• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.4
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• pp.37-52
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• 2012

In this study, a new 4-node general shell element with 6 DOFs per node is presented. Drilling rotational degrees of freedom are introduced by the variational principle with an independent rotation field. In formulation of the element, substitute transverse shear strain fields are used to avoid shear locking, while four nonconforming modes are applied in the in-plane displacement fields as a remedy for membrane locking. In addition, a direct modification method for nonconforming modes is employed in the numerical implementation of nonconforming modes to represent constant strain states. A 9-points integration rule is adopted for volume integration in the computation of the element stiffness matrix. With the combined use of these techniques, the developed shell element has no spurious zero energy modes, and can represent a constant strain state. Several numerical tests are carried out to evaluate the performance of the new element developed. The test results show that the behavior of the elements is satisfactory.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1407-1416
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• 1991

본 연구에서는 Liu의 수식화를 바탕으로 가공 경화성을 고려하여 수식화를 재 구성하고, 유한요소 프로그램을 개발하여 평면 변형 인발문제를 극한 해석함으로써, 성형에 필요한 한계 하중 및 최적 속도장을 직접적으로 구하였다.수렴되어진 최적 속도장으로 각 요송에서의 변형률 속도, 변형률 및 격자 변형등을 수치적으로 계산함 으로써 가공에 따른 변형 특성도 파악하였다. 한계 하중은 항공기 구조용 소재인 알 루미늄 6061 재료를 이용하여 판재 인발 실험을 행함으로써 얻은 결과치와 비교 검토 하였으며, 유동 특성을 관찰하기 위하여 격자 왜곡(grid distortion) 실험을 하여 얻 은 변형 패턴과 수치 계산에서 구한 격자변형 패턴을 상호 비교하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.101-110
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• 2015

Recently, nine $1397{\times}1397{\times}178mm$ RC panels were tested under in-plane pure-shear monotonic loading condition using the Panel Element Tester by Hsu (1997, ACI). By combining the equilibrium, compatibility, and the softened stress-strain relationship of concrete in biaxial state, Modern Truss Model (MCFT, RA-STM) are capable of producing the nonlinear analysis of RC membrane panel through the complicated trial-and-error method with double loop. In this paper, an efficient algorithm with one loop is proposed for the refined Mohr compatibility Method based on the strut-tie failure criteria. This algorithm can be speedy calculated to analyze the shear history of RC membrane element using the results of Hsu test. The results indicate that the response of shear deformation energy at Big Bang of shear strain significantly influenced by the principal compressive stress-strain (crushing failure).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1369-1375
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• 2011

Shot ball impacts to materials cause residual compressive stress on their surfaces. Improving the fatigue strength of a material that has this residual compress stress is the purpose of the shot peening process. A numerical study was performed to evaluate the effect of the strain rate sensitivity and hardness of the shot ball on the residual compressive stress. We calculated the residual compressive stress due to multiple impact shot peening using ABAQUS 6.9-1. AISI 4340 steel was the material used in this study. We compared the effects of high strain rate sensitivities and low strain rate sensitivities and found that when the material's sensitivity to the strain rate increased, the residual compressive stress decreased. In addition, the residual compressive stress of low-hardness material is higher than that of high-hardness material.

• Journal of the Korean Society of Safety
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• v.19 no.4 s.68
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• pp.135-140
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• 2004

Wear mechanisms may be briefly classified by mechanical, chemical and thermal wear. A plane strain finite element method is used with a new material stress and temperature fields to simulate orthogonal machining with continuous chip formation. Deformation of the workpiece material is healed as elastic-viscoplastic with isotropic strain hardening and the numerical solution accounts for coupling between plastic deformation and the temperature field, including treatment of temperature-dependent material properties. Effect of the uncertainty in the constitutive model on the distributions of strait stress and temperature around the shear zone are presented, and the model is validated by comparing average values of the predicted stress, strain, and temperature at the shear zone with experimental results.

• Journal of the KSME
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• v.31 no.4
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• pp.356-363
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• 1991

선형 탄성 유한요소 응력해석과 평균응력 효과를 고려한 저주기 피로실험으로부터 결정된 피로 특성, 그리고 국부변형률 방법을 종합하여 외경에 흠이 존재하는 자긴가공된 두꺼운 압력 용기의 피로수명이 평가되었다. 직사각형의 매우 날카로운 흠에서의 응력집중계수는 타원형 홈에서의 응력집중계수의 약 두배의 값이 얻어졌으며, 고강도 압력용기강인 ASTM A723의 저주기 피 로거동에 대한 평균응력 영향은 Morrow 및 SWT 파라메타를 이용하여 충분히 고려되었다. 균열발생이 예상되는 위험한 부분인 홈의 뿌리부분에서의 국부적인 응력, 변형률이 계산되었으며 예측된 피로수명은 실험적으로 얻어진 수명과 비교했을 때 2에서 4배의 오차를 보이면서 일치 하는 결과를 얻었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.191-196
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• 1993

본 연구에서는 이러한 방진궤도의 성능을 파악하고 또 적절한 방진궤도의 설계를 위하여 먼저 모형화하는 방법을 제시하였다. 이를 위해서는 궤도를 구성하는 방진요소의 특성을 결정하는 것이 필수적이므로 현재 사용되고 있 는 점탄성 방진재에 대하여 주파수, 온도, 초기 변형률, 동적변형률등 여러가 지 인자에 대한 물성치를 구하였으며, 이를 이용하여 궤도계의 진동전달 특 성을 파악하고 고찰하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.2
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• pp.212-213
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• 2005

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.841-849
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• 2013

In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of a dimple in a nuclear fuel spacer grid. First, the strains of curved part of dimple are characterized via a comparison with strain solutions in pure bending. A reference 2D finite element (FE) model of 1-step stamping is then established, and the corresponding maximum strain is obtained. By varying the values of design variables of the 1st stamping tool in the 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we demonstrate the enhanced formability of the proposed 2-step stamping model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.6
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• pp.464-470
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• 2018

In this paper, a practical method of estimating the flap hinge moments which change according to the aircraft flap operations was introduced. For the flap design, the hinge moment derived by structural load analysis and wind tunnel tests was able to be compared with the real flight hinge moment, and the static safety of the flap structure could be verified though this comparison. In order to perform the tests, two strain gauges were installed on the flap hinge and an onboard device for aircraft load monitoring was utilized. Through the ground test, the correlation between the strain and the moment of the flap hinge was calibrated with analytic and finite element analysis. During the flight test, strain signals together with the flap deflection angles and airspeed were recorded. Finally, the flight hinge moments could be predicted by the measured strain which was calibrated with the analytic and the finite element analysis.