• Title/Summary/Keyword: Fatigue Reliability

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Fatigue Life Prediction using Fuzzy Reliability theory (퍼지신뢰성이론에 의한 피로수명 예측)

  • 심확섭;이치우;장건의
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.10a
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    • pp.672-675
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    • 1995
  • Because of a sudden growth of the research of fatigue failure, recent machines or structures have been designed by damage tolerance design in many fields. Consequently, it is the most primary factor to clarity the specific character of fatique failure in the design of machines or structures considering reliability. A statistical analysis is required to analyze the outcome of an experiment or a life estimate by reason of that fatigue failure contains lots of random elements. Reliability analysis which has tukenn the place of the existing analyses in the consideration of the uncertainty of a material, is a very efficient way. Even reliability analysis, however, is not a perfect way to analyses the uncertainties of all the materials. This thesis would refer to a newly conceived data analysis that the coefficient of a system could cause the ambiguity of the relationship of an input and output.

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A Study on Reliability Estimation for Fatigue Life of the Spider from a Drum Washing Machine (드럼 세탁기 Spider의 피로수명 신뢰성 평가에 대한 연구)

  • 이성민;조상봉;조성진;김영수;강동우;정연수;정보선
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.46-49
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    • 2004
  • The spider of a drum washing machine receives the repeated fatigue loadings during laundering. Although the spider is designed statically safely, it often happens fatigue failure. Therefore it requires the safe design for fatigue and needs the prediction of quantitative fatigue life. The S-N diagram for a spider material is developed by fatigue test and statistical analysis. The stresses are measured directly from strain gages on the spider. To predict the fatigue life of spider, the rainflow counting method and Miner's rule are used. The data for fatigue life are analyzed statistically. From these data, reliability estimation for fatigue life can be done and also, equivalent fatigue life can be obtained. It will be applied to make and improve to a short period for design and prototype test.

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Reliability Assessment and Accelerated Life Prediction of Gas Welded Joint in the Rail Road Car Body (1. Plug and Ring Type) (철도차량 차체 가스용접 이음재의 가속수명예측과 신뢰도 평가)

  • Baek, Seung-Yeb
    • Journal of Welding and Joining
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    • v.28 no.1
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    • pp.77-85
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    • 2010
  • Stainless steel sheets are widely used as the structure material for the railroad cars and the commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. Gas welding is very important and useful technology in fabrication of a railroad car and vehicles structure.However fatigue strength of the gas welded joints is considerably lower than parent metal due to stress concentration at the weld, fatigue strength evaluation of gas welded joints are very important to evaluate the reliability and durability of railroad cars and to establish a criterion of long life fatigue design. In this paper, $({\Delta}{\sigma}_a)_R-N_f$ curve were obtained by fatigue tests. Using these results, the accelerated life test(ALT) was conducted. From the experimental results, an acceleration model was derived and acceleration factors are estimated. So it is intended to obtain the useful information for the fatigue lifetime of plug and ring gas welded joints and data analysis by statistic reliability method, to save time and cost, and to develop optimum accelerated life prediction plans.

Fatigue Reliability Evaluation of Steel-Composite High-Speed Railway Bridge with Tuned Mass Damper (동조질량감쇠기를 장착한 강합성형 고속철도교의 피로신뢰성 평가)

  • Kang, Soo-Chang;Seo, Jeong-Kwan;Koh, Hyun-Moo;Park, Kwan-Soon
    • Journal of the Earthquake Engineering Society of Korea
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    • v.9 no.5 s.45
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    • pp.1-10
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    • 2005
  • This study proposes a fatigue reliability evaluation procedure for steel-composite high-speed railway bridge based on dynamic analysis and investigates the effectiveness of Tuned Mass Damper(TMD) in terms of the extension of fatigue life of the bridge. For the fatigue reliability evaluation, the limit state is determined using S-N curve and linear fatigue-damage accumulation. Dynamic analyses are peformed repeatedly to consider the uncertainties of train-velocity and damping ratio of the bridge. The distribution of random variables related to fatigue damage for the intended service life is then statistically estimated from analytical results. Finally, the fatigue reliability indices are obtained by means of the Advanced First-Order Second-Moment (AFOSM) method. Through numerical simulation of a steel-composite bridge of 40m span, the effectiveness of TMD on fatigue life of the bridge is examined and the results are presented.

Reliability Evaluation of Thruster Break for Aerogenerator (풍력발전기용 쓰러스터 브레이크의 신뢰성 평가)

  • Jung, Dong Soo
    • Journal of Applied Reliability
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    • v.13 no.3
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    • pp.165-174
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    • 2013
  • Thruster break for aerogenerator performs a role that is stopping the rotor in case of emergency such as strong wind, system abnormality or maintenance check. In this study, failure analysis and test evaluation on the thruster break for aerogenerator are proposed, and the entire process to improve reliability of the product through design improvement is presented. The typical failure case is fatigue and wear, and failure cause on these are identified and improvement plan is presented. Lastly, reliability improvement is established to analyse test results before after the life test.

FATIGUE LIFE ESTIMATION OF IMPLANT USING A FINITE ELEMENT METHOD (유한요소법을 이용한 치아 임플랜트 피로수명 예측)

  • Han In-Sook;Son Jung-Hun;Yang Young-Soo;Lee Seung-Young
    • The Journal of Korean Academy of Prosthodontics
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    • v.44 no.4
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    • pp.414-420
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    • 2006
  • Purpose : The purpose of this study is to use finite element analysis to predict the fatigue life of an implant system subjected to fatigue load by mastication (chewing force). The reliability and the stability of implant system can be defined in terms of the fatigue strength. Not only an implant is expensive but also it is almost impossible to correct after it is inserted. From a bio-engineering standpoint, the fatigue strength of the dental implant system must be evaluated by simulation (FEA). Material and Methods Finite element analysis and fatigue test are performed to estimate the fatigue strength of the implant system. Mesh of implant is generated with the actual shape and size. In this paper, the fatigue strength of implant system is estimated. U-fit (T. Strong, Korea, internal type). The stress field in implant is calculated by elastic-plastic finite element analysis. The equivalent fatigue stress, considering the contact and preload stretching of a screw by torque for tightening an abutment, is obtained by means of Sine's method. To evaluate the reliability of the calculated fatigue strength, fatigue test is performed. Results: A comparison of the calculated fatigue strength with experimental data showed the validity and accuracy of the proposed method. The initiation points of the fatigue failure in the implant system exist in the region of high equivalent fatigue stress values. Conclusion: The above proposed method for fatigue life estimation tan be applied to other configurations of the differently designed and improved implant. In order to prove reliability of prototype implant, fatigue test should be executed. The proposed method is economical for the prediction of fatigue life because fatigue testing, which is time consuming and precision-dependent, is not required.

Bending Fatigue Reliability Improvements of Cu Interconnects on Flexible Substrates through Mo-Ti Alloy Adhesion Layer (Mo-Ti 합금 접착층을 통한 유연 기판 위 구리 배선의 기계적 신뢰성 향상 연구)

  • Lee, Young-Joo;Shin, Hae-A-Seul;Nam, Dae-Hyun;Yeon, Han-Wool;Nam, Boae;Woo, Kyoohee;Joo, Young-Chang
    • Journal of the Microelectronics and Packaging Society
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    • v.22 no.1
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    • pp.21-25
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    • 2015
  • Bending fatigue characteristics of Cu films and $8{\mu}m$ width Cu interconnects on flexible substrates were investigated, and fatigue reliability improvement was achieved through Mo-Ti alloy adhesion layer. Tensile bending fatigue reliability of Cu interconnects is 3 times lower than that of Cu films, and even compressive bending fatigue reliability of Cu interconnects is 6 times lower than that of Cu films. From these results, mechanical crack formation could be fatal in Cu interconnects. With Mo-Ti adhesion layer, fatigue reliability of Cu films and interconnects were enhanced due to the increase of adhesion strength and the suppression of slip induced crack initiation.

Reliability based optimization of spring fatigue design problems accounting for scatter of fatigue test data (피로시험 데이터의 산포를 고려한 스프링의 신뢰성 최적설계)

  • An, Da-Wn;Won, Jun-Ho;Choi, Joo-Ho
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1314-1319
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    • 2008
  • Fatigue reliability problems are nowadays actively considered in the design of mechanical components. Recently, Dimension Reduction Method using Kriging approximation (KDRM) was proposed by the authors to efficiently calculate statistical moments of the response function. This method, which is more tractable for its sensitivity-free nature and providing the response PDF in a few number of analyses, is adopted in this study for the reliability analysis. Before applying this method to the practical fatigue problems, accuracies are studied in terms of parameters of the KDRM through a number of numerical examples, from which best set of parameters are suggested. In the fatigue reliability problems, good number of experimental data are necessary to get the statistical distribution of the S-N parameters. The information, however, are not always available due to the limited expense and time. In this case, a family of curves with prediction interval, called P-S-N curve, is constructed from regression analysis. Using the KDRM, once a set of responses are available at the sample points at the mean, all the reliability analyses for each P-S-N curve can be efficiently studied without additional response evaluations. The method is applied to a spring design problem as an illustration of practical applications, in which reliability-based design optimization (RBDO) is conducted by employing stochastic response surface method which includes probabilistic constraints in itself. Resulting information is of great practical value and will be very helpful for making trade-off decision during the fatigue design.

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Reliability improvement of nonlinear ultrasonic modulation based fatigue crack detection using feature-level data fusion

  • Lim, Hyung Jin;Kim, Yongtak;Sohn, Hoon;Jeon, Ikgeun;Liu, Peipei
    • Smart Structures and Systems
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    • v.20 no.6
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    • pp.683-696
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    • 2017
  • In this study, the reliability of nonlinear ultrasonic modulation based fatigue crack detection is improved using a feature-level data fusion approach. When two ultrasonic inputs at two distinct frequencies are applied to a specimen with a fatigue crack, modulation components at the summation and difference of these two input frequencies appear. First, the spectral amplitudes of the modulation components and their spectral correlations are defined as individual features. Then, a 2D feature space is constructed by combining these two features, and the presence of a fatigue crack is identified in the feature space. The effectiveness of the proposed fatigue crack detection technique is experimentally validated through cyclic loading tests of aluminum plates, full-scale steel girders and a rotating shaft component. Subsequently, the improved reliability of the proposed technique is quantitatively investigated using receiver operating characteristic analysis. The uniqueness of this study lies in (1) improvement of nonlinear ultrasonic modulation based fatigue crack detection reliability using feature-level data fusion, (2) reference-free fatigue crack diagnosis without using the baseline data obtained from the intact condition of the structure, (3) application to full-scale steel girders and shaft component, and (4) quantitative investigation of the improved reliability using receiver operating characteristic analysis.

Reliability of Machine Elements Based on Static and Dynamic Factor of Allowable Safety under Fluctuating Load (변동하중을 받는 기계요소의 정 .동적 허용안전계수를 고려한 신뢰성)

  • 양성모;김강희
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.475-480
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    • 1997
  • It is common to assum identical allowable safety factors in static strength, defined by mean stress and in fatigue, defined by stress amplitude. Under the load with asymmetrical cycles the safety factor is not the same. In this paper, with the consideration of unequal allowable safety factors a general method for estimating fatigue reliability of a machine element under a combined state of stress is derived based on the theory proposed by Prof. Kececioglu and normal distribution. The calculation of fatigue reliability for limited life is discussed with example.

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