• Title/Summary/Keyword: 응력-수명 파라미터

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A Study on Evaluation of Crack Opening Point in Fatigue Crack Propagation Course (II);Parameter Sensitivity Study of Crack Opening Ratio by Using Numerical Calculation (피로크랙 진전과정에서의 크랙열림점 평가에 관한 연구(II))

  • 최병기;윤한용;박창언;정태권
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.3
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    • pp.931-935
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    • 1991
  • 본 연구에서는 유효응력확대계수로서 피로크랙 진전수명을 평가할 수 이용되 는 크랙열림비(본 논문에서는 후술하는 최대응력에 대한 크랙 열림응력의 비를 크랙 열림비로 하다)가 진전수명에 미치는 영향을 평가하기 위한것으로서, 제1보에서는 실 험에 의하여 크랙 열림점을 실측한 결과 측정입치에 따라 다른 값을 나타내며 수명평 가법 크랙 선단으로부터 떨어진 곳(크립게이지를 이용한 크랙마우스등)에서 측정한 크 랙 열림점 값을 이용함이 보다 정확함을 밝혔다.본 제2보에서는 크랙열림비가 수명 평가에 미치는 영향을 상기의 파라미터 영향도 평가수법을 이용하여 평가하고자 한다.

Inverse Estimation of Fatigue Life Parameter based on Bayesian Approach (베이지안 접근법을 이용한 피로수명 파라미터의 역 추정)

  • Heo, Chan-Young;An, Da-Wn;Choi, Joo-Ho;Jeon, Jeong-Il
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2010.04a
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    • pp.620-623
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    • 2010
  • 구조요소의 설계에서 유한요소해석은 매우 효과적인 방법이며 정확한 해석 기술을 요구한다. 그러나 제조 공정이나 환경에 따라 달라지는 재료 물성이나 불확실성을 내포하는 피로 물성을 확정적인 값으로 이용하는 등 입력 변수의 부정확한 정보로 인해 유한요소해석 결과를 신뢰하지 못하는 경우가 자주 발생한다. 실제 시험을 통해 설계의 결과를 예측하는 것은 경제적인 측면과 시간소요 면에서 한계가 따르기에 신뢰할 수 있는 유한요소해석 방법이 요구된다. 본 연구에서는 고주기의 피로 해석을 위해 유한요소해석을 이용하여 스프링의 응력-수명(S-N) 파라미터를 역 추정하고 수명을 예측해 보았다. 이를 위해 실제 산업현장에서 쓰이는 자동차 서스펜션 코일 스프링을 예제로 사용하였다. 시험 모델에 대해 불확실성을 고려한 베이지안 접근법을 이용하여 입력변수의 파라미터를 역 추정하였으며, 마코프체인몬테카를로(Markov Chain Monte Carlo) 기법을 이용하여 얻어진 피로 물성 파라미터의 샘플 데이터를 이용해서 유한요소해석을 실시하고 신뢰수준 내에서 새로운 구조요소의 피로수명을 예측하였다.

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Prediction of Fretting Fatigue Life on 2024-T351 Al-alloy (2024-T351 알루미늄 합금판 프레팅 피로수명 예측)

  • Kwon, Jung-Ho;Hwang, Kyung-Jung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.7
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    • pp.601-611
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    • 2007
  • Most of mechanically jointed aircraft structures are always encountered the fretting damages on the contact surfaces between two jointed structural members or at the edges of fastener holes. The partial slip and contact stresses associated with fretting contact can lead to severe reduction in service lifetime of aircraft structures. Thus a critical need exists for predicting fretting crack initiation in mechanically jointed aircraft structures, which requires characterizing both the near-surface mechanics and intimate relationship with fretting parameters. In this point of view, a series of fretting fatigue specimen tests for 2024-T351 Al-alloy, have been conducted to validate a mechanics-based model for predicting fretting fatigue life. And included in this investigaion were elasto-plastic contact stress analyses using commercial FEA code to quantify the stress and strain fields in subsurface to evaluate the fretting fatigue crack initiation.

Composites Fatigue Life Evaluation based on non-linear fatigue damage model (비선형 피로손상 모델을 이용한 복합재 피로수명 평가)

  • 김성준;황인희
    • Composites Research
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    • v.16 no.1
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    • pp.13-18
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    • 2003
  • Prediction of composite fatigue life is not a straightforward matter, depending on various failure modes and their interactions. In this paper, a methodology is presented to predict fatigue life and residual strength of composite materials based on Phenomenological Model(non-linear fatigue damage model). It is assumed that the residual strength is a monotonically decreasing function of the number of loading cycles and applied fatigue stress ratio and the model parameters(strength degradation parameter and fatigue shape parameter) are assumed as function of fatigue life. Then S-N curve is used to extract model parameters that are required to characterize the stress levels comprising a randomly-ordered load spectrum. Different stress ratios (${\sigma}_{min}/{\;}{\sigma}_{max}$) are handled with Goodman correction approach(fatigue envelope) and the residual strength after an arbitrary load cycles is represented by two parameter weibull functions.

A Study on the Fatigue Strength and Life Distribution of Carbon Steel Using the Database System (데이터베이스 시스템을 이용한 탄소강의 피로강도 및 수명분포)

  • Kim, Jung Kyu;Moon, Joon Ho;Kim, Do Sik
    • Journal of Korean Society of Steel Construction
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    • v.10 no.1 s.34
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    • pp.37-45
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    • 1998
  • The relational database system on fatigue strength was constructed, and the properties of fatigue life distribution were examined to analyze reliability and safety of metallic materials. Data manipulations were efficiently performed in relational fatigue strength database system using dependency diagram. Regardless of the distribution of fatigue strength, the proposed method, the Robust method and the complementary error function method using probability distribution, successfully estimated parameters of the 3-parameter Weibull distribution. The proposed criterion for estimating non-failure probability showed good results regardless of censoring time. The fatigue life distribution function described as a function of parameters of the Weibull distribution and applied stress ratio produced P-S-N characteristics reasonably.

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A Study on Statistical Characteristics of Fatigue Life of Carbon Fiber Composite (탄소섬유 복합재 피로수명의 통계적 특성 연구)

  • Joo, Young-Sik;Lee, Won-Jun;Seo, Bo-Hwi;Lim, Seung-Gyu
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.1
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    • pp.35-40
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    • 2019
  • The objective of this paper is to identify the fatigue properties of carbon-fiber composite which is widely applied for the development of aircraft structures and obtain data for full-scale fatigue test. The durability and damage tolerance evaluation of composite structures is achieved by fatigue tests and parameters such as fatigue life factor and load enhancement factor. The specimens are made with carbon-fiber/epoxy UD tape and fabric prepreg. Fatigue tests are performed with several stress ratios and lay-up patterns. The Weibull shape parameters are analyzed by Sendeckyj model and individual fatigue lives with Weibull distribution. And the fatigue life factor and load enhancement factor considering reliability are evaluated.

Cycling life prediction method considering compressive residual stress on liner for the filament-wound composite cylinders with metal liner (금속재 라이너를 갖는 복합재 압력용기의 라이너 압축잔류응력을 고려한 반복수명 예측 방법에 대한 연구)

  • Park, Ji-Sang;Jeung, Sang-Su;Chung, Jae-Han
    • Composites Research
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    • v.19 no.1
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    • pp.22-28
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    • 2006
  • In manufacturing process of composite cylinders with metal liner, the autofrettage process which induces compressive residual stress on the liner to improve cycling life can be applied. In this study, a finite element analysis technique is presented, which can predict accurately the compressive residual stress on the liner induced by autofrettage and stress behavior after. Material and geometrical non-linearity is considered in the finite element analysis, and the Von-Mises stress of a liner is introduced as a key parameter that determines pressure cycling life of composite cylinders. Presented methodology is verified through fatigue test of liner material and pressure cycling test of composite cylinders.

Fatigue Life Estimation Method Considering Traffic Properties for Steel Highway Girder Bridge (교통특성을 고려한 강도로교의 피로수명 평가 방안)

  • Lee, Hee-Hyun;Kyung, Kab-Soo;Jeon, Jun-Chang
    • Journal of Korean Society of Steel Construction
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    • v.22 no.3
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    • pp.209-218
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    • 2010
  • The fatigue phenomenon, which is induced by stress accumulation due to the repeated loading of vehicles in the long term, is one of the main factors of the span of life of a steel bridge. In this paper, the effects of traffic properties on the fatigue life of ordinary short- and medium-span steel plate girder bridges that are exposed to relatively large dynamic effects are investigated. From the analysis, it was known that the fatigue life of the bridge becomes shorter with increasing traffic volume and number of large vehicles, and is affected by the weights of the vehicles. Based on the analysis results, a new parameter that can represent the traffic property that affects the fatigue life of the subject bridge is suggested, and the validity of the parameter is confirmed.

Prediction of Fretting Fatigue Life for Lap Joint Structures of Aircraft (항공기 겹침이음 조립구조의 프레팅 피로수명 예측)

  • Kwon, Jung-Ho;Joo, Seon-Yeong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.7
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    • pp.642-652
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    • 2009
  • Most of lap jointed aircraft structures encounter the fretting damages, which provoke fretting cracks prematurely and lead to significant reduction of fatigue life. In the case of ageing aircrafts especially, this fretting fatigue problem is a fatal threat for the safety and airworthiness. Recently, as the service life extension program(SLEP) of ageing aircrafts has become a hot issue, the prediction of fretting fatigue life is also indispensable. On these backgrounds, a series of experimental tests of fretting fatigue on bolted lap joint specimens, were performed. And the fretting crack initiation and propagation life of each specimen were evaluated using existing and newly proposed prediction models with the fretting parameters obtained from the FEA results for elasto-plastic contact stress analyses. The validations of prediction models were also discussed, comparing the prediction results with experimental test ones.

ISM에 의한 발전용 고온 배관재료 2.25Cr1Mo강의 고온 크리프 수명 예측에 관한 연구

  • Lee, Sang-Guk;Jeong, Min-Hwa;O, Se-Gyu;Song, Jeong-Geun
    • Journal of Ocean Engineering and Technology
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    • v.12 no.2 s.28
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    • pp.71-78
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    • 1998
  • In this report for the assessment of creep properties of high-temperature tube materials in power plants, the long-time($10^4$~105h) creep life prediction by ISM for 2.25Cr1Mo steel was studied. It was clarified experimentally and quantitatively that the newly developed long-time creep life prediction equation was very coincident with the actual experimental data with high confidence, and the model was $t_r=\alpha\varepsilon_0^{\beta}\sigma^{-1}$.

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