• 연구논문집
• /
• 통권34호
• /
• pp.79-85
• /
• 2004

There are several types of life test method for hose assemblies. The two major tests used for hose assemblies are impulse test and burst test. And magnification adjustment of impulse pressure, heating of testing oil and repetitive motions of bending and straightening of testing hose are also performed for accelerating the life. According to the manufacture process of hose and swaging process of fitting, there is a difference in the life of hose assemblies from minimum 7 times to maximum 40 times during the life test in the same functioning condition. Like this, the life test of hose which has a wide scope of life distribution gives a problem that observation should take a long time to find out the existence of the bursting from the beginning of the test to the completion of bursting of hose assemblies. Therefore, this research proposes a process of concentrating on the defective section of hose assemblies and maximizing the life acceleration by giving 'Knockdown stress' to hose assemblies just until before the hose assemblies get out of order.

• 한국정밀공학회지
• /
• 제31권3호
• /
• pp.277-283
• /
• 2014

This paper presents the design, optimization and fabrication of a piezo driven micro-positioning stage constructed using a 3D-printer. 3D printing technology provides many advantageous aspects in comparison to traditional manufacturing techniques allowing more rapid prototyping freedom in design, etc. Micro-positioning stages have traditionally been made using metal materials namely aluminum. This paper investigates the possibility of fabricating stages using ABS material with a 3D printer. CAE simulations show that equivalent motion amplification can be achieved compared to a traditional aluminum fabricated stage while the maximum stress is 30 times less. This leads to the possibility of stages with higher magnification factors and less load on the driving piezo element. Experiment results agree with the simulation results. A micro-position stage was fabricated using a 3D printer with ABS material. The motion amplification is very linear and 50 nm stepping was demonstrated.

• 대한치과보철학회지
• /
• 제36권1호
• /
• pp.120-132
• /
• 1998

This stusy was to investigate the marginal fitness of porcelain-fused-to- metal crown after succesive firing cycle. Main variables were the degree of marginal curvature of labiocervical margin and the type of alloy. The exaggerated marginal curvature(EMC) was created by additional reduction at the faciocervical wall of the normallized marginal curvature (NMC)-typed ivorine tooth by using milling machine. The difference in the shape was the mid facial margin was placed 2mm apical to cemento- enamel junction in labial surface. Three types of alloy were high noble, noble, and base metal alloy. Test specimens were divided into 8 groups and each group had 8 specimens. Sixty four ceramometal crowns were made totally. Measurement stages were following degassing, opaquing. body porcelain firing, and glazing, and measuring sites were 4. (midmesial, midfacial, middistal, and midlingual). Digital, travelling measuring microscope (0.5 um precision, Olympus. Japan) was used under ${\times}250$ magnification. Within the limitation of this investigation, it was concluded as belows: 1. The pattern of marginal distortion was varied. Degassing stage was not a specific, causative stage that induce most of total marginal distortion during whole procedure fabricating a ceramometal crown. Body firing stage induced discrepancy relatively more than other firing stages. 2. The specimens that were Ni-based alloy and had EMC were distorted persistently following successive fabricating procedures. But marginal openings were decreased after glazing. 3. The release of metal grinding-induced stress was presumed as a cause that induce marginal distortion. 4. The amount of discrepancies of the labial and lingual margins were greater than that of the mesial and distal margin in the specimen that had EMC. 5. Silver-plated die was not enough to resist abrasion during repeated seating of metal copings on the die-holding device.

• 대한한방부인과학회지
• /
• 제19권3호
• /
• pp.121-134
• /
• 2006

Purpose : Cuscuta chinensis Lam. is utilized extensively as important medicines for threatened abortion habitual abortion. However, objective data related to an embryo is not existed until now. Therefore, this study is focused to find out stability of Cuscuta chinensis Lam. about an embryo during pregnancy based on data related to stability of nerve cell and antioxydative effect by using neural cell line, PC 12 cell. Methods : Experimentation concerns cytotoxic effects and antioxydative effect through methods such as MTT ssay, western botting after abstracting an undiluted solution from domestic Cuscuta chinensis Lam. Results : 1. As a result of experimentation on MTT assay according to each magnification from Cuscuta chinensis Lam. extraction solution with different abstraction methods, cytotoxic effect is not observed to all extract except an undiluted solution which is abstracted from MeOH stiring. Also, an undiluted solution in stiring with MeOH could not confirm whether come from Cuscuta chinensis Lam. or not. 2. As a result of revelation of Bax and GSK-3${\beta}$ which is responsive to the first stage from general stress in order to observe antioxydative effects of Cuscuta chinensis Lam. revelation of Bax by Cuscuta chinensis Lam. appeared to decrease. Conclusion : Cytotoxic effects with Cuscuta chinensis Lam. about PC12 cell is not discovered and it assume that it would be anti apoptotic effect by ROS as Bax and GSK-3${\beta}$ inviable effect. In the future, this study could be used as basic data for additional research on Cuscuta chinensis Lam. and effect and stability of complicated prescriptions for keeping pregnancy.

• 한국농공학회지
• /
• 제40권5호
• /
• pp.91-99
• /
• 1998

The widespread use of thin shell structures has created a need for a systematic method of analysis which can adequately account for arbitrary geometric form and boundary conditions as well as arbitrary general type of loading. Therefore, the stress and analysis of thin shell has been one of the more challenging areas of structural mechanics. A wide variety of numerical methods have been applied to the governing differential equations for spherical and cylindrical structures with a few results applicable to practice. The analysis of axisymmetric spherical shell is almost an every day occurrence in many industrial applications. A reliable and accurate finite element analysis procedure for such structures was needed. Dynamic loading of structures often causes excursions of stresses well into the inelastic range and the influence of geometry changes on the response is also significant in many cases. Therefore both material and geometric nonlinear effects should be considered. In general, the shell structures designed according to quasi-static analysis may fail under conditions of dynamic loading. For a more realistic prediction on the load carrying capacity of these shell, in addition to the dynamic effect, consideration should also include other factors such as nonlinearities in both material and geometry since these factors, in different manner, may also affect the magnitude of this capacity. The objective of this paper is to demonstrate the dynamic characteristics of spherical shell. For these purposes, the spherical shell subjected to uniformly distributed step load was analyzed for its large displacements elasto-viscoplastic static and dynamic response. Geometrically nonlinear behaviour is taken into account using a Total Lagrangian formulation and the material behaviour is assumed to elasto-viscoplastic model highly corresponding to the real behaviour of the material. The results for the dynamic characteristics of spherical shell in the cases under various conditions of base-radius/central height(a/H) and thickness/shell radius(t/R) were summarized as follows : The dynamic characteristics with a/H. 1) AS the a/H increases, the amplitude of displacement in creased. 2) The values of displacement dynamic magnification factor (DMF) were ranges from 2.9 to 6.3 in the crown of shell and the values of factor in the mid-point of shell were ranged from 1.8 to 2.6. 3) As the a/H increases, the values of DMF in the crown of shell is decreased rapidly but the values of DMF in mid-point shell is increased gradually. 4) The values of DMF of hoop-stresses were range from 3.6 to 6.8 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.3 to 2.6, and the values of DMF of stress were larger than that of displacement. The dynamic characteristics with t/R. 5) With the thickness of shell decreases, the amplitude of the displacement and the period increased. 6) The values of DMF of the displacement were ranged from 2.8 to 3.6 in the crown of shell and the values of factor in the mid-point of shell were ranged from 2.1 to 2.2.

• 한국농공학회지
• /
• 제40권3호
• /
• pp.113-121
• /
• 1998

The widespread use of thin shell structures has created a need for a systematic method of analysis which can adequately account for arbitrary geometric form. Therefore, the stress analysis of thin shell has been one of the more challenging areas of structural mechanics. The analysis of axisymmetric spherical shell is almost an every day occurrence in many industrial applications. A reliable and accurate finite element analysis procedure for such structures was needed. In general, the shell structures designed according to quasi-static analysis may fail under conditions of dynamic loading. For a more realistic prediction on the load carrying capacity of these shell, in addition to the dynamic effect, consideration should also include other factors such as nonlinearities in both material and geometry since these factors, in different manner, may also affect the magnitude of this capacity. The objective of this paper is to demonstrate the dynamic characteristics of spherical Shell. For these purpose, the spherical shell subjected to uniformly distributed step load was analyzed for its large displacements elasto-viscoplastic dynamic response. The results for the dynamic characteristics of spherical shell in the cases under various conditions of base-radius/central height(a/H) and thickness/shell radius(t/R) were summarized as follows: 1. The dynamic characteristics with a/H, 1) As the a/H increases, the amplitude of displacement increased. 2) The values of displacement Dynamic Magnification Factor (DMF) range from 2.9 to 6.3 in the crown of shell and the values of factor in the mid-point of shell range from 1.8 to 2.6. 3) As the a/H increases, the values of DMF in the crown of shell is decreased rapidly but the values of DMF in mid-point of shell is increased gradually. 4) The values of DMF of hoop-stresses range from 3.6 to 6.8 in the crown of shell and the values of factor in the mid-point of shell range from 2.3 to 2.6, the values of DMF of stress were larger than that of displacement. 2. The dynamic characteristics with t/R, 1) With the decrease of thickness of shell decreses, the amplitude of the displacement and the period increased. 2) The values of DMF of the displacement were range from 2.8 to 3.6 in the crown of shell and the values of factor in the mid-point of shell were range from 2.1 to 2.2.

• 한국암반공학회:학술대회논문집
• /
• 한국암반공학회 2000년도 암반공학문제의 수치해석(Numerical Analysis in Rock Engineering Problems)
• /
• pp.201-210
• /
• 2000

일반적으로 암반 구조물의 안정성에 심각한 영향을 미칠 수 있는 것으로 알려진, 암반 내의 rock bridges는 일종의 opening-mode fracture로 간주될 수 있다. 초창기에는 재료의 저항 특성을 고려하여 rock bridge 자체의 거동 특성에 대한 연구가 있었으나, 최근에 와서는 수치 해석적 연구를 통해 파괴역학의 개념을 적용하여 rock bridge의 분포특성이 암반 구조물의 안정성에 미치는 영향 등을 새롭게 연구하고 있다. 본 연구에서는 rock bridges가 수자파쇄 균열의 분포특성에 미치는 영향을 규명하고자, rock bridges의 분포형태에 따른 암반 내 응력 분포 특성과 균열의 bridge현상을 먼저 살펴보았다. 즉, 균열의 길이에 대한 균열의 간격의 비(s/L 비)와 균열의 길이에 대한 균열의 오버랩의 비(d/L 비)를 변화시키면서 응력 분포 특성을 수치 해석적으로 살펴본 결과, 2개의 균열만으로도 여러 개의 균열 분포 특성을 대표할 수 있음을 알았고, s/L 비가 감소할수록 또는 d/L 비가 증가할수록 암반 내 응력 집중은 커짐을 알 수 있었다. 이러한 수치 해석결과를 토대로, 수압파쇄 균열과 rock bridges의 상호 관계를 수치 해석적으로 연구한 결과, rock bridges가 없을 경우 탄성이론에 맞게 발전하던 수압파쇄 균열이, rock bridges의 존재에 의해 수압파쇄 균열의 전파 방향이 왜곡됨은 물론 수압파쇄 균열에 수직으로 작용하는 원거리 응력도 정확히 표현하지 못함을 알았다. 즉, 수압파쇄 균열 선단에서의 mode I 응력집중계수는 s/L 비가 감소할수록 또는 d/L 비가 증가할수륵 커짐을 알 수 있었다. 이러한 연구결과로부터, 균열의 분포특성을 규명하기 위해 노두에서 일반적으로 실시되는 scanline조사에서 얻을 수 있는 s/L비와 d/L비를 통하여 암반 내에 존재하는 응력의 평가 방법이 새로이 제안될 수 있을 것이다. 장기적인 유지를 필요로 하는 사면은 사면의 변형거동을 감시하기 위해 보다 체계적인 계측을 필요로 하며, 또한 사면이 많은 비에 노출되기 쉽기 때문에 사면의 풍화와 침식에 대한 대책연구도 수행되어야 한다. 15ng/$\textrm{cm}^2$로서 90분간 조사로 27ng/$\textrm{cm}^2$량이 생성되었다. 7-DHC은 당초의 123ng/$\textrm{cm}^2$으로부터 계속 감소되어 150분간 조사시 53ng/$\textrm{cm}^2$량까지 내려갔다.하였으며, 그 외의 항목간에는 대동소이하였다.ckarti 와 E. serrulatus가 스파르가눔의 중간숙주가 될 수 있음을 확인하였다. 충란의 배양에서부터 종숙주의 충란 배출까지 약 2개월 정도의 기간이 소요되었고, 우리 나라 자연환경에서는 5일에서 7월에 주로 이 충체의 유충이 발육되고 전파되는 것으로 추측되었다.러 가지 방법들을 적극 적용하여 금후 검토해볼 필요가 있을 것이다.잡은 전혀 삭과가 형성되지 않았다. 이 결과는 종간 교잡종을 자방친으로 하고 그 자방친의 화분친을 사용할 때만 교잡이 이루어지고 있음을 나타내고 있다. 따라서 여교잡을 통한 종간잡종 품종육성 활용방안을 금후 적극 확대 검토해야 할 것이다하였다.함을 보이고 있다.X> , ZnCl$_{3}$$^{-}$같은 이온과 MgCl$^{+}$, MgCl$_{2}$같은 이온종을 형성하기 때문인것 같다. 한편 어떠한 용리액에서던지 NH$_{4}$$^{+}$의 경우 Dv값이 제일 작았다. 바. 본 연구의 목적중의 하나인 인체유해 중금속이온인 Hg(II), Cd(II)등이 NaCl같은 염화물이 함유된 시료용액에 공해이온으로 존재할 경우 흡착에 의한 제거가 가능하다. 한편 이같은 중금속이

• 터널과지하공간
• /
• 제10권3호
• /
• pp.447-456
• /
• 2000

일반적으로 암반 구조물의 안정성에 심각한 영향을 미칠 수 있는 것으로 알려진, 암반 내의 rock bridges는 일종의 opening-mode fracture로 간주될 수 있다. 초창기에는 재료의 저항 특성을 고려하여 rock bridges 자체의 거동 특성에 대한 연구가 있었으나, 최근에 와서는 수치 해석적 연구를 통해 파괴역학의 개념을 적용하여 rock bridges의 분포특성이 암반 구조물의 안정성에 미치는 영향 등을 새롭게 연구하고 있다. 본 연구에서는 rock bridges가 수압파쇄 균열의 분포특성에 미치는 영향을 규명하고자, rock bridges의 분포형태에 따른 암반 내 응력 분포 특성과 균열의 bridge 현상을 먼저 살펴보았다. 즉 , 균열의 길이에 대한 균열의 간격의 비 (s/L 비) 균열의 길이에 대한 균열의 오버랩의 비 (d/L 비)를 변화시키면서 응력 분포 특성을 수치 해석적으로 살펴본 결과, 2개의 균열만으로도 여러 개의 균열 분포 특성을 대표할 수 있음을 알았고, s/L 비가 감소할수록 또는 d/L비가 증가할수록 암반 내 응력 집중은 커짐을 알 수 있었다. 이러한 수치 해석결과를 토대로, 수압파쇄 균열과 rock bridges의 상호 관계를 수치 해석적으로 연구한 결과, rock bridges가 없을 경우 탄성이론에 맞게 발전하던 수압파쇄 균열이, rock bridges의 존재에 의해 수압파쇄 균열의 전파 방향이 왜곡됨은 물론 수압파쇄 균열에 수직으로 작용하는 원거리 응력도 정확히 표현하지 못함을 알았다. 즉 , 수압파쇄 균열 선단에서의 mode I 응력집중계수는 s/L비가 감소할수록 또는 d/L 비가 증가할수록 커짐을 알 수 있었다. 이러한 연구결과로부터, 균열의 분포특성을 규명하기 위해 노두에서 일반적으로 실시되는 scanline 조사에서 얻을 수 있는 s/L 비와 d/L 비를 통하여 암반 내에 존재하는 응력의 평가 방법이 새로이 제안할 수 있을 것이다.로 제안하였다. 본 노천채탄장의 최종사면과 같이 장기적인 유지를 필요로 하는 사면은 사면의 변형거동을 감시하기 위해 보다 체계적인 계측을 필요로 하며, 또한 사면이 많은 비에 노출되기 쉽기 때문에 사면의 풍화와 침식에 대한 대책연구도 수행되어야 한다. 이 값이 감소할수록 Cox-Merz 법칙은 더욱 잘 성립한다.$_{TM4}$/$\bar{p}$$_{TM2}$, $\bar{p}$$_{TM4}$/$\bar{p}$$_{TM1}$, log($\bar{p}$$_{TM4}$/$\bar{p}$$_{TM3}$) 등과 상관이 높게 나타났다.이 소요되었고, 우리 나라 자연환경에서는 5일에서 7월에 주로 이 충체의 유충이 발육되고 전파되는 것으로 추측되었다.러 가지 방법들을 적극 적용하여 금후 검토해볼 필요가 있을 것이다.잡은 전혀 삭과가 형성되지 않았다. 이 결과는 종간 교잡종을 자방친으로 하고 그 자방친의 화분친을 사용할 때만 교잡이 이루어지고 있음을 나타내고 있다. 따라서 여교잡을 통한 종간잡종 품종육성 활용방안을 금후 적극 확대 검토해야 할 것이다하였다.함을 보이고 있다.X> , ZnCl$_{3}$$^{-}$같은 이온과 MgCl$^{+}$, MgCl$_{2}$같은 이온종을 형성하기 때문인것 같다. 한편 어떠한 용리액에서던지 NH$_{4}$$^{+}$의 경우 Dv값이 제일 작았다. 바. 본 연구의 목적중의 하나인 인체유해 중금속이온인 Hg(II), Cd(II)등이 NaCl같은 염화물이 함유된 시료용액에 공해이온으로 존재할 경우 흡착에 의한 제거가 가능하다. 한편 이같은 중금속이온의 흡착실험은 특히

• Restorative Dentistry and Endodontics
• /
• 제32권2호
• /
• pp.130-137
• /
• 2007

본 연구의 목적은 니켈티타늄 전동파일의 피로파절에 있어서 표면 결함의 역할을 규명하고자 fatigue tester에서 반복적 인 fatigue force를 부여한 후 파절된 단면을 주사전자현미 경으로 관찰하여 파절 역학을 규명하는 것이다. 총 45개의 #30/.04 taper와 21 mm의 HEROShaper 니켈-티타늄 전동파일을 15개씩 3개의 군으로 분류하였다. 제 1군은 결함이 없는 새 HEROShaper파일, 제 2군은 제조과정에서 metal rollover나 machining marks와 같은 표면결함을 갖는 HEROShaper파일, 제 3군은 임상에서 4- 6개의 구치부 근관의 확대에 사용한 HEROShaper 파일을 사용하였다. 모든 파일들은 회전속도(300 rpm)와 pecking distance (3 mm)가 일정하게 맞춘 fatigue tester에서 파절될 때까지 시간을 측정한 후 통계분석을 통해 각 군간의 유의성을 분석하였고, 파절 단면의 farctographic analysis를 통해 파절역학을 규명하고자 하였다 실험결과 평균 파절시간에 있어서 group 1과 2, group 1과 3사이에는 통계학적으로 유의할 만한 차이가 있었으나 (p<0.05), group 2와 3사이에는 통계학적인 차이가 없었다. Fractographic analysis 결과 대부분의 파절면에서 microvoid와 dimple 소견을 갖는 ductile fracture양상이 관찰되었다. 또한 brittle fracture가 일어난 파절면에서는 파절선 전방에 수 많은 striation들이 관찰되었고 transgranular 및 intergranular cleavage 소견도 보였다. 표면결함이 있는 제 2, 3 군의 파절단면에서는 모든 시편에서 표면결함이 관찰되었다. 이와 같은 결과로 미루어 보아 표면결함이 반복 피로파절에서 미세균열의 기시점으로 중요한 역할을 하며 fractography분석법은 Ni-Ti 파일의 파절역학을 규명하는데 유용함을 알 수 있었다.

• Restorative Dentistry and Endodontics
• /
• 제26권4호
• /
• pp.332-340
• /
• 2001

Flowable composite resin has lower filler content, increased flow, and lower modules of elasticity. It is suggested that flowable composite resin can be bonded to the tooth structure intimately and absorb or dissipate the stress. Therefore, it may be advantageous to use flowable composite resin for the base material of class II restoration and for the class V restoraton. The purpose of this study was to evaluate the microleakage and shear bond strength of four flowable composite resins (Aeliteflo, Flow-It, Revolution, Ultraseal XT Plus) compared to Z100 using Scotchbond Multi Purpose dentin bonding system. To evaluate the microleakage, notch-shaped class V cavities were prepared on buccal and lingual surfaces of 80 extracted human premolars and molars on cementum margin. The teeth were randomly divided into non-thermocycling group (group 1) and thermocycling group (group 2) of 40 teeth each. The experimental teeth of each group were randomly divided onto five subgroups of eight samples (sixteen surfaces). The Scotchbond Multi-Purpose and composite resin were applied for each group following the manufacturer's instructions. the teeth of group 2 were thermocycled five hundred times between 5$^{\circ}C$ and 55$^{\circ}C$. The teeth of group 2 were placed in 2% methylene blue dye for 24 hours, then rinsed with tab water. The specimens were embedded in clear resin, and sectioned longitudinally with a diamond saw. The dye penetration on each of the specimen were observed with a stereomicioscope at $\times$20 magnification. To evaluate the shear bond strength, 60 teeth were divided into five groups of twelve teeth each. The experimental teeth were ground horizontally below the dentinoenamel junction, so that no enamel remained. After applying Scotchbond Multi-Purpose on the dentin surface, composite resin was applied in the shape of cylinder. The cylinder was 4mm in diameter and 2mm in thickness. Shear bond strength was measured using Instron with a cross-head speed of 0.5mm/min. After shear bond strength measurement, mode of failure was evaluated with a stereomicroscope at $\times$30 magnification. All data were statistically analyzed by One Way ANOVA and Student-Newman-Keuls method. The correlation between microleakage and shear bond strength was analyzed by linear regression. The results of this study were as follows ; 1. In non-thermocycling group, the leakage value of Z100 was significantly lower than those of flowable composite resins at the enamel and dentin margin, margin, except that Revolution showed the lower leakage value than that of Z100 at the dentin margin (p<0.05). 2. In thermocycling group, the leakage values of Z100 and Ultraseal XT Plus were lower than those of other subgroup at the enamel and dentin margin, except that Flow-It showed the lower leakage value than that of Ultraseal XT Plus at the dentin margin (p<0.05). 3. The leakage value of Z100 and Ultraseal XT Plus in thermocycling group were not higher than that in non-thermocycling group at the enamel margin. The leakage value of Z100 in thermocycling group was not higher than that in non-thermocycling group at the dentin margin (p<0.05). 4. As for the shear bond strength measurement, there were no statistically significant differences among groups (p<0.05). The shear bond strengths given in descending order were as follows: Z100(16.81$\pm$2.98 MPa), Flow-It(14.8$\pm$4.43 MPa), Aeliteflo(14.34$\pm$3.69 MPa), Revolution(13.46$\pm$4.23 MPa), Ultraseal XT Plus(12.83$\pm$3.16 MPa). 5. Failure modes of all specimens were adhesive failures. 6. There was no correlation between microleakage and shear bond strength.