• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.328-336
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• 2004

This paper describes the effect of loading rate, specimen geometries and material properties for ModeⅠ and Mode Ⅱ interlaminar fracture toughness of hybrid composite by using double cantilever beam (DCB) and end notched flexure (ENF) specimen. In the range of loading rate 0.2~20mm/min, there is found to be no significant effect of loading rate with the value of critical energy release rate (Gc).The value of Gc for variation of initial crack length are nearly similar values when material properties are CF/CF and GF/GF, however, the value of Gc are highest with the increasing intial crack length at CF/GF. The SEM photographs show good fiber distribution and interfacial bonding of hybrid composites when the moulding is the CF/GF.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.4
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• pp.262-268
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• 2003

This paper describes the effect of loading rate, specimen geometries and material properties for Mode I interlaminar fracture toughness of hybrid composite by using double cantilever beam (DCB) specimen. In the range of loading rate 0.2-20mm/min, there is found to be no significant effect of loading rate with the value of critical energy release rate (G_IC). The value of $G_IC$ for variation of initial crack length are nearly similar values when material properties are CF/CF and GF/GF, however, the value of $G_IC/$ are highest with the increasing initial crack length at CF/GF. The SEM photographs show good fiber distribution and interfacial bonding of hybrid composites when the moulding is the CF/GF

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.511-517
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• 2009

In this paper an finite element approach for the edge crack analysis of silicon-steel sheet during cold rolling is presented. Based on the damage mechanics, the proposed approach follows the analysis steps which are composed of damage initiation, damage evolution and fracture. Through those steps, we can find out the initiation instant of crack and resulting propagated length and shape of the crack. The material constants related to fracture is experimentally obtained by tension tests using standard sheet-type specimen and notched sheet-type specimen. To evaluate the prediction accuracy, we performed a pilot rolling test with a initially notched sheets. It is shown that the results obtained by the approach converged to the experimental one concerning about the direction and length of propagated crack. The capability of the proposed one is demonstrated through the application to the actual silicon-steel rolling mill.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.138-144
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• 1990

In order to understand the probabilistic nature of fatigue crack propagation, not only the calculation of failure probability and parameter sensitivity, but also the clarification of probabilistic nature of various parameters should be executed. Therefore a method to evalute synthetically the effect of each parameter on the distribution of fatigue crack propagation life is required. In this study, the effects of the initial crack size and other paramaters on the distribution of fatigue crack propagation life are discussed according to the appropriate normalization of the life distribution, the validity of this method is also shown. Such an investigation as the present work may be useful to understand the nature of the life distribution and to utilize the probailistic fracture mechanics.

• Journal of Industrial Technology
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• v.8
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• pp.39-46
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• 1988

탄소강 평활재 및 미소결함재를 사용하여, 미소 정류크랙의 크랙 개폐구거동의 상세한 관찰과 초기결함을 상정한 미소 원공과의 상호 한계크기의 비교 검토를 통하여, 다음과 같은 결론을 얻었다. 평활재의 정규크랙은, 피로과정중에 압축잔류응역이 크랙선단의 개구를 억제하는 것에 의하여 정류하게 되고, 그 크기는 평활재의 피로한도를 저하시키지 않은 미소 원공의 한계크기와 거의 일치하여, 두 경우가 역학적으로 거의 등가함을 시사해 주고 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1635-1639
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• 1991

본 연구에서는 제1보에서의 수법을 이용하여 초기크랙길이의 분포를 고려한 재료의 불확정성 평가수법을 제시하고자 한다.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.301-310
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• 2001

Gypsum blocks with sixteen flaws have been prepared and tested in uniaxial compression. Results from these experiments are compared with observations from the same material with two and three flaws. The results indicate that the cracking pattern observed in specimens wish multiple flaws is analogous to the pattern obtained in specimens with two and three flaws such as initiation and propagation of wing, and secondary cracks and coalescence. Wing cracks initiate at an angle with the flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks initiate and propagate in a stable manner. As the load is increased, secondary cracks may propagate in an unstable manner and produce coalescence. Two types of secondary cracks are observed: quasi-coplanar, and oblique secondary cracks. Coalescence is produced by the linkage of two flaws: wing and/or secondary cracks. From the sixteen flaws test, four types of coalescence are observed. Observed types of coalescence and initiation stress of wing and secondary crackle depend on flaw geometries, such as spacing, continuity, flaw inclination angle, ligament angle, and steppings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4D
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• pp.367-376
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• 2012

Crack sealing is a maintenance technique commonly used to prevent water and debris penetration and reduce future degradation in pavement. The conventional crack sealing operations are, however, dangerous, costly, and labor-intensive. Automating crack sealing will improve productivity and quality, and offer safety benefits by getting worker off the road. During the last two decades, several teleoperated and machine-vision assisted systems have been developed to automate the overall process of routing and sealing pavement cracks. However, the developed systems have not been commonly used in the construction sites because of the technical problems. Especially, the performance of end-effector, related to the productivity and quality improvement, is very important factor to improve the practical use of the developed systems. The main objective of this research is to develop an end-effector in automated pavement crack sealing machine and to analyze the technical feasibility of the developed end-effector.

• Korean Journal of Construction Engineering and Management
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• v.12 no.5
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• pp.103-116
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• 2011

Crack sealing is a maintenance technique commonly used to prevent water and debris penetration and reduce future degradation in pavement. In recent years, several systems for automatically routing and sealing pavement cracks have been developed in the highway construction and maintenance area. Automating pavement crack sealing can improve safety, productivity and quality, and reduce road user cost as well. The reduction in crew size and the increase in productivity of the automated sealing process will be translated directly into significant potential cost savings. The main objective of this study is to illustrate conceptual models for the development of the automated pavement crack sealer which meets domestic road condition and regulation, and to discuss its technical feasibilities. Conclusions are made concerning the applicability and the value of cantilever-typed pavement crack which is selected as the most feasible alternative in both economical and technical aspects.

• Korean Journal of Construction Engineering and Management
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• v.11 no.4
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• pp.68-79
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• 2010

During the last two decades, several tele-operated and machine-vision-assisted systems have been developed in 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 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 previously developed pavement crack sealing systems. The comparison is based on computational cost versus overall gains in crack sealing efficiency. Finally, it is concluded that the proposed algorithm plays an important role in productivity improvement of the automatic pavement crack sealing system developed.