• The Journal of Advanced Prosthodontics
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• 제7권1호
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• pp.32-38
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• 2015

PURPOSE. The aim of this study was to compare the durability and retention of 4 types of attachments placed over computer aided design/computer aided manufacturing (CAD/CAM) titanium bars when subjected to different pH conditions. MATERIALS AND METHODS. Four commercially available attachments were investigated: Hader Yellow, Hader Red, Ackerman Gold and Ackerman Stainless Steel. These attachments and Ackerman CAD/CAM titanium bars were placed in 2 vessels containing different artificial saliva solutions (pH 7/pH 4) at $37^{\circ}C$ for one month to simulate corrosion conditions, and they were then subjected to mechanical testing (5400 cycles of insertion and removal). RESULTS. The results revealed that there were significant differences in the average values of insertion/removal force due to the pH (F (1, 24)=9.207, P<.05) and the type of attachment (F (3, 24)=11.742, P<.05). CONCLUSION. More acidic pH values were found to have a negative influence on the retention capacity of the attachments.

• 대한기계학회논문집A
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• 제31권9호
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• pp.903-909
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• 2007

A fatigue capsule is one of the special capsules to investigate the fatigue characteristics of the nuclear materials during an irradiation test in a research reactor, HANARO. In this study, the performance test and the preliminary fatigue test results by using a cyclic load device newly developed for a fatigue capsule are described. In order to obtain the characteristics such as a realization and a controllability of the periodic wave shape and the relationship between the pressure and the load, a spring and rigid bar specimens are used. The fatigue test for the 316L stainless steel specimen with 1.8mm in diameter and 12.5mm in gage length is also performed under the same conditions as the temperature($550^{\circ}C$) of the specimen during irradiation tests. As a result of the test, the fracture of the specimen occurs at a total of 70,120 cycles(about 12 days), and the displacement in this case is 2.02 mm. It is expected that these results will be used for determining test conditions and a comparison of the in-pile fatigue test results.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(2)
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• pp.336-343
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• 1998

An iteration method has been developed for determining crack growth and fracture resistance cure (J-R curve) from the load versus load-line displacement record only. In this method, the hardening curve, the load versus displacement curve at a given crack length, is assumed to be a power-law function, where the exponent varies with the crack length. The exponent is determined by an iterative calculation method with the assumption that the exponent varies linearly with the load-line displacement. The proposed method was applied to the static J-R tests using compact tension(CT) specimens, a three-point bend (TPB) specimen, and a cracked round bar (CRB) specimen as well as it was applied to the quasi-dynamic J-R tests using CT specimens. The J-R curves determined by the proposed method were compared with those obtained by the conventional testing methodologies. The results showed that the J-R curves could be determined directly by the proposed iteration method with sufficient accuracy in the specimens from SA508, SA533, and SA516 pressure vessel steels and SA312 Type 347 stainless steel.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.296-301
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• 2003

A study on the engineering design and numerical thermo-hydraulic analysis for KSTAR TF coil structure cooling system has been conducted. The numerical analyses have been done to verify the engineering design of cooling using the commercial code, FLUENT and in-house code for calculating helium properties which varies with cooling tube's heat transfer. Through the engineering design process based on the steady heat balance concepts, the circular stainless steel tube with inner diameter of 4 mm for TF coil has been selected as cooling tube. From normal operation mode analysis results, total 28 cooling tubes were finally chosen. Also, three dimensional cool down analysis for TF coil with designed cooling tube was satisfied with next three design criteria. First is cooling work termination within a month, second is maximum temperature difference within 50 K in TF coil structure and third is exit helium pressure above 2 bar. Consequently, these cool down scenario results can afford to adopt as operating scenario data when KSTAR facilities operate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.60-63
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• 2009

Manufacturing technologies of micro spur gear and micro mold by micro PIM were studied with stainless steel feedstock. For molding of gears, micro mold with gear cavity of 1.2 mm in diameter was produced by wire EDM. The proper injection pressure was selected to 70bar by observation and measuring of shapes and shrinkage of gears before/after sintering. For fabrication of micro mold, a tiny polymer gear was produced by injection into the mold. Then, 316L feedstock was again injected/compressed on the polymer gear and debinded together with polymer gear followed by sintering. As a result, another metal mold with gear cavity reduced to about 20% was fabricated and through repetition of this process chain, micro gear mold with cavity about below 800 um was finally obtained. In reduction of size by injection/compression molding, height of gear tooth was shrunk more and the effort for decrease of roughness of micro cavity were carried out ultrasonic polishing and as a result, the roughness in cavity decreased from 3-4 um to about 200 nm.

• 한국진공학회지
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• 제16권2호
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• pp.153-159
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• 2007

KSTAR 장치의 저온 component에 헬륨을 공급하기 위한 헬륨라인은 크게 두 가지로 이루어져 있다. 냉동기에서 KSTAR 저온용기 외부까지의 트랜스퍼 라인과, 저온용기 내부의 헬륨라인이다. KSTAR 장치는 3가지 종류의 헬륨을 사용하여 각 저온 component를 냉각하는데, 초전도 자석 시스템과 버스라인에는 초임계 헬륨, 전류인입장치에는 액체 헬륨, 열차폐체에는 가스 헬륨을 공급한다. 저온용기 내부의 헬륨라인은 냉동기에서 저온용기 근처까지 연결된 배관을 저온용기 내부의 각 장치에 최단거리로 열손실 없이 설치하여 각 장치가 정상 작동하도록 하는데 그 목적이 있다. 저온용기 내부의 헬륨라인은 최대 20bar로 가압되는 운전시간 동안에 헬륨누설 없이 설치되어야 한다. 그리고 상온으로 부터의 복사열을 차단하기 위하여 다층절연제로 배관을 감싸주어야 하고 고전압 부분은 프리프레그 테잎으로 절연되어야 한다. 전기절연체는 세라믹과 스테인레스 스틸 튜브를 브레이징 접합 방법으로 연결하여 만들어진 것으론 배관과 배관, 배관과 저온 component간의 절연을 위해 사용되고, 헬륨라인과 동일하게 4.5K 초임계 헬륨온도에서 누설이 없어야 한다. 따라서 모든 전기절연체는 액체질소에 침전시켜 열충격을 가하고, 내부에 30 bar를 가압하여 진공 누설시험을 한다. 그리고 초전도 자석과 배관의 절연체로 사용되므로 15kV 고전압 절연 검사를 한다. 전기절연체의 세라믹 부분은 구조적 보강을 위하여 추가적으로 표면에 절연 작업을 한다. 현재 대부분의 저온용기 내부의 헬륨 라인은 설치 완료되어 있으며, 최종 검사가 진행 중이다.

• 한국의학물리학회지:의학물리
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• 제13권3호
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• pp.114-119
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• 2002

조사 선량의 분포를 저해하지 않으면서 정확한 차폐가 가능하며, 짧은 시간 내에 쉽게 환자를 고정할 수 있으며, 치료 중에 환자가 의식을 잃는 경우에도 다치지 않고 지지될 수 있는, 한국인의 체형에 맞는 전신방사선치료를 위한 고정장치를 개발하고 그 효과를 평가하였다. 230 cm의 키, 100 kg의 체중을 가진 성인 환자도 지지될 수 있도록 지름 5 cm의 스텐레스 원형 봉을 사용하여 프레임을 제작하였고, 의자는 환자가 서 있는 상태에서 환자의 키, 몸의 두께에 맞추어 위치 조절이 가능하도록 고안하였다. 가슴부위의 전면 지지대는 1 cm 두께의 아크릴을 사용하여 지지의 기능과 차폐물의 고정 기능을 겸하게 하였고, 등면의 지지대는 1 cm 두께의 아크릴을 5 mm 두께, 3 cm 넓이의 스텐레스 스틸로 테를 둘러 환자의 지지와 엑스선 필름 카세트 고정장치를 겸하도록 고안하였으며 2개의 상부 도르래와 측면의 핸들로 쉽고 정확하게 조절할 수 있도록 하였다. 머리 고정장치는 비닐과 특수 스펀지를 사용하여 쇠약한 환자의 작은 흔들림도 방지할 수 있도록 하였다. 환자를 원하는 위치에 고정하는데 평균 4분 25초가 소요되었고 반복되는 분할조사의 검교정 필름에서 폐의 차폐물의 위치에 차이가 없었으며, 펜텀 실험과 환자치료에서 $\pm$5%의 선량차이를 보였다. 치료중 환자가 의식을 잃은 경우도 수차 있었으나 쓰러지지 않고 지지할 수 있었다.

• 전자공학회논문지SC
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• 제42권6호
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• pp.67-76
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• 2005

본 논문에서는 근전의수용 소형 근전위 센서를 제안한다. 근전의수용 근전위 센서를 의수 소켓에 내장시키기 위해서는 소형이어야 한다. 제안된 근전위 센서는 피부와 접촉하는 전극과 신호처리를 위한 회로부가 일체화된 형태로 소형화 하였다. 기준 전극은 두 입력전극의 가운데에 나란히 배치되고, 입력전극은 막대형, 기준전극은 막대형과 원형의 두 가지 형상으로 설계하였다. 두 입력전극 사이의 간격은 근섬유의 근전위 신호의 전도속도와 중심주파수를 고려하여 18mm, 20mm, 22mm 의 세 개의 서로 다른 간격을 가진 전극을 제작하였다. 사용된 전극의 재료는 땀이나 습기에 강한 SUS440 금속을 사용하였다. 신호처리 회로부는 대역통과 필터를 갖는 차동 증폭기, 전원노이즈를 제거하기 위한 대역저지 필터, 교류결합증폭기, 절대평균값 회로로 구성되어 있다. 실험에서는 정상인의 전완에서 근전위 신호를 취득하여 주파수 분석하고, 입력전극 사이의 간격과 기준전극의 형상에 따른 출력특성 평가하였다. 본 논문에서는 실험의 결과로부터 두 입력전극간의 거리가 18mm 이면서, 입력전극의 형상과 기준전극의 형상이 모두 막대형인 표면 근전위 센서가 근전의수에 최적임을 보인다.

• The Journal of Advanced Prosthodontics
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• 제9권6호
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• pp.439-446
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• 2017

PURPOSE. To evaluate the effects of different surface treatments on the bond strength of novel CAD/CAM restorative materials to resin cement by four point bending test. MATERIALS AND METHODS. The CAD/CAM materials under investigation were e.max CAD, Mark II, Lava Ultimate, and Enamic. A total of 400 bar specimens ($4{\times}1.2{\times}12mm$) (n=10) milled from the CAD/CAM blocks underwent various pretreatments (no pretreatment (C), hydrofluoric acid (A), hydrofluoric acid + universal adhesive (Scotchbond) (AS), sandblasting (Sb), and sandblasting + universal adhesive (SbS)). The bars were luted end-to-end on the prepared surfaces with a dual curing adhesive resin cement (Variolink N, Ivoclar Vivadent) on the custom-made stainless steel mold. Ten test specimens for each treatment and material combination were performed with four point bending test method. Data were analyzed using ANOVA and Tukey's test. RESULTS. The surface treatment and type of CAD/CAM restorative material showed a significant effect on the four point bending strength (FPBS) (P<.001). For LDC, AS surface treatment showed the highest FPBS results ($100.31{\pm}10.7MPa$) and the lowest values were obtained in RNC ($23.63{\pm}9.0MPa$) for control group. SEM analyses showed that the surface topography of CAD/CAM restorative materials was modified after treatments. CONCLUSION. The surface treatment of sandblasting or HF acid etching in combination with a universal adhesive containing MDP can be suggested for the adhesive cementation of the novel CAD/CAM restorative materials.

• 대한금속재료학회지
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• 제48권6호
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• pp.477-488
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• 2010

Zr-based amorphous alloy matrix composites reinforced with stainless steel (STS) and tantalum continuous fibers were fabricated without pores or defects by a liquid pressing process, and their quasi-static and dynamic deformation behaviors were investigated by using a universal testing machine and a Split Hopkinson pressure bar, respectively. The quasi-static compressive test results indicated that the fiberreinforced composites showed amaximum strength of about 1050~1300 MPa, and its strength maintained over 700 MPa until reaching astrain of 40%. Under dynamic loading, the maximum stresses of the composites were considerably higher than those under quasi-static loading because of the strain-rate hardening effect, whereas the fracture strains were considerably lower than those under quasi-static loading because of the decreased resistance to fracture. The STS-fiber-reinforced composite showed a greater compressive strength and ductility under dynamic loading than the tantalum-fiber-reinforced composite because of the excellent resistance to fracture of STS fibers.