• 한국소음진동공학회논문집
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• 제17권10호
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• pp.1002-1009
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• 2007

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid with an attached mass is investigated. Also, the effect of attached mass on the dynamic stability of a simply supported pipe conveying fluid is presented for the different positions and depth of the crack. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by the energy expressions using extended Hamilton's principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of a fracture and to be always opened during the vibrations. Finally, the critical flow velocities and stability maps of the pipe conveying fluid are obtained by changing the attached mass and crack severity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.306-309
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• 2009

The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

• Structural Engineering and Mechanics
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• 제35권5호
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• pp.617-630
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• 2010

Different types of moment resisting connections are commonly used to transfer the induced seismic moments between frame elements in an earthquake resisting structure. The local connection behavior may drastically affect the global seismic response of the structure. In this study, the finite element and experimental seismic investigations are implemented on two frequently used connection type to evaluate the local behavior and to reveal the failure modes. An alternative connection type is then proposed to eliminate the unfavorable brittle fracture modes resulted from probable poor welding quality. This will develop a reliable predefined ductile plastic mechanism forming away from the critical locations. Employing this technique, the structural reliability of the moment resisting connections shall be improved by achieving a controllable energy dissipation source in form of yielding of the cover plates.

• 한국정밀공학회지
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• 제25권5호
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• pp.121-131
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• 2008

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid with an attached mass is investigated. Also, the effect of attached masses on the dynamic stability of a simply supported pipe conveying fluid is presented for the different positions and depth of the crack. Based on the Euler-Bernoulli beam theory, the equation of motion can be constructed by the energy expressions using extended Hamilton's principle. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of a fracture and to be always opened during the vibrations. Finally, the critical flow velocities and stability maps of the pipe conveying fluid are obtained by changing the attached masses and crack severity. As attached masses are increased, the region of re-stabilization of the system is decreased but the region of divergence is increased.

• 한국초전도ㆍ저온공학회논문지
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• 제8권4호
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• pp.26-29
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• 2006

The study to be presented related on initial behavior of quench concerned with many considerations, such as epoxy impregnated coil, critical current density related on strain and temperature, winding effect and behavior of internal superconducting wire. Especially, the deformation behavior of coils under magnetic field and thermal contractions at cryogenic temperatures to be dealt with the analytical method related on Fracture Mechanics. From the results, we know that the strain by self weight contribute to epoxy cracking at the edge of deformed coils and the deformation behavior relate on epoxy cracking must be dealt with biaxial loading problem. Then, the epoxy crack on $r\theta-plane$ under biaxial loading have been propagated with inclined crack angle and joined superconducting wire. Also, we can explain transfer of epoxy crack propagation energy from epoxy resin to superconducting wire.

• Advances in concrete construction
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• 제13권3호
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• pp.243-254
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• 2022

Reinforced concrete (RC) deep beams are critical structural elements used in offshore pile caps, rectangular cross-section water tanks, silo structures, transfer beams in high-rise buildings, and bent caps. As a result of the low shear span ratio to effective depth (a/d) in deep beams, arch action occurs, which leads to shear failure. Several studies have been carried out to improve the shear resistance of RC deep beams and avoid brittle fracture behavior in recent years. This study was performed to investigate the behavior of RC deep beams numerically and experimentally with different reinforcement arrangements. Deep beams with four different reinforcement arrangements were produced and tested under monotonic static loading in the study's scope. The horizontal and vertical shear reinforcement members were changed in the test specimens to obtain the effects of different reinforcement arrangements. However, the rebars used for tension and the vertical shear reinforcement ratio were constant. In addition, the behavior of each deep beam was obtained numerically with commercial finite element analysis (FEA) software ABAQUS, and the findings were compared with the experimental results. The results showed that the reinforcements placed diagonally significantly increased the load-carrying and energy absorption capacities of RC deep beams. Moreover, an apparent plastic plateau was seen in the load-displacement curves of these test specimens in question (DE-2 and DE-3). This finding also indicated that diagonally located reinforcements improve displacement ductility. Also, the numerical results showed that the FEM method could be used to accurately predict RC deep beams'behavior with different reinforcement arrangements.

• Computers and Concrete
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• 제7권3호
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• pp.203-220
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• 2010

In the present study, exterior beam-column sub-assemblage from a regular reinforced concrete (RC) building has been considered. Two different types of beam-column sub-assemblages from existing RC building have been considered, i.e., gravity load designed ('GLD'), and seismically designed but without any ductile detailing ('NonDuctile'). Hence, both the cases represent the under-designed structure at different time frame span before the introduction of ductile detailing. For designing 'NonDuctile' structure, Eurocode and Indian Standard were considered. Non-linear finite element (FE) program has been employed for analysing the sub-assemblages under cyclic loading. FE models were developed using quadratic concrete brick elements with embedded truss elements to represent reinforcements. It has been found that the results obtained from the numerical analysis are well corroborated with that of experimental results. Using the validated numerical models, it was proposed to correlate the energy dissipation from numerical analysis to that from experimental analysis. Numerical models would be helpful in practice to evaluate the seismic performance of the critical sub-assemblages prior to design decisions. Further, using the numerical studies, performance of the sub-assemblages with variation of axial load ratios (ratio is defined by applied axial load divided by axial strength) has been studied since many researchers have brought out inconsistent observations on role of axial load in changing strength and energy dissipation under cyclic load.

• 접착 및 계면
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• 제4권3호
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• pp.33-40
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• 2003

본 연구에서는 이관능성 에폭시 (diglycidyl ether of bisphenol A. DGEBA)와 Polyetherimide(PEI) 블랜드를 Amime계 경화제인 DDM을 이용하여 경화를 시켰으며, PEI의 함량 변화가 순수 에폭시 수지의 열적특성과 파괴인성에 미치는 영향에 대해 고찰하였다. 경화된 시편의 열적특성은 DSC에 의한 열분석을 통해 Kissinger 식을 이용하여 경화 활성화 에너지 ($E_a$)를 구하였고, 파괴인성은 크랙성장의 저항을 나타내는 임계응력세기 인자 ($K_{IC}$)을 측정하여 알아보았다. 시편의 파단특성은 주사전자현미경 (SEM)을 통해 조사하였으며, 기계적 계면특성을 알아보기 위해 contact angle로 표면자유에너지를 측정하였다. 실험 결과 DGEBA/PEI 블랜드계의 $E_a$, $K_{IC}$는 PEI 함량이 7.5 phr에서 최대값을 보였다. 이는 PEI 도입에 따른 치밀한 네트워크 구조가 증가했기 때문으로 판단되어 진다. 또한 DGEBA/PEI 블랜드계의 표면자유에너지는 $K_{IC}$와 유사한 경향을 보였으며, 이는 에폭시의 하이드록실기와 PEI의 imide 그룹 사이의 수소결합에 의해 극성요소가 증가되었기 때문으로 판단되어진다.

• 한국안전학회지
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• 제33권2호
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• pp.8-13
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• 2018

The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location about a delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. The initial crack location and fiber laminates thickness were changed with several types. The MMB specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 2 types of 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at 1/3 of the upper part of the PVC foam core was the most rapid progression. And the critical energy release rate was $0.40kJ/m^2$, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 5 plies. Meanwhile, the highest value of $1.27kJ/m^2$ was obtained when the initial crack was located at the center line in case of the 8 plies.

• 접착 및 계면
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• 제4권1호
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• pp.1-8
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• 2003

본 연구에서는 이관능성 에폭시와 PMR-15 블렌드계의 접촉각 측정과 파괴인성 측정을 통하여 PMR-15 조성비에 따른 표면자유에너지가 기계적 계면특성에 미치는 영향에 대하여 고찰하였다. 블렌드계의 FT-IR 분석 결과, PMR-15의 이미드화에 따른 특성 밴드가 1,722, $1,778cm^{-1}$ (C=O)와 $1,372cm^{-1}$ (C-N)에서 나타났고, 에폭시의 개환 반응에 따른 -OH peak는 PMR-15 phr의 함량에서 가장 크게 나타나는 것을 확인할 수 있었다. 증류수와 diiodomethane을 젖음액으로 사용하여 sessile drop 방법으로 접촉각을 측정한 결과, 표면자유에너지는 극성 요소의 증가에 의해서 PMR-15의 함량이 10 phr일 때 최고값을 나타내었다. 또한, 기계적 계면특성을 파괴인성 측정을 통하여 알아본 결과 $K_{IC}$와 $G_{IC}$ 또한 표면자유에너지와 유사한 경향을 나타내는 것을 알 수 있었는데, 이는 PMR-15 10 phr의 조성에서 수소결합의 증가에 의한 블렌드계의 극성요소가 증가함에 따라 분자들간의 계면결합력이 증가했기 때문인 것으로 관찰된다.