• Title, Summary, Keyword: 모드 혼합도

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혼합모드 피로균열의 응력재분배 상태 하의 전파거동

  • 이정무;송삼홍
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.103-103
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    • 2004
  • 실제 작용하는 하중상태는 요소의 형상과 작용하중의 복잡성 때문에 혼합모드 하중상태를 나타낸다. 또한 혼합모드 피로균열은 전파과정 동안 부재의 구속형상이나 외부 작용하중의 급격한 변화에 의해서도 영향 받게 된다. 이로 인하여 피로균열은 균열선단에서 지속적이면서 급격한 응력 재분배의 상태를 경험한다. 그러므로 다양한 응력 재분배 상태에서의 혼합모드 피로균열에 대한 고찰이 필요하다. 본 연구에서는 응력 재분배상태 하에서 나타나는 혼합모드 피로균열의 전파거동에 대한 특징이 실험적으로 고찰되었다.(중략)

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혼합모드 I+II 피로 하한계 영역에서의 모드II 영향에 관한 고찰

  • 홍석표;송삼홍;이정무
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.113-113
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    • 2004
  • 실제 사용중인 기계나 기계구조물은 다양한 환경 및 복잡한 설계조건으로 인하여 변동하중과 다축에서 작용하는 혼합모드 하중 상태에 놓이는 경우가 대부분이다. 하지만, 순수 모드 I 하중상태 하에서의 연구는 활발히 이루어졌으나, 실제 구조물에서 대부분 발생하는 혼합모드 하중상태 하에서의 연구는 아직 부족한 실정이다. 또한 기계구조물내의 많은 성분요소에 존재하는 작용 하중 방향에 수직적이지 않게 되며, 초기균열의 균열선상에서 성장하지 않는다.(중략)

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밀도구배 및 후류손실을 가지는 혼합층의 불안정성에 관한 연구

  • 신동신;황승환
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.23-23
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    • 1999
  • 후류손실을 가지는 혼합 전단층에 대하여 밀도변화가 없는 유동 및 밀도변화가 있는 유동의 선형 불안정성 해석을 수행하였다. 기본 유동의 속도장 및 밀도장은 tanh 함수를 사용하였으며, Gaussian 형태의 해석적 함수를 사용하여 두 유동을 분리시키는 평판 바로 다음에 존재하는 후류 손실 유동을 포함시켰다. 공간적 선형 불안정성 해석을 수행하여 불안정성 모드의 성장률과 파장속도를 주파수의 함수로서 구하였다. 해석 결과로부터 후류 손실을 가지는 혼합층은 sinuous 모드와 varicose 모드의 두 개의 불안정성 모드를 가짐을 알았다. 밀도가 균일한 경우에는 varicose 모드보다 sinuous 모드가 지배적이다. 밀도가 균일한 경우에는 varicose 모드보다 sinuous 모드가 지배적이다. 밀도구배가 존재하나 빠른 자유유동의 밀도가 높은 경우에는 밀도가 균일한 경우와 마찬가지로 sinuous 모드가 지배적인 모드가 된다. 그러나 느린 자유 유동의 밀도가 높은 경우에는 밀도장의 두께가 속도장의 두께보다 상대적으로 얇아지면 varicose 모드가 sinuous 모드보다 더욱 불안정하여질 수 있다. varicose 모드와 sinuous 모드의 성장률이 비슷한 밀도장의 두께에서는 두 불안정성 모드가 주파수 변화에 따라 분지 되어지는 경향을 보인다.

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Mode effects in concurrent mixed-mode surveys (병행적 혼합조사의 모드효과 분석)

  • Baek, Jeeseon;Min, Kyung A
    • The Korean Journal of Applied Statistics
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    • v.29 no.5
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    • pp.787-806
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    • 2016
  • Mixed-mode (MM) designs in which data are collected by different modes in one design have become increasingly popular. An MM data collection has several advantages such as reductions of coverage error, non-response and cost. However, MM designs may introduce mode effects that are confounded by selection effects and measurement effects, which can make MM data quality poor. In order to investigate mode effects, SRI implemented a concurrent mixed-mode experiment in 2014 where respondents could choose between a self-administrated Web survey and a self-administrated paper survey. This paper separately estimates selection effects and measurement effects. We found that measurement effects on some items are large.

Effects of Failure Mode II on Crack Initiation and Crack propagation Steps Using Multilevel Fatigue Loading Test (다단계 피로하중 실험을 통한 균열 발생 및 전파단계에서 파괴모드 II 영향 분석)

  • Hong, Seok Pyo;Park, Sae Min;Kim, Ju Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.9
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    • pp.853-860
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    • 2017
  • To evaluate the effects of mode II on the crack initiation and propagation stages, the effects in the fatigue threshold region under a mixed-mode I+II loading state was experimentally investigated. In the case of mixed-mode I + II, during the crack initiation stage, as the loading application angle (${\theta}$) increased, cracks occurred in the lower load owing to the effects of mode II, while the crack propagation rate decreased. The effects of mode II were experimentally investigated in the crack propagation stage by means of multilevel loading direction variation. Following mixed-mode I+II ($0^{\circ}{\rightarrow}{\theta}{\rightarrow}60^{\circ}$), as the load application angle increased, the fatigue crack propagation rate decreased, as did the fatigue crack propagation rate, which occurred later. Following mixed-mode I + II in case of(${\theta}{\geq}75^{\circ}$), the fatigue crack propagation rate was found to increase, while the fatigue life decreased.

Data-Driven Signal Decomposition using Improved Ensemble EMD Method (개선된 앙상블 EMD 방법을 이용한 데이터 기반 신호 분해)

  • Lee, Geum-Boon
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.19 no.2
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    • pp.279-286
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    • 2015
  • EMD is a fully data-driven signal processing method without using any predetermined basis function and requiring any user parameters setting. However EMD experiences a problem of mode mixing which interferes with decomposing the signal into similar oscillations within a mode. To overcome the problem, EEMD method was introduced. The algorithm performs the EMD method over an ensemble of the signal added independent identically distributed white noise of the same standard deviation. Even so EEMD created problems when the decomposition is complete. The ensemble of different signal with added noise may produce different number of modes and the reconstructed signal includes residual noise. This paper propose an modified EEMD method to overcome mode mixing of EMD, to provide an exact reconstruction of the original signal, and to separate modes with lower cost than EEMD's. The experimental results show that the proposed method provides a better separation of the modes with less number of sifting iterations, costs 20.87% for a complete decomposition of the signal and demonstrates superior performance in the signal reconstruction, compared with EEMD.

Fracture Behavior of Rail Steel under Mixed Mode Loading (혼합모드하에서의 레일강의 파괴거동)

  • Chang, Dong Il;Kim, Sung Hoon
    • Journal of The Korean Society of Civil Engineers
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    • v.14 no.4
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    • pp.761-769
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    • 1994
  • Actual load acting on rail surface in the track is the combined mode loading due to the contact rolling load of the wheels. To investigate the fracture behavior on rail steel under combined modes I and II, fracture tests were performed by using the test jigs and fracture specimen which were designed by Richard. The analysis results of experimental fracture data were compared with various fracture criteria that have been introduced for determination of the crack propagation direction and the critical stress of fracture of a crack submitted to a mixed mode loading. From the results, it was shown that the actual crack propagation direction of rail steel agree with the crack propagation directions predicted by maximum tangential stress criterion and strain energy density criterion, and that fracture criterion follows principal strain criterion.

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Design of Control Mixer for 40% Scaled Smart UAV (스마트무인기 축소모형의 조종면 혼합기 설계)

  • Gang, Yeong-Sin;Park, Beom-Jin;Yu, Chang-Seon
    • Aerospace Engineering and Technology
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    • v.5 no.2
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    • pp.240-247
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    • 2006
  • Tilt rotor aircraft is a multi-configuration airplane which has three independent flight modes; helicopter, conversion, and aiplane. The control surface mixer resign is reqctired to generate and distribute efficient control forces and moments in each flight mode. In the conversion mode, the thrust vector is changed from helicopter mode to airplane, therefore the thrust vector makes undesired forces and moments which affect on pitch, roll and yaw dynamics. This paper describes the design results of control surface mixer design which minimize the undesired forces and moments due to nacelles tilting angle change for 4O% scaled model.

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Mixed-mode fracture toughness measurement of a composite/metal interface (복합재료/금속 접착 계면의 혼합모드 파괴인성 측정)

  • Kim, Won-Seock;Jang, Chang-Jae;Lee, Jung-Ju
    • Composites Research
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    • v.24 no.2
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    • pp.1-8
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    • 2011
  • Interfacial fracture toughness under various mixed-mode loading is measured to provide a mixed-mode fracture criterion of a composite/metal bonded joint. Experimental fracture characterization tests were carried out using a SLB (single leg bending) specimen, which controls mode ratio with the specimen thickness. The experimental result of the SLB test conforms that interfacial fracture toughness increases as the mode II component increases. The effect of loading mode on interfacial crack growth is investigated on the basis of crack path observation using microscopic image acquisition technique. The influence of interfacial roughness on adhesion strength is also discussed.

Mode II and Mixed Mode Fracture of Single Layer Graphene Sheet (단층 그래핀시트의 모드 II 및 혼합모드 파괴)

  • Nguyen, Minh-Ky;Yum, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.2
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    • pp.105-113
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    • 2014
  • The mode II fracture behavior of a single-layer graphene sheet (SLGS) containing a center crack was characterized with the results of an atomistic simulation and an analytical model. The fracture of zigzag graphene models was analyzed with molecular dynamics and the mode II fracture toughness was found to be $2.04MPa{\sqrt{m}}$. The in-plane shear fracture of a cellular material was analyzed theoretically for deriving the $K_{IIc}$ of SLGS, and FEM results were obtained. Mixed-mode fracture of SLGS was studied for various mode I and mode II ratios. The mixed-mode fracture criterion was determined, and the obtained fracture envelope was in good agreement with that of another study.