreversible plastic behavior of concrete/mortar (3) implementation of linear and nonlinear softening in tension and compression regions, respectively, to express the complex behavior of concrete material during short time loading condition. Validation upon existing experimental test results is conducted, from which the impact behavior of concrete beams are best described using the SPH model adopting an average velocity and erosion algorithm, where instability in terms of numerical fragmentation is reduced considerably.