• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.930-932
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• 2017

본 논문은 모드 I 하중하에서 곡률이 있는 복합재 적층판의 점진적 층간파손 예측에 대해 서술하였다. 곡률을 갖는 복합재 적층판의 층간파손 예측은 ABAQUS V6.13의 응집영역모델을 사용하여 수행하였다. 응집영역모델의 입력값인 층간파괴인성치는 모드 I, 모드 II, 그리고 혼합모드에 대한 층간파괴인성 시험을 통해 도출하였다. 곡률을 갖는 복합재 적층판의 점진적 층간파손 거동은, 시험과 수치해석결과가 잘 일치하는 것을 확인하였다.

• Structural Engineering and Mechanics
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• 제11권6호
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• pp.591-604
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• 2001

In this paper, a finite element with embedded displacement discontinuity which eliminates the need for remeshing of elements in the discrete crack approach is applied for the progressive fracture analysis of concrete structures. A finite element formulation is implemented with the extension of the principle of virtual work to a continuum which contains internal displacement discontinuity. By introducing a discontinuous displacement shape function into the finite element formulation, the displacement discontinuity is obtained within an element. By applying either a nonlinear or an idealized linear softening curve representing the fracture process zone (FPZ) of concrete as a constitutive equation to the displacement discontinuity, progressive fracture analysis of concrete structures is performed. In this analysis, localized progressive fracture simultaneous with crack closure in concrete structures under mixed mode loading is simulated by adopting the unloading path in the softening curve. Several examples demonstrate the capability of the analytical technique for the progressive fracture analysis of concrete structures.

• 콘크리트학회지
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• 제9권4호
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• pp.187-196
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• 1997

시멘트를 기초로하는 복합재료의 파괴거동은 주균열이 진행하기 이전에 파괴진행영역이라고 하는 미세균열대가 콘크리트 내부에 형성고기 때문에 선형파괴역하게 입각하여 해석하게 되면 실험치와 상당한 차이를 나타낸다. 이러한 문제점을 해결하기 위해 가상균열모델이나 균열띠 모델, 두 파라메터 파괴모델 등 비선형해석에 따른 여러 파괴역학모델들이 제안되었으나 이들 모델들은 2차원 해석에 근거를 두고 있기 때문에 구조체의 두께 방향으로 동일한 균열이 형성되며, 특히 콘크리트 실험에서 관찰되는 비연속적 균열발생에 대해서 설며이 어려웠다. 이에 본 연구는 콘크리트를하나의 다종복합체로 가정하고 연립변형모드 및 진행파괴모드 방향으로 구성재료를 배열한 상태에서 가상균열 이론에 근거한 비선형해석방법으로 모델링하였다. 진행파괴모드로 구성재료를 배열하면 강성이 높은 구성재료를 통과하여 균열이 진행될 때 균열선단으로부터 분포된 응력이 상층의 허용인장강도를 초과하게 되어 균열이 발생되며 이러한 균열은점진적인 균열진행과는 달리 비연속 동시 발생 균열ㄹ로 나타났다. 본 연구는 진행파괴모드에서의 파괴 해석 방법과연립변형모드에서의 해석 방법을 제시하였으며, 해석결과를 실험결과와 비교함으로써 검증하였다.

• Geomechanics and Engineering
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• 제12권6호
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• pp.919-933
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• 2017

A series of Brazilian tests under diameter compression for disc specimens was carried out to investigate the strength and failure behavior by using acoustic emission (AE) and photography monitoring technique. On the basis of experimental results, load-displacement curves, AE counts, real-time crack evolution process, failure modes and strength property of granite specimens containing two pre-existing holes were analyzed in detail. Two typical types of load-displacement curves are identified, i.e., sudden instability (type I) and progressive failure (type II). In accordance with the two types of load-displacement curves, the AE events also have different responses. The present experiments on disc specimens containing two pre-existing holes under Brazilian test reveal four distinct failure modes, including diametrical splitting failure mode (mode I), one crack coalescence failure mode (mode II), two crack coalescences failure mode (mode III) and no crack coalescence failure mode (mode IV). Compared with intact granite specimen, the disc specimen containing two holes fails with lower strength, which is closely related to the bridge angle. The failure strength of pre-holed specimen first decreases and then increases with the bridge angle. Finally, a preliminary interpretation was proposed to explain the strength evolution law of granite specimen containing two holes based on the microscopic observation of fracture plane.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.233-238
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• 1999

Localized failure analysis of concrete structures can be carried out effectively by modeling fracture process zone of concrete during crack initiation and propagation. But, the analysis techniques are still insufficient for crack modeling because of difficulties in numerical analysis procedure which describe progressive crack. In this paper, a finite element with embedded displacement discontinuity is introduced to remove the difficulties of remeshing for crack propagation in discrete crack model during progressive failure analysis of concrete structures. The performance of this so-called embedded crack approach for concrete failure analysis is verified by several analysis examples. The analysis results show that the embedded crack approach retains mesh size objectivity and can simulate localized failure under mixed mode loading. It can be concluded that the embedded crack approach cab be an effective alternate to the smeared and discrete crack approaches.

• 콘크리트학회논문집
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• 제17권6호
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• pp.1053-1064
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• 2005

The mechanical damage of concrete is normally attributed to the formation of microcracks and their propagation and coalescence into macroscopic cracks. This physical degradation is caused from progressive and hierarchical damage of the microstructure due to debonding and slip along bimaterial interfaces at the mesoscale. Their growth and coalescence leads to initiation of hairline discrete cracks at the mesoscale. Eventually, single or multiple major discrete cracks develop at the macroscale. In this paper, from this conceptual model of mechanical damage in concrete, the computational efforts were made in order to characterize physical cracks and how to quantify the damage of concrete materials within the laws of thermodynamics with the aid of interface element in traditional finite element methodology. One dimensional effective traction/jump constitutive interface law is introduced in order to accommodate the normal opening and tangential slips on the interfaces between different materials(adhesion) or similar materials(cohesion) in two and three dimensional problems. Mode I failure and mixed mode failure of various geometries and boundary conditions are discussed in the sense of crack propagation and their spent of fracture energy under monotonic displacement control.

• 콘크리트학회지
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• 제11권1호
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• pp.119-127
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• 1999

본 연구는 시멘트를 기초로 하는 준 취성재료를 2개 결합시킨 복합구조체의 파괴거동을 시뮬레이션 하는 데 그 목적이 있다. 이를 위해 작용하중방향에 직각으로 콘크리트와 시멘트를 적층하여 시편을 제작하였고, 비선형파괴해석에서 사용되는 각 구성재료별 파괴계수들을 구하기 위해 콘크리트와 시멘트 각각에 대해 3점휨시험 및 간접인장강도시험을 실시하였다. 시험을 통해 산정한 계수들을 도출한 이론식에 적용하여 복합체로 제작한 시편의 실험 결과치와 비교한 결과, 가상균열이론에 입각한 이론치와 실험결과치는 거의 유사한 경향을 나타내었다. 또한, 파괴에너지와 강도의 향상은 복합체를 구성하는 구성재료의 적층순서에 크게 의존하는 것으로 나타났다. 따라서 구조물의 목적에 맞게 복합체를 적절히 배열하므로써 구조물의 취성과 연성을 상승시킬 수 있음을 본 연구를 통해 알 수 있었다.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1265-1272
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• 2014

본 논문에서는 CZM(Cohesive Zone Model)을 이용하여 돔 분리형 복합재 압력용기 접착 체결부의 점진적 파손 해석에 대한 연구를 수행하였다. 접착 요소(cohesive element)의 물성을 도출하기 위해 모드I, II 그리고 혼합모드에 대한 층간파괴인성들을 시험을 통해 도출하였다. 이때, 모든 시험편은 복합재 압력용기와 동일한 필라멘트 와인딩 제작공정을 통해 제작되었다. 이중 겹치기 이음(double-lap joint) 시험은 접착제의 전단강도와 CZM을 이용한 점진적 파손해석의 신뢰도 검증을 위해 수행하였다. 그 결과, 접착제의 전단강도는 시험으로부터 32MPa을 얻었고, 시험과 해석의 오차는 약 4.4%의 오차가 발생하여 CZM이 접착 체결부의 점진적 파손 거동을 비교적 잘 모사함을 확인하였다. 최종적으로 신뢰성이 검증된 CZM을 복합재 압력용기 접착 체결부에 적용하여 운용하중조건에서의 점진적 파손해석을 수행한 결과, 전체 200mm를 갖는 접착 체결부 길이의 약 5.8%만이 점진적 파손이 발생하는 것으로 나타나 복합재 압력용기의 구조 안전성에는 영향을 주지 않음을 확인하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.389-392
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• 1999

Fatigue is a process of progressive permanent internal structural change in a material subjected to repeitive stresses. These change may be damaging and result in progressive growth of cracks and complete fracture if the stress repetitins are sufficiently large. For structural members subjected to cyclic loads, the continuous and irrecoverable damage processes are taking place. These processes are referred as the cumulative damage processes due to fatigue loading. Moreover, increased use of high strength concrete makes the fatigue problem more important because the cross-section and dead weight are reduced by using high strength concrete. The purpose of this study is to investigate the shear fatigue behavior of reinforced concrete beams according to shear reinforcement ratio and concrete compressive strength under repeated loadings. For this purpose, comprehensive static and fatigue tests of reinforced concrete beams were conducted. The major test variables for the fatigue teats are the concrete strength and the amount of shear reinforcements. The increase of deflections and steel strains according to load repetition has been plotted and analyzed to explore the damage accumulation phenomena of reinforced concrete beams. An analytical model for shear fatigue behavior has been introduced to analyze the damage accumulation under fatigue loads. The failure mode and fatigue lives have been also studied in the present study. The comparisons between analytical results and experimental data show good correlation.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1231-1235
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• 2010

The tensile failure behavior of polymer matrix composite materials was investigated with the aid of a nondestructive evaluation (NDE) technique. The materials, E-glass fiber reinforced epoxy matrix composites, which are applicable to carbody materials in railway vehicles to reduce weight, were used for this investigation. In order to explain stress-strain behavior of polymer matrix composite sample, the infrared thermography technique was employed. A high-speed infrared (IR) camera was used for in-situ monitoring of progressive damages of polymer matrix composite samples during tensile testing. In this investigation, the IR thermography technique was used to facilitate a better understanding of damage evolution, fracture mechanism, and failure mode of polymer matrix composite materials during monotonic loadings.