Al-Cr-Si ternary quench ribbons are fabricated using a single roll method and investigated for their structural and thermal properties. In particular, the sinterability is examined by pulse current sintering to obtain the following results. The Al74Cr20Si6 composition becomes a quasicrystalline single phase; by reducing the amount of Cr, it becomes a twophase mixed structure of Al phase and quasicrystalline phase. As a result of sintering of Al74Cr20Si6, Al77Cr13Si10 and Al90Cr6Si4 compositions, the sintering density is increased with the large amount of Al phase; the sintering density is the highest in Al90Cr6Si4 composition. In addition, as a result of investigating the effects of sintering temperature and pressurization on the sintered density of Al90Cr6Si4, a sintered compact of 99% or more at 513 K and 500 MPa is produced. In particular, since the Al-Cr-Si ternary crystal is more thermally stable than the Al-Cr binary quaternary crystal, it is possible to increase the sintering temperature by about 100 K. Therefore, using an alloy of Al90Cr6Si4 composition, a sintered compact having a sintered density of 99 % or more at 613 K and 250 MPa can be manufactured. It is possible to increase the sintering temperature by using the alloy system as a ternary system. As a result, it is possible to produce a sintered body with higher density than that possible using the binary system, and at half the pressure compared with the conventional Al-Cr binary system.

In this study, using the plasma spray method, tensile and compression fatigue tests are performed in saline solution to examine the effect of Ti undercoat on corrosion fatigue behavior of alumina-coated specimens. The alumina-coated material using Ti in the undercoat shows better corrosion fatigue strength than the base material in the entire stress amplitude range. Fatigue cracking of UT specimens occurs in the recess formed by grit-blasting treatment and progresses toward the base metal. Subsequently, the undercoat is destroyed at a stage where the deformation of the undercoat cannot follow the crack opening displacement. The residual stress of the UT specimen has a tensile residual stress up to about 100 μm below the surface of the base material; however, when the depth exceeds 100 μm, the residual stress becomes a compressive residual stress. In addition, the inside of the spray coating film is compressive residual stress, which contributes to improving the fatigue strength characteristics. A hardened layer due to grit-blasting treatment is formed near the surface of the UT specimen, contributing to the improvement of the fatigue strength characteristics. Since the natural potential of Ti spray coating film is slightly higher than that of the base material, it exhibits excellent corrosion resistance; however, when physiological saline intrudes, a galvanic battery is formed and the base material corrodes preferentially.

In this study, high temperature wetting analysis and AZ80/Ti interfacial structure observation are performed for the mixture of AZ80 and Ti, and the effect of Al on wetting in Mg alloy is examined. Both molten AZ80 and pure Mg have excellent wettability because the wet angle between molten droplets and the Ti substrate is about 10° from initial contact. Wetting angle decreases with time, and wetting phenomenon continues between droplets and substrate; the change in wetting angle does not show a significant difference when comparing AZ80-Ti and Mg-Ti. As a result of XRD of the lower surface of the AZ80-Ti sample, in addition to the Ti peak of the substrate, the peak of TiAl3, which is a Ti-Al intermetallic compound, is confirmed, and TiAl3 is generated in the Al enrichment region of the Ti substrate surface. EDS analysis is performed on the droplet tip portion of the sample section in which pure Mg droplets are dropped on the Ti substrate. Concentration of oxygen by the natural oxide film is not confirmed on the Ti surface, but oxygen is distributed at the tip of the droplet on the Mg side. Molten AZ80 and Ti-based compound phases are produced by thickening of Al in the vicinity of Ti after wetting is completed, and Al in the Mg alloy does not affect the wetting. The driving force of wetting progression is a thermite reaction that occurs between Mg and TiO2, and then Al in AZ80 thickens on the Ti substrate interface to form an intermetallic compound.

Veratric aicd is a phenolic compound, which is derived from medicinal mushrooms. In our study, veratric acid showed the effect on the reduction of nitric oxide (NO) production in LPS-stimulated RAW264.7 cells. The negative regulation of NO production in LPS-induced RAW264.7 cells were caused by the modulation of iNOS at mRNA and protein levels. The transcription factors for iNOS expression, including NF-κB, STAT-1, c-Jun, ATF-2, and Elk-1, were down-regulated by veratric acid. Because c-Jun, ATF-2, and Elk-1 is induced by p38, we determined that the effect of veratric acid on p38 expression, which was inactivated. Additionally, Akt and p110β, the catalytic subunit of PI3K, were inactivated by veratric acid. In the inhibition of p38 and PI3K, the inhibition of p38 did not modulate the expression of iNOS, the inhibition of PI3K, although, induced the synergic effect on the reduction of NO production. The results indicated veratric acid required p38 to regulate the expression of iNOS in LPS-stimulated RAW264.7 cells.

최근 건설현장에서 작업자의 고령화 및 숙련공 부족 현상이 중요 문제로 부각되고 있으며, 또한 최근 건설구조물이 점차 고층화, 대형화됨에 따라 부재의 형상이 복잡해지고 있다. 이러한 건설 환경의 변화에 따라 국내 및 국외에서 고유동 콘크리트에 대한 연구 및 개발이 증대되고 있다. 고유동 콘크리트는 재료분리 없이 굳지 않은 콘크리트의 유동성을 개선시켜 다짐 작업 없이 자기 충전이 가능한 콘크리트를 말한다. 하지만 고유동 콘크리트는 인장 및 휨 강도의 저하와 균열 등의 문제점을 가지고 있다. 따라서 본 연구에서는 문제점을 해결하기 위하여 고유동 콘크리트에 양마섬유를 혼입하였다. 양마섬유의 경우 천연섬유로 친환경적이며 이산화탄소의 흡수량이 많아 콘크리트 생산과정에서 배출되는 이산화탄소의 양을 상쇄시킬 수 있을 것으로 보인다. 또한, 기존 콘크리트의 섬유 보강재로 사용되었던 황마와 유사한 특성을 지녔으며 짧은 생육 기간으로 대량생산이 가능하여 경제적이다. 양마섬유는 섬유 표면이 거칠어 콘크리트와의 부착력이 뛰어나고 섬유의 인장력이 우수하여 콘크리트의 인장강도 증진과 균열 저감 효과가 있을 것으로 사료된다. 또한, 산업부산물의 일종인 플라이애쉬와 고로슬래그를 혼입하여 탄소저감 효과와 폐기물의 처리로 환경적인 측면에서 긍정적인 효과가 기대된다. 따라서 본 연구에서는 이와 같은 재료로 시멘트의 일부를 대체하여 양마섬유를 혼입한 고유동 콘크리트의 강도 특성을 알아보고자 하였다.

This study is an experimental program developed to estimate the effect of size on the shear performance of reinforced concrete (RC) beams with stirrups made from recycled coarse aggregates (RCA). The test was conducted on eight RC beams with shear reinforcement, and the main variables were section size and RCA replacement ratio (Rr = 0% or 30%). The tension reinforcement ratio (ρ = 0.012), shear span-to-depth ratio (a/d = 1.5), and width-to-depth ratio (h/b = 1.5) were fixed. Empirical test results, theoretical results, and code calculations were compared for each specimen. The results demonstrated that the empirical test results of each sample compared favorably with the theoretical calculations within a sufficient safety margin (1.32-2.61). Also, a comparison between RCA-RC beams with Rr = 30% and RC beams containing natural coarse aggregates (NCAs) showed that the two beams exhibited similar load-displacement curves and shear strengths. Consequently, RCA-RC beams made using a RCA replacement ratio of up to 30% do not cause safety or serviceability problems.

본 연구는 섬유를 혼입한 고강도 콘크리트의 온도 변화에 따른 내화특성 분석에 관한 연구로 고강도 콘크리트에 고온이 가해질 경 우 발생되는 폭렬현상에 대하여 방지효과가 있는 것으로 알려져 있는 하이브리드섬유와 강섬유를 함께 혼입하여 만든 복합섬유를 사용하여 온도 변화(100∼800°C)에 따른 고강도 콘크리트의 내화특성 및 역학적 메커니즘을 분석하였다. 또한 본 논문에서는 고강도 콘크리트 구조물 에서 가장 문제가 되는 폭렬현상을 막는 대책 중의 하나인 섬유 혼입을 통한 방법을 사용하여 SEM 및 XRD 분석 등의 방법으로 고온을 받은 고 강도 콘크리트의 열적 특성 및 역학적 특성을 규명하고자 하였다.

Recently, demand for construction aggregates is increasing due to the growth of construction site scale. As natural aggregate sources are becoming depleted due to high demand in construction field, the utilization of recycled aggregate (RA) as coarse aggregate in concrete is becoming more important. In this study, the authors analyze the mechanical properties of normal- and high-strength concrete beams using RA and investigate the usefulness of the minimum steal ratio for RA reinforced concrete beams. The experimental results show that application of the minimum steel ratio to RA reinforced concrete beams is possible.

This paper describes design method of Passive-type Radar Reflector (PRR) which is to provide the requirement of newly revised 2000 SOLAS regulations on the Radar Reflector. The main target of this work is to find the optimum shape of a radar target having large Radar Cross Section (RCS). Through the RCS analysis based on the theoretical approach, two kinds of PRR models, RRR-F model for use in fisheries and PRR-S model for use in small sized ship, are designed and discussed their RCS performance. RCS measurement tests for the various sized samples are carried out in an anechoic chamber. As evaluation results it was clearly shown that the conventional sphere-type shows optimum shape in case of PRR-S, while the cylinder-type which consists of large sized corner clusters or zig-zag flat plats gives best performance in case of PRR-F.