• Journal of Construction Engineering and Project Management
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• 제2권1호
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• pp.35-44
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• 2012

In the last two decades, several tele-operated and machine-vision-assisted systems have been developed in the construction and maintenance area, such as pavement crack sealing, sewer pipe rehabilitation, and excavation. In developing such tele-operated and machine-vision-assisted systems, trajectory plans are very important tasks for the optimal motions of robots whether their environments are structured or unstructured. This paper presents an optimal trajectory planning algorithm used for a machine-vision-assisted automatic pavement crack sealing system. In this paper, the performance of the proposed optimal trajectory planning algorithm is compared with the greedy trajectory plans, which are used in the previously developed pavement crack sealing systems. The comparison is based on the computational cost vs. the overall gains in crack sealing efficiency. Finally, it is concluded that the proposed algorithm plays an important role in the productivity improvement of the developed automatic pavement crack sealing system.

• Structural Engineering and Mechanics
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• 제7권6호
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• pp.575-588
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• 1999

A boundary element method is applied to the analysis of crack trajectory in materials with complex microstructure, such as discontinuously reinforced composite materials, and systems subjected to complex loading, such as indentation. The path followed by the crack(s) has non-trivial geometry. A study of the stress intensity factors and fracture toughness of such systems must therefore be accompanied by an analysis of crack trajectory. The simulation is achieved using a dual boundary integral method in planar problems, and a single boundary integral method coupled with substructuring in axisymmetric problems. The direction of crack propagation is determined using the maximum mechanical energy release rate criterion. The method is demonstrated by application to (i) a composite material composed of components having the elastic properties of aluminium (matrix) and silicon carbide (reinforcement), and (ii) analysis of contact damage induced by the action of an indenter on brittle materials. The chief advantage of the method is the ease with which problems having complex geometry or loading (giving rise to complex crack trajectories) can be treated.

• 한국건설관리학회논문집
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• 제11권4호
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• pp.68-79
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• 2010

도로면 크랙실링 공법은 예방적 차원에서 도로면에 발생된 크랙을 초기에 효과적으로 보수할 수 있는 공법으로 국내외에 서는 1990년대 초반부터 기존 도로면 크랙실링 작업의 생산성, 안전성 및 품질의 균일성 확보를 목적으로 크랙실링 자동화 장비의 개발을 위한 지속적인 연구개발 노력을 수행해 왔다. 도로면 크랙실링 자동화 장비를 개발함에 있어 특히 경로계획은 주어진 작업 영역 내에서 개발 장비로 하여금 실링될 크랙 네트워크를 시간 효과적으로 횡단할 수 있도록 하는 운항 정보를 제공하게 되므로 이는 개발 장비의 성능을 결정 짖는 매우 중요한 연구주제라 할 수 있다. 본 연구의 목적은 작업 영역 내 경로계획 데이터의 효과적인 모델링을 통해 크랙실링 자동화 장비의 최적 경로계획 알고리즘을 개발하는 것으로써, 경로 집합전체를 완전 탐색하는 2단계 트리 알고리즘과 크랙의 순열만을 탐색하는 1단계 트리 알고리즘을 개발하였으며, 알고리즘의 성능 측정 및 분석을 통해 최적 경로계획 알고리즘의 적용 범위와 그에 따른 성능 향상 정도를 평가하였다. 이 연구의 결과는 도로면 크랙실링 자동화 장비의 생산성 향상에 크게 기여할 수 있을 것으로 기대된다.

• Journal of Welding and Joining
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• 제29권2호
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• pp.64-71
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• 2011

In this paper, crack propagation analyses in the inner diameter (ID) repair weld of the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). To calculate the theoretical solution for the crack tip stress intensity factor, a weak type singular integral equation consisted of crack surface traction and dislocation density function was constructed and solved in conjunction with the FEAM. A two-dimensional axisymmetric finite element nozzle model was prepared and ID repair welding was simulated. An initial crack, 10% depth of weld thickness, was assumed and crack propagation trajectory from the initial crack to the 75% depth of thickness was calculated using the FEAM. Crack growth versus time curve was also calculated and compared with the curves obtained from ASME code method. With the method constructed in this paper, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Journal of Welding and Joining
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• 제28권1호
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• pp.100-106
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• 2010

In this paper crack propagation analyses in the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). A two-dimensional axisymmetric finite element nozzle model was prepared and welding simulation including the thermal heat transfer analysis and the thermal stress analysis was performed. Initial cracks were inserted at weld and heat affected zone in the finite element model which has welding residual stress distribution obtained from the welding simulation. To calculate crack propagation trajectories of these cracks, a new fatigue crack evaluation module was developed in addition to the previous FEAM program. With the new FEAM fatigue crack evaluation module, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Computers and Concrete
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• 제23권2호
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• pp.121-131
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• 2019

Due to the heterogeneity nature of the concrete, it is difficult to simulate the hyperdynamic behaviour and crack trajectory of concrete material when subjected to explosion loads. In this paper, a 3D nonlinear numerical study was conducted to simulate the hyperdynamic behaviour of concrete under various loading conditions using Riedel-Hiermaier-Thoma (RHT) model. Detailed calibration was conducted to identify the optimal parameters for the RHT model on the material level. For the component level, the calibrated RHT parameters were used to simulate the failure behaviour of plain concrete (PC) slab under free air blast load. The response was compared with an available experimental result. The results show the proposed numerical model can accurately simulate the crack trajectory and the failure mode of the PC slab under free air blast load.

• 비파괴검사학회지
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• 제23권6호
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• pp.622-634
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• 2003

This paper is concerned with a computational method for recovering a crack shape of steam generator tubes of nuclear plants. Problems on the shape identification are discussed arising in the characterization of a structural defect in a conductor using data of eddy current inspection. A surface defect on the generator tube ran be detected as a probe impedance trajectory by scanning a pancake type coil. First, a mathematical model of the inspection process is derived from the Maxwell's equation. Second, the input and output relation is given by the approximate model by virtue of the hybrid use of the finite element and boundary element method. In that model, the crack shape is characterized by the unknown coefficients of the B-spline function which approximates the crack shape geometry. Finally, a parameter estimation technique is proposed for recovering the crack shape using data from the probe coil. The computational experiments were successfully tested with the laboratory data.

• 대한토목학회논문집
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• 제35권2호
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• pp.481-491
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• 2015

콘크리트 표면에 발생된 균열은 구조물의 수명에 영향을 미치는 주요원인으로 작용하기 때문에 주기적인 검사와 유지관리가 필요하다. 콘크리트 표면 유지관리를 위한 실링작업은 표면에 발생된 균열을 초기에 보수하는 방법으로 시간 경과에 따른 균열의 추가생성 및 확산을 방지하는데 효과적이다. 하지만, 교량 하부의 실링작업은 열악한 작업환경으로 인하여 작업자들의 안전성 확보에 문제가 있다. 이런 이유로, 콘크리트 구조물의 유지관리를 위한 실링자동화의 필요성이 부각되고 있다. 본 논문은 콘크리트 교량 하부에 발생된 균열의 실링작업에 로봇을 적용하기 위한 두 가지 제어방법에 대하여 제안한다. 하나는, 균열의 궤적을 자동으로 추적하는 방법이다. 로봇은 카메라로부터 취득되는 영상정보로 균열의 궤적을 파악하는데, 이전 시점의 궤적 정보를 통하여 다음 이동할 시점의 정보를 유추할 수 있다면, 실시간으로 변동되는 궤적 정보에 대응이 가능하면서 자동으로 균열을 추적할 수 있다. 다른 하나는 접촉면에 일정한 힘을 유지하여 실링하는 방법이다. 장기간 외부 환경에 노출된 거친 표면에서도 로봇이 일정한 접촉력을 유지하며 실링작업을 수행한다면, 균등한 완성도를 유지할 수 있다. 이러한 균일한 힘의 유지를 위하여 임피던스를 이용한 힘 제어 기법을 제안한다. 본 논문에서는 실링 로봇에 적용하기 위하여 개발한 두 가지 제어기법들을 소개하고, 그것을 적용한 Lab Test와 Field Test를 수행한다. 이 시험결과를 토대로 로봇의 현장적용에 대한 의견을 제시한다.

• 한국철도학회논문집
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• 제2권1호
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• pp.38-46
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• 1999

This study proposes the analysis and evaluation method of time series ultrasonic signal using the attractor analysis. Features extracted from time series signal analyze quantitatively characteristics of weld defects. For this purpose, analysis objective in this study is fractal dimension and attractor quadrant feature. Trajectory changes in the attractor indicated a substantial difference in fractal characteristics resulting from distance shifts such as parts of head and flange even though the types of defects are identified. These differences in characteristics of weld defects enables the evaluation of unique characteristics of defects in the weld zone. In quantitative fractal feature extraction, feature values of 3.848 in the case of part of head(crack) and 4.102 in the case of part of web(side hole) and 3.711 in the case of part of flange(crack) were proposed on the basis of fractal dimensions. Proposed attractor feature extraction in this study can enhance the precision rate of ultrasonic evaluation for defect signals of rail weld zone such as side hole and crack.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.25-26
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• 2005

This study suggested the occurrence source of weld-defects and its solution methods in a welding of Electrolyte injection hole by pulsed Nd:YAG laser. In experiment, the ramp down was used in order that solidification crack was removed. Furthermore, shrinkage stress and heat input were reduced by changing of weld trajectory and defocused distance. As a results of a experiment, a sound weld bead shape and crack-free weld bead can be obtained.