• 제목/요약/키워드: fatigue Model

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환경하중을 이용하는 콘크리트 포장 슬래브 피로모형의 개선 (Improvement of Fatigue Model of Concrete Pavement Slabs Using Environmental Loading)

  • 박주영;임진선;김상호;정진훈
    • 한국도로학회논문집
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    • 제13권4호
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    • pp.103-115
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    • 2011
  • 온도와 수분의 불균일한 분포로 인하여 콘크리트 슬래브는 컬링과 와핑 거동을 하고 슬래브에는 항상 응력이 도입되어 있다. 따라서 교통하중 외에도 환경하중을 고려해야만 콘크리트 슬래브에 발생하는 응력을 보다 정확하게 예측할 수 있다. 콘크리트 포장에 반복적으로 재하되는 교통하중과 환경하중에 의해 콘크리트 슬래브의 강도는 지속적으로 감소하고 응력 이하로 낮아지게 되면 피로균열이 발생한다. 본 연구에서는 기존에 수행된 연구들로부터 피로실험 결과를 수집하고 피로 회귀모형을 개발하였다. 개발된 모형을 검증하기 위하여 모형개발에 사용되지 않은 실내 휨피로실험 결과를 예측하고 기존 모형으로 예측된 결과와 비교하였다. 콘크리트 포장 누적 피로손상 해석 프로그램을 개발한 후 본 연구에서 제안된 모형과 기존 모형들을 적용하고 예측 결과를 비교 및 평가하였다. 피로모형 별로 슬래브 두께, 줄눈간격, 복합 지지력계수, 그리고 하중전달률에 따른 누적 피로손상의 민감도 분석을 실시하였다. 그 결과 본 연구에서 개발된 모형이 최소-최대응력비 R을 고려하는 기존 모형들의 경향을 개선하여 환경하중을 더욱 합리적으로 반영할 수 있는 것으로 나타났다.

Probabilistic fatigue assessment of rib-to-deck joints using thickened edge U-ribs

  • Heng, Junlin;Zheng, Kaifeng;Kaewunruen, Sakdirat;Zhu, Jin;Baniotopoulos, Charalampos
    • Steel and Composite Structures
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    • 제35권6호
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    • pp.799-813
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    • 2020
  • Fatigue cracks of rib-to-deck (RD) joints have been frequently observed in the orthotropic steel decks (OSD) using conventional U-ribs (CU). Thickened edge U-rib (TEU) is proposed to enhance the fatigue strength of RD joints, and its effectiveness has been proved through fatigue tests. In-depth full-scale tests are further carried out to investigate both the fatigue strength and fractography of RD joints. Based on the test result, the mean fatigue strength of TEU specimens is 21% and 17% higher than that of CU specimens in terms of nominal and hot spot stress, respectively. Meanwhile, the development of fatigue cracks has been measured using the strain gauges installed along the welded joint. It is found that such the crack remains almost in semi-elliptical shape during the initiation and propagation. For the further application of TEUs, the design curve under the specific survival rate is required for the RD joints using TEUs. Since the fatigue strength of welded joints is highly scattered, the design curves derived by using the limited test data only are not reliable enough to be used as the reference. On this ground, an experiment-numerical hybrid approach is employed. Basing on the fatigue test, a probabilistic assessment model has been established to predict the fatigue strength of RD joints. In the model, the randomness in material properties, initial flaws and local geometries has been taken into consideration. The multiple-site initiation and coalescence of fatigue cracks are also considered to improve the accuracy. Validation of the model has been rigorously conducted using the test data. By extending the validated model, large-scale databases of fatigue life could be generated in a short period. Through the regression analysis on the generated database, design curves of the RD joint have been derived under the 95% survival rate. As the result, FAT 85 and FAT 110 curves with the power index m of 2.89 are recommended in the fatigue evaluation on the RD joint using TEUs in terms of nominal stress and hot spot stress respectively. Meanwhile, FAT 70 and FAT 90 curves with m of 2.92 are suggested in the evaluation on the RD joint using CUs in terms of nominal stress and hot spot stress, respectively.

Reliability-based combined high and low cycle fatigue analysis of turbine blade using adaptive least squares support vector machines

  • Ma, Juan;Yue, Peng;Du, Wenyi;Dai, Changping;Wriggers, Peter
    • Structural Engineering and Mechanics
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    • 제83권3호
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    • pp.293-304
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    • 2022
  • In this work, a novel reliability approach for combined high and low cycle fatigue (CCF) estimation is developed by combining active learning strategy with least squares support vector machines (LS-SVM) (named as ALS-SVM) surrogate model to address the multi-resources uncertainties, including working loads, material properties and model itself. Initially, a new active learner function combining LS-SVM approach with Monte Carlo simulation (MCS) is presented to improve computational efficiency with fewer calls to the performance function. To consider the uncertainty of surrogate model at candidate sample points, the learning function employs k-fold cross validation method and introduces the predicted variance to sequentially select sampling. Following that, low cycle fatigue (LCF) loads and high cycle fatigue (HCF) loads are firstly estimated based on the training samples extracted from finite element (FE) simulations, and their simulated responses together with the sample points of model parameters in Coffin-Manson formula are selected as the MC samples to establish ALS-SVM model. In this analysis, the MC samples are substituted to predict the CCF reliability of turbine blades by using the built ALS-SVM model. Through the comparison of the two approaches, it is indicated that the reliability model by linear cumulative damage rule provides a non-conservative result compared with that by the proposed one. In addition, the results demonstrate that ALS-SVM is an effective analysis method holding high computational efficiency with small training samples to gain accurate fatigue reliability.

통행차량 특성을 반영한 강교량 피로설계트럭의 피로파괴 신뢰도해석 (Reliability Analysis of Fatigue Truck Model Using Measured Truck Traffic Statistics)

  • 신동구;권태형;박영석
    • 한국강구조학회 논문집
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    • 제19권2호
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    • pp.211-221
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    • 2007
  • 교량의 피로파괴에 대한 Miner의 피로손상법칙을 적용하여 여러 확률변수로 표현된 피로파괴 한계상태함수에 대한 신뢰도해석을 국내에서 측정된 통행차량의 통계적 특성을 반영하여 수행하였다. 신뢰도지수의 산정에 필요한 확률변수 가운데 등가모멘트, 충격계수비, 등가하중비는 국내의 최근 측정자료를 분석하여 통계치를 산정하였으며, 피로강도, 활하중 횡분배비, 연행하중비는 국외에서 측정된 문헌자료의 통계치를 적용하였다. 신뢰도해석을 통하여 피로설계트럭의 종류, 교량수명, ADTT, 피로상세, 등가하중비, 피로설계트럭의 총중량 등의 피로손상에 관련된 여러 파라미터가 신뢰도지수에 미치는 영향을 분석하였다. 본 논문의 피로파괴에 대한 신뢰도해석 결과는 국내 LRFD 설계기준의 피로설계트럭모형과 피로한계상태의 하중계수를 결정할 때 기초 자료로 이용할 수 있을 것으로 판단된다.

AR 모델을 이용한 EMG 신호의 근육피로 특성 (The Characteristics of Muscle Fatigue of EMG Signal Using the AR Model)

  • 김홍래;왕문성
    • 대한의용생체공학회:의공학회지
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    • 제10권1호
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    • pp.11-16
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    • 1989
  • This paper describes the AR model of EMG signal during maximum voluntary contraction. By comparing the AR coefficients and the reflection coefficients of the AR model with the median frequency of power spectrum, it is proved that muscle fatigue can be measured by the AR and the reflection coefficients. In the estimation procedure of AR model parameter, the autocorrelation method is superior to the covariance method, and it is determined that the optimal order is six. As the muscle becomes fatigue, the median frequency of power spectrum is declined, and the AR coefficient [$a_1$] and the reflection coefficient [$k_1$] are also decreased. Therefore the muscle fatigue can be measured by the AR parameter.

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Roll 수명예측모델에 의한 열연작업롤 진단 (Work Roll Diagnosis by Roll Life Prediction Model in Hot Rolling Process)

  • 배용환;장삼규;이석희
    • 한국정밀공학회지
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    • 제10권3호
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    • pp.69-80
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    • 1993
  • It is important to prevent roll failure in hot rolling process for reducing maintenance coat and production loss. Roll material and rolling conditions such as the roll force and torque have been intensively investigated to overcome the roll failures. In this study, a computer roll life prediction system under working condition is developed and evaluated on IBM-PC level. The system is composed and fatigue estimation models which are stress analysis, crack propagation, wear and fatigue estimation. Roll damage can be predicted by calculating the stress anplification, crack depth propagation and fatigue level in the roll using this computer model. The developed system is applied to a work roll in actual hot rolling process for reliability evaluation. Roll failures can be diagnosed and the propriety of current working condition can be determined through roll life prediction simulation.

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비선형 이동 경화모델을 이용한 십자형 필릿 용접부의 변형율 해석 (Notch Strain Analysis of Cruciform Welded Joint using Nonlinear Kinematic Hardening Model)

  • 김유일;김경수
    • 대한조선학회논문집
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    • 제50권1호
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    • pp.41-48
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    • 2013
  • Several fatigue damages have recently been reported which cannot be resolved in the context of the existing fatigue design procedure, and they are suspected to be the cracks induced by the low cycle fatigue mechanism. To tackle the problem, a series of material tests together with fatigue tests have been carried out, and elasto-plastic notch strain analysis using nonlinear kinematic hardening model has been performed. The cyclic stress-strain curves are obtained and the nonlinear kinematic hardening model was calibrated based on the obtained material data. Also, the fatigue test with non-load-carrying cruciform fillet welded joint has been performed in low cycle fatigue regime. Then, the notch strain analyses have been carried out to find the precise elasto-plastic behavior of the material at the notch root of the cruciform joint. The variation of the material property from the base metal via HAZ up to the weld metal was taken into account using spatial variation of the material property. Then the detail elasto-plastic behavior of the welded joint subjected to the repeated cyclic loading has been investigated further through the comparison with the prediction with Neuber's rule. The calibration of the nonlinear kinematic hardening model and nonlinear notch strain analyses have been performed using the commercial FE program ABAQUS.

Fatigue life evolution of steel wire considering corrosion-fatigue coupling effect: Analytical model and application

  • Yang Ding;Xiao-Wei Ye;Hong Zhang;Xue-Song Zhang
    • Steel and Composite Structures
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    • 제50권3호
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    • pp.363-374
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    • 2024
  • The fatigue life of steel wire is affected not only by fatigue load, but also by corrosion environment in service period. Specially, the corrosion pit will lead to stress concentration on the surface of steel wire inducing the formation of fatigue cracks, and the fatigue cracks will accelerate the corrosion process. Therefore, the corrosion fatigue of steel wire is a coupling effect. In this study, the corrosion-fatigue coupling life curve is derived with considering corrosion-fatigue pitting stage, corrosion-fatigue short crack stage and corrosion-fatigue long crack stage. In addition, the stress concentration factors of different corrosion pits are calculated by COMSOL software. Furthermore, the effect of corrosion environment factors, that is, corrosion rate, corrosion pit morphology, frequency and action factor of fatigue load, on fatigue life of steel wire is analyzed. And then, the corrosion-fatigue coupling life curve is compared with the fatigue life curve and fatigue life curve with pre-corrosion. The result showed that the anti-fatigue performance of the steel wire with considering corrosion-fatigue coupling is 68.08% and 41.79% lower than fatigue life curve and fatigue life curve with pre-corrosion. Therefore, the corrosion-fatigue coupling effect should be considered in the design of steel wire.

선체구조의 용접이음부의 피로강도 해석법에 관한 연구 (A Study on the fatigue strength analysis of the welded joints in ship hull construction)

  • 엄동석;강성원;이성구;김원범
    • Journal of Welding and Joining
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    • 제10권4호
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    • pp.259-267
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    • 1992
  • In this report, a method to predict the fatigue strength in welded structure member of ship construction is studied considering the effects of statistical characteristics of mild steels and weld toe shapes on the fatigue crack initiation life. The fatigue test under pulsating bending load is carried out with the model specimens of the web frame in double bottom of ship hull. The propriety of the fatigue life curve with probability of failure in the transverse strength members of ship hull construction is confirmed by the comparison with the results of fatigue test on the model of the various transverse strength members.

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열화된 증기 터빈블레이드의 피로강도에 대한 확률론적 해석 (A Stochastic Analysis in Fatigue Strength of Degraded Steam Turbine Blade Steel)

  • 김철수;정화영;김정규
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집A
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    • pp.262-267
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    • 2001
  • In this study, the Reliability of degraded steam turbine blade was evaluated using the limited fatigue data. The statistical estimation of limited fatigue data implies that some unknown uncertainties which may be involved in fatigue reliability analysis. Therefore, an appropriate distribution in the fatigue strength was determined by the characteristic distribution - linear correlation coefficient, fatigue physics, error parameter. 3-parameter Weibull distribution is the most appropriate distribution to assume for infinite region. The load applied on the blade is mainly tensile. The maximum Von-Mises stress is 219.4 MPa at the steady state service condition. The failure probability($F_p$) derived from the strength-stress interference model using Monte carlo simulation under variable service condition is 0.25% at the 99.99% confidence level.

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