• 항공우주시스템공학회지
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• 제17권2호
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• pp.1-8
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• 2023

회전익 항공기의 동력전달축은 경량화를 위하여 중공축을 적용하였으며 선형탄성 파괴역학을 이용해 균열 전파 거동을 예측할 수 있다. 본 논문에서는 유한요소해석을 통하여 원주방향 관통형 균열을 가지는 중공축의 균열성장수명을 예측하였다. 비틀림을 부여하고 균열을 고려한 요소를 형성하여 2차원 유한요소모델을 생성하였다. 초기 균열 길이를 정의하고 균열 길이를 증가시켜 유한요소해석을 수행해 균열 선단의 응력확대계수를 도출하였다. 응력확대계수가 중공축을 구성하는 재료의 파괴인성을 초과하기 직전의 길이를 한계 균열 길이로 정의한다. 응력확대계수 핸드북을 통해 응력확대계수를 계산하여 한계 균열 길이를 도출하고 균열성장속도식을 수치적분하여 각각의 균열성장수명을 비교해 제안한 유한요소해석 기법을 검증하였다.

• 대한조선학회논문집
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• 제45권6호
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• pp.669-678
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• 2008

The fatigue life of ship structure under cyclic loading condition is made up of initiation and propagation stages. In this study, crack growth test is carried out on large scale structure test specimens and fracture mechanical analysis is performed. The fatigue lives measured from fatigue tests are compared with DNV, Matsuoka and BS 5400 S-N curve. And to predict the crack initiation life, S-N curve, corresponding to crack length 20mm at welded joint, is developed based on hot spot stress range. Also crack propagation life is calculated using crack growth equation. Consequently, computed crack propagation life is compared with experiment results.

• 한국정밀공학회지
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• 제13권8호
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• pp.80-87
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• 1996

The present paper will give some results of the fatigue behavior of typical axi-symmetric forward extrusion die. The extrusion process is analyzed by rigid-plastic FEM and the deformation analysis of extrusion die is conducted by elasto-plastic FEM. To approach the crack problem LEFM (Linear Elastic Fracture Mechanics) is introduced. Using special element in order to conside the sigularity of stress/ strain in the vicinity of the crack tip, stress intensity factor and the effective stress intensity factor is calculated. Applying proper fatigue crack propagation criterion such as Paris/Erdogan fatigue law and maximum principal criterion to these data, then, the angle and the direction of fatigue crack propagation is simulated. In result, it is proved that the simulated fatigue crack propagates in the zigzag path along the radial direction and fatigue life of the extrusion die is evaluated by using the computed crack growth rate.

• 한국작물학회지
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• 제68권4호
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• pp.285-293
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• 2023

한반도 남부지방(진주)에서 콩 생태형에 따라 생육단계별 생육일수를 적산온도로 환산하여 한반도 북방지역 7개 농업기후지대의 콩 생육예측을 실시하였다. 그 결과는 아래와 같다. 1. 수양산 이남, 수양산 이북, 동해 남부, 중부 내륙, 북부내륙 지역들은 모든 생태형에서 정상적인 생육과 수확이 가능할 것으로 예측되었다. 2. 북부 고산지대는 모든 생태형에서 정상적인 생육이 불가능한 것으로 나타났고, 동해 북부지역은 조생종, 중생종은 정상적인 생육이 가능하지만 중만생종은 생육일수가 부족한 것으로 나타났다. 3. 파종 한계기는 수양산 이남, 수양산 이북, 동해 남부 지역은 생태형에 따라 6월 6일~26일까지, 중부 내륙 6월 2일~17일, 북부 내륙은 5월 24~6월 12일, 동해 북부는 5월 16일~6월 7일경인 것으로 조사되었다. 그러나 북부고산지대는 9℃기준인 4월 30일 파종하여도 생육일수가 부족한 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제38권4호
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• pp.443-457
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• 2011

The loss of strength in a structure as a result of cyclic loads over a period of life time is an important phenomenon for the life-cycle analysis. Service loads are accentuated at the areas of stress concentration, mainly at the connection of components. Structural components unavoidably are affected by defects such as surface scratches, surface roughness and weld defects of random sizes, which usually occur during the manufacturing and handling process. These defects are shown to have an important effect on the fatigue life of the structural components by promoting crack initiation sites. The value of equivalent initial flaw size (EIFS) is calculated by using the back extrapolation technique and the Paris law of fatigue crack growth from results of fatigue tests. We try to analyze the effect of EIFS distribution in a multiple site damage (MSD) specimen by using the extended finite element method (XFEM). For the analysis, fatigue tests were conducted on the centrally-cracked specimens and MSD specimens.

• 한국항공우주학회지
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• 제35권1호
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• pp.46-51
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• 2007

연구는 Al 2024-T3511 재료를 사용하여 피로균열성장 시험을 통한 비부식과 부식에서의 일정진폭 피로균열 전파 테이터(a-N)를 구하여 비부식과 부식에서의 균열진전의 차이를 규명하였다. 또한 비부식과 부식에서의 균열진전 속도 선도(da/dN-${\Delta}K$)를 구하여 Paris의 식을 이용하여 비부식과 부식의 차이를 규명하였다. 그리고 ${\beta}c$(corrosion factor)의 새로운 개념을 도입하여 피로수명을 예측해 본 결과 실험치를 잘 모사할 수 있었다.

• 한국자동차공학회논문집
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• 제10권1호
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2107-2119
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• 2022

Accurate remaining useful life (RUL) prediction for critical components of nuclear power equipment is an important way to realize aging management of nuclear power equipment. The electric gate valve is one of the most safety-critical and widely distributed mechanical equipment in nuclear power installations. However, the electric gate valve's extended service in nuclear installations causes aging and degradation induced by crack propagation and leakages. Hence, it is necessary to develop a robust RUL prediction method to evaluate its operating state. Although the particle filter(PF) algorithm and its variants can deal with this nonlinear problem effectively, they suffer from severe particle degeneracy and depletion, which leads to its sub-optimal performance. In this study, we combined the whale algorithm with regularized particle filtering(RPF) to rationalize the particle distribution before resampling, so as to solve the problem of particle degradation, and for valve RUL prediction. The valve's crack propagation is studied using the RPF approach, which takes the Paris Law as a condition function. The crack growth is observed and updated using the root-mean-square (RMS) signal collected from the acoustic emission sensor. At the same time, the proposed method is compared with other optimization algorithms, such as particle swarm optimization algorithm, and verified by the realistic valve aging experimental data. The conclusion shows that the proposed method can effectively predict and analyze the typical valve degradation patterns.

• 대한기계학회논문집
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• 제15권3호
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• pp.907-915
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• 1991

본 연구에서는 피로 크랙 발생 및 파단수명의 통계학적 분포특성을 명확히 하 기 위해서 단축인장을 받고, 크랙 선단 곡율반경이 일정한 중앙 크랙을 가진 81개의 시험편을 사용하여 4개의 응력 레벨하에서 피로 시험을 행한후 많은 데이터들로 부터 피로크랙의 발생, 파단특성에 대한 신뢰성 있는 통계학적 확률특성을 제시하고, 이들 데이터를 활용하여 수명예측을 행해보고저 한다.

• 국제강구조저널
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• 제18권4호
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• pp.1284-1296
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• 2018

Carbon fiber reinforced polymer (CFRP), plates bonding repair method is one of the simple repair methods for cracked steel structures. In this study, the influence of width of CFRP plates on bending fatigue life of out-of-plane gusset joint strengthened with CFRP plates was investigated from the experimental and numerical point of view. In the bending fatigue test of cracked out-of-plane gusset joint strengthened with CFRP plates, the effect of width of CFRP plates on crack growth life was clarified experimentally. Namely, it was revealed that the crack growth life becomes larger with increasing the width of CFRP plates. In the numerical approach, the stress intensity factor (SIF) at the surface point of a semi-elliptical surface crack was estimated based on the linear fracture mechanics. Furthermore, the extended fatigue life of cracked out-of-plane gusset joint strengthened with CFRP plates was evaluated by using the estimated SIF at the surface point and the empirical formula of the aspect ratio of semi-elliptical crack. As the results of numerical analysis, the estimated fatigue life of the specimen strengthened with CFRP plates showed the good agreement with the test results.