• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.66-74
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• 2004

The sliding wear behavior of $ZrO_2-22wt\%MgO\;(MZ)\;and\;ZrO_2-8wt\%Y_2O_3\;(YZ)$ deposited on a casting aluminum alloy with bond layer (NiCrCoAlY) by plasma spray against an SiC ball was investigated under dry test conditions at room temperature. At all load conditions, the wear mechanisms of the MZ and the YZ coatings were almost the same. The wear mechanisms involved the forming of a smooth film by material transferred on the sliding surface and pullout. The wear rate of the MZ coating was less than that of the YZ coating. With an increase normal load the wear rate of the studied coatings increased. The SEM was used to examine the sliding surfaces and elucidate likely wear mechanisms. The EDX analysis of the worn surface indicated that material transfer was occurred from the SiC ball to the disk. It was suggested that the material transfer played an important role in the wear performance.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.331-334
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• 2005

The nature of bond of untensioned prestressed strand in concrete differs from that of plain or deformed reinforcing bar as well as tensioned prestressed strand. There is a very limited amount of published research information regarding bonding of this type reinforcing. In order to use and design untensioned strand as reinforcing, relationships defining the load transfer characteristics of the strand are necessary. A program based upon pullout tests was designed to develop data relating the critical parameters for determining load transfer behavior of the untensioned strand. The purpose of this study is to investigate the characteristics of bond and development length between untensioned strand and concrete. The test variables include diameter of strands (9.3mm, 12.7mm) and development lengths. The maximum bond stress at the 9.3mm and 12.7mm strands decreases with the increase of the rate of development length. The untensioned prestressed strands displayed bond performance when secure development length more than 80$\%$ according to the development of deformed bars equation.

• 한국지반공학회논문집
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• 제21권10호
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• pp.123-131
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• 2005

본 연구에서는 양압력을 받는 기초구조물의 보강공법으로 앵커를 시공할 경우, 이에 대한 파괴메카니즘 및 안정해석법의 개발에 기초적인 자료를 제공하기 위해 나선형 앵커에 대한 실내인발시험 및 유한요소해석을 수행하였다. 실내인발시험은 강우시 지하수위 상승으로 인해 기초구조물에 양압력이 작용하는 경우를 고려하기 위해 포화사질토 내에서의 하중-변위특성을 분석한 후, 이를 건조시의 경우 등에 대해 유한요소 해석결과와 비교${\cdot}$분석하였으며, 앵커의 극한인발저항력에 미치는 영향인자 및 앵커의 인발에 따른 거동특성 등을 평가하였다. 또한, 군형태 앵커의 설치간격을 변화시켜가면서 하중-인발변위 특성을 비교한 후, 나선형 앵커의 무리효과에 의한 간섭영향 요인을 분석하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.774-780
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• 1999

The study of bond behavior between concrete and rebar has been performed for a long time. On this study, we tried to analysed variation of bond behaviors quantitatively with varying the strength of concrete. Bond stress which observed below the neutral surface of beam and at connecting part of beam and column is affected by various bond parameters. Resistance of deformed bars which embedded in concrete to the pullout force is divided 1) chemical adhesive force 2) frictional force 3) mechanical resistance of ribs to the concrete and these horizontal components of resistance is being bond strength. We selected the most common and typical variable which is concrete strength among various variables. So we used two kinds of concrete strength like as 25MPa(NSC) and 65MPa(HSC). Tension Test was performed to verify how bond behavior varied with two kinds of concrete strength. Concentration of bond stress was observed at load-end commonly in Tension Test of the initial load stage. At this stage stress distribution was almost coincident at each strength. As tension load added, this stress distribution had difference gradually and movement of pick point of bond stress to free-end and central section was observed. This tendency was observed at first and moving speed was more fast in NSC. At the preceeding result the reason of this phenomenon is considered to discretion of chemical adhesion and local failure of concrete around rebar in load-end direction. Especially, when concrete strength was increased 2.6 times in tension test, ultimate bond strength was increased 1.45 times. In most recent used building codes, bond strength is proportioned to sqare root of concrete compressive strength but comparison of normalized ultimate bond strength was considered that the higher concrete strength is, the lower safety factor of bond strength is in each strength if we use existing building codes. In Tension Test, in case of initial tensile force state, steel tensile stress of central cross section is not different greatly at each strength but tensile force increasing, that of central cross section in NSC was increased remarkably. Namely, tensile force which was shared in concrete in HSC was far greater than that of concrete in NSC at central section.

• 대한기계학회논문집
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• 제18권6호
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• pp.1388-1398
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• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.

• Structural Engineering and Mechanics
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• 제32권2호
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• 한국지반공학회논문집
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• 제27권6호
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• pp.17-26
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• 2011

그라운드 앵커공법은 현재 우리나라에서 가장 일반적으로 사용되는 사면보강공법들 중 하나이다. 그러므로 앵커로 보강된 사면의 안정성을 장기간 확인하기 위해서는 그라운드 앵커의 긴장력을 측정하는 것이 매우 중요하다. 그러나 전통적인 로드 셀 방식의 측정기술을 제외하고는 특별한 기술이 개발된 것이 없다. 본 논문에서는 지반구조물의 보강을 위해 널리 사용되는 그라운드 앵커의 단기 및 장기 장력을 측정하기 위해 기존에 현장에서 주로 사용되는 스트레인게이지 또는 V/W 타입 로드 셀을 대체할 수 있는 새로운 방법에 대하여 기술하였다. 사용된 센서는 스트레인게이지 또는 V/W타입의 센서에 비해 크기가 작고 내구성이 우수하며 전자기파에 의한 노이즈 발생이 없는 광섬유 브래그격자(Fiber Bragg Grating ; FBG)센서이다. FBG 센서를 내장한 7연 강연선을 이용하여 원하는 위치에서 변형률 감지가 가능한 인장형 앵커를 제작하고 앵커 정착장을 연암과 화강풍화토 지반조건에 각각 2세트(set)씩 시공하여 현장인발실험을 수행하였다. 재하-제하단계를 포함하는 전 하중단계에서 FBG센서로 측정된 변형률로부터 장력 모니터링을 수행하였고 기존 로드 셀로 측정된 결과와 비교하였다. 현장 인발실험 결과, 제안된 광섬유 센서를 이용한 그라운드 앵커의 시공 중 긴장력 측정결과 실내 UTM 결과와 달리 약간의 차이가 있으나 실용적인 차원에서는 충분히 활용 가능한 것으로 확인되었다.

• Steel and Composite Structures
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• 제1권3호
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• pp.329-340
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• 2001

Cyclic response of "shear" connections between steel outrigger beams and reinforced concrete core walls is presented in this paper. The connections investigated in this paper consisted of a shear tab welded onto a plate that was connected to the core walls through multiple headed studs. The experimental data from six specimens point to a capacity larger than the design value. However, the mode of failure was through pullout of the embedded plate, or fracture of the weld between the studs and plate. Such brittle modes of failure need to be avoided through proper design. A capacity design method based on dissipating the input energy through yielding and fracture of the shear tab was developed. This approach requires a good understanding of the expected capacity of headed studs under combined gravity shear and cyclic axial load (tension and compression). A model was developed and verified against test results from six specimens. A specimen designed based on the proposed design methodology performed very well, and the connection did not fail until shear tab fractured after extensive yielding. The proposed design method is recommended for design of outrigger beam-wall connections.

• 한국지반공학회지:지반
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• 제11권4호
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• pp.99-110
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• 1995

본 연구에서는 정규압밀 건조 모래 지반내의 연직 강체 지반앵커에 대한 모형 인발실험을 실시해서 앵커 표면의 마찰각을 실측했다. 마찰각은 앵커 표면의 깊이 방향으로 설치된 다수의 2 방향 로드셀을 사용해서 측정된 수직응력, 전단응력으로 구했다. 실험은 평면변형률 앵커와 축대칭 앵커에 대해서 실시했는데 실험 분석 결과, 앵커표면의 최대마찰각은 평면변형률 압축시험에 의한 무신축방향의 면상의 응력경각의 최대치와 거의 일치한다는 것을 알았다. 이 결론은 모래의 강도 이방성과 구속압 의존성 등을 고려하여 얻은 것으로 앵커 표면 마찰각에 모래의 전단저항각을 적용해서 설계하면 위험측이 된다는 것도 알 수 있다.

• 비파괴검사학회지
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• 제21권3호
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• pp.251-260
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• 2001

단조인장시험하에서 CFRP적층재의 손상과정을 음향방출과 초음파시험에 의해 평가하였다. 시험편으로부터의 음항방출신호의 진폭 분포는 기지재 균열(matrix crack), 박리(debonding), 섬유 pull-out 및 섬유 과단(fiber fracture)과 같은 CFRP에서의 파괴기구를 분석하는데 도움을 주며, 초음파 진폭감쇠의 특성 또한 각각의 파괴기구를 분석하는데 유용하다. 여러종류의 CFRP시험편을 사용하여 음향방출신호와 초음파신호의 진폭감쇠를 조사하였다. 끝으로 하중 제하중(loading-unloading) 시험이 초음파내의 진폭비에 대한 Felicity effect와 감쇠를 조사하기 위해서 수행되었다. 전 실험에 걸쳐 초음파신호의 진폭감쇠와 음향방출 파라미터(parameter)들은 동시에 검출되었다. 이로써 음향방출과 초음파시험의 두 파라미터들이 CERP에서의 파괴기구를 분석하기 위해 효과적으로 사용될 수 있음이 확인되었다.