• Proceedings of the KSME Conference
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• 2000.11a
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• pp.177-184
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• 2000

In this work, some inaccuracies and limitation of prior indentation theory, which is based on the deformation theory of plasticity and experimental observations, are first investigated. Then effects of major material properties on the configuration of indentation load-deflection curve are examined via incremental plasticity theory based finite element analyses. It is confirmed that subindenter deformation and stress-strain distribution from the deformation theory of plasticity are quite dissimilar to those from incremental theory of plasticity. We finally suggest the optimal data acquisition location, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.187-194
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• 2012

The strength of particle-reinforced metal matrix composites is, in general, known to be increased by the geometrically necessary dislocations punched around a particle that form during cooling after consolidation because of coefficient of thermal expansion (CTE) mismatch between the particle and the matrix. An additional strength increase may also be observed, since another type of geometrically necessary dislocation can be formed during extensive deformation as a result of the strain gradient plasticity due to the elastic-plastic mismatch between the particle and the matrix. In this paper, the magnitudes of these two types of dislocations are calculated based on the dislocation plasticity. The dislocations are then converted to the respective strengths and allocated hierarchically to the matrix around the particle in the axisymmetric finite-element unit cell model. The proposed method is shown to be very effective by performing finite-element strength analysis of $SiC_p$/Al2124-T4 composites that included ductile failure in the matrix and particlematrix decohesion. The predicted results for different particle sizes and volume fractions show that the length scale effect of the particle size obviously affects the strength and failure behavior of the particle-reinforced metal matrix composites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.627-635
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• 2019

A programmable drone is a drone developed not only to experience the basic principles of flight but also to control drones through Arduino-based programming. Due to the nature of the training drones, the main users are students who are inexperienced in controlling the drones, which often cause frequent collisions with external objects, resulting in high damage to the drones' frame. In this study, the structural stability of the drone was evaluated by means of a structural dynamics based collision simulation for educational drone frame. Collision simulations were performed on three cases according to the impact angle of $0^{\circ}$, $+15^{\circ}$ and $-15^{\circ}$, using an analytical model with approximately 240,000 tetrahedron elements. Using ANSYS LS-DYNA, which provides excellent functions for the simulation of the dynamic behavior of three-dimensional structures, the stress distribution and strain generated on the drone upper, the drone lower, and the ring assembly were analyzed when the drones collided against the wall at a rate of 4 m/s. Safety factors resulting from the equivalent stress and the yield strain were calculated in the range of 0.72 to 2.64 and 1.72 to 26.67, respectively. To ensure structural stability for areas where stress exceeds yield strain and ultimate strain according to material properties, the design reinforcement is presented.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.50-60
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• 2023

Ball Grid Array (BGA) is a widely used package type due to its high pin density and good heat dissipation. In BGA, solder balls play an important role in electrically connecting the package to the PCB. Therefore, understanding the inelastic deformation of solder balls under various mechanical loads is essential for the robust design of semiconductor packages. In this study, the geometrical effect on the inelastic deformation and fracture of solder balls were analyzed by finite element analysis. The results showed that fracture occurred in both tilted and hourglass shapes under shear loading, and no fracture occurred in all cases under compressive loading. However, when bending was applied, only the tilted shape failed. When shear and bending loads were combined with compression, the stress triaxiality was maintained at a value less than zero and failure was suppressed. Furthermore, a comparison using the Lagrangian-Green strain tensor of the critical element showed that even under the same loading conditions, there was a significant difference in deformation depending on the shape of the solder ball.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1854-1861
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• 1996

A reliable and practical finite element modeling technique to estimate the behavior of complex structures with bolted joints is important for engineeres in the industry. Accordingly, we have examined several simplified modeling techinques which do not require the use of special elements such as a gap eloement. The dynamic and static erxperiments have confirmed that the technique to model the bolted joints with eight-noded three dimensional elemnts which fill the bolt space gdives most satisfactory results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1996.11a
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• pp.3-11
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• 1996

본 연구는 고체 추진기관의 각종 밀봉 부에 많이 사용되는 O-링의 설계시 고려되는 각종 형상인자의 변화에 따른 O-링의 거동과 응력 상태를 분석하여 설계 최적조건을 찾기 위한 내용을 다루고 있다. 조립 부의 내외경과 조립 공차, 챔퍼길이와 각도, 조립 홈의 외경, 깊이, 폭, 구성반경, O-링의 내경과 선 직경 등의 설계 변수에 의한 조립부 형상과 재료의 물성치, 유한요소 선택 및 요소 분할, 경계조건, 하중조건, 접촉부 정의 등을 MSC/PATRAN3의 $PCL^{[1]}$/로 프로그래밍 하여 설계변수에 의한 결과 분석을 손쉽게 수행할 수 있도록 시도하였다 고무의 Hyperelastic 물성치는 문헌상의 자료$자료^{[2]}$에 제시된 Ogden 상수를 사용하였으며 추후에는 인장시험, 순수전단시험, 이 축 인장시험을 통해 실험적으로 측정$^{[3]}$ 하여 적용할 예정이다. 고무의 대변형, 대 변형률을 고려한 비선형 응력해석은 MSC/PATRAN3의 Advanced FEA 모듈과 ABAQUS 5.5를 사용하였다. 본 연구에서의 해석결과를 설계변수들의 영향을 비교 분석하는데 사용하였으나 그 정확도가 입증된 상태는 아니며 추후 실제 조립 및 수압시험을 통해 평가할 예정이다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.513-516
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• 2000

This paper presents the analytical studies on the stress and strain of driven valve system of internal combustion engines. The stress and strain is predict using FEM. The particular interest is the dynamic strain at a specific point of the valve and valve seat. Cam and follower Assuming that one rigid surface. This study forced the effects changing Young's modulus and density of valve and valve seat contact area. It supports that the indirect method using FEM is reliable for prediction the actual displacement, stress and strain in the valve system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1211-1219
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• 1995

An upper bound elemental technique (UBET) program has been developed to analyze forging load, die-cavity filling and effective strain distribution for flash and flashless forgings. The simulation for flash and flashless forgings are applied axisy mmetric and plane-strain closed-die forging with rib-web type cavity. Inverse triangular and inverse trapezoidal elements are used to analyze flashless forging. The analysis is described for merit of flashless precision forging. Experiments have been carried out with pure plasticine billets at room temperature. Theoretical predictions of the forging load and the flow pattern are in good agreement with experimental results.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.507-512
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• 2003

A finite element analysis for near-net-shape forming of Al6061 powder was performed under warm pressing. The advantages of warm compaction by rubber isostatic pressing were discussed to obtain parts with better density distributions. To simulate densification and deformed shape of a powder compact during warm pressing, the elastoplastic constitutive equation based on yield function of Shima-Oyane was implemented into a finite element program(ABAQUS). The hyperelastic constitutive equation based on the Ogden strain energy potential was employed to analyze nonlinear elastic response of rubber. Finite element results were compared with experimental data for Al6061 powder compacts under warm pressing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1844-1853
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• 1995

Theoretical and experimental drawing characteristics for the single circular and square drawbeads are discussed. During the blank holding process, the strain distributions of upper and lower skins of specimens, and the die reactional forces are analysed by F. E. M., and they are compared with the experimental results. The drawbead restraining forces and strain distributions for the drawn specimens by the various drawing length are also analysed and compared with the experimental results. It is concluded that the theoretical simulations and results could be very useful for the prediction of real cases.