• 대한치과교정학회지
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• 제30권6호
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• pp.731-738
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• 2000

본 연구의 목적은 재생된 니켈-티타늄 호선의 3점 굴곡물성의 변화를 조사하여, 임상적으로 니켈-티타늄 호선을 재생하여 사용하는 것이 타당한지를 알아보는 것이다. 4종의 니켈-티타늄 호선(Align, NiTi, Optimallo, Sentalloy)을 처리전(T0: 대조군)과 인공타액에 4주간 처리한 군(T1), 그리고 인공타액 처리 후 가압증기 멸균소독한 군(T2)으로 구분하여 3점 굴곡실험을 하였다. 3mm 변형시의 loading force, unloading force, hysteresis와 1mm 변형시의 loading, unloading force, stress hysteresis의 변화를 관찰하여 다음과 같은 결과를 얻었다. 1. Align은 재생 (T2)후에 3mm 변형시의 loading force, unloding force가 통계적으로 유의성 있게 증가하였다(loading force: p,0.05, unloading force:p<0.01). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성 있는 차이가 보이지 않았다. 2. Align은 재생(T2)후에 hysteresis가 통계적으로 유의성 있게 감소하였다(p<0.01). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성있는 차이가 보이지 않았다. 3. 모든 호선에서 1mm 변형시의 loading force는 재생(T2)후에 통계적으로 유의성있는 차이를 보이지 않았다. 4. Align은 재생(T2)후에 1mm 변형시의 unloading force가 통계적으로 유의성있게 증가하였다(p<0.05). NiTi, Optimmalloy, Sentalloy에서는 통계적으로 유의성있는 차이가 보이지 않았다. 5. Align의 loading force와 unloading force는 T1과 T0는 통계적으로 유의한 차이가 없었으며, T2와 T0사이에 유의성 있는 차이가 있었다(각각 p<0.05, p<0.01). 6. Align은 T1에서 pseudoelasticity가 감소하고, T2에서는 pseudoplasticity와 pseudoelasticity가 감소하였다.

• 한국추진공학회지
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• 제5권1호
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• pp.76-81
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• 2001

A structural test of the wind turbine rotor blade is to evaluate the uncertainty of design due to selection of material, design concepts, production processes and so on, and their possible impacts on the structural integrity. In the full-scale static strength test, the measuring parameters are strain and displacements vs. loads, weight and the center of gravity. In order to simulate the aerodynamics load, the three-point loading method is applied. There is slight difference between the measured results and the predicted results for the reference fiber volume fraction of 60% . However, the agreement between the measured results and the predicted results with the actual fiber volume fraction of 52.5% is good. Even though a slightly non-linearity from 80% loading to 100% loading exists, a linear static solution is sufficient for the design purpose due to te small amount of non-linearity. Comparison between measured and predicted strain results at the maximum thickness positions of the blade profile for 0.236R(5.56m), 0.493R(11.59m) and 0.574R(13.43m), under 20%, 40%, 60%, 80% and 100% loadings for the upper part of the blade. The predicted values are in good agreement with the measured values.

• 비파괴검사학회지
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• 제29권5호
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• pp.415-420
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• 2009

이 논문은 표면파의 비선형특성을 이용하여 재료 표면의 열화손상을 평가한 사례 연구의 결과를 보고한다. 이 연구에서는 3점 굽힘 피로시험에 의해 표면에 피로열화를 가한 알루미늄 T6 시편을 대상으로 표면파의 음향 비선형 파라미터를 측정하기 위한 실험장치를 구성하였으며, 피로시험 전후에서 측정된 비선형파라미터의 크기를 비교하였다. 특히 3점 굽힘 피로시험에 의한 표면피로손상은 시편의 중앙부 표면에 집중 될 것이 예상되므로 이 주변에서의 비선형 파라미터의 변화를 세밀히 관찰하였다. 실험결과 피로손상이 거의 없는 시편의 가장자리에서는 비선형 파라미터가 피로시험 전후에서 큰 변화가 없었지만, 표면 피로열화가 집중된 중앙부에서는 뚜렷하게 증가하는 것으로 나타났다.

• 한국안전학회지
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• 제27권6호
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• pp.93-98
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• 2012

In order to capture the fast crack propagation in an unmanipulated concrete fracture test, we employed mechanoluminascent(ML) material, which emits visible light when stressed, as a crack visualization tool. Three-point bending fracture test setup, a paint type ML material and a high speed camera were used to capture the images of fast moving cracks. The maximum size of coarse aggregates of concrete was used as an experimental parameter. The crack images, loading, and crack mouth opening displacement were successfully recorded as a function of time elapsed. From the test results, several interesting cracking behavior in the unmanipulated fracture test was observed in such that (1) the crack moves fast while the load is slowly decreased after the maximum loading, and (2) the crack in concrete with larger coarse aggregates moves faster than the others.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.725-736
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• 2020

In this work the mixed mode I/III fracture of sandstone has been studied experimentally and numerically. The experimental work used three-point bending specimens containing pre-existing cracks, machined at various inclination angles so as to achieve varying proportions of mode I to mode III loading. Dimensionless stress intensity factors were calculated using the extended finite element method (XFEM) for and compared with existing results from literature calculated using conventional finite element method. A total of 28 samples were used to conduct the fracture test with 4 specimens for each of 7 different inclination angles. The fracture load and the geometry of the fracture surface were obtained for different mode mixities. Prediction of the fracture loads and the geometry of the fracture surface were made using XFEM coupled with a cohesive zone model (CZM) and showed a good comparison with the experimental results.

• 한국안전학회지
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• 제9권2호
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• pp.18-25
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• 1994

In this thesis, the fatigue tests were performed on a series of reinforced concrete to Investigate the variation of strength and the safety of reinforced concrete structures under fatigue load. The specimens were of the same rectangular cross-section, of effective height 24cm and width 30cm and their span was 330cm. The three point loading system is used in the fatigue tests. In these tests, the fracture mode of reinforced concrete structures under fatigue load, relationship between the repeated loading cycles and the mid-span displacement of the specimens were observed. According to the test results, the following fatigue behavior of reinforced concrete specimens were observed. By increasing of the number of repeated loading cycles, the mid-span displacement became greater, however the Incremental amounts of the displacement were reduced. It could be also known that the inelastic strain energy of the doubly reinforced rectangular beams was larger than that of the singly reinforced rectangular beams as increasing the number of repeated loading cycles. Compliance of reinforced concrete structures tended to be reduced as increasing the repeated loading cycles, and the compliance of the doubly reinforced rectangular beams was generally smaller than that of the singly reinforced rectangular beams. Based on the above investigation, it could be concluded that the doubly reinforced rectangular beams under fatigue load were more efficient to resist the brittle fracture than the singly reinforced rectangular beams.

• Computers and Concrete
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• 제24권6호
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• pp.527-539
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• 2019

In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.677-682
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• 1998

Concrete is an inhomogeneous material consisting of larger aggregates and sand embedded in a cement paste matrix. In this study, an acoustic emission technique has been used to clarify the microscope failure mechanisms of concrete under three point bending test. AE source location has also been done to monitor the activities of internal damage and the progress of microscopic failure path during the loading. The relationship between AE characteristic and microscopic and microscopic failure mechanism is discussed.

• 한국안전학회지
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• 제37권5호
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• pp.7-13
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• 2022

Digital image correlation (DIC) is a method used to measure the displacement and strain of structures. It involves transforming and analyzing images before and after deformation using correlation coefficients from irregular light and shade on the surface of structures. In the present study, a microspeckle pattern was applied to the surface of a specimen to identify initial cracking. The test specimen constituted CFRP composites laminated on a curved Al liner The specimen was manufactured by stacking 100 ply of CFRP prepregs in the 0° and 90° directions in a three-point bending test. The equivalent strain was evaluated through DIC analysis after monitoring deformation using a CCD camera. Fracture shape was observed using a microscope. The equivalent strain contour distribution was checked until the maximum load fracture occurred at the center of the test specimen. Variations in the strain indicated the initial occurrence and progression of microcracks. These results can be used to improve the accuracy of detecting micro crack initiation and to achieve structural stability.

• 콘크리트학회지
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• 제10권6호
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• pp.203-211
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• 1998

고체내부의 미소파괴시 발생하는 탄성파 방출을 이용하는 음향방출기법은 구조물 또는 재료 내부의 미시적 변형기구를 이해하는데 매우 유익한 수단으로 최근 각 분야에서 다양하게 응용되고 있다. 따라서 본 연구에서는 모르타르 부재의 휨재하 시험시 부재 내부에 발생하는 미시적 손상거동 및 파괴특성을 시험시 연속적으로 모니터링한 AE 신호특성으로부터 평가하였다. 나아가 삼각법을 이용한 2차원 AE 발생원 위치추정으로부터 시험체 노치선단 주변에 대한 AE 발생원 위치를 명확히 하였으며 이들 결과로부터 미소균열의 성장 거동을 연속적으로 모니터링 하였다.