• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.258-265
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• 2001

Turbine blade is subject to force of three type ; torsional force by torsion-mount, centrifugal force by rotation of rotor and cyclic bending force by steam pressure. Cyclic bending force of them is main factor on fatigue fracture. In the X-ray diffraction method, the change in the values related to plastic deformation and residual stress near the fracture surface mat be determined, and information of internal structure of material can be obtained. Therefore, to find a fracture mechanism of torsion-mounted blade in nuclear plant, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined, and then the load applied to actual broken turbine blade parts was predicted. Failure analysis is performed by finite element method and Goodman diagram on torsion-mounted blade.

• 한국세라믹학회지
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• 제27권2호
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• pp.233-243
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• 1990

For theinvestigation of MgO addition effect on 12Ce-TZP ceramics, MgO-CeO2-ZrO2 ceramics was fabricated using commercial powders under sintering condition of 130$0^{\circ}C$-1$600^{\circ}C$ for 2hr. Fully tetragonal phase could be obtained by proper heat treatment and MgO addition amount. Minor cubic phase was appeared in relatively high MgO content composition at each sintering temperature. As alloying amount of MgO increased, tetragonal stability increased and grain size decreased. Grain size dependence on MgO content was verified by SEM observation of fractured surface. Surface bloating was observed from the 2 m/o to 6m/o in the temperature range of 150$0^{\circ}C$ to 1$600^{\circ}C$. In spite of very porous microstructure owing to surface bloating, 100% TZP could be maintained in 2.0m/o MgO composition by heat treatment of 150$0^{\circ}C$. This result indicated that MgO was more powerful stabilizer than CeO2. Mechanical proprties of MgO-CeO2-ZrO2 ceramics were consistent with the stability observation of tetragonal phase very well.

• 한국표면공학회지
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• 제48권6호
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• pp.283-291
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• 2015

The purpose of this study was to investigate effects of TiN coating on the fatigue fracture of dental implant system with various cyclic loads. TiN coated abutment screw, the fixture, and abutment of internal hex type were prepared for fatigue test. The fatigue test was carried out according to ISO 14801:2003(E) using tensile and compression tester with repeated load from 30% to 80% of static fracture force. Morphology and fractured surface was observed by field emission scanning electron microscope(FE-SEM) and energy dispersive X-ray spectroscope(EDS). The fracture cycle drastically decreased as repeated load increased. Especially, in the case of TiN-coated abutment screw, fracture cycle increased compared to non-coated abutment screw. The fatigue crack was propagated fast as repeated load increased. The plastic deformation region decreased, whereas, cleavage fracture region increased as repeated load increased.

• 한국표면공학회지
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• 제45권5호
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• pp.212-217
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• 2012

High strength steel sheets used for automobile outer-panels have been intensively studied for developing a lightweight automobile under a strong pressure of the requirements for enhancing the mileage and energy saving in production of automobile parts. It is known that high strength steels are susceptible to hydrogen embrittlement, The susceptibility to hydrogen embrittlement increases with increasing its strength. However, the effect of hydrogen on the fracture behavior of high strength steels, though investigated extensively, has not been fully understood. In this paper, hydrogen was charged with 590DP steels by electrochemical method and its content was measured by hydrogen determinator with the different charging conditions. It was shown that the SP energy and maximum load decreased with increasing charging time. The results of SEM-fractography investigation for the hydrogen contained samples showed that a small portion of dimples on cleavage-fractured surface were observed and the size of the dimples were decreased with increasing hydrogen charging time.

• 한국해양공학회지
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• 제25권6호
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• pp.42-48
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• 2011

The present study makes three original contributions to nanoskinned Ti-6Al-4V materials. The nanoskins were fabricated on Ti-6Al-4V material using various surface treatments: deep rolling (DR), laser shot peening (LSP), and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular in industrial fields. A fatigue strength comparison at up to 106 cycles was conducted on these nanoskinned Ti-6Al-4V materials. Fatigue tests were carried out using MTS under axial loading tension-compression fatigue (R = -1, RT, 5 Hz, sinusoidal wave). The analysis of the crack initiation patterns in the nanoskinned Ti-6Al-4V materials found an interior originating crack pattern and surface originating crack type. Microscopic observation was mainly used to investigate the fatigue fractured sites. These surface modification techniques have been widely adopted, primarily because of the robust grade of their mechanical properties. These are mainly the result of the formation of a large-scale, deep, and useful compressive residual stress, the formation of nanocrystals by the severe plastic deformation (SPD) at the subsurface layer, and the increase in surface hardness.

• 한국재료학회지
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• 제19권1호
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• pp.18-23
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• 2009

The influence of various surface morphologies on the mechanical strength of silicon substrates was investigated in this study. The yield for the solar cell industry is mainly related to the fracturing of silicon wafers during the manufacturing process. The flexural strengths of silicon substrates were influenced by the density of the pyramids as well as by the size and the rounded surface of the pyramids. To characterize and optimize the relevant texturing process in terms of mechanical stability and the fabrication yield, the mechanical properties of textured silicon substrates were investigated to optimize the size and morphology of random pyramids. Several types of silicon substrates were studied, including the planar type, a textured surface with large and small pyramids, and a textured surface with rounded pyramids. The surface morphology and a cross-section of the as-textured and fractured silicon substrates were investigated by scanning electron microscopy.

• Restorative Dentistry and Endodontics
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• 제21권2호
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• pp.602-618
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• 1996

The purpose of this study was to investigate the effect of acid treatment of fluoride applied dentin surface with various concentrations of phosphoric acid for various periods of time on dentin bonding. Dentin specimens prepared from freshly extracted bovine mandibular anterior teeth were divided into fluoridated and nonfluoridated groups. Specimens of nonfluoridated group were pretreated with 10% phosphoric acid for 15 seconds. Those of fluoridated groups were treated with 2% sodium fluoride or 2% stannous fluoride solution for 5 minutes and stored in $37^{\circ}C$ distilled water for 3 days, followed by phosphoric acid treatment. The concentrations of phosphoric acid were 10%, 32% or 50% and the treatment periods of time were 15, 30 or 60 seconds. All the specimens were bonded with All Bond$^{(R)}$ 2 and Bisfil$^{TM}$ composite resin. After bonded specimens were stored in $37^{\circ}C$ distilled water for 24 hours, tensile bond strengths of each specimens were measured and the pretreated dentin and the fractured dentin surfaces were examined under the scanning electron microscope. The results were as follows : The tensile bond strengths from the fluoridated groups were significantly lower than those from the nonfluoridated group when the concentrations of phosphoric acid and the treatment periods of time were equal in all the groups (p<0.05). In general, the higher the concentration of phosphoric acid and the longer the treatment period of time for acid etching on the fluoride applied dentin surface, the higher were the bond strength values. Recovery of bond strength of the dentin bonding agent was better in the NaF applied group than in the $SnF_2$ applied one. SEM findings of NaF applied and $SnF_2$ applied dentin surfaces demonstrated reaction product-covered and partially or completely obstructed dentinal tubules. SEM findings of dentin surfaces fluoridated for 5 minutes followed by etching showed wider tubular openings and more clean dentin surfaces when dentin was etched with higher concentration of phosphoric acid for longer period of time. On the SEM observations of the fractured dentin-resin interface, the etched specimens of fluoridated group showed an adhesive failure mode when the concentration of phosphoric acid and the treatment period of time were same as in the nonfluoridated group. As the concentration of phosphoric acid and the treatment period of time increase during acid etching, the cohesive failure area increased. However, excessive acid etching caused adhesive failure.

• 대한소아치과학회지
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• 제36권2호
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• pp.310-317
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• 2009

치외치는 치아의 교합면에 부가적인 교두나 돌기(tubercle)를 가진 치아의 형태 이상이다. 치외치는 1-4%의 유병율을 보이며 하악 소구치에서 발생 빈도가 높다 치외치의 돌기는 쉽게 마모되거나 파절되어 치수 노출, 치수 생활력 상실, 안면부 감염, 골수염 등을 일으킬 수 있다. 또한, 돌기가 파절될 때 치외치의 치근단이 미성숙 상태인 경우가 많아 근관 치료가 쉽지 않다. 미성숙 영구치의 근관치료 시 수산화칼슘이 널리 사용되어 왔으나 내원 빈도 단축을 위해 여러 대체 재료들이 제안되어 왔다. 그 중 하나인 Mineral Trioxide Aggregate는 우수한 생체적합성과 변연 폐쇄성을 특징으로 하며, 미성숙 영구치의 근관치료 시 치료 기간을 단축시킬 수 있다. 본 증례보고에서는 치외치로 인한 치수 괴사로 봉와직염이 발생한 환자를 Mineral Trioxide Aggregate로 치료하였다. 미성숙 치근단을 가진 하악 소구치에 Mineral Trioxide Aggregate를 이용한 치근단형성술(apexification)을 시행하여 임상적 및 방사선학적으로 양호한 결과를 얻었으며, 한 증례에서는 치근단유도술(apexogenesis)의 결과와 같이 계속적인 치근 성장이 관찰되었다.

• 자원환경지질
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• 제51권2호
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• pp.121-130
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• 2018

KAERI Underground Research Tunnel(이하 KURT)는 한국원자력연구원의 연구지역에 건설된 지하처분연구시설이다. 현재 KURT에서는 방사성폐기물의 심층 처분의 주요 핵심 요소인 공학적 방벽과 천연방벽에 대한 연구를 수행하고 있다. 본 연구에서는 심부영역의 부지특성평가기술을 구축하기 위해 수행된 KURT 연구지역의 부지특성조사를 종합하여, 부지 지질모델을 구축하고, 이로부터 3차원 수리지질모델을 도출하였다. 연구지역에서 수행된 지질조사와 시추공 조사 결과를 이용하여 분석한 결과, 수리지질학적 관점에서 중요한 풍화대, 상부 단열암반대, 하부 단열암반대와 심부 영역에 존재하는 결정론적 단열대를 정의하여 이들을 3차원으로 모형화 하였고, 구축된 지질모델과 현장수리시험 결과를 종합하여 지하수유동모델링 및 처분 안전성 평가에 주요한 입력 자료가 될 수리지질모델을 도출하였다.

• 마이크로전자및패키징학회지
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• 제15권1호
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• pp.33-37
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• 2008

Kirkendall void는 전해도금 Cu/Sn-Ag 솔더 접합부에서 형성되었으며 Cu 도금욕에 함유되는 첨가제에 의존한다. 첨가제로 사용된 SPS의 함량의 증가와 함께 $150^{\circ}C$에서 열처리 후 많은 양의 Kirkendall void가 $Cu/Cu_3Sn$ 계면에 존재하였다. AES 분석은 void 표면에 S가 편석되어 있음을 보여주었다. $Cu/Cu_3Sn$ 계면을 따라 파괴된 시편에서 Cu, Sn, S peak만 검출되었고 AES 깊이 프로파일에서 S는 급격하게 감소하였다. $Cu/Cu_3Sn$ 계면에서 S 편석은 계면에너지를 낮추고 Kirkendall void 핵생성을 위한 에너지장벽을 감소시킨다. 낙하충격시험은 SPS를 사용하여 도금된 Cu의 경우 Kirkendall void가 형성된 $Cu/Cu_3Sn$ 계면에서 파괴가 진행되고 급격하게 신뢰성이 감소됨을 보였다.