• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2063-2070
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• 2024

A series of ordinary concrete is casted in order to examine the influence of the manganiferous siltstone rocks on the physical, mechanical, and gamma-ray shielding properties. Thus, a partial replacement for the coarse aggregates by siltstone rocks was performed during the fabrication of the currently ordinary concrete. The test revealed that raising the siltstone concentration improved the mechanical characteristics and density of the developed concretes. The addition of siltstone rocks at concentrations ranging from 0 to 40 wt% of the coarse aggregate concentration raises the density of the concrete from 2.05 g/cm³ to 2.3 g/cm³. Furthermore, partial substitution of basalt with siltstone rocks improves gamma-ray shielding properties. The experimental results for the linear attenuation coefficient show an increase in its value from 0.146 cm1 to 0.160 cm^-1 when the siltstone concentration is increased between 0 and 40 wt% at 0.662 MeV. Furthermore, increasing the concentrations of siltstone affected the half-value thickness, which varied between 4.759 and 4.319 cm at 0.662 MeV. Therefore, the replacement presents a new alternative coarse aggregate that can enhance the mechanical and radiation shielding properties of ordinary concretes.

• Composites Research
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• 제22권4호
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• pp.41-49
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• 2009

천연섬유복합재료는 저비용, 경량, 재생성, 친환경적인 재료로 최근 제조되고 있다. 또한 이들 재료는 생체분해성과 비연마 특성을 갖고 있다. 천연섬유의 친환경적이고 생체분해성으로 인해 천연섬유복합재료는 기존의 섬유를 대체할 잠재적인 대체재로 관심을 받고 있다. 천연섬유의 화학적, 기계적, 물리적 특성은 다양한 섬유의 셀룰로스양에 따라 명확한 특정이 구분되며, 이러한 복합재료의 기계적인 물성치는 기지재와 섬유간의 접착에 의해 주로 영향을 받고 있다. 천연섬유표면의 여러 화학적인 물리적인 개질방법은 섬유와 기지의 접착력 향상에 영향을 주어 결국 복합재료의 기계적인 물성치를 향상시킬 수 있다. 본 논문은 최근 개발되고 있는 천연섬유복합재료의 섬유종류, 고분자기지, 제조기술, 섬유의 처리, 섬유 기지간 계면등에 관한 최근의 연구결과들을 정리하여 소개한 것이다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.194-205
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• 2009

In geotechnical engineering, the mechanical characteristics of soil, the main material of geotechnical engineering, is highly related to the confining stress. Reduced-scale physical modeling is often conducted to evaluate the performance or to verify the behavior of the geotechnical systems. However, reduced-scale physical modeling cannot replicate the behavior of the full-scale prototype because the reduced-scale causes difference of self weight stress level. Geotechnical centrifuges are commonly used for physical model tests to compensate the model for the stress level. Physical modeling techniques using centrifuge are widely adopted in most of geotechnical engineering fields these days due to its various advantages. In this paper, fundamentals of geotechnical centrifuge modeling and its application area are explained. State-of-the-art geotechnical centrifuge equipment is also described as an example of KOCED geotechnical centrifuge facility at KAIST.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1247-1252
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• 2014

본 연구에서는 온도조건에 따른 MR 유체의 물리적 특성을 연구하고자 침전 및 전단응력실험을 수행하였다. MR 댐퍼에 사용되는 MR 유체는 자성 파우더를 포함하고 있어 침전현상이 발생하므로 침강성과 인가전류에 의한 전단응력 변화를 상온과 고온조건에서 실험하였다. 침강특성을 조사하기 위하여 강제 대류형 오븐을 인가전류에 의한 전단응력을 측정하기 위하여 점도계를 사용하였다. 실험결과로부터 MR 유체는 시간과 온도에 따른 침강 특성이 다름을 그리고 교반시간이 큰 경우에 MR 유체의 분산성이 2배 이상 우수하였다. 전단률이 증가할수록 전단응력은 로그함수의 증가분포를 인가전류를 증가할수록 2차 함수의 증가분포를 그리고 MR 유체의 전단응력은 상온보다 고온에서 6-18% 낮은 분포를 보였다.

• 대한기계학회논문집B
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• 제30권1호
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• pp.48-56
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• 2006

We investigated gas residence time and mixing characteristics due to various swirl numbers generated by normal injection of secondary air to a lab-scale cylinderical combustor. The residence time was estimated by measuring the temporal pressure difference which was caused by deposition of test particles on a filter media after the injection by a syringe. The mixing characteristics were evaluated by standard deviation value of test gas concentration at different measuring points. The test gas concentration was detected by a gas analyzer. The swirl number of $20{\sim}30$ for ${\theta}=5^{\circ}$ caused long residence time enough to improve mixing characteristics. Numerical calculations were also carried out to understand physical meanings of the experimental results.

• Journal of the Korean Wood Science and Technology
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• 제44권2호
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• pp.172-183
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• 2016

Densification of the inner part of oil palm trunk (OPT) by the close system compression (CSC) method was performed in this study. The effects of the compression temperature and time on the anatomical, physical and mechanical properties of OPT were evaluated. The inner part of OPT with an initial average density of $0.3g/cm^3$ was used as samples. Oven-dried samples were immersed in water and vacuumed until fully saturated and then compressed by CSC at 120, 140, 160 or $180^{\circ}C$ for 10, 20, 30 or 40 min. The anatomical characteristics of transverse and radial sections before and after compression were compared by optical microscopy. The physical and mechanical properties, including the density, recovery of set (RS), modulus of elasticity (MOE), modulus of rupture (MOR), and compression parallel to grain were examined. It was observed that the anatomical characteristic of the inner part of OPT (i.e., vascular bundles, vessels, and parenchyma tissue) became flattened, fractured, and collapsed after compression by CSC. The RS decreased with increasing compression temperature and time. The lower RS indicated high dimensional stability. The physical and mechanical properties (i.e., density, MOR, MOE, and compressive strength) of the inner part of OPT increased with increasing compression temperature and time. Compression by the CSC method at $160^{\circ}C$ for 40 min was the optimum treatment.

• Journal of the Korean Wood Science and Technology
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• 제26권1호
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• pp.70-75
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• 1998

In this paper, the relationships between volumetric mixing ratio of rubber chip and physical and mechanical properties of wood/rubber composite panel was examined in order to investigate the mixture characteristics of wood and rubber chip. Because of the specific gravity of rubber differed from wood chip, physical properties of wood/rubber composite panel was shown very different values by mixing rate of chip element. Specific gravity in air-dry of composite panel was increased rapidly as volumetric percent of rubber chip was increased. Moisture content of composite panel was decreased as volumetric percent of rubber chip element was increased. This results was considered that wood weight is light and porosity material for moisture absorption. Compressive strength and modulus of rupture in bending test were decreased as volumetric percent of rubber chip increased. By mixing ratio control of chip elements, various wood/rubber composite panel can be applicable to every interior materials such as subfloor, playground, and exterior materials such as road blocks for recreational facilities in garden and forest and city parks.

• Tribology and Lubricants
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• 제33권3호
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• pp.106-111
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• 2017

Sapphire is an anisotropic material with excellent physical and chemical properties and is used as a substrate material in various fields such as LED (light emitting diode), power semiconductor, superconductor, sensor, and optical devices. Sapphire is processed into the final substrate through multi-wire saw, double-side lapping, heat treatment, diamond mechanical polishing, and chemical mechanical polishing. Among these, chemical mechanical polishing is the key process that determines the final surface quality of the substrate. Recent studies have reported that the material removal characteristics during chemical mechanical polishing changes according to the crystal orientations, however, detailed analysis of this phenomenon has not reported. In this work, we carried out chemical mechanical polishing of C(0001), R($1{\bar{1}}02$), and A($11{\bar{2}}0$) substrates with different sapphire crystal planes, and analyzed the effect of crystal orientation on the material removal characteristics and their correlations. We measured the material removal rate and frictional force to determine the material removal phenomenon, and performed nano-indentation to evaluate the material characteristics before and after the reaction. Our findings show that the material removal rate and frictional force depend on the crystal orientation, and the chemical reaction between the sapphire substrate and the slurry accelerates the material removal rate during chemical mechanical polishing.

• Journal of the Korean Wood Science and Technology
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• 제42권6호
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• pp.659-665
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• 2014

목재의 조직, 물리, 역학적 특성은 토양조건과 기후변화 등의 환경적 인자에 의해서도 바뀌게 됨으로 남부 세 지역의 임분 특성이 목재의 재질특성에 미치는 영향과 지역별 조직, 물리, 역학적 특성 등을 비교 검토하였다. 경상도, 전라도, 제주도의 졸참나무임지에 대해 임분 특성과 목재특성을 평가 분석하였는데 이들 간에는 대부분 높은 상관관계가 나타났다. 남부지역의 졸참나무는 온대에서 난대로 기후가 변화하는 난대 지역의 산림자원으로 본 목재재질특성 분석결과 유용한 산림자원으로 활용할 수 있을 것으로 생각된다.

• 임산에너지
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• 제22권2호
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• pp.26-35
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• 2003

Bamboo strand board (BSB) was made with Phyllostachys banbusoides growing in Damyang district. Physical and mechanical properties of this BSB were summarized as follows; The specific gravity of BSB was 0.63∼0.79. Specific gravity decreased slightly with the thickness and length of BSB. Moisture content of BSB manufactured was 5.8∼6.9%. The absorption ate of BSB (42∼48%) did not show any relationship with the thickness and length of BSB. The thickness swelling rate of BSB was 13.9∼17.0%, relatively higher than any other panel products. Thickness swelling rate increased with the thickness of BSB, showing the strand thickness influenced much more on the rate of thickness swelling of BSB than the length of strand. The 3-point bending strength of BSB was 98∼126kgf/$\textrm{cm}^2$. Bending strength of showed the tendency of increase with the increased length of BSB, but with the decreased thickness. In particular, the length of BSB showed more effect on the increase of bending strength of BSB than the thickness of BSB. The compression strength perpendicular to BSB surface was 411 ∼ 465 kgf/$\textrm{cm}^2$, and the optimal length of strand for the 1mm- and 2mm-thickness of strand was 40mm and 60mm, respectively. Compression strength paralleled to BSD was 160∼221kgf/$\textrm{cm}^2$ and the optimal length of strand for the 2mm-thickness of strand appeared to be 60mm. The present work showed that appearance, physical and mechanical strength of BSB appeared quite positive in terms of board qualities, suggesting that bamboo would be appropriate for the production of board materials. In addition, our work showed that the crucial factor for determining the mechanical characteristics of BSB was the dimension of strand.