• 전산구조공학
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• 제9권4호
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• pp.173-179
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• 1996

용접구조물의 파괴거동을 분석하기 위해서는 용접중의 열전달 해석, 잔류응력 해석, 그리고 파괴해석이 같이 병행되어야 한다. 잔류응력이 존재하면 J-적분은 적분 경로에 관계없이 일정한 값을 갖는 특성을 잃게 된다. 그러므로 용접부의 J-적분 해석을 위해서는 별도의 프로그램을 개발하여야 한다. 본 연구에서는 균열선단에서의 J-적분을 계산하기 위한 이론식 및 프로그램을 개발하였으며 적용사례로 박판 및 후판의 다층용접에 대한 J-적분값을 계산하였다.

• Fibers and Polymers
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• 제5권4호
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• pp.259-263
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• 2004

Rubber-modified epoxy resins have been employed as adhesive and matrix materials for glass and corbon-fiber composites. The behavior of fracture around a crack tip for rubber-modified epoxy resin is investigated through the acoustic emission (AE) analysis of compact tension specimens. Damage zone and rubber particles distributed around a crack tip were observed by a polarized optical microscope and an atomic force microscope (AFM). The damage zone in front of pre-crack tip in rubber-modified specimen $(15wt\%\; rubber)$ began to form at about $13\%$ level of the fracture load and grew in size until $57\%$ load level. After that, the crack propagated in a stick-slip manner. Based on time-frequency analysis of AE signals and microscopic observation of damage zone, it was thought that AE signals with frequency bands of 0.15-0.20 MHz and 0.20­0.30 MHz were generated from cavitation in the damage zone and crack propagation, respectively.

• Computers and Concrete
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• 제17권4호
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• pp.553-566
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• 2016

Fracture energy is one of the key parameters reveal cracking resistance and fracture toughness of concrete. The main purpose of this study is to determine fracture behavior, mechanical properties and microstructural analysis of high strength basalt fiber reinforced concrete (HSFRC). For this purpose, three-point bending tests were performed on notched beams produced using HSFRCs with 12 mm and 24mm fiber length and 1, 2 and $3kg/m^3$ fiber content in order to determine the value of fracture energy. Fracture energies of the notched beam specimens were calculated by analyzing load versus crack mouth opining displacement curves by the help of RILEM proposal. The results show that the effects of basalt fiber content and fiber length on fracture energy are very significant. The splitting tensile and flexural strength of HSFRC increased with increasing fiber content whereas a slight drop in flexural strength was observed for the mixture with 24mm fiber length and $3kg/m^3$ fiber content. On the other hand, there was no significant effect of fiber addition on the compressive strength and modulus of elasticity of the mixtures. In addition, microstructural analysis of the three components; cement paste, aggregate and basalt fiber were performed based on the Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy examinations.

• Structural Engineering and Mechanics
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• 제64권1호
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• pp.59-69
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• 2017

The field of fracture mechanics has gained significance because of its ability to address the behaviour of cracks. Predicting the fracture properties of concrete based on experimental investigations is a challenge considering the quasi-brittle nature of concrete. So, there is a need for developing a standard numerical tool which predicts the fracture energy of concrete which is at par with experimental results. The present study is an attempt to evaluate the fracture energy and characteristic length for different grades of concrete using Concrete Damage Plasticity (CDP) model. Indian Standard and EUROCODE are used for the basic input parameters of concrete. Numerical evaluation is done using Finite Element Analysis Software ABAQUS/CAE. Hsu & Hsu and Saenz stress-strain models are adopted for the current study. Mesh sensitivity analysis is also carried to study the influence of type and size of elements on the overall accuracy of the solution. Different input parameters like dilatation angle, eccentricity are varied and their effect on fracture properties is addressed. The results indicated that the fracture properties of concrete for various grades can be accurately predicted without laboratory tests using CDP model.

• 콘크리트학회논문집
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• 제12권1호
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• pp.3-12
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• 2000

A fracture energy concept proposed by Ouyang and Shah's fracture mechanics approach was used to predict cracking of reinforced concrete members subjected to tension. In this approach, fracture properties in plain concrete which incorporate the presence of the fracture process zone are first determined from the generalized size effect method, then fracture energy required for crack propagation with the same dimension and material properties are evaluated using an R-curve. Subsequently taking into account the material properties in Ouyang and Shah's approach, a theoretical analysis to predict the mechanical behavior of reinforced concrete members subjected to tension was performed and compared to observed experimental results. It is seen that the predicted average crack spacing curves agree well with the experimental results, whereas the analytical method seems to predict lower values for this study. The analytical approach predicts well responses of stress-strain curves before and after the first crack is formed. It is concluded from this study that a fracture energy concept based on the R-curve and the generalized size effect method is a rational approach to predict cracking of reinforced concrete members subjected to tension.

• 국제강구조저널
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• 제18권5호
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• pp.1784-1800
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• 2018

Tension-shear loading is a common loading condition in steel structures during the earthquake shaking. To study ductile fracture in structural steel under multiple stress states, experimental investigations on the different fracture mechanisms in Chinese Q235 steel were conducted. Different tension-shear loading conditions achieved by using six groups of inclined notch butterfly configurations covering pure shear, tension-shear and pure tension cases. Numerical simulations were carried out for all the specimens to determine the stress and strain fields within the critical sections. Two tension-shear fracture models were calibrated based on the hybrid experimental-numerical procedure. The equivalent fracture strain obtained from the round bar under tensile loading was used for evaluating these two models. The results indicated that the tension-shear criterion as a function of the shear fracture parameter had better performance in predicting the fracture initiation of structural steel under different loading conditions.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.213-219
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• 2006

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.

• 대한토목학회논문집
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• 제4권4호
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• pp.1-11
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• 1984

콘크리트의 복잡한 파괴거동(破壞擧動)을 모델할 수 있는 비선형파괴이론(非線型破壞理論)이 본(本) 논문(論文)에서 유도되었다. 본(本) 이론(理論)은 콘크리트균열끝의 파괴진행대(破壞進行帶)에서의 미세균열현상(微細龜裂現象)과 변형연화현상(變形軟化現象)으로 인한 비선형거동(非線型擧動)에 그 근거(根據)를 두고 있다. 이로부터 실제적이고도 단순화(單純化)된 파괴해석(破壞解析)모델이 유도되었으며, 이 단순화된 모델은 파괴진행대(破壞進行帶)의 변화에도 콘크리트의 파괴(破壞)에너지를 일정하게 유지할 수 있는 특정을 가지고 있다. 파괴해석(破壞解析)에 비선형응력(非線型應力)-변형거동(變形擧動)을 이용함으로써 균열면에 평행하게 작용하는 압축응력에 대한 영향이 쉽게 고려될 수 있다. 본 모델을 콘크리트의 많은 파괴실험자료와 비교한 결과 만족스러운 결과를 얻었으며, 종래의 선형파괴이론에 의한 결과는 실제 콘크리트 실험결과와 많은 차이를 보이고 있음을 알 수 있다. 콘크리트 구조의 균열 및 파괴해석에 필요한 콘크리트 파괴에너지의 근사공식이 본 이론으로부터 유도되었다. 끝으로, 철근콘크리트에 대한 파괴이론의 응용 및 확장연구 문제가 토의되었다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제9권1호
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• pp.79-86
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• 2004

암석 내 균열을 따른 수리전도도는 균열의 기하학적 요소, 즉 방향, 간극, 거칠기 그리고 상호 연결도에 주로 좌우된다. 따라서, 균열 내 투수계수를 정확하게 계산하기 위해서는 이와 같은 기하 요소들을 최대한 계산모델에 반영할 필요가 있다. 이 연구에서는 균열 기하양상을 최대한 정확히 반영한 균열모델에서 기존 수치해석과는 다른 새로운 방법인 균질화 해석법(homogenization analysis method)을 이용하여 균열을 따른 투수계수를 구하기 위해 수치해석을 수행하였다. 먼저, 공초점 레이저 스캔 현미경(Confocal Laser Scanning Microscope)을 이용하여 암석시료의 균열 조도와 균열에 가한 수직압축력의 변화에 따른 간극 변화량을 직접 측정하고, 이와 같이 획득한 자료는 균열모델 재현을 위한 입력자료로 사용되었다. 재현된 균열모델을 토대로 한 균질화 해석법은 미시규모(microscale) 매질특성과 거시규모(macroscale) 매질특성을 동시에 고려하여 투수계수를 계산할 수 있는 것이다. 즉, 균질화 해석법은 주기적 미세구조(microstructure)를 갖는 미소 불균질 물질의 거동특성을 구명하기 위해 개발된 새로운 형태의 섭동(perturbation) 이론이다. 이는 균질한 미시규모에서 미시 투수특성을 계산한 후, 거시규모에서의 균질화 투수계수를 계산하게 된다. 그러므로, 이 방법은 균열 기하양상의 국부적 영향을 고려한 투수특성을 정확히 해석할 수 있다. 균질화법을 이용한 투수계수 산정결과를 기존 연구에서 제안한 경험식과 비교하여 그 타당성을 검증하기 위해 전술한 2차원 균열모델을 이용한 투수계수 계산을 수행하였다. 균열모델은 거칠기(roughness)를 반영하고 동일한 간극을 할당한 평행판 모델을 가정하였다. 계산결과에 의하면, 균질화 해석법에 의해 계산한 C-투수계수는 실내투수시험에 의해 구한 투수계수와 같은 범위의 값을 가지거나 $10^1$ 정도의 차이를 보여, 그 계산결과는 타당하다고 볼 수 있다. 그러나, 균질화 해석법은 국부적으로 불균질한 균열 기하양상과 물질특성이 미시규모와 거시규모에서 모두 고려되므로, 이들 특성을 정확히 알고 있을 경우 기존에 제안된 경험식들에 의한 계산결과 보다 균질화 해석법의 결과가 훨씬 정확함을 주목하여야 한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.40-44
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• 1999

A finite element analysis has been performed to investigate the effect of die clearance on shear planes in the fine blanking of a part of automobile safety belt. For the analysis S45$^{\circ}C$ is selected as an material which is used in manufacturing the part of automobile safety belt and Cockcroft-Latham fracture criterion is applied, Effect of die clearance on die-roll width die-roll depth burnish zone and fracture zone has been concentrately investigated in the finite element analysis. From the analytical results it has been found that die-roll width and depth of the shear plane increase with increasing die clearance. And the burnish zone has been concentrately investigated in the finite element analysis. From the analytical results it has been found that die-roll width and depth of the shear plane increase with increasing die clearance. and the burnish zone decreases with increasing die clearance but the variation of fracture zone is opposite to that of burnish zone because the increase in die clearance requires less fracture energy Theoretical predictions are compared with experimental results, There is a good agreement between theory and experiment