• 터널과지하공간
• /
• 제31권6호
• /
• pp.428-439
• /
• 2021

뿜칠 멤브레인은 폴리머로 구성된 재료로서 지보 또는 차수 목적으로 기존 방수포와 같은 재료를 대체 할 수 있을 것으로 기대되는 뿜어 붙이는 방식의 재료이다. 이전의 해외 연구에서 기존 시멘트계 지보 재료들에 추가로 뿜칠 멤브레인을 시공할 경우 숏크리트와 같은 지보재의 시공 두께를 줄일 수 있을 것으로 기대하고 있으나 국내에서는 아직까지 실험이나 분석 결과가 많이 보고되고 있지 못하다. 본 연구에서는 고성능 숏크리트에 뿜칠 멤브레인을 바깥면에 타설하여 3점 휨시험을 수행하고 고성능 숏크리트와 뿜칠 멤브레인이 시공된 경우를 비교하여 분석하였다. 실내 표준 시험과 실대형 휨시험을 통해 산정된 값을 서로 비교한 결과 휨강도 측면에서는 큰 차이를 보이지 않았으나 휨인성 부분에서 차이를 보이는 것으로 나타났다.

• 구강회복응용과학지
• /
• 제29권4호
• /
• pp.327-336
• /
• 2013

본 연구에서는 두 종류의 유리 섬유 의치상 강화재인 Quarts Splint$^{TM}$Mesh와 SES MESH$^{(R)}$의 의치상 보강 효과와 열 순환이 의치상의 굽힘 강도와 강화재의 강화 효과에 미치는 영향을 알아보고자 하였다. 시편은 $2.5{\times}10.0{\times}65.0mm$ 크기로 강화재를 사용하지 않은 대조군, 금속 격자 강화재, Splint$^{TM}$Mesh, SES MESH$^{(R)}$로 보강한 시편을 각각 20개씩 제작하였으며 그 중 10개에는 열 순환을 시행하였다. 3점 굽힘 실험을 시행하여 의치상의 굽힘 강도를 측정하였다. Quarts Splint$^{TM}$Mesh와 SES MESH$^{(R)}$로 강화한 군은 대조군보다 유의하게 높은 굽힘 강도를 나타내었으며(P<.05), 금속 격자 강화재로 보강한 군보다 유의하게 낮은 굽힘 강도를 나타내었다(P<.05). 모든 군에서 열 순환을 시행한 경우가 열 순환을 시행하지 않은 경우에 비해 낮은 굽힘 강도를 나타내었지만 대조군에서만 유의한 차이를 나타내었다(P<.05).

• 구강회복응용과학지
• /
• 제27권2호
• /
• pp.197-207
• /
• 2011

의치상의 첨상에 사용하는 레진의 종류가 의치상의 굴곡강도와 굴곡계수에 미치는 영향을 비교하는데 있다. 국제표준규격 제 1567 호(ISO 1567:1999)를 참고로 2 가지의 의치상용 열중합레진(Lucitone199(Dentsply Int., NewYork, USA), SR-Ivocap(Ivoclar AG, Schaan, Liechtenstein))을 이용하여 길이 64 mm ${\times}$ 폭 50 mm ${\times}$ 두께 3.3 mm 의 시편을 제작하였다. 각각의 제작된 시편을 다시 두께 2.0 mm 로 규격화한 뒤 3 종류의 레진(Lucitone199 (Dentsply), SR-Ivocap(Ivoclar), Rebase II(Tokuyama Co., Ltd, Tokyo, Japan))으로 각각 1.3 mm 의 두께로 첨상을 하였다. 제작된 시편(n=10)을 증류수가 담긴 밀폐된 용기 내에 $37^{\circ}C$에서 50 시간 동안 보관하였다. 그 후 만능시험기를 이용하여 시편의 3 점 굴곡강도와 굴곡계수를 측정하였다. 지지대간의 거리는 50 mm, crosshead speed 는 5 mm/min 였다. 측정값은 One-way ANOVA 로 비교 분석하였고, Tukey test 를 이용하여 사후 검정하였다. 열중합형 레진과 자가중합형 레진으로 첨상한 군들은 모두 첨상을 시행하지 않은 대조군보다 통계적으로 유의하게 낮은 굴곡강도와 굴곡계수를 나타났다. 본래의 의치상용 레진의 종류와 무관하게 Lucitone199 을 이용해 첨상한 군이 SR-Ivocap 을 이용한 군보다 통계적으로 유의하게 높은 굴곡강도와 굴곡계수를 보였다. 자가중합형 레진을 이용한 군은 열중합형 레진을 이용한 군 보다 통계적으로 유의하게 낮은 굴곡강도와 굴곡계수를 보였다. 의치상의 첨상 시 자가중합형 레진 보다 열중합형 레진을 이용하는 것이 우수한 기계적 성질을 보였다. 열중합형 레진을 이용한 첨상 시 본래의 의치상과 같은 종류의 레진을 사용하는 것은 의치상의 기계적 성질에 영향을 미치지 않았으며 Lucitone199 를 이용한 가압주형법에서 가장 우수한 물성을 나타냈다.

• 대한기계학회논문집A
• /
• 제24권3호
• /
• pp.743-751
• /
• 2000

Because welding residual stress is formidable result in electric resistance spot welding process, and it detrimentally affect to fatigue crack initiation and growth at nugget edge of spot welded la p joints, it should be considered in fatigue analysis. Thus, accurate prediction of residual stress is very important. In this study, nonlinear finite element analysis on welding residual stress generated in process of the spot welding was conducted, and their results were compared with experimental data measured by X-ray diffraction method. By using their results, the maximum principal stress considered welding residual stress at nugget edge of the spot welded lap joint subjected to tension-shear load was calculated by superposition method. And, the $\Delta$P- $N_f$ relations obtained through fatigue, tests on the IB-type spot welded lap joints was systematically rearranged with the maximum principal stress considered welding residual stress. From the results, it was found th2at fatigue strength of the IB-type spot welded lap joints could be systematically and more reasonably rearranged by the maximum principal stress($\sigma$1max-res considered welding residual stress at nugget edge of the spot welding point.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.266-270
• /
• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine because it has excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiC/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing jiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiC/SiC composites by hot pressing method. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method in Ar atmosphere at $1800^{\circ}C$ under 20MPa using $Al_2O_3,\;Y_2O_3\;and\;SiO_2$ as sintering additives in order to low sintering temperature and sintering pressure. The starting powder was high purity $\beta-SiC$ nano-powder with all average particle size of 30mm. The characterization of LPS-SiC was investigated by means of SEM and three point bending test. Base on the composition of sintering additives-, microstructure- and mechanical property correlation, tire compositions of sintering additives are discussed.

• The Journal of Advanced Prosthodontics
• /
• 제5권2호
• /
• pp.133-139
• /
• 2013

PURPOSE. This study was to evaluate the effect of the solution temperature on the mechanical properties of dualcure resin cements. MATERIALS AND METHODS. For the study, five dual-cure resin cements were chosen and light cured. To evaluate the effect of temperature on the specimens, the light-cured specimens were immersed in deionized water at three different temperatures (4, 37 and $60^{\circ}C$) for 7 days. The control specimens were aged in a $37^{\circ}C$ dry and dark chamber for 24 hours. The mechanical properties of the light-cured specimens were evaluated using the Vickers hardness test, three-point bending test, and compression test, respectively. Both flexural and compressive properties were evaluated using a universal testing machine. The data were analyzed using a two way ANOVA with Tukey test to perform multiple comparisons (${\alpha}$=0.05). RESULTS. After immersion, the specimens showed significantly different microhardness, flexural, and compressive properties compared to the control case regardless of solution temperatures. Depending on the resin brand, the microhardness difference between the top and bottom surfaces ranged approximately 3.3-12.2%. Among the specimens, BisCem and Calibra showed the highest and lowest decrease of flexural strength, respectively. Also, Calibra and Multilink Automix showed the highest and lowest decrease of compressive strength, respectively compared to the control case. CONCLUSION. The examined dual-cure resin cements had compatible flexural and compressive properties with most methacrylate-based composite resins and the underlying dentin regardless of solution temperature. However, the effect of the solution temperature on the mechanical properties was not consistent and depended more on the resin brand.

• 한국기계가공학회지
• /
• 제18권1호
• /
• pp.24-30
• /
• 2019

The deck floor of a the cargo truck becomesis damaged and aged due to the continuous loading of the loading cargo and external environmental factors. Floor boards made of wood and metal are often used. In the case of wood, the cost is high due to the use of imported wood, and the strength is easily deterioratesd due to environmental factors. In the case of metal materials, the durability is higher than that of wood, but problems are raised due to the effect of major factors that hinder the weight reduction, and the effects of corrosion. In order to replace this stucturestructural design, this study proposed a wood fiber composite using natural raw materials. Woody composites are being used as environmentally and friendly exterior materials with the combined advantages of plastic, and wood,; low cost and low density. However, due to the nature of the woody composites, the properties are differentdiffer depending on the contents of the matrix, reinforcing agent, additives, compatibilizer, etc. In this study, we investigate these problems through analysis of the microstructure and mechanical properties according to proper content and injection molding conditions. As a result, it is considered that the wood deck composite can replaced the current Deck Floor Boardreplace current deck floor boards through continuous continued research and results of this study.

• Restorative Dentistry and Endodontics
• /
• 제47권3호
• /
• pp.32.1-32.11
• /
• 2022

Objectives: This study aimed to evaluate the influence of inorganic composition and filler particle morphology on the mechanical properties of different self-adhesive resin cements (SARCs). Materials and Methods: Three SARCs including RelyX Unicem-2 (RUN), Maxcem Elite (MAX), and Calibra Universal (CAL) were tested. Rectangular bar-shaped specimens were prepared for flexural strength (FS) and flexural modulus (FM) and determined by a 3-point bending test. The Knoop microhardness (KHN) and top/bottom microhardness ratio (%KHN) were conducted on the top and bottom faces of disc-shaped samples. Sorption (Wsp) and solubility (Wsl) were evaluated after 24 hours of water immersion. Filler morphology was analyzed by scanning electron microscopy and X-ray energy dispersive spectroscopy (EDS). FS, FM, %KHN, Wsp, Wsl, and EDS results were submitted to 1-way analysis of variance and Tukey's post-hoc test, and KHN also to paired t-test (α = 0.05). Results: SARC-CAL presented the highest FS value, and SARC-RUN presented the highest FM. SARC-MAX and RUN showed the lowest Wsp and Wsl values. KHN values decreased from top to bottom and the SARCs did not differ statistically. Also, all resin cements presented carbon, aluminum, and silica in their composition. SARC-MAX and RUN showed irregular and splintered particles while CAL presented small and regular size particles. Conclusions: A higher mechanical strength can be achieved by a reduced spread in grit size and the filler morphology can influence the KHN, as well as photoinitiators in the composition. Wsp and Wsl can be correlated with ions diffusion of inorganic particles.

• Computers and Concrete
• /
• 제13권1호
• /
• pp.31-47
• /
• 2014

This research is focused on obtaining the fracture property of steel fiber reinforced concrete(SFRC) specimens at early ages of 1, 2, 3 and 7-day, respectively. For this purpose, three point bending tests of nine groups of SFRC beams with notch of 40mm depth and different steel fiber ratios were conducted. The experimental results of early age specimens were compared with the 28-day hardened SFRC specimens. The test results indicated that the steel fiber ratios and curing age significantly influenced the fracture properties of SFRC. A reasonable addition of steel fiber improved the fracture toughness of SFRC, while the fracture energy of SFRC developed with curing age. Moreover, a quadratic relationship between splitting strength and fracture toughness was established based on the experiment results. Additionally, afinite element (FE) method was used to investigate the fracture properties of SFRC.A comparison between the FE analysis and experiment results was also made. The numerical analysis fitted well with the test results, and further details on the failure behaviors of SFRC could be revealed by the suggested numerical simulation method.

• Computers and Concrete
• /
• 제21권1호
• /
• pp.11-20
• /
• 2018

The possibilities of non-linear analysis of reinforced-concrete structures are under development. In particular, current research areas include structural analysis with the application of advanced computational and material models. The submitted article aims to evaluate the possibilities of the determination of material properties, involving the tensile strength of concrete, fracture energy and the modulus of elasticity. To evaluate the recommendations for concrete, volume computational models are employed on a comprehensive series of tests. The article particularly deals with the issue of the specific properties of fracture-plastic material models. This information is often unavailable. The determination of material properties is based on the recommendations of Model Code 1990, Model Code 2010 and specialized literature. For numerical modelling, the experiments with the so called "classic" concrete beams executed by Bresler and Scordelis were selected. It is also based on the series of experiments executed by Vecchio. The experiments involve a large number of reinforcement, cross-section and span variants, which subsequently enabled a wider verification and discussion of the usability of the non-linear analysis and constitutive concrete model selected.