• Title/Summary/Keyword: Critical Load

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Microhardness measurement for a few micron thick TiN thin films (수미크론 두께를 갖는 TiN코팅층의 미소경도 측정법)

  • Jo, Yeong-Rae;Fromm, E.
    • Korean Journal of Materials Research
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    • v.5 no.3
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    • pp.310-315
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    • 1995
  • 기계적으로 연마한 고속도강과 구리 두 종류의 서로 다른 기판상에 dc 마그네트론 스파터법으로 TiN 박막을 성막시켜 코팅층의 비커스 미소경도를 측정하였다. 압입체의 침투깊이와 시험하중과의 관계를 log-log 좌표상에 도시함으로써 기판의 영햐응ㄹ 받지 않고 코팅층만의 경도를 측정할수 있는 최대하중인 임계하중(critical load)을 구할수 있었다. 임계하중을 가했을 때 압입체의 침투깊이와 코팅층 두께간의 비율은 코팅층의 두께에 무관하였고 기판의 경도에 크게 의존하였다.

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A Study on the Dynamic Instability of Shallow Sinusoidal Arches (얕은 정현형(正弦型) 아치의 동적불안정에 관한 연구)

  • 김승덕;박지윤;권택진
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.233-242
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    • 1998
  • Many papers which deal with the dynamic instability for shell-like structures under the step load have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. Dynamic buckling process in the phase plane is a very important thing for understanding why unstable phenomena are sensitively originated in nonlinear dynamics by various initial conditions. In this study, the direct and the indirect snap-buckling of shallow arches considering geometrical nonlinearity are investigated numerically and compared with the static critical load.

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A Study on the Analysis and Control of Voltage Stability (전압안정성 분석 및 제어에 관한 연구)

  • 장수형;김규호;유석구
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.43 no.6
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    • pp.869-876
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    • 1994
  • This paper presents an efficient method to calculate voltage collapse point and to avoid voltage instability. To evaluate voltage stability in power systems, it is necessary to get critical loading points. For this purpose, this paper uses linear programming to calculate efficiently voltage collapse point. Also, if index value becomes larger than given threshold value, voltage stability is improved by compensation of reactive power at selected bus. This algorithm is verified by simulation on the IEEE 14-bus sample system.

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On the stability of Rubber Isolation Bearings (면진 고무 베어링의 안정성에 대하여)

  • 이종세
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • pp.85-92
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    • 1998
  • As an analytical approach, the area reduction formula of rubber bearings has been proposed to account for the reduction in bucking load due to shear. The result obtained from the formula is presumed to be conservative but the degree of conservatism is unknown. This paper describes a numerical study which aims at determining the effect of high shear strain on the critical load of rubber bearings using a finite element analysis program. The results from the finite element analysis which accounts for both the material and geometric non-linearities are compared against the theoretical results in order to examine the validity of the theoretical formulas.

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Dynamic Instability of Arch Structures Considering Geometric Nonlinearity by Sinusoidal Harmonic Excitation (기하학적 비선형을 고려한 아치 구조물의 정현형 조화하중에 의한 동적 불안정 현상에 관한 연구)

  • 윤태영;김승덕
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.69-76
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    • 2003
  • We investigate the fundamental mechanisms of the dynamic instability when the sinusoidal shaped arch structures subjected to sinusoidal harmonic excitation with pin-ends. In nonlinear dynamics, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and the indirect snap-buckling of shallow arches considering geometrical nonlinearity are investigated numerically and compared with the step excitation critical load.

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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.

A Study on the friction and Wear Characteristics of C-N Coated SCM415 Steel (C-N코팅 SCM415강의 마찰$\cdot$마모 특성에 관한 연구)

  • Lyu Sung-ki;Lu Long;Jin Tai-yu;Lian Zhe-Man;Cao Xing-Jin;Cho Sung-Min
    • Journal of the Korean Society of Safety
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    • v.20 no.1
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    • pp.18-23
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    • 2005
  • This study deals with the friction and wear characteristics of C-N coated SCM415 steel. The PSII(plasma source ion implantation) apparatus was built and a SCM415 test piece with steel substrate was treated with carbon nitrogen by this apparatus. The composition and structure of the surface layer were analyzed and compared with that of PVD(physical vapor decomposition) coated TiN layer. It was found that both of friction coefficient of C-N coating and TiN coating decreased with increasing load, however, C-N coating showed relatively lower faction coefficient than that of TiN coating. The micro-vickers hardness of C-N film is 3200 Hv, which is $32\~43\%$ higher than that of TiN film. The critical load of C-N film is 52N, which is $25\%$ higher than that of TiN film. The hardness of C-N film fabricated by Plasma ion implantation is $61\~70\%$ higher than that of base material, and faction coefficient is $14\~50\%$ lower than that of base material. It is also interesting to note that the friction was changed from adhesive wear mode to light oxidizing wear mode.

The Eigenvalues and Their Relationships for the Rectangular Frame (4각형 골조의 고유치와 고유치 간의 관계)

  • Lee, Soo-Gon;Kim, Soon-Cheol;Song, Chang-Young;Song, Sang-Yong
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.9 no.3
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    • pp.139-150
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    • 2005
  • Finite element method is applied to the determinations of the two eigenvalues(the elastic critical load and the natural frequence of lateral vibrations) of single story-3 equal bay rectangular frame. The analysis parameters are taper parameter ${\alpha}$ for column, and beam span to column height ratio, ${\beta}$ and second moment area ratio of beam to column, ${\Upsilon}$. Support condition at the column base and sway condition at the column top are also considered in the stability analysis of frame. The changes in the coefficient of eigenvalue are represented by algebraic function of analysis parameter. The coefficients estimated by the proposed algebraic function show good agreement with those determined by finite element method, which suggest the design aid role of the proposed function. By increasing the column axial forces step by step, the corresponding frequencies are also determined, which makes one examine or confirm the relationship suggested by other studies.

Determination of Eigenvalues of Sinusoidally Tapered Members by Finite Element Method (유한요소법을 이용한 정현상으로 taper진 부재의 고유치 산정)

  • Lee, Soo-Gon;Kim, Soon-Chul
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.13 no.1
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    • pp.87-95
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    • 2000
  • The two eigenvalues (elastic critical load and natural frequency of lateral vibration) of sinusoidally tapered bats with simply supported ends were determined by the finite element method. For the convenience of structural engineers who are engaged in the structural design or vibration analysis of tapered beam-columns, eigenvalue coefficients were expressed by simple algebraic equations. The validity of each algebraic equation was confirmed by the value of unity for each correlation coefficient. The influence of axial thrust on the lateral vibration frequency was also investigated. For this purpose, the axial thrust was increased successively and the corresponding frequency was calculated. The approximate linear relationship between the axial thrust and the square of the frequency was confirmed lot each of the tapered members.

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Prediction on load carrying capacities of multi-storey door-type modular steel scaffolds

  • Yu, W.K.;Chung, K.F.
    • Steel and Composite Structures
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    • v.4 no.6
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    • pp.471-487
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    • 2004
  • Modular steel scaffolds are commonly used as supporting scaffolds in building construction, and traditionally, the load carrying capacities of these scaffolds are obtained from limited full-scale tests with little rational design. Structural failure of these scaffolds occurs from time to time due to inadequate design, poor installation and over-loads on sites. In general, multi-storey modular steel scaffolds are very slender structures which exhibit significant non-linear behaviour. Hence, secondary moments due to both $P-{\delta}$ and $P-{\Delta}$ effects should be properly accounted for in the non-linear analyses. Moreover, while the structural behaviour of these scaffolds is known to be very sensitive to the types and the magnitudes of restraints provided from attached members and supports, yet it is always difficult to quantify these restraints in either test or practical conditions. The problem is further complicated due to the presence of initial geometrical imperfections in the scaffolds, including both member out-of-straightness and storey out-of-plumbness, and hence, initial geometrical imperfections should be carefully incorporated. This paper presents an extensive numerical study on three different approaches in analyzing and designing multi-storey modular steel scaffolds, namely, a) Eigenmode Imperfection Approach, b) Notional Load Approach, and c) Critical Load Approach. It should be noted that the three approaches adopt different ways to allow for the non-linear behaviour of the scaffolds in the presence of initial geometrical imperfections. Moreover, their suitability and accuracy in predicting the structural behaviour of modular steel scaffolds are discussed and compared thoroughly. The study aims to develop a simplified and yet reliable design approach for safe prediction on the load carrying capacities of multi-storey modular steel scaffolds, so that engineers can ensure safe and effective use of these scaffolds in building construction.