• Proceedings of the Optical Society of Korea Conference
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• 2004.02a
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• pp.374-375
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• 2004

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1195-1203
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• 2012

Welding is a well-developed, widely used process for permanently joining metal components. However, the mechanical reliability of welded parts still offers room for improvement. A weld region consists of a fusion zone, a partially melted zone, and a heat-affected zone, and each zone has different material properties. In addition, the geometrical shape of a weld bead or fillet influences the mechanical reliability. A precise structural analysis must consider how a local welded region influences the mechanical behavior of the entire structure. This study focuses on an effective modeling scheme for the weld region. It relies on experimental and numerical methods to determine the proper correlation based on experimental results and to propose a modeling scheme for welded parts.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.6
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• pp.537-545
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• 2013

In this paper, the vibration for actuators having lens module, confined to lateral and torsional directions of suspensions, is described by mathematically analyzing its suspension configuration and motion. In order to prove the accuracy of this result, it is compared to a finite element analysis. Also it is shown that modal frequencies can be modified by changing design parameters in mathematical motion expressions.

• Journal of the korean Society of Automotive Engineers
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• v.18 no.4
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• pp.1-17
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• 1996

자동차의 안전에 대한 연구는 객실의 변형제한과 승객의 감속도 축소를 위한 여러가지 구조부재의 에너지 흡수능력 및 흡수 메카니즘을 연구하는데 초점이 맞추어져 왔다. 그 이유는 충돌사고시에 인명을 보호하기 위해서는 차제변형에 의한 물리적 접촉의 회피 뿐 아니라 충돌에너지를 적절히 흡수조절하여 충돌력을 감소시키도록 구조부재를 설계함으로써 충돌안전성이 확보되기 때문이다. 충돌에너지 흡수 특성은 구조부재의 단면 형상과 재질에 따라 달라지며 압괴모드도 구분되어진다. 즉, 복합재료의 압축붕괴특성은 금속이나 플라스틱 재질과는 다르다. 일반적으로 복합재는 재질의 파손으로 에너지가 흡수되지만 금속재는 소성변형으로 에너지를 흡수한다. 이때의 붕괴양상은 작용하중에 따라 축방향 붕괴, 굽힘붕괴, 측면붕괴의 경우는 정규압괴모드(compact mode) 및 불규칙압괴모드(noncompact mode)로 나뉘고, 원통쉘의 경우는 축대칭모드 및 다이아몬드형 모드 등으로 나뉠수 있다. 원형 및 사각 튜브는 광범위한 형상비와 후폭비를 가지도록 제작할 수 있으며 산업전반에 걸쳐 널리 쓰이므로 충돌특성 연구의 대상으로 많은 연구들이 진행되어 왔다. 또한, 충돌특성의 해석을 위한 이론적 모델이 제시되었으며 계속적인 보완이 이루어져 오고 있다.

• Korean Journal of Materials Research
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• v.6 no.9
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• pp.878-884
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• 1996

본 연구는 가스압소결 질화규소의 혼합모드에 있어서 파괴거동을 실온 및 100$0^{\circ}C$에서 조사하였다. 실험은 누프압흔을 도입한 시험편을 사용하여 소둔처리에 의해 잔류응력을 제거하고, 4점굽힘법을 이용하였다. 실험결과, 종래 제창되고 있는 파괴기준과 일치하지 않고, 그래서 새롭게 4차관수의 근사식을 제안하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.73-78
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• 2013

In this paper, the vibration for a pickup actuator is described by mathematically analyzing its suspension configuration and motion, confined to lateral and torsional directions of suspensions. In order to prove the accuracy of this result, it is compared to a finite element analysis. Also it is shown that modal frequencies can be modified by changing design parameters in mathematical motion expressions.

• Composites Research
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• v.18 no.1
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• pp.30-37
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• 2005

The bending strength characteristics and local deformation behaviors of honeycomb sandwich composites were investigated using three-point bending experiment and finite element simulation with a real model of honeycomb core. Two kinds of cell sizes of honeycomb core, two kinds of skin layer thicknesses, perfect bonding specimen as well as initial delamination specimen were used for analysis of stress and deformation behaviors of honeycomb sandwich beams. Various failure modes such as skin layer yielding, interfacial delamination, core shear deformation and local buckling were considered. Its simulation results were very comparable to the experimental ones. Consequently, cell size of honeycomb core and skin layer thickness had dominant effects on the bending strength and deformation behaviors of honeycomb sandwich composites. Specimens of large core cell size and thin skin layer showed that bending strength decreased by $30\~68\%$.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.18-25
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• 2018

This research aims to establish the finite-element modeling techniques for computational modal analyses of liquid propellants and flange joints of launch-vehicle structures. MSC.NASTRAN is used for the present computational modal analyses of the liquid-propellant tank and the small-scaled first-stage model. By means of the correlation between the measured and computed natural frequencies, the finite modeling techniques for liquid propellants and flange joints of launch-vehicle structures are established appropriately. This modal analysis using the virtual-mass method predicts well the bell mode of the liquid-propellant tank containing liquid. In addition, the present computation using RBE2 elements for modeling of flange joints predicts the first and second bending-mode frequencies within a relative error of 10%, which is better than the measured frequencies obtained from the modal test, for the small-scaled first-stage model containing liquid.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.8-17
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• 2003

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear Power Plant. In Pipes of energy Plants, sometimes, the local wall thinning may result from severe erosion-corrosion (E/C) damage. However, the effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. In this paper, the monotonic bending tests were performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and fracture strength of locally thinned pipe were manifested systematically. The observed failure modes were divided into four types; ovalization. crack initiation/growth after ovalization, local buckling and crack initiation/growth after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.2
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• pp.77-86
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• 2022

This study investigates the effect of the diameter and thickness on crack initiation location and orientation of 90° elbows under in-plane mode displacement-controlled cyclic bending loads. Finite element (FE) analysis of cyclic failure test is conducted for elbow specimens under in-plane mode displacement-controlled cyclic bending to identify the parameters affecting crack location and orientation. Furthermore, parametric FE analysis of the pipe elbows with various pipe nominal sizes and Schedules is performed, and the crack location and orientation from the results of FE analysis are determined. It is found that the crack location and orientation in the pipe elbows are determined mianly by the radius to thickness ratio of pipe elbows (R_m/t). It is also found that the presence of internal pressure slightly increases the value of R_m/t at which the failure mode changes.