• The Journal of Advanced Prosthodontics
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• 제9권1호
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• pp.22-30
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• 2017

PURPOSE. The aim of this study was to investigate the effect of reinforcing materials on the fracture resistances of glass fiber mesh- and Cr-Co metal mesh-reinforced maxillary complete dentures under fatigue loading. MATERIALS AND METHODS. Glass fiber mesh- and Cr-Co mesh-reinforced maxillary complete dentures were fabricated using silicone molds and acrylic resin. A control group was prepared with no reinforcement (n = 15 per group). After fatigue loading was applied using a chewing simulator, fracture resistance was measured by a universal testing machine. The fracture patterns were analyzed and the fractured surfaces were observed by scanning electron microscopy. RESULTS. After cyclic loading, none of the dentures showed cracks or fractures. During fracture resistance testing, all unreinforced dentures experienced complete fracture. The mesh-reinforced dentures primarily showed posterior framework fracture. Deformation of the all-metal framework caused the metal mesh-reinforced denture to exhibit the highest fracture resistance, followed by the glass fiber mesh-reinforced denture (P<.05) and the control group (P<.05). The glass fiber mesh-reinforced denture primarily maintained its original shape with unbroken fibers. River line pattern of the control group, dimples and interdendritic fractures of the metal mesh group, and radial fracture lines of the glass fiber group were observed on the fractured surfaces. CONCLUSION. The glass fiber mesh-reinforced denture exhibits a fracture resistance higher than that of the unreinforced denture, but lower than that of the metal mesh-reinforced denture because of the deformation of the metal mesh. The glass fiber mesh-reinforced denture maintains its shape even after fracture, indicating the possibility of easier repair.

• 한국터널지하공간학회 논문집
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• 제8권3호
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• pp.227-235
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• 2006

최근 터널에서 균열, 누수 등과 같은 변상이 많이 발생하고 있어 터널의 안정성에 큰 문제가 되고 있으며, 기존 터널의 효율적인 안전 및 유지관리를 위해서는 터널 콘크리트 라이닝의 역학적 건전도를 평가하는 것이 필수적이라 할 수 있다. 본 연구에서 사용된 콘크리트 라이닝 모형 시험체는 실제 도로터널의 축소모형으로서 단일라이닝으로 구성되어 있으며, 하중조건, 라이닝 두께, 천단부 배면 공동 유무 및 강섬유 혼입률 등과 같은 라이닝 조건에 따른 모형실험을 실시하였다. 이러한 모형실험으로부터 터널 콘크리트 라이닝의 균열발생하중과 파괴하중, 처짐과 균열발생 형태를 조사하여 터널 콘크리트 라이닝의 변형 및 역학적 특성을 평가하였다.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.49-57
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• 2020

This paper presents a full-scale experimental test to investigate the flexural behavior of an innovative dovetail ultra-high performance concrete (UHPC) joint designed for the 5^th Nanjing Yangtze River Bridge. The test specimen had a dimension of 3600 × 1600 × 170 mm, in accordance with the real bridge. The failure mode, crack pattern and structural response were presented. The ductility and stiffness degradation of the tested specimens were explicitly discussed. Test results indicated that different from conventional reinforced concrete slabs, well-distributed cracks with small spacing were observed for UHPC joint slabs at failure. The average nominal flexural cracking strength of the test specimens was 7.7 MPa, signifying good crack resistance of the proposed dovetail UHPC joint. It is recommended that high grade reinforcement be cooperatively used to take full advantage of the superior mechanical property of UHPC. A new ductility index, expressed by dividing the ultimate deflection by flexural cracking deflection, was introduced to evaluate the post-cracking ductility capacity. Finally, a strut-and-tie (STM) model was developed to predict the ultimate strength of the proposed UHPC joint.

• Geomechanics and Engineering
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• 제20권5호
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• pp.399-410
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• 2020

Cavities often develop behind the vault during the construction of double-arch tunnels, generally in the form of various defects. The study evaluates the impact of cavities behind the vault on the mechanical and failure behaviors of double-arch tunnels. Cavities of the same sizes are introduced at the vault and the shoulder close to the central wall of double-arch tunnels. Physical model tests are performed to investigate the liner stress variation, the earth pressure distribution and the process of progressive failure. Results reveal that the presence of cavities behind the liner causes the re-distribution of the earth pressure and induces stress concentration near the boundaries of cavities, which results in the bending moments in the liner inside the cavity to reverse sign from compression to tension. The liner near the invert becomes the weak region and stress concentration points are created in the outer fiber of the liner at the bottom of the sidewall and central wall. It is suggested that grouting into the foundation soils and backfilling injection should be carried out to ensure the tunnel safety. Changes in the location of cavities significantly impact the failure pattern of the liner close to the vault, e.g., cracks appear in the outer fiber of the liner inside the cavity when a cavity is located at the shoulder close to the central wall, which is different from the case that the cavity locates at the vault, whereas changes in the location of cavities have a little influence on the liner at the bottom of the double-arch tunnels.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.389.2-389.2
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• 2014

Polydimethylsiloxane (PDMS) based electronic devices are widely used for various applications in large area electronics, biomedical wearable interfaces and implantable circuitry where flexibility and/or stretchability are required. A few fabrication methods of electronic devices directly on PDMS substrate have been reported. However, it is well known that micro-cracks appear in the metal layer and in the lithography pattern on a PDMS substrate. To solve the above problems, a few studies for fabrication of stiff platform on PDMS substrate have been reported. Thin-film islands of a stiff region are fabricated on an elastomeric substrate, and electronic devices are fabricated on these stiff islands. When the substrate is stretched, the deformation is mainly accommodated by the substrate, and the stiff islands and electronic devices experience relatively small strains. Here, we report a new method to achieve stiff islands structures on an elastomeric substrate at a various thickness, as the platform for stretchable electronic devices. The stiff islands were defined by conventional photolithography on a stress-free elastomeric substrate. This technique can provide a practical strategy for realizing large-area stretchable electronic circuits, for various applications such as stretchable display or wearable electronic systems.

• 대한치과보철학회지
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• 제36권2호
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• pp.336-354
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• 1998

Traditionally, many kinds of mechanical bonding techniques were used for bonding resins to the surface of the metal alloys. If there is a seperation between resin and metal junction by stress accumulation and temperature change of oral cavity, the cracks or crazing may occur, accompanied by failure of resin bonding to metal. This study was designed to compare the shear bond strength of the type IV gold alloy and Cr-Co alloy surfaces treated with various methods and thermocycling. Universal Instron (Model 1000) and scanning electron microscope (JEOL, Japan) was used to record the shear bond strength of 5 groups. Forty specimens were made for each group ; group 1 was treated with sandblasting only, group 2 was coated with V-primer after sandblasting, group 3 was coated with Metal primer, group 4 wase coated with MR Bond and group 5 was coated with silane. After treated with various methods, thermocycling was done for half of the each group. The surfaces of failed pattern were observed with SEM. The results were as follows : 1. Shear bond strength of the group 1 was lower than that of another groups in type IV gold alloys and bond strength of the group 1, 2 were lower than that of group 3, 4, 5 in Cr-Co alloys. 2. Shear bond strength of the gold alloy with resin was higher than that of Cr-Co alloy when specimens were coated with V-primer. 3. Shear bond strength of the Co-Cr alloys with resin was higher than that of gold alloys when specimens were coated with Metal primer. 4. The bond strength of all specimens did not decreased significantly after thermocycling. 5. Adhesive failures were found in group 1 and Cr-Co alloy in group 2, but adhesive and cohesive failures were found in another groups.

• 한국전자파학회논문지
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• 제27권1호
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• pp.8-13
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• 2016

본 논문에서는 잉크젯 프린팅 기술을 이용하여 종이 필름 위에 전도성 잉크를 인쇄하여 방사 패턴 변환이 가능한 종이접기 형태의 안테나를 제안한다. 제안된 안테나는 접었을 때와 펼쳤을 때 각각 다이폴 안테나와 루프 안테나로 동작하며, 종이 필름을 접고 펼치는 방식에 따라 상호 변환될 수 있다. 제안된 안테나는 다이폴 상태와 루프 상태일 때 모두 동일하게 1.85 GHz에서 동작하도록 설계되었다. 종이 필름을 접었을 때 종이 필름의 코팅과 그 위에 인쇄된 전도성 잉크가 깨짐 현상을 해결하기 위해 액체금속(liquid metal)중 하나인 EGaIn(Eutectic Gallium Indium)을 사용하였다. 제안된 안테나의 성능은 시뮬레이션과 실제 측정 결과로 확인할 수 있으며, 다이폴 상태와 루프 상태일 때 안테나 이득은 각각 -4 dBi, -5 dBi이다. 또한, 측정 결과, 다이폴 상태와 루프 상태일 때 서로의 Null 부분을 서로 상호 보완해 주는 것을 확인할 수 있다.

• 한국전산구조공학회논문집
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• 제31권2호
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• pp.105-114
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• 2018

본 연구에서 페리다이나믹 이론 모델을 이용하여 준정적하중과 동적 하중, 균열전파와 분기균열 패턴 그리고 등방성재료, 직교 이방성 재료의 균열 진전 해석 등 다양한 조건을 고려한 전산 시뮬레이션을 수행하여 그 적합성을 검토하였다. 초기 균열은 없지만 중심에 홀이 있는 등방성 재료, 초기 균열이 존재하는 등방성 및 이방성 재료에 대한 전산 시뮬레이션이 수행되었다. 조정 동적 완화 기법이 사용되어 준정적 하중을 모사하였고, 이방성 재료 해석에서는 고전 연속체 역학과 페리다이나믹의 변형률 에너지를 고려한 균질화 방법이 사용되었다. 균열 전파와 분기 균열이 성공적으로 확인되었으며 파괴 거동의 시작과 그 방향 역시 페리다이나믹 이론으로 확인되었다. 페리다이나믹을 균질화 방법을 사용하여 비교적 복잡한 이방성 재료에 적용한 경우 역시 실험 결과 값과 비교하여 검증하였다.

• 대한조선학회논문집
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• 제43권2호
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• pp.213-219
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• 2006

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo leading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life, but those have difficulties of considering stress concentration at notched location and complicated material behavior of welded joint or heat affected zone. Electronic speckle pattern interferometry(ESPI) system is nondestructive and non-contact measurement system which can get the relatively accurate full field strain at critical positions such as welded zone and structural discontinuous location. In this study, local strain was measured on welded cruciform joint by ESPI system and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by measured values using ESPI system. Moreover, experimental fatigue life was compared with established S-N curves using theoretical local strain and stress calculated by Neuber's rule.

• 치과방사선
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• 제25권2호
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• pp.409-422
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• 1995

The purpose of this study was to investigate the effects of radiation on the formation of rat molar enamel at the developmental stage. The experimental animals were divided into five groups and were irradiated single dose of 396cGy ; 1 st group on 14th day of gestation, 2nd group on 19th day of gestation, 3rd group on 3 days after birth, 4th group on 8 days after birth, 5th group on 28 days after birth. The control and 1, 2, 3, and 4th experimental groups were sacrificed on 2, 4, and 6 weeks and the 5th groups were sacrificed on 1 day and 2 weeks after irradiation. Distal 1/2 and occlusal 1/3 enamel surface of lingual side of lingual cusp, and fractured surface of lingual side of lingual cusp in a longitudinal direction of the mandibular first molar were examined using scanning electron microscope. The following results were obtained. 1. The roughness of enamel surface and enamel hypoplasia were increased in a sequence of 4th, 1st, 2nd, and 3rd experimental group, and the enamel cracks were increased in the 1st and 2nd experimental group. 2. The pattern of enamel hypoplasia had a network form on the 1st and 2nd experimental group, and appeared a linear shape on the 3rd experimental group, and then the crator-like enamel defects were observed in all experimental groups (especially 1st and 2nd experimental group) except 5th. 3. Dentinoenamel junction showed the clear-cut and straight appearance except 5th experimental group. 4. There was no significant difference between 5th experimental and control group.