• 터널과지하공간
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• 제19권2호
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• pp.86-94
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• 2009

암석파괴역학과 파괴인성(rock fracture toughness) 이하의 응력확대계수(stress intensity factor)에서 균열이 성장하는 현상을 이용하여 암석 절리면의 비선형 강도특성과, 시간의 경과에 따라 파괴가 진행되는 특성을 고려한 수치해석용 3차원 절리면 요소를 개발하였다. 이 절리면 요소를 사용하여 암석 절리면 전단시험을 수치해석으로 모사한 결과, 전단응력이 증가하고 시간이 경과함에 따라 절리면 사이에 연결된 절리면 내 접점(asperity in joint)에서 암석의 파괴인성보다 응력확대계수가 작음에도 불구하고 균열이 발생하였고 시간이 경과하면서 균열이 성장, 절리면 내 접점이 파괴되었다. 이와 같이 각각의 절리면 내 접점의 파괴에 따라 절리면의 강도는 감소하고, 절리면의 전단응력은 응력경화와 응력연화 후 잔류응력에 도달하는 비선형거동을 보이면서 시간의 경과에 따라 점진적으로 파괴되었다.

• 한국해양공학회지
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• 제7권2호
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• pp.19-29
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• 1993

The static tensile tests of GFRP, ID300, CFRID300 and CFRPEEK were made on the plain and notched specimens at room temperature. The results were discussed based on linear notch mechanics which was proposed by H.Nistani. The fracture of notched GFRP, ID300, CFRID300 and CFRPEEK specimens is controlled by the elastic maximum stress, $({\sigma}_max)$, and the notch root racius,$\rho$, alone, independently of the other geometrical conditions. The relation between fracture nominal stress,$({\sigma}_max)$, and stress concentration factor, $K_t$ and a part where $({\sigma}_c)$ is nearly constant independent of $K_t$. A similar phenomenon can be seen in the fatigue tests of notched specimes under rotating bending or push-pull. The almost constant $({\sigma}_c)$ values correspond to the nearly constant apparent stress intensity factor, $K_{1pc}$ values, obtained by assuming ,$\rho$=0. This can be attributed to the existence of the stable crack. Linear notch mechanics is very useful for analyzing the static tensile fracture behavior of notched GFRP, ID300, CFRPEEK specimens.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.298-303
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• 2001

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for a compact tension specimen in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives very much. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• Structural Engineering and Mechanics
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• 제18권5호
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• pp.691-707
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• 2004

This paper presents the micro-mechanical modeling for predicting concrete behavior under compressive loading. The model is able to represent the heterogeneities in the microstructure up to three phases, i.e., aggregate particles, matrix and interfaces. The smeared crack concept based on non-linear fracture mechanics is implemented in order to formulate the constitutive relation for each component. The splitting tensile strength is considered as a fracture criterion for cracking in micro-level. The finite element method is employed to simulate the model based on plane stress condition by using quadratic triangular elements. The validation of the model is verified by comparing with the experimental results. The influence of tensile strength from both aggregate and matrix phases on the concrete compressive strength is demonstrated. In addition, a guideline on selecting appropriate tensile strength for each phase to obtain specified concrete compressive strength is also presented.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.141-149
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• 2002

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization for three types of specimens, which are very typical ones in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was concluded that shapes of three types of specimens optimized by the growth-strain method prolong their fatigue lives very much.

• Steel and Composite Structures
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• 제23권3호
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• pp.263-271
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• 2017

A theoretical study was carried-out of mode II delamination fracture behavior of the End Loaded Split (ELS) functionally graded beam configuration with considering the material non-linearity. The mechanical response of ELS was modeled analytically by using a power-law stress-strain relation. It was assumed that the material is functionally graded transversally to the beam. The non-linear fracture was investigated by using the J-integral approach. Equations were derived for the crack arm curvature and zero axes coordinate that are needed for the J-integral solution. The analysis developed is valid for a delamination crack located arbitrary along the beam height. The J-integral solution was verified by analyzing the strain energy release rate with considering material non-linearity. The effects of material gradient, non-linear material behavior and crack location on the fracture were evaluated. The solution derived is suitable for parametric analyses of non-linear fracture. The results obtained can be used for optimization of functionally graded beams with respect to their mode II fracture performance. Also, such simplified analytical models contribute for the understanding of delamination fracture in functionally graded beams exhibiting material non-linearity.

• 콘크리트학회지
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• 제2권2호
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• pp.81-92
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• 1990

콘크리트는 혼합물로서 비균질성, 이방성 및 비선형성 재료이기 때문에 그의 파괴해석에 있어서 재래의 강도 개념보다 파괴역학 개념을 적용하여 콘크리트의 파괴인성을 도입하여 평가하는 것이 보다 합리적이라 할 수 있다. 지금까지 콘크리트에 적용되어 온 파괴역학 개념은 두가지로 대별될 수 있는데 하나는 선형탄성파괴역학 개념이고 다른 하나는 비선형파괴역학 개념이다. 그러너 전자를 콘크리트에 적용하는데는 문제점과 불합리성이 지적되어 왔다. 본 연구에서는 비선형파괴역학에서 많이 이용되어온 J-적분법과 COD법을 도입하여 굵은골재의 최대치수와 노치깊이의 변화가 콘크리트의 파괴거동, 파괴에너지 및 균열성장에 미치는 영향, 균열개구변위와 파괴에너지의 관계 등을 고찰하기 위하여 콘크리트 작사각형 보를 제작하여 3점 휨 파괴실험을 수행하였다. 그 결과 굵은골재의 최대치수와 노치깊이가 증가할수록 하중-치 짐거동의 비선형성이 더욱 두드러졌고, 굵은골재 최대치수의 증가는 콘크리트의 연성을 증가시켜 보다 안정된 파괴를 유도하였으며, 균열전파경로는 굵은골재의 최대치수가 증가할수록 점점 더 직선에서 벗어나 불규칙적이었으나 노치깊이의 변화에는 거의 영향을 받지 않았다. 또한 파괴에너지는 굵은골재의 최대치수가 증가하고 노치깊이가 감소할수록 증가하였으나, 균열개구변위는 노치깊이가 증가할수록 감소하였으며 굵은골재의 최대치수의 변화에는 거의 영향을 받지 않았다.

• Computers and Concrete
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• 제27권1호
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• pp.55-62
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• 2021

The concrete fatigue analysis can be performed with the use of fracture mechanics. The fracture mechanics defines the fatigue crack propagation as the relationship of crack growth rate and stress intensity factor. In contrast to metal, the application of fracture mechanics to concrete is more complicated and therefore many authors have introduced empirical expressions using Paris law. The topic of this paper is development of a new prediction of fatigue crack propagation for concrete using rheological-dynamical analogy (RDA) and finite element method (FEM) in the frame of linear elastic fracture mechanics (LEFM). The static and cyclic fatigue three-point bending tests on notched beams are considered. Verification of the proposed approach was performed on the test results taken from the literature. The comparison between the theoretical model and experimental results indicates that the model proposed in this paper is valid to predict the crack propagation in flexural fatigue of concrete.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1995년도 가을 학술발표회 논문집
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• pp.171-177
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• 1995

Fracture mechanics does work for concrete, provided that one uses a proper, nonlinear form of fracture mechanics in which a finite nonlinear zone at fracture front is being considered. The fracture process zone is a region ahead of a traction-free crack, and the development of model of fracture process zone is most important to describe fracture phenomena in concrete. This paper is about fracture behavior of concrete cylinder under lateral pressure. Concrete cylinders were made of high strength normal connote, steel fiber reinforced concrete and steel fiber reinforced polymer-impregnated concrete and concrete and the fracture behavior such as cracking propagation and ultimate load are observed. The fracture process zone is modelled by a Dugdale-Barenblatt type model with linear tension-softening curve and are implemented to the boundary element technique for the fracture analyses of the cylinders. The experimental results are compared with analysis results and tension-softening curves for the steel fiber reinforced concrete and steel fiber reinforced polymer-impregnated concrete are obtained by back analyses.

• Structural Engineering and Mechanics
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• 제54권6호
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• pp.1201-1216
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• 2015

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-${\delta}$ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.