• 동력기계공학회지
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• 제16권6호
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• pp.38-44
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• 2012

In this paper, the bending characteristics of the corrugated plates is analyzed. The trapezoidally, triangularlly and sinusoidally corrugated plates are considered. The corrugated plate is treated as an orthotropic plate that has different flexural properties in two perpendicular directions. The equivalent bending and twisting rigidities for the equivalent orthotropic plates are derived. The equivalent flexural rigidities are estimated under the following postulations: (1) The angle of continuously corrugated plate is not changed after the deformation. (2) When the pure bending moment is applied in corrugated direction of the plate, the its plane is in pure bending. Several numerical examples are analyzed with the proposed method and compared with published results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.69-70
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• 2010

본 연구는 중공 형성체의 재료가 중공 슬래브의 휨 성능에 미치는 영향에 관하여 살펴보기 위하여 실험적 연구를 수행하였다. 중공형성체의 재료를 일반 플라스틱과 유리섬유 보강 플라스틱으로 제작하였으며, 이를 적용한 중공 슬래브의 일방향 휨 성능 평가를 수행하였다. 그리고 이를 통하여, 중공 형성체의 재료가 중공 슬래브에 미치는 영향을 확인하고, 그 성능을 파악하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.615-618
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• 2004

The primary role of fibers in High performance fiber reinforced cement composites(HPFRCCs) is to improve the toughness, or energy absorption capacity, of the composite material, However, there is still no general agreement as to how this toughness should be characterized, or how it might be used in the design of structures containing HPFRCCs. In this paper, therefore, we focus on test techniques for measuring flexural toughness. For mechanical properties, HPFRCCs can be tested in the same way as fiber reinforced concrete(FRC). Both the significance and the limitations of somewhat different national and industrial standards of FRC are discussed. For flexural toughness, with depend on the presence of fibers, new test methods was developed and verified. We also suggest evaluation method of tensile toughness indices using the moment curvature relationship in flexural tests.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.673-676
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• 2006

Steel FibreReinforced Shotcrete(SFRS) is one of the main tunnel support along with the rock bolt during the excavation and after the completion of the tunnel. In the standard qualification of the SFRS defined by Korea Highway Corporation, 28 day core specimen has to meet the compressive strength of 19.6 MPa and over 90 % fibre contents. Furthermore, for the 28 days brick shaped specimen made by shooting, flexural strength should be over 4.4 MPa and flexural toughness ratio which can be calculated from flexural toughness factor has to meet more than 68% of flexural strength. In shotcrete, accelerating agent is added for the rapid strength development. Silicate and aluminate type agents are known to develop shotcrete strength rapidly, however, has such problem to degrade the middle and long term strength. Hence, using poly carboxylic super plasticizer, it was aimed to enhance the quality of the shotcrete with the lower water-cement ratio and the same level of workability. The present paper shows the part of the field test result and its analysis.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• 한국세라믹학회지
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• 제51권5호
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• pp.386-391
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• 2014

Silicon nitride ($Si_3N_4$) is regarded as one of the most promising materials for high temperature structural applications due to its excellent mechanical properties at both room and elevated temperatures. However, one high-temperature $Si_3N_4$ material intended for use in radomes has a relatively high dielectric constant of 7.9 - 8.2 at 8 - 10 GHz. In order to reduce the dielectric constant of the $Si_3N_4$, an in-situ reaction process was used to fabricate $Si_3N_4-SiO_2$-BN composites. In the present study, an in-situ reaction between $B_2O_3$ and $Si_3N_4$, with or without addition of BN in the starting powder mixture, was used to form the composite. The in-situ reaction process resulted in the uniform distribution of the constituents making up the composite ceramic, and resulted in good flexural strength and dielectric constant. The composite was produced by pressure-less sintering and hot-pressing at $1650^{\circ}C$ in a nitrogen atmosphere. Microstructure, flexural strength, and dielectric properties of the composites were evaluated with respect to their compositions and sintering processes. The highest flexural strength (193 MPa) and lowest dielectric constant (5.4) was obtained for the hot-pressed composites. The strength of these $Si_3N_4-SiO_2$-BN composites decreased with increasing BN content.

• 한국해양공학회지
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• 제25권3호
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• pp.28-33
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• 2011

The thermal shock properties of SiC materials were investigated for high temperature applications. In particular, the effect of thermal shock temperature on the flexural strength of SiC materials was evaluated, in conjunction with a detailed analysis of their microstructures. The efficiency of a nondestructive technique using ultrasonic waves was also examined for the characterization of SiC materials suffering from a cyclic thermal shock history. SiC materials were fabricated by a liquid phase sintering process (LPS) associated with hot pressing, using a commercial submicron SiC powder. In the materials, a complex mixture of $Al_2O_3$ and $Y_2O_3$ powders was used as a sintering additive for the densification of the microstructure. Both the microstructure and mechanical properties of the sintered SiC materials were investigated using SEM, XRD, and a three point bending test. The SiC materials had a high density of about 3.12 Mg/m3 and an excellent flexural strength of about 700 MPa, accompanying the creation of a secondary phase in the microstructure. The SiC materials exhibited a rapid propagation of cracks with an increase in the thermal shock temperature. The flexural strength of the SiC materials was greatly decreased at thermal shock temperatures higher than $700^{\circ}C$, due to the creation of microcracks and their propagation. In addition, the SiC materials had a clear tendency for a variation in the attenuation coefficient in ultrasonic waves with an increase in thermal shock cycles.

• 한국산학기술학회논문지
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• 제7권4호
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• pp.743-748
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• 2006

본 논문에서는 연구에서는 Nylon6를 기재로 하여 두 가지 Melamine계 난연제(melamine cyanurate: MC-100 and melamine phosphate:MPP-100)를 사용한 난연 Nylon를 개발하여 난연성 및 물성평가를 수행하였다. 난연Test는 UL-94 측정방법(수직연소 시험방법)을 이용하였고, 물성평가는 만능물성시험기(UTM)를 이용하여 인장강도, 굴곡강도, 굴곡탄성율 등을 측정하였고, 충격강도 시험기를 이용하여 충격강도를 측정하였다. 또한 Nano-clay(Cloisite 30B) 5wt%를 사용하여 물성에 미치는 효과를 관찰하였다. 수지의 난연성 평가결과에 의하면, 난연제의 함량이 5wt% 이상이면 V0급을 얻을 수 있었다. 난연제 함량이 증가함에 따라 인장강도. 굴곡강도는 감소하고, 굴곡탄성율은 증가하였다. MC-100의 경우, 5wt%까지는 Nylon6의 동등 이상의 물성을 유지하였다. Nano-clay의 경우, 분산 상태가 불량하여 기대 수준의 물성 향상과 난연 효과는 얻지 못했다.

• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.265-272
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• 2020

PURPOSE. The aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS. Four groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness. RESULTS. XRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P<.05. CONCLUSION. Hydrothermal aging caused reduction in mechanical properties such as surface hardness, biaxial flexural strength, and fracture toughness of Y-TZP zirconia. However, cubic-containing zirconia (more than 30% by volume of cubic crystal) was assumed to have high resistance to hydrothermal degradation. Clinical significance: Cubic-containing zirconia could withstand the intraoral aging condition. It could be suggested to use as a material for fabrication of esthetic dental restoration.

• 자원리싸이클링
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• 제24권6호
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• pp.61-68
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• 2015

본 연구에서는 천연수경성석회(NHL) 모르타르에 바잘트 섬유를 혼합하여 섬유혼합에 따른 강도특성을 연구하고자 하였다. 건식 및 습식 4가지로하여 혼합방법에 따른 물리적 특성발현을 확인하였으며, 압축강도 및 휨강도 등을 고려하여 강도 특성이 최대로 발현되는 혼합방법 한 가지를 선택하였다. 실험결과 물성 발현은 습식혼합보다 건식혼합에서 더 우수하였으며, 건식혼합 중 바인더(NHL)와 섬유를 pre-mixing 한 후 물과 골재를 순차적으로 혼합하여 섬유의 분산력을 높여주는 혼합방법을 선택하였다. 이후 섬유 길이에 따른 물리적 특성 발현성을 확인하였다. 바잘트 섬유 길이에 따른 압축강도 및 휨강도 측정결과, Plain 샘플 대비 섬유 혼합에 따라 압축강도는 감소하는 경향성을 보였으며, 휨강도는 증가하는 경향을 나타내었다. 또한 섬유를 혼합한 샘플 중에서 섬유길이 6 mm일 때 가장 우수한 강도 특성을 나타내었다.