• Composites Research
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• v.17 no.4
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• pp.68-73
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• 2004

An analytical study was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates repaired with asymmetric bonded composite patch. For single-sided repairs, due to the asymmetry and the presence of out-of$.$plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from Previous studies. Therefore, for the accurate investigation of fatigue behavior, it is necessary to predict the actual crack front evolution and take it into consideration in the analysis. In this study, the fatigue analysis of single-sided repairs considering crack front shape development was conducted by implementing three-dimensional successive finite element method coupled with linear elastic fracture mechanics (LEFM) concept, which enables the growing crack front to be directly traced and modeled in a step by step way. Through conducting present analysis technique, crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations.

• The Journal of the Convergence on Culture Technology
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• v.7 no.2
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• pp.405-410
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• 2021

In this study, a finite element analysis was performed applying a nonlinear material model and fatigue load conditions to evaluate the service life and spring stiffness of the resilient pad for rail fastening system. As a result of the fatigue analysis, the rate of change in spring stiffness compared to the initial condition was about 16%, indicating that fatigue hardening occurred. As for the stress generated in the longitudinal direction of the resilient pad, the difference between the stress generated at the center and the edge was about 10 times or more. In addition, it was analyzed that the equivalent stress of the outer boundary was more than twice as large as that of the central part. Therefore, it was analyzed that the damage and deformation of the resilient pad are the corners of the resilient pad under actual service conditions. The fatigue life diagram of the resilient pad (S-N curve) was derived using the equivalent stress of the resilient pad according to the fatigue cycles. Using the fatigue life diagram of the resilient pad derived in this study, it is considered that it can be used to predict the fatigue life under the relevant conditions by calculating the equivalent stress of the resilient pad under various load conditions.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.13-18
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• 2009

In this study, an equivalent unit load methodology has been presented to simplify the fatigue analysis procedure. And fuselage structure fatigue life has been evaluated based on equivalent unit load. Finite element analysis has been carried out to analyze the stress intensity factor and geometrical correction factor that is needed for crack growth analysis. And strain energy density factor is used to predict the initial direction of crack propagation.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.4
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• pp.393-400
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• 2011

In this study, a procedure for the inverse estimation of the fatigue life parameters of springs which utilize the field fatigue life test data is proposed to replace real test with the FEA on fatigue life prediction. The Bayesian approach is employed, in which the posterior distributions of the parameters are determined conditional on the accumulated life data that are routinely obtained from the regular tests. In order to obtain the accurate samples from the distributions, the Markov chain Monte Carlo (MCMC) technique is employed. The distributions of the parameters are used in the FEA for predicting the fatigue life in the form of a predictive interval. The results show that the actual fatigue life data are found well within the posterior predictive distributions.

• Journal of Ocean Engineering and Technology
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• v.5 no.2
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• pp.85-93
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• 1991

피로 파괴연구의 급격한 발전에 따라 최근의 기계나 구조물들은 많은 분야에서 손상허용설계원리에 근거하여 설계되고 있다. 이러한 상황 하에서 피로파손의 정확한 특성을 밝히는 것은 신뢰성을 고려한 기계나 구조물의 설계에 있어 가장 중요한 요인이 된다. 피로파손은 많은 랜덤요소를 내포하고 있으므로 실험결과 분석 및 수명예측을 분석하기 위해서는 통계학적 해석이 요구되고 있다. 본 연구의 목적은 회전굽힘피로시험을 수행하고 피로수명을 분석하는데 정규분포, 대수분포, 지수분포 및 Weibull분포를 이용하여 실험결과와 비교하고 파손확률을 찾는데 있다.

• Journal of Aerospace System Engineering
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• v.13 no.5
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• pp.65-71
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• 2019

In this study, as a part of the aging aircraft performance improvement project for which no design information is provided, a new type of blade antenna is installed on the main part of the aging aircraft, and the method of proving the fatigue life of the main part of the aircraft is reviewed and summarized. There are various methods to prove fatigue life according to the manufacturer and aircraft design conditions. The fatigue life prediction and damage tolerance range of the relevant site were obtained through related regulations and industry examples. From these results, the fatigue life of newly installed antennas around the main parts of the aging aircraft was evaluated and the maintenance period and criteria were set according to the damage tolerance.

• 기계와재료
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• v.23 no.3
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• pp.114-123
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• 2011

주조품 설계 및 제조에 있어서 기존의 유동 및 응고 해석뿐 아니라 최근에는 응력 해석 기법의 적용이 대두 되고 있다. 특히 자동차 산업에 있어서 부품의 경량화는 필수 불가결한 선택이며, 이는 설계자 및 제조업체에 복잡하고 얇은 알루미늄, 마그네슘 주물품에 대하여, 치수적인 문제와 강성의 문제를 동시에 해결하도록 요구하고 있다. 또한 경제적인 관점에서 긴 금형 수명이 요구되나 열 및 기계적인 피로 균열인 'heat checking'은 이러한 금형 수명을 저하시키는 가장 흔한 요소이다. 이런 무제를 해결하기 위해 해석 기법을 이용하여 주조 설계 및 공정을 최적화 함으로써 변형의 최소화 및 금형 수명의 최대화를 달성할 수 있을 것으로 판단된다. 이러한 기법을 성공적으로 적용하기 위해서는 주조 공정 해석, 재료 시험, 제품 설계 및 공정 최적화 설계가 통합적으로 이루어져야 한다. 본 고에서는 현재 최신 주조 해석 기법을 이용하여, 주조품 제조 공정에서 발생하는 응력과 관련된 문제들에 대한 수치해석 기법을 살펴보고, 이에 대한 리뷰를 제공하고자 한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.18-21
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• 2009

The life of components under high thermal load is typically shorter than other components. The turbopump turbine of liquid rocket is operated under these environments like high temperature and high centrifugal dorce due to high rotating velocity during operating time. These conditions may often cause low-cycle fatigue problem in the turbopump turbine. First of all, to analyze heat stress, ABAQUS/CAE is used and Coffin-manson's equation is used to consider elasticity and plasticity strain. S.W.T's method is used to consider the mean stress effect, using strain history, low-cycle fatigue analysis is done for turbopump turbine which may have FCL(fracture critical location). In this paper, strain life method is applied to analyze low-cycle fatigue.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.87-100
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• 1989

해양구조물의 원통형 조인트에 대한 파괴역학적 피로수명 산출방법이 개발되었다. 개발된 방법을 이용해서 2평면 K형 조인트에 대한 피로수명을 구체적인 파괴역학적 방법으로 산출 하였다. 이 분석을 위해 용접부위 표면균열의 응력확대 계수를 3차원 유한요소법에 의해 계산하였다. 계산된 결과에 의하면 용접부위 표면균열 첨단은 단순한 Mode I형태를 보이지 않고 Mode I, II, III이 복합된 형태임이 입증되었다. 계산된 응력확대 계수를 사용해서 16개의 용접부위균열 성장형태를 일반적인 피로균열 성장법칙을 적용해서 계산하였고, 균열성장의 안정분석을 통해 각 균열의 최종 파괴상태를 파괴해석도면(failure assessment diagram)법을 이용해서 계산하였다.