• 한국강구조학회 논문집
• /
• 제24권6호
• /
• pp.613-625
• /
• 2012

철도교는 일반적으로 설계하중에 근접한 열차하중이 빈번하게 통과할 가능성이 있으므로, 초기설계단계부터 여러 구조상세에 대해 피로특성을 충분한 반영하는 것이 필요하다. 그럼에도 불구하고 철도교에 작용하는 축하중의 크기 및 배치 특성, 피로에 대한 부적절한 구조상세의 적용 등으로 인하여 강철도 플레이트거더교에서 부분적으로 피로균열이 보고되고 있다. 상부플랜지와 복부의 용접이음부에서의 피로균열의 주요 발생 원인의 하나는 침목을 지지하는 주거더와 열차하중이 작용되는 레일과의 중심간격 차이에 따른 열차하중의 편심작용에 의한 것이다. 이 연구에서는 공용중인 강철도 상로플레이트거더교를 대상으로 현장조사 및 현장계측, 일련의 구조해석을 실시하고, 대상교량의 구조거동 특성 및 피로균열의 발생 원인의 규명, 보수 보강(안)에 대하여 검토하였다.

• 보존과학회지
• /
• 제35권5호
• /
• pp.453-469
• /
• 2019

청자 '순화4년'명 항아리는 굽바닥에 명문이 새겨져 용도와 사용처, 제작자를 알 수 있는 등 초기 청자의 제작 정황을 보여주는 중요한 편년자료이다. 청자 항아리는 과거에 여러 번 수리복원 되었으나 시간이 지나면서 다양한 환경변화로 인해 처리 재료가 노화되어 균열부의 이격 및 단차가 발생하는 등 구조적 안정성이 우려되었다. 보존상태를 정밀 진단한 결과, 청자 항아리는 정면의 '입(入)'자형 균열, 좌면의 'V'자형 결실부를 포함한 균열, 후면의 'J'자형 균열이 주요 손상부위로 확인되었다. 균열부는 장뇌, 건성유, 송진 등이 포함된 정제 옻을 접착제로 토분을 첨가하여 접합하고 접합선은 다시 정제 옻을 칠한 후 금분으로 표면 처리한 것을 알 수 있었다. 결실부는 석고로 복원 후 아크릴 물감으로 색맞춤하였다. 이후 수리복원 재료가 노화되어 1981년에 국립중앙박물관에서 응급처리를 실시하였는데, 균열부 보강을 위해 Cemedine C를 쓰거나 Cemedine C에 Microballoon을 첨가하여 사용하였다. 보존처리는 유물의 보존상태 진단 결과를 근거로, 과거 수리복원 재료를 제거하고 물리적으로 취약한 부분을 다시 접합복원을 통해 보강하는데 중점을 두었다. 또한 추후 전시하는데 활용될 수 있도록 복원부를 중심으로 색맞춤을 실시하였다.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.235-243
• /
• 2002

Ni-base superalloys are used extensively in industry, both in aeroengines and land based turbines. About 60% by weight of most modern gas turbine engine structural components are made of Ni-base superalloys. To satisfy practical demands, the efficiency of gas turbine engines has been steadily and systematically increased by design modifications to handle higher turbine inlet or firing temperatures. However, the increase in operating temperatures has lead to a decrease in the life of components and increase in costs of replacement. Moreover, around 80% of the large frame size industrial/utility gas turbines operating in the world today were installed in the mid-sixties to early seventies and are now 25 to 30 years old. Consequently, there are greater opportunities now to repair and refurbish the older models. Basically, there are two major factors influencing the weldability of the cast alloys: strain-age cracking and liquation cracking. Susceptibility to strain-age cracking is due to the total Ti plus AI content of the alloy; Liquation cracking is due either to the presence of low melting constituents or constitutional liquation of constituents. Though Rene 41 superalloy has 4.5wt.% total Ti and Al content and falls just below the safe limit proposed by Prager et al., controlled grain size and special heat treatments are needed to obtain crack-free welds. Varying heat treatments and filler materials were used in a laboratory study, then the actual welding of service parts was carried out to verity the possibility of crack-tree weld of components fabricated from Rene 41 superalloy. The microstructural observations indicated that there were two kinds of carbides in the FCC matrix. MC carbides were located along the grain boundaries, while M$_{23}$C$_{6}$ carbide was located both inter and intra granularly. Two kinds of filler materials, Rene 41 and Hastelloy X were used to gas tungsten arc weld a patch into the sheet metal, along with varying pre-weld heat treatments. The microstructure, hardness and tensile tests were determined. The service distressed parts were categorized into three classes: with large cracks, with medium cracks and with small or no visible cracks. No significant difference in microstructure among the specimens was observed. Specimens were cut from the corner and the straight edge of the patch repair, away from the corner. The only cracks present were found to be associated with inadequate surface preparation to remove oxidation. Guidelines for oxide removal and the welding procedures developed in the research enabled crack-free welds to be produced.d.

• 한국기계가공학회지
• /
• 제16권4호
• /
• pp.9-15
• /
• 2017

In hot forming process, the dies in which excessive worn or crack occurs is reused after repair. Generally hot forming dies are recycled through a welding repair method. Welding repair methods are highly dependent on the skills of engineer. It causes process defects such as dimensional defects and structural defects. Recently, the metal 3D printing method has been applied to the repair of used dies. The aim of this study is to evaluate the wear characteristics of AISI H13 tool steel repaired by 3D printing method. Three kinds of wear specimens were fabricated by using 3D printing, welding, and initial material. A pin-on-disk wear test was carried out to evaluate the wear characteristics. From the result of wear test, the wear characteristics of 3D printing method was superior to that of the welded material, and was similar to that of the initial material.

• 농업과학연구
• /
• 제47권4호
• /
• pp.1159-1168
• /
• 2020

The conduits of agricultural reservoirs undergo deterioration over a considerable period of time and this is highly likely to cause structural problems such as cracks. It is therefore important to consider the effects of structural defects on the body from the viewpoint of stability and maintenance of the embankment. In this study, basic data on the effects of the crack location on the stability of the embankment is obtained by identifying, comparing, and analyzing the erosion characteristics and pore water pressure behavior through a large-scale model experiment that involves classifying the location of the conduit cracks. From the results of the experiment, it was confirmed that when a crack occurred, the amount of leakage increased as the location of the crack portion was closer to the water level, and the internal erosion phenomenon accelerated, thereby increasing the possibility of piping. It was also found that an upstream conduit crack affects the erosion and water pressure change of the central and downstream conduit of the embankment, and the conduit crack has a very large effect on the pore water pressure despite the low upstream water level. Therefore, the seepage behavior of the embankment for each conduit crack identified in this study is considered to be useful basic data for preparing a repair and reinforcement plan according to the crack location in the future.

• 소성∙가공
• /
• 제29권2호
• /
• pp.103-112
• /
• 2020

This study explores the effects of different pre-machining conditions on the deposition characteristics and mechanical properties of austenitic stainless steel samples repaired using direct energy deposition (DED). In the DED repair process, defects such as pores and cracks can occur at the interface between the substrate and deposited material. In this study, we varied the shape of the pre-machined zone for repair in order to prevent cracks from occurring at the slope surface. After repairs by the DED process, macro-scale cracks were observed in samples that had been pre-machined with elliptic and trapezoidal grooves. In addition, it was not possible to completely prevent micro-crack generation on the sloped interfaces, even in the capsule-type grooved sample. From observation of the fracture surfaces, it was found that the cracks around the inclined interface were due to a lack of fusion between the substrate and the powder material, which led to low tensile properties. The specimen with the capsule-type groove provided the highest tensile strength and elongation (respective of 46% and 571% compared to the trapezoidal grooved specimen). However, the tensile properties were degraded compared to the non-repaired specimen (as-hot rolled material). The fracture characteristics of the repaired specimens were determined by the cracks at the sloped interfaces. These cracks grew and coalesced with each other to form macro-cracks, they then coalesced with other cracks and propagated to the substrate, causing final fracture.

• 한국항공우주학회지
• /
• 제41권12호
• /
• pp.959-966
• /
• 2013

이 논문에서는 설계정보가 없는 노후 항공기를 사용한 P-3CK 해상초계기 사업을 바탕으로, 끝단거리 부족 결함 수리를 위한 패스너 홀 구조특성 연구를 수행하였다. 이를 위해 끝단거리 결함이 많이 발생했던 낫셀 론저론 부분을 선택하고, 1.5, 1.8, 2.0배 끝단거리에 대한 정적 해석을 수행하여 보수적인 응력을 구하였다. 이 응력을 바탕으로 TWIST의 표준하중 스펙트럼을 적용하여 비행하중을 생성하고, 이 비행하중을 이용하여 균열성장 피로해석을 수행하였다. 이 결과를 통하여 P-3CK 사업 중 수리된 패스너 홀의 유효성을 평가하고 정비주기 및 기준을 설정하였다.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
• /
• pp.250-253
• /
• 2001

Recently, based on the smart structure concept, optical fiber sensors have been increasingly applied to monitor the various engineering and civil structural components. Repairs based on adhesively bonded fiber reinforce composite patches are more structurally efficient and much less damaging to the parent structure than standard repairs based on mechanically fastened metallic patches. As a result of the high reinforcing efficiency of bonded patches fatigue cracks can be successfully repaired. However, when such repairs are applied to primary structures, it is needed to demonstrate that its loss can be immediately detected. This approach is based on the "smart patch" concept in which the patch system monitors its own health. The objective of this study is to evaluate the potentiality of application of transmission-type extrinsic Fabry-Perot optical fiber sensor (TEFPI) to the monitoring of crack growth behavior of composite patch repaired structures. The sensing system of TEFPI and the data reduction principle for the detection of crack detection are presented. Finally, experimental results from the tests of center-cracked-tension aluminum specimens repaired with bonded composite patch is presented and discussed.

• Structural Engineering and Mechanics
• /
• 제61권3호
• /
• pp.325-334
• /
• 2017

In the present study, a numerical model for probability analysis of optimal design of fatigue non-uniform crack growth behaviour of a cracked aluminium 2024 T3 plate repaired with a bonded composite patch is investigated. The proposed 3D numerical model has advanced in literatures, which gathers in a unique study: problems of reliability, optimization, fatigue, cracks and repair of plates subjected to tensile loadings. To achieve this aim, a finite element modelling is carried out to determine the evolution of the stress intensity factor at the crack tip Paris law is used to predict the fatigue life for a give n crack. To have an optimal volume of our patch satisfied the practical fatigue life, a procedure of optimization is proposed. Finally, the probabilistic analysis is performed in order to a show that optimized patch design is influenced by uncertainties related to mechanical and geometrical properties during the manufacturing process.

• 한국건설관리학회논문집
• /
• 제3권1호
• /
• pp.115-123
• /
• 2002

공간의 효율적 이용 및 법정 주차대수 확보 등으로 아파트 단지의 지하층은 대부분 지하주차장으로 활용되고 있으며, 주차장상부도 시공 중에 성토 및 포장공사가 완성되지 않은 상태에서 작업차량의 통로 및 자재 야적장으로 사용되고 있어 과하중이 작용되고 있는 실정이다. 그러므로 시공중이거나 완공된 지하구조물에서 지속적으로 균열 및 누수현상이 발생하여 구조물의 성능저하는 물론 많은 금액의 하자보수비 투입, 민원유발 및 대외적인 신뢰도 저하 등 많은 문제점이 발생하고 있다. 따라서 본 연구의 목적은 시공중인 아파트와 준공된 아파트 지하주차장을 대상으로 현장조사를 실시하고, 그동안 실시한 안전진단 사례를 참고하여 아파트 지하주차장의 균열 및 누수현상 원인을 파악하고 그에 따른 설계 및 시공상의 방지대책을 마련하는데 있다.