• 대한치과기공학회지
• /
• 제12권1호
• /
• pp.103-106
• /
• 1990

The purpose of this study was to determine if homogeneity of the resin associated with benchcuring could be obtained in the curing unit as the water increased from room temperature to curing temperature. The results of the experiment were as follows : 1. Long periods of bench-curing are not necessary. 2. Bench-curing can take place in the water bath of the curing unit. When this procedure is used, the water should be far enough below the temerature at which active polymerization of the resin proceeds to allow the bench-curing to occur.

• 대한치과기공학회지
• /
• 제14권1호
• /
• pp.91-94
• /
• 1992

This study was made to change dimension of self-curing resin by various curing technics. Specimens were fabricated 45 by 7 curing method. Six measurements(distances AB,BC,CD, AD, AC, and BD) were made of mold section and recorded with micrometer(1/20 mm). The results of the experiment were as follows : 1. The air pressure cured specimens exhibited more distoration than the bench-cured, watercured, and monomer atmosphere-cured specimens(P < 0.05). 2. The water pressure cured specimens exhibited more distoration sphere-cured specimens (P < 0.(15).

• 한국농공학회:학술대회논문집
• /
• 한국농공학회 2001년도 학술발표회 발표논문집
• /
• pp.119-122
• /
• 2001

Annual demand of a precast concrete bench flume used in the irrigation canal of arable land readjustment has continuously increased units recently. The average life time of the precast concrete bench flume was estimated $8{\sim}10$ years, which is too shorter than the life time of in-site placed concrete structures. In order to increase the compressive strength of the precast concrete bench flumes, the highest temperature of being lower than $95^{\circ}C$ was suggested in this study, Through analyzing the relation between the compressive strength and the amount of chloride penetration into concrete specimens, a new formula early estimating durability of the concrete structure was suggested.

• 구강회복응용과학지
• /
• 제16권3호
• /
• pp.221-227
• /
• 2000

Provisional fixed partial dentures(FPDs) are an important part of many prosthodontic treatment procedures. These provisional fixed prostheses must fulfill biologic, mechanical, and esthetic requirements to be considered successful. Consideration of all these factors and requirements are important because provisional resin restorations may be worn over a long period to assess the results of periodontal and endodontics therapies, and also during the restorative phase of implant reconstructive procedures. This in vitro study examined flexual strength of four resins commonly used for fixed provisional prostheses. The effects of polymerization conditions were also evaluated. The four resins tested were : Caulk Temporary bridge resin(L.D. Caulk Co. Dentsply International Millford), Jet(Lang Dental Mfg. Co. Chicago. ILL. U.S.A), Alike (Coe Laboratories. Inc. Chicago. ILL. U.S.A) and Tokuso Curefast (Coe Laboratories. Inc. Chicago. ILL. U.S.A) The test specimens were 65mm long, 14mm wide, and 3.5mm thickness. 10 specimens of four resins were cured for 15 minutes at atmospheric pressure and 10 specimens of four resins were cured at an additional pressure of approximately 20 psi. A total of 80 specimens were prepared. The flexual strength was determined by three-point bending test. Data were analysed with the Paired samples T-test and Tukey student-range test Within the limitations imposed in this study, the following conclusions can be drawn : 1. Under the condition of bench curing, Caulk Temporary bridge resin showed the highest flexual strength. In decreasing order, the flexual strength of the other materials was as follows : Jet, Tokuso Curefast, Alike, and Caulk Temporary bridge resin demonstrated significantly higher strength than other resins. 2. Under the condition of pressure curing, Jet showed the highest flexual strength. In decreasing order, the flexual strength of the other materials was as follows : Caulk Temporary bridge resin, Tokuso Curefast, and Alike. There were all statistically significant differences among four resins 3. There was a statistically significant difference between bench- and pressure-cured specimens in all four materials.

• Advances in concrete construction
• /
• 제4권3호
• /
• pp.221-230
• /
• 2016

This paper presents a preliminary study on the influence of laterite soil replacing conventional fine aggregates on the strength properties of GGBS-blended-concrete. For this purpose, GGBS-blended-concrete samples with 40% GGBS, 60% Portland cement (PC), and locally available laterite soil was used. Laterite soils at 0, 25, 50 and 75% by weight were used in trails to replace the conventional fine aggregates. A control mix using only PC, river sand, course aggregates and water served as bench mark in comparing the performance of the composite concrete mix. Test blocks including 60 cubes for compression test; 20 cylinders for split tensile test; and 20 beams for flexural strength test were prepared in the laboratory. Results showed decreasing trends in strength parameters with increasing laterite content in GGBS-blended-concrete. 25% and 50% laterite replacement showed convincing strength (with small decrease) after 28 day curing, which is about 87-90% and 72-85% respectively in comparison to that achieved by the control mix.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
• /
• pp.57-60
• /
• 2003

This Paper contains the development procedure of Mach small-scaled composite rotor blade for helicopter articulated rotor system. This mach small-scaled composite blade design is conducted by using CORDAS program developed by KARI. The Dynamic analysis for an articulated rotor system with this blade is conducted by using FLIGHTLAB which is commercial software for helicopter analysis. Also the optimizing procedure of iterative design was described. The designed composite blades were manufactured after establishing the effective curing method. For small-scaled rotor test, strain gauges were embedded in composite blade spar to obtain bending & torsion strain value. To verify sectional properties of a blade, the bench test is accomplished. After comparing a designed data and tested data, Dynamic Calculation was repeated using tested data. Through this research, experiences of mach small-scaled composite blade development were accumulated and will be applied to the related research field.

• 한국건설순환자원학회논문집
• /
• 제11권3호
• /
• pp.276-281
• /
• 2023

기존 보통포틀랜드시멘트를 사용하여 제작한 수로관은 시멘트의 수화생성물이 산에 취약한 특성으로 인하여 열화가 빠르게 진행되고 내구성이 저하되는 문제점이 발생되고 있다. 따라서 본 연구에서는 다양한 산업에서 발생되는 산업부산물인 고로슬래그와 플라이 애시를 이용하여 수로관을 제작하고 그 특성을 분석하였다. 실험결과 굳지 않은 콘크리트에서 슬럼프는 플라이애시의 볼베어링작용으로 인해 증가되는 경향을 나타내었고, 공기량은 미연탄분으로 인해 감소되어 내동해성에 대한 대책이 필요할 것으로 나타났다. 또한 압축강도는 증기양생을 통해 초기강도가 증가되었고, 슬래그 50 %이상의 배합에서는 OPC와 동등이상의 결과가 나타났다. 내산성결과는 질량감소율이 5 % 미만으로 나타나 내구성에 우수한 성능을 나타내었고, 벤치플룸의 휨파괴하중도 KS기준을 모두 상회하여 상용화가 가능할 것으로 판단된다.

• 한국해양환경ㆍ에너지학회지
• /
• 제11권1호
• /
• pp.46-49
• /
• 2008

폐FRP의 로빙층을 매트층과 수지로부터 분리하여 섬유 형태의 'F섬유'를 얻었으며, 이것의 용도로 콘크리트 제품 또는 구조물을 고려하였다. 골재는 시멘트의 2.45 배(무게비)로 하고 F섬유(밀도 1.45)는 시멘트와 골재의 부피비로 계산하여 만든 공시체에 대한 휨강도를 실험하였다. 1%의 F섬유를 갖는 것이 양생한 지 28일째 되었을 때 넣지 않은 것에 비해 23%의 강도 증가를 보였다. 그러나 0.5%를 포함한 공시체의 경우는 강도의 변화를 보이지 않음으로써 강도 보강용으로 쓰일 수 있는 최소 혼입량이 0.5% 보다는 크다는 것을 알았다. 철근 콘크리트 시제품인 벤치 플룸의 경우 1% F섬유를 포함할 때 포함하지 않은 것에 비해 휨강도가 21%증가하였다.

• Restorative Dentistry and Endodontics
• /
• 제27권4호
• /
• pp.421-431
• /
• 2002

C-shaped canal configuration is very difficult to treat because that clues about preoperative canal anatomy cannot be ascertained from clinical crown morphology and limited information can be derived from radiographic examination. This study was done to get more informations about the root and canal configuration of C-shape root by 3-dimensionally reconstructing for the purpose of enhancing success rate of endodontic treatment. 30 mandibular molars with C-shaped root were selected. Six photo images from occlusal, apical, mesial, distal, buccal, lingual directions and radiographic view were taken as preoperative ones to compare them with 3-D image. After crown reduction to the level of 1-2mm over pulpal floor was performed, teeth were stored in 5.25% sodium hypochlorite solution for the removal of pulp tissue and debris. They were cleaned under running water, allowed to bench dry and embedded in a self-curing resin. This resin block was serially ground with a microtome (Accutom-50, Struers, Denmark) and the image of each level was recorded by digital camera (FinePix S1-pro, Fuji Co., Japan). The thickness of each section was 0.25mm. Photographs of serial sections through all root canal were digitized using Adobe Photoshop 5.0 and then minimum thickness of open and closed sites were measured (open site is the surface containing occluso-apical groove closed site is oppsite). After dizitization using 3-D Doctor (Able software Corp, USA). 3D reconstruction of the outer surface of tooth and the inner surface of pulp space was made. Canal classsification of C-shaped roots was performed from this 3-D reconstructed image. The results were as follows : 1. Most C-shape rooted teeth showed lingual groove (28/30). 2 According to Vertuccis' calssification, type I, II, III, IV, VII were observed. but also new canal types suck as 2-3-2, 1-2-3-2. 2-3-2-1, 2-3-2-3 were shown. 3 There was little difference in minimum thickness on coronal and apical portions, but open site were thinner than closed site on mid portion. Conclusively, 3D reconstruction method could make the exact configurations of C-shape root possible to be visualized and analyzed from multi-directions. Data from minimum thickness recommend cleaning and shaping be more carefully done on dangerous mid portion.

• 대한치과보철학회지
• /
• 제39권6호
• /
• pp.709-734
• /
• 2001

The aims of this experiment were to investigate the strain and temperature changes simultaneously within autopolymerzing acrylic resin specimens. A computerized data acquisition system with an electrical resistance strain gauge and a thermocouple was used over time periods up to 180 minutes. The overall strain kinetics, the effects of stress relaxation and additional heat supply during the polymerization were evaluated. Stone mold replicas with an inner butt-joint rectangular cavity ($40.0{\times}25.0mm$, 5.0mm in depth) were duplicated from a brass master mold. A strain gauge (AE-11-S50N-120-EC, CAS Inc., Korea) and a thermocouple were installed within the cavity, which had been connected to a personal computer and a precision signal conditioning amplifier (DA1600 Dynamic Strain Amplifier, CAS Inc., Korea) so that real-time recordings of both polymerization-induced strain and temperature changes were performed. After each of fresh resin mixture was poured into the mold replica, data recording was done up to 180 minutes with three-second interval. Each of two poly(methyl methacrylate) products (Duralay, Vertex) and a vinyl ethyl methacrylate product (Snap) was examined repeatedly ten times. Additionally, removal procedures were done after 15, 30 and 60 minutes from the start of mixing to evaluate the effect of stress relaxation after deflasking. Six specimens for each of nine conditions were examined. After removal from the mold, the specimen continued bench-curing up to 180 minutes. Using a waterbath (Hanau Junior Curing Unit, Model No.76-0, Teledyne Hanau, New York, U.S.A.) with its temperature control maintained at $50^{\circ}C$, heat-soaking procedures with two different durations (15 and 45 minutes) were done to evaluate the effect of additional heat supply on the strain and temperature changes within the specimen during the polymerization. Five specimens for each of six conditions were examined. Within the parameters of this study the following results were drawn: 1. The mean shrinkage strains reached $-3095{\mu}{\epsilon},\;-1796{\mu}{\epsilon}$ and $-2959{\mu}{\epsilon}$ for Duralay, Snap and Vertex, respectively. The mean maximum temperature rise reached $56.7^{\circ}C,\;41.3^{\circ}C$ and $56.1^{\circ}C$ for Duralay, Snap, and Vertex, respectively. A vinyl ethyl methacrylate product (Snap) showed significantly less polymerization shrinkage strain (p<0.01) and significantly lower maximum temperature rise (p<0.01) than the other two poly(methyl methacrylate) products (Duralay, Vertex). 2. Mean maximum shrinkage rate for each resin was calculated to $-31.8{\mu}{\epsilon}/sec,\;-15.9{\mu}{\epsilon}/sec$ and $-31.8{\mu}{\epsilon}/sec$ for Duralay, Snap and Vertex, respectively. Snap showed significantly lower maximum shrinkage rate than Duralay and Vertex (p<0.01). 3. From the second experiment, some expansion was observed immediately after removal of specimen from the mold, and the amount of expansion increased as the removal time was delayed. For each removal time, Snap showed significantly less strain changes than the other two poly(methyl methacrylate) products (p<0.05). 4. During the external heat supply for the resins, higher maximum temperature rises were found. Meanwhile, the maximum shrinkage rates were not different from those of room temperature polymerizations. 5. From the third experiment, the external heat supply for the resins during polymerization could temporarily decrease or even reverse shrinkage strains of each material. But, shrinkage re-occurred in the linear nature after completion of heat supply. 6. Linear thermal expansion coefficients obtained from the end of heat supply continuing for an additional 5 minutes, showed that Snap exhibited significantly lower values than the other two poly(methyl methacrylate) products (p<0.01). Moreover, little difference was found between the mean linear thermal expansion coefficients obtained from two different heating durations (p>0.05).