• 대한기계학회논문집A
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• 제25권10호
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• pp.1528-1534
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• 2001

In order to improve Leak-Be(ore-Break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result.

• 대한치과교정학회지
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• 제53권2호
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• pp.89-98
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• 2023

Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods: The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions: The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.

• 대한치과기공학회지
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• 제32권4호
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• pp.351-356
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• 2010

Purpose: The purpose of this study was to evaluate the fracture strength between the core and veneering ceramic according to 2 core materials, In-Ceram Alumina and In-Ceram Zirconia, fabricated by electro ceramic layering technique. 2 different fixed partial denture cores of three units were veneered by veneering ceramic(Ceranion, Noritake) (n=10). Methods: The fracture strengths between the core and veneering ceramic were measured through the 3 point bending test. The interfaces between the core and veneering ceramic were observed with the X-ray dot mapping of EPMA. Results: The result of fracture strength was observed that IZP group, In-Ceram Zirconia core, had higher fracture strength. IPA group, In-Ceram Alumina core, had fracture strength of 359.9(${\pm}$86.2) N. IZP group, In-Ceram Zirconia core, had fracture strength of 823.2(${\pm}$243.0) N. X-ray dot mapping observation showed that a major element in the core and veneering ceramic of IPA group was alumina and silica, respectively. No binder was observed in interfaces between the core and veneering ceramic, and no ion diffusion or transition was observed between the core and veneering ceramic. However, apparent ion diffusion or transition was observed between the core and veneering ceramic of IZP group.

• 한국재난정보학회 논문집
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• 제11권2호
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• pp.211-218
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• 2015

본 연구에서는 방폭 성능 강화를 위하여 유기계 다발형 섬유보강재를 제안하였으며, 제안된 섬유는 폴리아미드섬유, PET섬유 및 아라미드섬유이고, ATY 가공방식을 통해 다발형 단섬유를 제조하였다. 유기계 섬유보강재를 혼입한 콘크리트의 방폭 성능 평가를 대신하여 변형에너지 흡수 능력을 평가하였으며, 이를 위해 4점 휨시험과 노치보의 3점 휨시험을 수행하였다. 3종류의 유기계 단섬유를 혼입한 콘크리트의 휨성능 평가 결과, PET섬유 보강 콘크리트가 가장 우수한 결과를 나타내어, 방폭 성능 강화를 위하여 상당히 효과적일 것으로 판단된다.

• 대한기계학회논문집A
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• 제29권1호
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• pp.107-114
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• 2005

In order to analyze the elastic-plastic fracture behavior of a structure, the fracture resistance curve of the material should be known first. The standard CT specimen was used to obtain the fracture resistance curves of a piping system. However, it is known that the fracture resistance curve by the standard CT specimen is very conservative to evaluate the integrity of a structure. Also the fracture resistance curve is effected by the specimen geometry and the dimensions because of the constraint effect. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen and to provide an additional safety margin. For these, the fracture tests using a real pipe specimen and the standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. Also finite element analyses were performed with a CT specimen and a pipe in order to prove the additional safety margin. From the result of tests and analyses of the pipe and the standard CT specimen, it was observed that the fracture analysis with the standard CT specimen is conservative and the additional safety margin was proved.

• 마이크로전자및패키징학회지
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• 제28권2호
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• pp.29-37
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• 2021

3 차원 패키징을 위한 저온 Cu-Cu직접 접합부의 계면접착에너지를 향상시키기 위해 Cu박막 표면에 대한 Ar/N₂ 2단계 플라즈마 처리 전, 후 Cu표면 및 접합계면에 대한 화학결합을 X-선 광전자 분광법(X-ray photoelectron spectroscopy)을 통해 정량화한 결과, 2단계 플라즈마 처리로 인해 Cu표면에 Cu₄N이 형성되어 Cu산화를 효과적으로 억제하는 것을 확인하였다. 2단계 플라즈마 처리하지 않은 Cu-Cu시편은 표면 산화막의 영향으로 접합이 제대로 되지 않았으나 2단계 플라즈마 처리한 시편은 효과적인 표면 산화방지효과로 인해 양호한 Cu-Cu접합을 형성하였다. Cu-Cu직접접합 계면의 정량적 계면접착에너지를 double cantilever beam 시험방법 및 4점 굽힘(4-point bending, 4-PB) 시험방법을 통해 비교한 결과, 각각 1.63±0.24, 2.33±0.67 J/m²으로 4-PB 시험의 계면접착에너지가 더 크게 측정되었다. 이는 계면파괴역학의 위상각(phase angle)에 따른 계면접착에너지 증가 거동으로 설명할 수 있는데 즉, 4-PB의 계면균열선단 전단응력성분 증가로 인한 계면거칠기의 효과에 기인한 것으로 판단된다.

• 대한기계학회논문집A
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• 제38권12호
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• pp.1387-1394
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• 2014

광탄성 실험법에 의해 측정된 등색프린지 차수를 응력으로 변환시키기 위해서는 광탄성 재료 응력 프린지 상수를 알아야 한다. 광탄성 재료 응력 프린지 상수는 단순 인장시편 또는 압축하중을 받는 원형디스크를 이용하여 측정하는 방법 등이 있다. 이들 방법에서는 시편에 여러 하중을 가하여 하중에 응답하는 프린지 차수의 관계를 최소자승법 등을 이용하여 재료 상수를 결정한다. 본 논문에서는 4점 굽힘 시편에 하중을 가하여 나타나는 프린지로부터 재료 응력 프린지 상수를 결정하였다. 4점 굽힘 시편의 순수 굽힘 구간에서는 주응력 방향이 일정하므로 4단계 위상이동법의 적용이 가능하다. 이 방법은 원형편광기에서 검광판을 0, ${\pi}/4$, ${\pi}/2$, 그리고 $3{\pi}/4$ 라디안 회전시켜 얻은 4개의 광탄성 프린지를 필요로 한다. 4점 굽힘 시편을 이용한 재료의 프린지 상수를 결정하는 방법에서는 일정 하중을 가하여 서로 다른 위치에서도 측정할 수 있는 장점이 있다. 이 방법으로 측정된 재료 응력 프린지 상수는 제조회사에서 제시한 범위이내에 분포하였다.

• Journal of Biosystems Engineering
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• 제15권3호
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• pp.177-185
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• 1990

The break of rotary blade is occured from a stress concentration of the inside of blade by the outside impulsive load. In order to examine its inside stress and stress concentration of rotary blade, a epoxy plate which is suitable to applicate by photoelastic system is used to experiment. These results are summarized as follow. 1. Refer to the existence of bolt hole and a size of its of rotary blade, a stress concentration which cause the break of rotary blade is not exposed. 2. It is expected to be break to section of hold of rotary blade and the break of this is due to that there are concentrated by shearing force, bending moment and bending stress. 3. When the crack which caused from processing are set up to any location, the stress concentration taken to the creak point. 4. Without regard to the location of the reaction points of rotary blade, the bending stress which is greated than the bending moment is occured within about 6 em toward the center line of bolt hole and it was possible to break that section.

• 한국해양공학회지
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• 제12권2호통권28호
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• pp.57-64
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• 1998

This study is concerned with criterion for membrane to shell conversion in two-dimensional elastic-plastic finite element analysis using membrane/shell mixed element. It is well known that in the sheet metal forming some parts of the sheet deform under almost pure stretching (membrane) conditions, whereas other parts in contact with sharp tooling surfaces can develop significant bending strains. The membrane analysis has a short computational time however, in the membrane analysis the bending effects can not be condidered at all. On the other hand, the shell analysis allows the consideration of bending effects, but involves too much computational time. So Onatel),2), Yang et al3),4) developed the membrane/shell mixed element. Onate introduced the energy ratio parameter and Yang et al introduced the ratio of thickness to radius of curvature as the criterion. In the present study we propose a new criterion by using the angle between both side elements in the nodal point.

• Steel and Composite Structures
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• 제21권3호
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• pp.537-551
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• 2016

A new type of composite beam which consists of a wide flange steel shape beam and an innovative type of composite slab was introduced. The composite slab is composed of concrete slab and normal flat steel plates, which are connected by perfobond shear connectors (PBL shear connectors). This paper describes experiments of two large-scale specimens of that composite beam. Both specimens were loaded at two symmetric points for 4-point loading status, and mechanical behaviors under hogging and sagging bending moments were investigated respectively. During the experiments, the crack patterns, failure modes, failure mechanism and ultimate bending capacity of composite beam specimens were investigated, and the strains of concrete and flat steel plate as well as steel shapes were measured and recorded. As shown from the experimental results, composite actions were fully developed between the steel shape and the composite slab, this new type of composite beams was found to have good mechanical performance both under hogging and sagging bending moment with high bending capacity, substantial flexure rigidity and good ductility. It was further shown that the plane-section assumption was verified. Moreover, a design procedure including calculation methods of bending capacity of this new type of composite beam was studied and proposed based on the experimental results, and the calculation methods based on the plane-section assumption and plastic theories were also verified by comparisons of the calculated results and experimental results, which were agreed with each other.