• 한국정밀공학회지
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• 제20권8호
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• pp.54-61
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• 2003

The first stage rotating blade of industrial gas turbine is one of the components that is normally run in exposed state at the highest temperature of the combustion gas stream. For this reason superior materials and advanced cooling technology are required to allow higher heat resisting characteristics of the component. The 1st stage blade of a selected commercial gas turbine blade made of directionally solidified Ni-based superalloy has a row of cooling holes on its trailing edge. In most cases, minor cracks have been found at some of the root cooling holes after one cycle operation (24,000 hrs) or even shorter operation time because of the high temperature gradient and the frequently alternating thermal stress. In the repair process, unfortunately, it is usually very difficult to get rid of the damage due to the fact that cracks are initiated at the root cooling hole and propagated deep into the hole. In this study, the feasibility of removing the sidewall cracks in the hole by utilizing EDM drilling has been investigated. Also the criteria of surface integrity for EDM drilling were established to achieve high quality repair as well as machining accuracy.

• 설비공학논문집
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• 제29권2호
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• pp.82-88
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• 2017

There are main issues of defect type that condensation, concrete crack and noise in apartment buildings. Especially, according to the Apartment Defect Dispute Mediation Committee in Korea (ADDMC) at Ministry of Land Infrastructure and Transport in Korea (MLIT), condensation defects are great importance (14 percent) on whole number of reported cases of faults from 2015 in Korea. Most condensation defects have many different causes that take a toll on the resident's life and space. So it is very important to early detection and repair. For preventing the condensation in apartment buildings, there are building codes in Korea such as 'Standard of Method and Judgment for Apartment defect of investigation, Repair cost Estimate'. This research aims to study on the improvement of preventing the condensation aforementioned korea standard. Types and characteristics (opaque wall, windows, doors) of cause of occurrence and existing state condensation defect is analyzed from evaluation of real application 100 case in 2015 ADDMC data.

• Journal of Ship and Ocean Technology
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• 제3권1호
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• pp.27-41
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• 1999

The objective of the paper is to study the impact of changing the traditional hull design of bulk carriers by providing them with a double hull while keeping the same deadweight. It is demonstrated that by introducing the double hull the structural reliability is increased throughout the entire life and also the extend of the needed repair is reduced. The results are obtained with recently developed mathematical tools for the reliability assessment of ship hulls subjected to the existence of multiple cracks both in the stiffeners and in the plating and it models the crack growth process. The effect of corrosion is represented as time dependent. The long-term stress range acting on the elements is defined as a function of the local transverse pressure of the internal cargo and outside sea water combined with the stresses resulting from the longitudinal bending of the hull, which is a combined with the stresses resulting from the longitudinal bending of the hull, which is a combineation of horizontal and vertical bending moments. The effect of maintenance actions is modelled as a stochastic process. The results show that a different design of the midship section improves the structural safety and also the economy with respect to structural repair of bulk carriers.

• 한국항공운항학회지
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• 제27권3호
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• pp.24-29
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• 2019

The paste-type adhesive can be stored for a certain period of time and can be cured at room temperature. So it is mainly used for crack patching repair of aircraft airframe structures. This study analysed the influence of environmental factors and evaluated the adherence strength characteristics according to the adherence delay time of the paste-type adhesive. The test specimens were made of aluminum alloy(AL 2024-T3) with reference to ASTM D1002 which is generally performed to measure the adherence strength of the adhesive used for metal bonding. As a result of analysing the influence of temperature and humidity, it was found that the optimal temperature range is $24.5{\pm}0.5^{\circ}C$ and the optimal humidity range is $71{\pm}1%$ for maintenance work of the aircraft using EA-9320 adhesive. In addition, the adherence strength did not decrease with the inherent application time of the EA-9320, but it was found that the adherence strength dropped rapidly when the applied time exceeded the inherent application time of it.

• Structural Engineering and Mechanics
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• 제84권6호
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• pp.799-811
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• 2022

Adhesive bonding has seen rapid development in recent years, with emphasis to composite patch repairing processes of geometric defects in aeronautical structures. However, its use is still limited given its low resistance to climatic conditions and requirement of specialized labor to avoid fabrication induced defects, such as air bubbles, cracks, and cavities. This work aims to numerically analyze, by the finite element method, the failure behavior of a damaged plate, in the form of a bonding defect, and repaired by an adhesively bonded composite patch. The position and size of the defect were studied. The results of the numerical analysis clearly showed that the position of the defect in the adhesive layer has a large effect on the value of J-Integral. The reduction in the value of J-Integral is also related to the composite stacking sequence which, according to the mechanical properties of the ply, provides better load transfer from the plate to the repair piece through the adhesive. In addition, the increase in the applied load significantly affects the value of the J-Integral at the crack tip in the presence of a bonding defect, even for small dimensions, by reducing the load transfer.

• 한국건축시공학회지
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• 제21권2호
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• pp.129-139
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• 2021

신축 공동주택 보급률이 상승하면서 입주민 개인별 자산의 관리적 측면과 함께 품질에 관한 관심이 높아져 공동주택 품질과 관련된 분쟁이 급격하게 증가되고 있는 실정이다. 이에 본 연구에서는 분쟁을 저감할 목적으로 관리주체가 제소하는 집단하자보수비 청구 소송을 확인하여 가장 빈번하게 분쟁이 발생된 콘크리트의 층간이음부와 관련하여 각 사건별로 층간이음부가 차지하는 비중과 쟁점을 분석하였다. 그 결과 분쟁 발생의 원인에는 첫째, 표준시방서가 부재한 점, 둘째, 보수공법에 대한 표준이 없는 점, 셋째, 공동주택의 공통적인 사항이나 법원에서는 이를 관대한 개념에서 배상 범위를 인정하고 있는 점에 있음이 확인되었다. 이에, 하자예방을 위해서는 첫째, 층간이음부 시공에 대한 국토교통부의 표준시방서가 개정되어야하고, 둘째, 표준시방서 이행 여부에 따라 하자판정이 진행되어야 하며, 셋째, 하자로 판정 시 명확한 하자보수공법이 적용될 수 있는 제도개선이 필요한 부분임을 확인할 수 있었다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
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• pp.113-117
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• 2005

The ceramic metal resin paints for waterproof and anti corrosion is not long history in development of materials even many actual result. So far, no standard have been given to construction and maintenance method, Quality and property, it is real state that cannot afford to proper quality control in job site or production. This study has been test for the ceramic metal resin paints for water and anti corrosion, as the result, it have proper performance of job site and mechanical performance of compare to other existing. In particular, tensile strength indicates more high about $14.1N/mm^2$ than epoxy resin paints, and in elongation per unit length is more high It is shows having better adhesive strength than epoxy resin paint for crack on the concrete structure. Moreover, The ceramic metal paint for water and corrosion proofing have to have main performance is watertightness and resistance for external impact, chloride ion permeation, drinkable water elution.

• 복합신소재구조학회 논문집
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• 제4권4호
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• pp.22-29
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• 2013

Accumulation of more than 20,000,000 vehicles since the establishment of the quality of life and economic development needs several parking lots and cause crack problem in Korea. Related structures in large cities due to the lack of parking garage attached to secure underground parking structures are actively being built, and the basement parking lot will continue to increase more stories and the trend is expected to be larger. But so far, construction of the underground parking structure is related to a number of problems, including cracks in the structure. Therefore, in this study, repair, reinforcement and a few non-economic losses in the current design criteria are presented. The review of the structure used to current design criteria is to minimize crack and maximize usability.

• Structural Engineering and Mechanics
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• 제56권1호
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• pp.123-136
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• 2015

The proposed techniques to repair concrete members such as steel plates, fiber-reinforced polymers or concrete have important deficiencies in adherence and durability. The use of ultra high performance fiber concrete (UHPFC) can overtake effectively these problems. In this paper, the possibility of using UHPFC to strengthen reinforced concrete beams under torsion is investigated. Seven specimens of concrete beams reinforced with longitudinal and transverse reinforcements. One of these beams consider as control specimen while the others was strengthened by UHPFC on four, three, and two sides. This study includes experimental results of all beams with different types of configurations and thickness of UHPFC. As well as, finite element analysis was conducted in tandem with experimental test. Results reveal the effectiveness of the proposed technique at cracking and ultimate torque for different beam strengthening configurations, torque - twist graphs and crack patterns. The UHPFC can generally be used as an effective external torsional reinforcement for RC beams. It was noted that the behavior of the beams strengthen with UHPFC are better than the control beams. This increase was proportional to the retrofitted beam sides. The use of UHPFC had effect in delaying the growth of crack formation. The finite element analysis is reasonably agreement with the experimental data.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문 발표회
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• pp.27-31
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• 2003

To maintain serviceability of concrete structure more than proper it is necessary not only predict service life through periodical monitor but also need monitoring system to recognize optimal time and method for repair. Recently, CPGFRP, replacing some GFRP with CF, is developed and used for monitoring concrete fraction. But dramatic resistance change of CPGFRP is showed below 0.5% strain and it is not small strain in terms of monitoring micro crack in concrete. In other word, monitoring with CF is not suitable in low stress hut hight stress. In this study, we accessed applicable possibility and reliability of CPGFRP composite as monitoring sense that is proved very sensitive to stress through domestic and oversea previous study. CPGFRP composite plays a role in specimen like steel and increases flexural strength. CPGFRP composite shows resistance increasement in micro crack. In particular, CPUFRP is more sensitive than strangage in low stress. Resistance change ratio curve is very similar to strain curve so sensitivity and reliability is very excellent to monitor concrete fracture.