• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.399-405
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• 2008

콘크리트 슬래브 표면의 영상처리 목적은 구조물의 균열발생을 최소화하고 발생한 균열에 대해서 지속적인 기록 관리로 균열의 진행 상태를 분석하여 보수시기 및 보수공법 적용의 합리적 운영체계를 수립하고자 하는 것이다. 일반적으로 콘크리트에서의 균열은 육안으로 분간할 수 있을 정도로 큰 반면 프리스트레스트 콘크리트의 균열은 기기를 사용하여야 측정, 분별할 수 있다. 본 논문에서는 균열의 명함도와 인접한 표면의 명함도 차이를 이용하여 균열과 잡음을 분리한다. 그리고 균열과 잡음 영역에서 형태학적인 정보를 이용하여 잡음 영역만을 제거한다. 잡음 영역이 제거된 균열 영역에서도 미세한 잡음이 존재하므로 균열 영역을 평활화를 한 후, 미세 잡음을 하나의 객체로 인식하여 제거하고 끊어진 영역의 균열을 미디언 필터를 이용하여 균열을 연결한다. 그리고 제안된 방법으로 추출된 균열을 원본 영상에 적용하여 최종적으로 균열만을 검출한다. 검출된 균열에서 균열의 특정부분을 선택하고 선택되어진 균열 영상을 대상으로 균열의 길이, 방향, 폭을 순차적으로 분석한다. 실제 균열 영상을 대상으로 실험한 결과, 균열이 비교적 정확히 검출되었고 균열 검사기가 한번에 측정할 때에 비해 비교적 빠르고 적은 노력으로 측정할 수 있는 것을 확인하였다.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.561-564
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• 2011

다양한 공학/산업적 측면에서 동적 취성 파괴 현상은 매우 중요하다. 취성 균열은 다른 균열 전파에 비해 그 전파 속도가 매우 빠르고 전파 범위가 넓기 때문에 대규모의 파괴 현상을 일으킨다. 동적 전파 중인 취성 균열 거동을 모델화하기 위해 오랜 기간 동안 많은 연구가 진행되었지만, 여전히 많은 부분들이 해석되지 못한 채 남아있다. 특히 균열 생성 및 전파를 위해 인위적인 조건들을 도입해야 하는 것은 기존 방법론들이 가지는 공통적인 문제점이다. 본 연구는 peridynamics를 동적 분기 균열 문제 해석에 도입한다. Peridynamics는 전통적인 연속체 이론에 기반한 수치해석 모델화 기법으로 균열과 같은 비연속성이 있는 문제의 모델화에 강점이 있으며, 인위적인 조건 없이 매우 간단한 방법으로 파괴 현상을 해석할 수 있다. 본 연구에서는 peridynamics 모델이 실험적으로 관측된 분기균열 형상과 균열 전파 속도를 매우 잘 예측해 낼 수 있음을 보인다. 또한 균열팁 주변에 높은 응력이 발생할 때 나타나는 연쇄 분기 현상도 해석할 수 있다. 이와 같은 연구를 통해 응력파가 균열 전파 속도를 변화시키고 전파 방향에도 영향을 주는 것을 알 수 있었다. 수치해석 결과도 또한 실험 결과들과 잘 부합함을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1257-1264
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• 2014

Efforts are presently underway for developing an optimal design methodology for GEN-IV nuclear reactors based on target failure probabilities. A typical example is the system-based code, in which the results are represented in the form of partial safety factors (PSFs). Thus, a PSF is one of the crucial elements in either component design or integrity assessment based on target failure probabilities during the operation period. In the present study, a procedure for calculating the PSF of a circumferential through-wall cracked pipe based on the elastic-plastic crack initiation criterion is established, in which the importance of each input variable is assessed. Elastic-plastic J-integrals are calculated using the GE/EPRI and reference stress methods, and the PSF values are calculated using both first- and second-order reliability methods. Moreover, the effect of statistical distributions of assessment variables on the PSF is also evaluated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.411-418
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• 2012

In this study, behavior of unpatched and patched cylindrical shells with through-wall cracks has been estimated using numerical experiments, and patching effect of them has been investigated according to various patching parameters. To show credibility of numerical models considered, two ways such as h- and p-methods have been adopted. Also, domain integral method and virtual crack extension method have been considered to calculate energy release rates based on linear elastic fracture mechanics. For examples, the unpatched cylindrical shells with circumferential cracks under remote tension have firstly been analyzed to show the validity of finite element modeling with h-method or p-method, and then the results have been compared with literature values published. Next, the sensitive analysis of patch repaired problems in terms of thickness of patch and adhesive, shear modulus of adhesive, composite material type of patch, crack length, etc. has been carried out.

• Korean Journal of Materials Research
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• v.7 no.1
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• pp.62-68
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• 1997

In the first part of the paper, the crack growth process in rolling contact fatigue has been investigated on ring type plate specimens, in which crack growth is two dimensional and cracks are observed on the side surface of the specimens. The results have shown that cracks are initated from the contact surface in tensile mode in the direction approximately normal to the contact surface and after some short length of growth, shear mode growth occurs from the tip of the crack and it grows until the separation of the surface layer, namely flakung type failure, occurs. In the second part, mode U fatigue crack growth tests have been made by using an apparatus designed based on the concept that the subsurface fatigue crack growth in rolling contact fatigue is the mode U fatigue crack growth under the stress state where the tensile mode growth is suppressed by compression stress. The rest results have shown that the mode U fatigue crack growth occurs if the superposed compression stress is enough to suppress the tensile mode growth.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.91-100
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• 2006

This paper presents an analytical model for evaluation of crack widths in structural concrete members. The model is mathematically derived from the actual bond stress-slip relationships between the reinforcement and the surrounding concrete, and the relationships summarized in CEB-FIP Model Code 1990 are employed in this study together with the assumption of a linear slip distribution along the interface at the stabilized cracking stage. With these, the actual strains of the steel and the concrete are integrated respectively along the embedment length between the adjacent cracks so as to obtain the difference in the axial elongation. The model is applied to the test specimens available in literatures, and the predicted values are shown to be in good agreement with the experimentally measured data.

• Korean Journal of Heritage: History & Science
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• v.46 no.2
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• pp.136-149
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• 2013

We studied the characteristics and the growth mechanism of surface cracks from the Naksansa seven-storied stone pagoda(Treasure No. 499). The pagoda is composed of both medium-grained, porphyritic biotite granite and hornblende-biotite granite. Alkali feldspar megacrysts are easily found as phenocrysts in the rocks. Surface cracks intensely developed at the lower part of the stone pagoda, and their directions are of vertical, horizontal, and diagonal. The rocks of the pagoda have intrinsic microcracks which can be defined as rift and grain rock cleavages. Both rock cleavages seems likely to have led to the crack growth and consequently to the mechanical deterioration of the pagoda. The vertical cracks developed parallel to the vertical compressive stress, whereas horizontal ones formed by tensile strength normal to the vertical compression. In addition mineral cleavages and twin planes of alkali feldspar phenocrysts seems to have been closely related to the mechanical breakdown of the rocks in the NE part of the pagoda.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.851-858
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• 2010

A generalized elastic solution for a transient mode III crack propagating along the gradient in functionally graded materials (FGMs) is obtained through an asymptotic analysis. The shear modulus and density of the FGMs are assumed to vary exponentially along the gradient. The stress and displacement fields near the crack tip are obtained in terms of powers of radial coordinates, and the coefficients depend on the time rates of the change of the crack tip speed and stress intensity factors. The influence of nonhomogeneity and transients on the higher order terms of the stress and displacement fields is discussed.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.725-726
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• 2008

This paper proposes elastic stress intensity factors and crack opening displacements (CODs) for a slanted axial through-wall cracked cylinder under an internal pressure based on detailed 3-dimensional (3-D) elastic finite element (FE) analyses. Based on the elastic FE results, the stress intensity factors along the crack front and CODs through the thickness at the center of the crack were provided. These values were also tabulated for three selected points, i.e., the inner and outer surfaces and at the mid-thickness. The present results can be used to evaluate the crack growth rate and leak rate of a slanted axial through-wall crack due to stress corrosion cracking and fatigue. Moreover, the present results can be used to perform a detailed Leak-Before-Break analysis considering more realistic crack shape development.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.383-390
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• 2008

This paper presents the formulation and numerical implementation of a spectral scheme specially developed to simulate dynamic fracture events in unidirectional and cross-ply fiber-reinforced composites. The formulation is based on the spectral representation of the transversely isotropic elastodynamic relations between the traction stresses along the fracture plane and the resulting displacements. Example problem of dynamically propagating cracks in fiber-reinforced composites is investigated and compared with reference solutions available in the literature and/or experimental observations. This scheme can be directly applicable to the interfacial fracture analysis in the FRP reinforced concrete structures.