• 대한기계학회논문집
• /
• 제19권1호
• /
• pp.61-78
• /
• 1995

In this study the method of analysis for three-dimensional plane crack problem by fractional linear mapping is given. Using this method we can obtain the exact solutions of significantly different configurations of the crack. In the example image crack configurations by mapping of elliptic crack are illustrated. And the stress intensity factors along the image crack tips are calculated.

• Smart Structures and Systems
• /
• 제1권4호
• /
• pp.385-404
• /
• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.

• 대한기계학회논문집
• /
• 제17권7호
• /
• pp.1710-1718
• /
• 1993

This paper investigates the problem of a crack approaching two circular holes in an orthotropic infinite plate. The stress intensity factors were obtained by using the modified mapping-collocation method. The present results show excellent agreement with existing solutions for a crack approaching two circular holes in an isotropic infinite plate. In the numerical examples, various types of cross-ply laminated composites were considered. To investigate the effect of orthotropy and geometry(d/R and a/(d-R)) on crack tip singularity, stress intensity factors were considered as functions of the normalized crack length. It is expected that the modified mapping-collocation method can be applied to the analysis of various kinds of cracks existing around the stress-concentration region of composite laminate.

• 한국정밀공학회지
• /
• 제12권2호
• /
• pp.162-172
• /
• 1995

In this paper new mesh generation method is proposed for crack propagation analysis based on the finite element method. The main tool of the method is the Delaunay Triangulation, Transfinete element mapping, and it allows the setting of the arbitrary crack-growth increment and the arbitrary crack direction. It has the form of a subroutine, and it is easily introduced as a subroutine for any mesh generation method which is based on the blocking method.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2004년도 제5회 정기학술발표대회 논문집
• /
• pp.561-564
• /
• 2004

국내외에서는 크랙실링 공법의 이점 및 도로면 유지보수 공사의 위험 요소를 인식하여 90년대 초반부터 크랙실링 자동화 장비 개발을 위한 연구를 진행하여 왔다. 기존 문헌 고찰과 도로면 크랙실링 자동화 장비(Automated Pavement Crack Sealer; APCS)의 실험실 및 현장 실험 결과, 도로면에 존재하는 크랙 네트워크를 자동으로 탐지하고 모델링하는 과정의 속도와 정확성을 향상시키는 것은 개발된 크랙실링 자동화 장비의 실용화를 위해 매우 중요한 요인으로 인식되었다 그러나, CCD 카메라를 통해 습득된 도로면 영상에서 크랙 네트워크를 완전 자동으로 인식하는 기술은 일반적인 영상 인식 분야에서 보다 외부 환경적인 요인으로 인해 낮은 인식률을 가지고 있다 본 연구를 통해 기존에 개발된 APCS 머신비전 알고리즘의 경우 도로면 영상의 환경 요인에 의해 발생된 문제점들을 많이 해결하였으나 실용화 단계에서 요구되는 크랙 인식률에는 도달하지 못하였다. 따라서, 본 연구의 목적은 기존 APCS 머신 비전 알고리즘의 완전 자동화 방식 크랙 탐지 및 모델링 알고리즘의 문제점을 분석하고 신경망 학습 기법을 이용한 크랙 인식 알고리즘을 개발하는 것이다.

• 한국건설관리학회논문집
• /
• 제5권2호
• /
• pp.90-105
• /
• 2004

크랙실링 자동화 장비는 도로면에 존재하는 크랙 네트워크의 위치를 정확히 탐지 및 맵핑(mapping)하고 이를 모델링(modeling)한 후 경로 계획(path planning) 과정을 통해 크랙 네트워크의 중앙(spine)을 따라 실런트(sealant)를 분사하여 크랙을 효과적으로 실링할수 있도록 하는 장비이다. 따라서 실링될 크랙 네트워크의 정확한 위치를 모델링하기 위한 디지털 영상처리 알고리즘 및 최적 경로계획 알고리즘의 개발은 품질 및 생산성, 경제성 측면에서 크랙실링 자동화 장비의 성공적 개발을 위한 핵심 연구 주제로 인식되어 왔다. 기존 국외 도로면 크랙실링 자동화 장비에 적용된 디지털 영상처리 알고리즘은 크랙을 탐지하고 모델링하는 일련의 과정을 전적으로 컴퓨터에 의존하는 완전자동화 방식과 인간과 컴퓨터 간의 협업체제를 이용한 반자동화 방식으로 양분되어 개발되었다. 그러나 도로면에 존재하는 다양한 노이즈 및 그림자 등을 포함한 작업영역 내에서의 열악한 영상처리 여건 등으로 인해 만족할 만한 성과를 제시하지 못하였다. 따라서 본 연구에서는 크랙실링 자동화 장비를 개발함에 있어 디지털 영상처리 기술을 기반으로 한 완전자동화 방식과 그래피컬 프로그래밍을 활용한 반자동화 방식이 지닐 수 있는 강점만을 혼용하여 신속하고도 정확하게 크랙 네트워크를 모델링하고 최적 경로계획을 바탕으로 크랙실링 작업을 수행할 수 있는 머신비전 알고리즘을 제시하고자 한다.

• Smart Structures and Systems
• /
• 제22권2호
• /
• pp.201-207
• /
• 2018

This paper proposes a line laser thermography scanning (LLTS) system for multiple crack evaluation on a concrete structure, as the core technology for unmanned aerial vehicle-mounted crack inspection. The LLTS system consists of a line shape continuous-wave laser source, an infrared (IR) camera, a control computer and a scanning jig. The line laser generates thermal waves on a target concrete structure, and the IR camera simultaneously measures the corresponding thermal responses. By spatially scanning the LLTS system along a target concrete structure, multiple cracks even in a large scale concrete structure can be effectively visualized and evaluated. Since raw IR data obtained by scanning the LLTS system, however, includes timely- and spatially-varying IR images due to the limited field of view (FOV) of the LLTS system, a novel time-spatial-integrated (TSI) coordinate transform algorithm is developed for precise crack evaluation in a static condition. The proposed system has the following technical advantages: (1) the thermal wave propagation is effectively induced on a concrete structure with low thermal conductivity of approximately 0.8 W/m K; (2) the limited FOV issues can be solved by the TSI coordinate transform; and (3) multiple cracks are able to be visualized and evaluated by normalizing the responses based on phase mapping and spatial derivative processes. The proposed LLTS system is experimentally validated using a concrete specimen with various cracks. The experimental results reveal that the LLTS system successfully visualizes and evaluates multiple cracks without false alarms.

• 대한기계학회논문집A
• /
• 제25권4호
• /
• pp.734-740
• /
• 2001

In this paper the stress intensity factor under uniform pressure in the arbitrarily-shaped plane crack configuration transformed elliptic crack by Mobius mapping are determined. Using Dysons formula Boussinesq-Papkovich potentials for mode I deformation are constructed. In the example the stress intensity factors are approximately calculated by least square method.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.117-122
• /
• 2000

In this paper the stress intensity factor under uniform pressure in the arbitrarily-shaped plane crack configuration transformed elliptic crack by Mobius mapping are determined. Using Dyson's formula Boussinesq-Papkovich potentials for mode I deformation are constructed. In the example the stress intensity factors are approximately calculated by least square method.

• Structural Engineering and Mechanics
• /
• 제28권4호
• /
• pp.461-477
• /
• 2008

An adaptive finite element method for analyzing two-dimensional and axisymmetric nonlinear elastic fracture mechanics problems with cracks is presented. The J-integral is used as a parameter to characterize the severity of stresses and deformation near crack tips. The domain integral technique, for which all relevant quantities are integrated over any arbitrary element areas around the crack tips, is utilized as the J-integral solution scheme with 9-node degenerated crack tip elements. The solution accuracy is further improved by incorporating an error estimation procedure onto a remeshing algorithm with a solution mapping scheme to resume the analysis at a particular load level after the adaptive remeshing technique has been applied. Several benchmark problems are analyzed to evaluate the efficiency of the combined domain integral technique and the adaptive finite element method.