• Title, Summary, Keyword: 임계하중

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A Study on the Stability Boundaries for Single Layer Latticed Domes and Arch under Combined Loads (조합하중를 받는 단층 래티스 돔과 아치의 안정경계에 관한 연구)

  • Han, Sang-Eul;Lee, Sang-Ju;Lee, Kap-Su
    • Journal of the Korean Association for Spatial Structures
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    • v.4 no.3
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    • pp.103-109
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    • 2004
  • The lowest load when the equilibrium condition becomes to be unstable is defined as the buckling load. The primary objective of this paper is to be analyse stability boundaries for star dome under combined loads and is to investigate the iteration diagram under the independent loading parameter. In numerical procedure of the geometrically nonlinear problems, Arc Length Method and Newton-Raphson iteration method is used to find accurate critical point(bifurcation point and limit point). In this paper independent loading vector is combined as proportional value and star dome was used as numerical analysis model to find stability boundary among load parameters and many other models as multi-star dome and arch were studied. Through this study we can find the type of buckling mode and the value of buckling load.

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A Geometrically Nonlinear Dynamic Analysis of Shallow Circular Arches Using Total Lagrangian Formulation (Total Lagrangian 문제형성에 의한 낮은 원호아치의 동적 비선형거동 해석)

  • Kim, Yun Tae;Kim, Moon Kyum;Hwang, Hak Joo
    • Journal of The Korean Society of Civil Engineers
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    • v.10 no.2
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    • pp.39-48
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    • 1990
  • For shallow circular arches with large dynamic loading, use of linear analysis is no longer considered as practical and accurate. In this study, a method is presented for the dynamic analysis of the shallow circular arches in which geometric nonlinearity is dominant. A program is developed for analysis of the nonlinear dynamic behavior and for evaluation of the critical buckling loads of the shallow circular arches. Geometric nonlinearity is modeled using Lagrangian description of the motion and finite element analysis procedure is used to solve the dynamic equations of motion in which Newmark method is adopted as a time marching scheme. A shallow circular arch subject to radial step load is analyzed and the results are compared with those from other researches to verify the developed program. The critical buckling loads of shallow arches are evaluated using the non-dimensional parameter. Also, the results are compared with those from linear analysis.

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Development of Nonlinear Dynamic Program for Buckling Analysis of Plane Circular Arches (평면 원호아치의 좌굴해석을 위한 동적 비선형해석 프로그램의 개발)

  • 허택녕;오순택
    • Computational Structural Engineering
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    • v.7 no.1
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    • pp.69-81
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    • 1994
  • This paper summarizes a dynamic analysis of the shallow circular arches under dynamic loading, considering the geometric nonlinearity. The major emphasis is placed on the development of computer program, which is utilized for the analysis of the nonlinear dynamic behavior and for the evaluation of the critical buckling loads of the shallow circular arches. Geometric nonlinearity is modeled using Lagrangian description of the motion and a finite element analysis procedure is used to solve the dynamic equation of motion. A circular arch subject to normal step load is analyzed and the results are compared with those from other researches to verify the developed program. The critical buckling loads of arches are estimated using the non-dimensional time, load and shape parameters and the results are also compared with those from the linear analysis. It is found that geometric nonlinearity plays and important role in the analysis of shallow arches and the probability of buckling failure is getting higher as arches become shallower.

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Critical Strengthening Ratio of CFRP Plate Using Probability and Reliability Analysis for Concrete Railroad Bridge Strengthened by NSM (확률.신뢰도 기법을 적용한 CFRP 플레이트 표면매립보강 콘크리트 철도교의 임계보강비 산정)

  • Oh, Hong-Seob;Sun, Jong-Wan;Oh, Kwang-Chin;Sim, Jong-Sung;Ju, Min-Kwan
    • Journal of the Korea Concrete Institute
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    • v.21 no.6
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    • pp.681-688
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    • 2009
  • The railroad bridges have been usually experienced by vibration and impact in service state. With this reason, it is important that the effective strengthening capacity should be considered to resist the kind of service loading. In this study, NSM strengthening technique is recommended for the concrete railroad bridge because of its better effective resistance for dynamic loading condition and strengthening cost than the conventional externally bonded strengthening using fiber sheet. However, to widely apply NSM method for the concrete railroad bridge, it needs that the strengthening ratio has to be reasonably evaluated with geometrical and material uncertainties, especially for the concrete bridge under long-term service state without the apparent design history and detail information such as concrete compressive strength, reinforcing ratio, railroad characteristics. The purpose of this study is to propose the critical strengthening ratio of CFRP plate for the targeted concrete railroad bridge with uncertainties of deterioration of the structures. To do this, Monte Carlo Simulation (MCS) for geometrical and material uncertainties have been applied so that this approach may bring the reasonable strengthening ratio of CFRP plate considering probabilistic uncertainties for the targeted concrete railroad bridge. Finally, the critical strengthening ratio of NSM strengthened by CFRP plate is calculated by using the limit state function based on the target reliability index of 3.5.

Evaluation of Fracture Behavior of Adhesive Layer in Fiber Metal Laminates using Cohesive Zone Models (응집영역모델을 이용한 섬유금속적층판 접착층의 모드 I, II 파괴 거동 물성평가)

  • Lee, Byoung-Eon;Park, Eu-Tteum;Ko, Dae-Cheol;Kang, Beom-Soo;Song, Woo-Jin
    • Composites Research
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    • v.29 no.2
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    • pp.45-52
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    • 2016
  • An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.

Characterization of Cavitation Damage on the Stainless steel alloy by Solid Particle Collapse (스테인리스강의 케비테이션 고체입자충격에 의한 침식손상 특성)

  • Hong, Seong-Mo;Han, Byeong-Seon;Lee, Min-Gu;Park, Jin-Ju;Lee, Sang-Hun;Lee, Chang-Gyu
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • pp.28-28
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    • 2007
  • 해수 임펠러(impeller) 재료로 사용되고 있는 스테인리스강을 이용하여 케비테이션 발생 시 고체입자 충격에 의한 충격하중 및 침식손상을 조사하였다. 충격하중은 압전센서를 이용하여 측정되었으며, 고체입자충격의 경우 기포붕괴에 비해 전체적으로 높은 충격하중을 가한 것으로 나타났다. 또한 충격하중과 침식손상과의 관계를 고찰하기 위해 침식표면에 형성된 침식핏(pit)을 측정하였으며, 고체입자충격 및 기포붕괴 조건에서의 임계충격하중을 구하였다.

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Surface structure and critical load of thin metal films on SiC substrate (SiC 기판상의 금속박막의 표면구조 및 임계하중)

  • 임창성
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.5 no.4
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    • pp.358-369
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    • 1995
  • Surface structure and adhesion by the reaction between thin metal films and SiC were studied at temperatures between 550 and $1450^{\circ}C$ for various times. The reaction with the formation of various silicides was initially observed above $850^{\circ}C$ for SiC/Co system and $650^{\circ}C$ for SiC/Ni system. The cobalt reacted with SiC and consumed completely at $1050^{\circ}C$ for 0.5 h and the nickel at $950^{\circ}C$ for 2 h. The observed CoSi phase in SiC/Co and Ni$_2$Si phase in SiC/Ni are thermodynamically stable in the reaction zone up to 125$0^{\circ}C$ and $1050^{\circ}C$ respectively. Carbon was crystallized as graphite above $1450^{\circ}C$ for SiC/Co reaction surface and $1250^{\circ}C$ for SiC/Ni. The critical loads of the thin metal films on SiC substrate were qualitatively compared in terms of the scratch test method. At temperatures between 850 and $1050^{\circ}C$, relatively higher values of 20~33 N were observed for SiC/Ni couples.

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Critical Speed Analysis of the Turbopump considering the Casing Structural Flexibility (케이징 구조 유연성을 고려한 터보펌프 임계 속도 해석)

  • 전성민;김진한;곽현덕;윤석환
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.6
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    • pp.92-97
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    • 2006
  • A critical speed analysis is performed for a 30 ton thrust turbopump considering the casing structural flexibility. A full three-dimensional finite element method including rotor and casing is used to predict rotordynamic behavior. Rotor alone model and rotor-casing coupled model with fixed-fixed and free-free boundary conditions are calculated to investigate the effects of the casing structural flexibility. The stiffness of ball bearings are applied as unloaded and loaded values to consider rotor operating conditions in vacuum and real engine respectively. From the results of the numerical analyses, it is found that the effect of the casing structural flexibility reduces the critical speeds of the turbopump. Especially, the loaded rotor condition with higher bearing stiffness is affected dramatically rather than the unloaded rotor condition with lower bearing stiffness.

Experimental and Finite Element Study of Tribological Characteristics of SU-8 Thin Film (실험 및 유한요소해석에 의한 SU-8 박막의 Tribological 특성 연구)

  • Yang, Woo Yul;Shin, Myounggeun;Kim, Hyung Man;Han, Sangchul;Sung, In-Ha
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.4
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    • pp.467-473
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    • 2013
  • In this study, two-dimensional finite element models were developed and experiments were conducted using an atomic force microscope to investigate the tribological characteristics of an SU-8 layer coated on a patterned wafer for microsystem applications. The results revealed that both the adhesion and the friction forces measured by the atomic force microscope were lower for the SU-8 coated surface than for the bare silicon surface. This is attributed to the hydrophobicity of SU-8. Another important result derived from the finite element analysis was the critical load required to fracture the SU-8 film with respect to the thickness. The critical loads for thicknesses of 200, 400, and 800 nm were approximately 13, 22, and 28 mN, respectively, which corresponded to a Hertzian contact pressure of 1.2-1.8 GPa. These results will aid in the design of a suitable SU-8 thickness for microsystem components that are in contact with one another.

Design of Safety Valve Installations (安全 밸브 設備 設計에 關한 規定( II ))

  • 조성환
    • Journal of the KSME
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    • v.18 no.3
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    • pp.57-61
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    • 1978
  • 안전벨브설비의 기계적설계와 해석에관련된 가장 중요한 고려사항중의 하나는 설비내의 임계점을 찾아내고 그 점에서의 모우멘트를 계산하는 것이다. 만약 굽힘모우멘트를 적절히 계산하지 않으 연 기술기순에 포함된 하중 및 응력기준에 합격할 수 없을 것이다. 이 모우멘트를 결정하는데 최 소한도 본 부록의 2부에 설명된 다음 하중들을 포함함이 바람직하다. 1. 열팽창 2. 사하중 3. 지진 4. 벨브 송출로부터의 반작용력 5. 기타 기계적하중 안전밸브설비의 핵석에서 교차점, 엘보우, 변이점등을 포함한 모든 중요단면 및 기타 관련된 배 관, 용기및 배관설비와 상호작용하는 그들의 지지점들을 포함함이 바람직하다. 안전밸브설비와 그 에 관련된 배관을 직선 또는 곡선 요소들을 연결된 하나의 통합된 질량계로서 모형화하는 것이 가장 적절하다.

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