• 대한기계학회논문집
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• 제18권8호
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• pp.2139-2157
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• 1994

In order to understand the delamination between leadframe and epoxy molding compound in an electronic packaging of surface mounting type, the stress intensity factor, T-stress and J-integral in fracture mechanics are obtained. The effects of geometry, material properties and molding process temperature on the delamination are investigated taking into account the temperature dependence of the material properties, which simulates as more realistic condition. As the crack length increases the J-integral increases, which suggest that the crack propagates if it starts growing from the small size. The effects of the material properties and molding process temperature on stress intensity factor, T-stress is and J-integral are less significant than the chip size for the practical cases considered here. The T-stress is negative in all eases, which is in agreement with observation that interfacial crack is not kinked until the crack approaches the edge of the leadframe.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.170-177
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• 2003

This paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

• 한국정밀공학회지
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• 제31권9호
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• pp.777-782
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• 2014

Usually, railway axles are designed for infinite life based on endurance limit of the material and the axle is not fractured immediately when a surface crack initiated. The railway axles have been inspected regularly by NDT such as ultrasonic testing, magnetic testing and eddy current testing and so on. Because the axle failure is profoundly influenced by the probability of missing a fatigue crack during an NDT inspection, it is necessary to evaluate the Non Destructive Interval of railway axle. In the present paper, the Non Destructive Interval of railway axle based on fracture mechanics and finite element analysis was investigated. It was shown that the Non Destructive Interval of railway axle can be evaluated using fracture mechanics approach and extended using NDT which a crack can detect clearly.

• 대한조선학회논문집
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• 제39권2호
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• pp.61-68
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• 2002

K-a 관계가 동일하면, 선형파괴역학적 견지에서 균열개구 거동이 같다고 가정할 수 있다. 본 연구에서는 실제 구조물과 같은 K-a 관계를 주는 무한판 관통균열의 응력분포를 등가분포응력으로 정의한다. 실제 구조물과 동일한 K-a 관계가 구현되는 응력분포를 간단한 시험편에 작용시켜, 피로균열전파 해석을 수행하면 실제 구조요소의 피로전파수명 추정이 가능하다. 구조물에 대한 K-a 관계는 유한요소법 등의 이산화 수법 혹은 간이 추정법 등에 의하여 추정이 가능하다. 등가분포응력을 이용하여 유효 균열진전 음력을 구하는 방법의 타당성을 검토한다.

• 대한기계학회논문집A
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• 제24권9호
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• pp.2246-2251
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• 2000

Adhesive bonding repair methods has been used for a number of decades for construction of damaged structures. In order to evaluate the life of cracked aging aircraft structures, the repair technique which uses adhesively bonded boron/epoxy composite patches is being widely considered as a cost-effective and reliable method. But, this repair method contains many shortcomings. One of these shortcomings, debonding is major issue. When the adhesive shear stress increases, debonding is caused at the end of patch and plate interface. And this debonding is another defect except cracks propagation. In this paper, we assess safety at the cracked AI-plate repaired by Br/Epoxy composite patch. Firstly, from the view of fracture mechanics, reduction of stress intensity factors is determined by the variety of patch feature. Secondly, using the elastic analysis and finite element analysis, the distribution of adhesive shear stresses is acquired. Finally, The problem of how to optimize the geometric configurations of the patch has been discussed.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1571-1578
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• 2003

This paper proposes a robust method for the Ramberg-Osgood(R-O)fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

• 대한기계학회논문집A
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• 제40권8호
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• pp.693-701
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• 2016

본 논문에서는 파괴역학적 방법으로 노치 결함을 평가해 보았다. 인장 하중과 굽힘하중이 작용하는 중앙 균열, 모서리 균열 평판 구조물을 바탕으로 노치 크기를 달리하며 한계하중 및 에너지해방률을 유한요소 해석의 J-적분으로 도출하였다. 노치의 반경이 커짐에 따라 한계하중은 큰 변화가 없었으며, 에너지해방률는 커지는 양상을 보였다. 노치 반경에 따른 재료 파괴인성($J_{IC}$)측정을 위해 실험을 대신한 유한요소 연성파손 모사기법을 사용하였다. 그 결과 노치 크기 증가에 따른 에너지해방률 증가량 대비 파괴인성($J_{IC}$) 증가량이 더욱 큰 양상을 보였다. 이런 결과를 통해 노치 반경이 커질수록 균열 진전에 대한 저항성이 커진다는 사실을 알 수 있었다.

• 대한기계학회논문집A
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• 제31권12호
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• pp.1214-1220
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• 2007

The vertical roller mill, which performs the grinding and partly blending of raw material, is the one of the important machine to produce ordinary portland cement. It has been reported that an unexpected fatigue failure occurred in a table liner in the course of grinding portland cement. The life of table liner is estimated to $4{\times}10^7$ cycles in the design stage, but at the field, when its operating time reaches to $2{\times}10^6{\sim}8{\times}10^6$ cycles, the fracture of table liner begins to be found. The fracture of table liner is initiated from the outside edge of grinding path contacting with the grinding roller. Its maintenance normally take 30 % of the total maintenance costs of the roller mill. Therefore, this study shows the clarification of the reasons occurring the fatal destruction of the table liner by fatigue fracture analysis utilizing fracture mechanics and by the finite element method. And, the results from Goodman diagram illustrate relationship of including information on the transition between tensile and bending fatigue strength in the fatigue characterization of table liner.

• Computers and Concrete
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• 제4권3호
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• pp.221-241
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• 2007

Based on the experiment results, the damage and fracture behavior of concrete at the ages of 1d, 2d, 7d and 28d, in three-point bending and uniaxial tensile tests, were simulated with a finite element program, ABAQUS. The critical stress intensity factor $K_{IC}^s$ and the critical crack tip opening displacement ($CTOD_C$) of concrete were calculated with effective-elastic crack approach for the three-point bending test of grade C30 concrete. Based on the crack band model, a bilinear strain-softening curve was derived to simulate the LOAD-CMOD curves and LOAD-Displacement curves. In numerical analysis of the uniaxial tension test of concrete of grade C40, the damage and fracture mechanics were combined. The smeared cracking model coupling with damaged variable was adopted to evaluate the onset and development of microcracking of uniaxial tensile specimen. The uniaxial tension test was simulated by invoking the damage plastic model which took both damage and plasticity as inner variables with user subroutines. All the numerical simulated results show good agreement with the experimental results.

• 터널과지하공간
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• 제12권4호
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• pp.304-311
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• 2002

절리의 기하학적 특성이 절리의 수직변형 및 투수성에 미치는 영향에 대해 수치해석적 방법을 통해 연구하였다. 실험적 계측 결과에 의하면, 절리의 간극은 통계적 방법에 의해 묘사되며 이에 근거하여 수치해석에 사용할 수 있는 절리를 모사할 수 있었다. 이를 위해. 자동 상관관계 함수를 이용하여 다양한 공간 상관길이의 인공 절리를 발생하였으며, 이를 토대로 수직변천 모델 및 수리해석 모델을 개발하였다. 수직변형 모델은 수직응력에 의한 절리면의 압축과 변형을 고려하여 절리의 변형거동을 해석하려 시도하였으며, cubic law에 근거한 유한차분법을 이용하여 수리해석을 수행하였다. 여러 가지 공간 상관길이의 인공 절리에 대한 수직변형 거동 및 이에 따른 수리해석의 결과, 간극의 공간 상관길이가 증가함에 따라 절리의 수직변형 및 투수성 감소가 분명하였다. 절리의 수직강성 역시 간극의 상관길이에 영향을 받는 것으로 나타났으며, 이로 인해 절리의 투수성이 수직강성과 내재적 관계가 있음을 유추할 수 있겠다. 본 연구 결과는 공학적 프로젝트로 인한 절리 암반의 수리-역학적 거동을 이해하는데 공헌할 것으로 사료된다.