• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.121-126
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• 2008

A plane strain problem of a crack on interface between an isotropic elastic conductor and a transversely isotropic piezoelectric ceramics is considered. The problem is reduced to system integrodifferential equations on the interface. These equations relate the normal and tangential components of the crack opening vector with distribution of normal and shear stresses on the crack surfaces. It therefore make it possible to obtain an exact solution as a function of the loading applied to the crack surfaces. As an example, some analytical solutions of the crack problem are given.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2003년도 추계학술대회 논문집(III)
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• pp.79-84
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• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.

• 터널과지하공간
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• 제9권4호
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• pp.364-372
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• 1999

우리나라의 대표적인 암석의 하나인 화강암에 대하여 내부결합에 의한 역학적 특성을 고찰하였다. 조사선(scanline)을 이용하여 암석 내에 존재하는 불연속면의 간격과 길이를 펑가하였다. 화강암에 잠재적으로 존재하는 미소균열의 선택적 배향성과 분포성상을 관찰하기 위해서 암석시펀을 Rift, Grain및 Hardway축의 3방향으로 구분하여 각각의 박편을 제작하여 균열밀도와 균열길이를 정량적으로 평가하였다. 그 결과 균열은 결의 세 방향에 대하여 직교하는 경향이었다. 균열 밀도는 방향에 따라 달랐으나 길이는 큰 영향이 없었다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.335-342
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• 2001

In this paper, an improved Element-Free Galerkin (EFG) method is proposed by adding enrichment function to the standard EFG approximation and a discontinuity function is implemented in constructing the shape function across the crack surface. In this method, the singularity and the discontinuity of the crack are efficiently modeled by using initial node distribution to evaluate reliable stress intensity factor, though the standard EFG method requires placing additional nodes near the crack tip. The proposed method enables the initial node distribution to be kept without any additional nodal d.o.f. and expresses the asymptotic stress field near the crack tip successfully. Numerical example verifies the improvement and the effectiveness of the method.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.281-286
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• 1999

Nonlinear temperature distribution induced by the hydration heat generates thermal stress in mass concrete. At early ages, such thermal stress may induce thermal cracks in the structure which can affect on the durability and safety of the structure. Up to now, a lot of works have focused on the prediction of temperature distribution and thermal stress in the structure. In most of such works, however, the inside of structure was considered as adiabatic state to predict temperature distribution and the thermal stress. And due to the lacks of appropriate analysis models after crack, there was little research on the crack occurrence. This paper deals with the prediction of the temperature distribution in the structure using the rate of hydration heat generation and also estimates the behavior of structure before and after cracking due to hydration heat using crack band model.

• 한국세라믹학회지
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• 제31권12호
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• pp.1449-1458
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• 1994

A new analytical model which can discribe the relationship between the bridging stress and the crack opening displacement was proposed to investigate the microstructural effect on the R-curve behavior in a polycrystalline alumina. The crack opening displacement according to the distance behind the stationary crack tip was measured using in-situ fracture technique in an SEM, and then used for a fitting procedure to obtain the distribution of bridging stress. The current model and an empirical power law relation were introduced into the fitting procedure. The results indicated that the bridging stress function and R-curve computed by the current model were consistent with those computed by the power law relation. The microstructural factor, e.g., the distribution of grain size, was also found to be closely related to the bridging stress. Thus, this model explained well the interaction effect between the distribution of bridging stress and the local-fracture-controlling microstructure, providing important information for the systematic interpretation of microfracture mechanism including R-curve behavior of a monolithic alumina.

• 수산해양기술연구
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• 제29권2호
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• pp.152-161
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• 1993

This paper deals with the effect of spatial distribution of material properties on its statistical characteristics and numerical estimation method of reliability of fatigue sensitive structures with respect to the fatigue crack growth. A method is proposed to determine experimentally the probability distribution functions of material parameters of Paris law. da/dN=C(ΔK/K sub(0) ) super(m), using stress intensity factor controlled fatigue tests. The result with a high tensile strength steel shows that the distribution of the parameter m is approximately normal and that of 1/C, is a 3-parameter Weibull. The main result obtained are : (1) The theoretical autocorrelation of the resistance, 1/C, to fatigue crack growth are almost same for different lengths. (2) The variance decreases with the increasing a averaging length. When spatial correlation length is very small. the variane decreases significantly were the averaging length. (3) The probability distribution of load cycles or the number for a crack to reach a certain length can be estimated using these functions by simulation of non-Gaussian(expecially Weibull) Stochastic Process.

• KCI Concrete Journal
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• 제12권1호
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• pp.131-138
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• 2000

The research purpose of this paper is to investigate the influential Parameters on the unbonded tendon stress. The parameters were the reinforcing ratio, the prestressing ratio, and the loading type. To this end. first, the influence of parameters were examined with twenty eight test results obtained from references. Then, an experimental study was carried out with nine specimens. Test variables were the reinforcing ratio and the prestressing ratio. Specimens were divided equally into three groups and each group had a different level of the reinforcing ratio. Each specimen within a group has a different level of the prestressing ratio. The investigation with previous and current tests revealed the followings; (1) the length of crack distribution zone does not have a close relation with the length of plastic hinge. (2) the prestressing ratio does not affect both the length of crack distribution and the length of plastic hinge, (3) the tendon stress variation is in reverse relation with the ratios of mild steels and tendons, (4) the loading type nay not affect significantly the length of crack distribution zone, (5) AASHTO LRFD Code equation and Moon/Lim's design equation predicted the test results well with some safety margins.

• Structural Engineering and Mechanics
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• 제23권3호
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• pp.217-232
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• 2006

A crack model for the fracture in concrete based on meshless method is proposed in this paper. The cracks in concrete are classified into micro-cracks or macro-cracks respectively according to their widths, and different numerical approaches are adopted for them. The micro-cracks are represented with smeared crack approach whilst the macro-cracks are represented with discrete cracks that are made up with additional nodes and boundaries. The widely used meshless method, Element-free Galerkin method, is adopted instead of finite element method to model the concrete, so that the discrete crack approach is easier to be implemented with the convenience of arranging node distribution in the meshless method. Rotating-Crack-Model is proved to be preferred over Fixed-Crack-Model for the smeared cracks of this composite crack model due to its better performance on mesh bias. Numerical examples show that this composite crack model can take advantage of the positive characteristics in the smeared and discrete approaches, and overcome some of their disadvantages.

• 대한금속재료학회지
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• 제48권9호
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• pp.791-797
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• 2010

The creep crack growth rate (da/dt) of the Cr-Mo steels tested by pre-crack and the voltage (or resistance) variables were related into fracture parameter (Ct), crack growth coefficient (H), and an exponent (q) in the parts of Base, weld and HAZ. The fracture parameter (Ct) has various variables relating to the specimen and crack shape, applied stress, and creep strain curve. The H and q was inferred by OLS regression (ordinary least square method), and the H values were solved in statistics and probability assessment, which were attained fromPDF's distributions (probability density function). The HAZ part has the highest value of q by OLS regression and the widest distribution of H by PDF of WEIBULL, which means that the crack sensitivity of HAZ should be cautioned against the creep crack growth and failure.