• Title/Summary/Keyword: high-aspect-ratio

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Recent Topics on Injection and Combustion in High Speed Flow (Keynote)

  • Tomioka, Sadatake
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.3-8
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    • 2009
  • Wall flush mounted injector with various orifice shape and injection conditions, were examined to enhance jet penetration and mixing in supersonic cross flow, in view of application to air-breathing accelerator vehicle. Orifice shapes with high aspect ratio were found to preferable for better penetration in the cold flow, and in the reacting flow for scramjet-mode combustion conditions. However, the effectiveness of the high aspect ratio was diminished in the dual-mode combustion conditions. Supersonic injection was applied to the high aspect ratio orifice, and further increase in penetration was observed in the cold and reactive flow for scramjet-mode combustion conditions, however, mixing enhancement due to mixing layer / pseudo-shock wave system interaction was dominant in the dual-mode combustion conditions. Difficulty in attaining ignition in the case with the high aspect ratio orifice was encountered during the combustion tests.

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Spalling Properties of High Strength Concrete Made with Various Aspect Ratios and Fiber Contents of Nylon Fiber (나일론 섬유의 형상비 및 혼입률 변화에 따른 고강도 콘크리트의 폭렬특성)

  • Song, Yong-Won;Heo, Young-Sun;Lee, Seong-Yeun;Hann, Chang-Pyung;Yang, Seong-Hwan;Han, Cheon-Goo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2007.04a
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    • pp.55-58
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    • 2007
  • This study investigates the spatting properties of high strength concrete, $60\sim80MPa$ class, designed with diverse aspect ratios and fiber content of nylon(NY). Test showed that increase of fiber content and aspect ratio in concrete decreased the fluidity of fresh concrete, especially for 1580 and 3000 aspect ratio of fiber. As for the compressive and tensile strength, adding NY fiber did not significantly affect the values In the range of high strength. After completing the fire test, the specimens containing both 750 and 1000 aspect ratios of fiber protected the spatting occurrence even in 0.05vol.% of fiber content. This specimens indicated the residual compressive strength ratio at 37%, showing the most favorable value among other specimens. Therefore, it is demonstrated that to protect the spalling in high strength concrete considering the effective fluidity, strength and economic efficiency altogether, adding 0.05vol.% of NY fiber with 750 aspect ratio Is beneficial.

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Mechanical Properties of Steam Cured High-Strength Steel Fiber-Reinforced Concrete with High-Volume Blast Furnace Slag

  • Yang, Jun-Mo;Yoo, Doo-Yeol;Kim, You-Chan;Yoon, Young-Soo
    • International Journal of Concrete Structures and Materials
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    • v.11 no.2
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    • pp.391-401
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    • 2017
  • In this study, the effects of water-to-binder (W/B) ratio and replacement ratio of blast furnace slag (BFS) on the compressive strength of concrete were first investigated to determine an optimized mixture. Then, using the optimized high-strength concrete (HSC) mixture, hooked steel fibers with various aspect ratios and volume fractions were used as additives and the resulting mechanical properties under compression and flexure were evaluated. Test results indicated that replacement ratios of BFS from 50 to 60% were optimal in maximizing the compressive strength of steam-cured HSCs with various W/B ratios. The use of hooked steel fibers with the aspect ratio of 80 led to better mechanical performance under both compression and flexure than those with the aspect ratio of 65. By increasing the fiber aspect ratio from 65 to 80, the hooked steel fiber volume content could be reduced by 0.25% without any significant deterioration of energy absorption capacity. Lastly, complete material models of steel-fiber-reinforced HSCs were proposed for structural design from Lee's model and the RILEM TC 162-TDF recommendations.

SU-8 Mold Fabrication with Low Internal Stress and High Aspect Ratio for UV LIGA Process (고 형상비 UV LIGA 공정을 위한 낮은 내부응력의 SU-8 도금틀 제작)

  • Jang, Hyeon-Gi;Kim, Yong-Gwon
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.48 no.8
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    • pp.598-604
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    • 1999
  • This paper describes the research to minimize the film stress and maximize the aspect ratio of photoresist structure, especially about SU-8 for electroplating mold. UV LIGA process using SU-8 allows fabricating high aspect ratio polymer structures. However, it is hard to get fine patterns in the high aspect ratio structures because of high internal stress and difficulty of removing SU-8. The purpose of this paper is to setup the process condition for the obtainment of both low film stress and high aspect ratio and to find design rules that make the pattern be less dependent on stress problem. Firstly, the process of heat treatment and exposure of SU-8 are proposed. These two conditions control the amount of cross-linkage in polymer structure, which is the most important parameter of both pattern generation and remaining stress. Heat treatment is dealed with soft bake and post-exposure-bake. Temperature and time duration of each step are varied with heat treatment condition. Some test patterns are fabricated to evaluate the proposed process. Nickel electroplating is performed with the mold fabricated through the proposed process to confirm the SU-8 as a good electroplating mold.

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Manufacture of High-Aspect-Ratio Polymer Nano-Hair Arrays by UV Nano Embossing Process (UV 나노 엠보싱 공정을 이용한 고종횡비 고분자 나노 섬모 어레이 제작)

  • Kim Dong-Sung;Lee Hyun-Sup;Lee Jung-Hyun;Lee Kun-Hong;Kwon Tai-Hun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.7 s.250
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    • pp.773-778
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    • 2006
  • High-aspect-ratio nano-hair or nano-pillar arrays have great potential in a variety of applications. In this study, we present a simple and cost-effective replication method of high-aspect-ratio polymer nano-hair arrays. Highly ordered nano-porous AAO (anodic aluminum oxide) template was utilized as a reusable nano-mold insert. The AAO nano-mold insert fabricated by the two-step anodization process in this study had close- packed straight nano-pores, which enabled us to replicate densely arranged nano-hairs. The diameter, depth and pore spacing of the nano-pores in the fabricated AAO nano-mold insert were about 200nm, $1{\mu}m$ and 450nm, respectively. For the replication of polymer nano-hair arrays, a UV nano embossing process was applied as a mass production method. The UV nano embossing machine was developed by our group for the purpose of replicating nano-structures by means of non-transparent nano-mold inserts. Densely arranged high-aspect-ratio nano-hair arrays have been successfully manufactured by means of the UV nano embossing process with the AAO nano-mold insert under the optimum processing condition.

Injection Molding Experiments for Small Diameter Column (미소 원주의 사출 성형 실험)

  • 제태진;이응숙;김재구
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.10a
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    • pp.85-88
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    • 1995
  • Recently, the micro mold maching techining technology is developed by means of the mechanical and high energy beam process. It is possible to make the micro structure mold with high aspect ratio by the LIGA technology. This mode is used for mass production of plastic parts by the micro injection molding method. In this study, we intend to research on the basic technology of micro injection molding. As the result, we developed the injection molding technology for small column plastic parts which diameter is 500 .mu. m and 200 .mu. m respectively with wbout aspect ratio 20.

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Tensile Characteristics of High-Ductile Cementless Composite According to Aspect Ratio of Fiber (섬유의 형상비에 따른 고연성 무시멘트 복합재료의 인장특성)

  • Choi, Jeong-Il;Park, Se Eon;Kang, Su-Tae;Oh, Sungwoo;Lee, Bang Yeon
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.3
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    • pp.160-166
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    • 2018
  • The purpose of this study is to investigate experimentally the effects of aspect ratio of polyethylene fiber on the compressive strength and tensile behavior of alkali-activated cementless composite. Two mixtures were determined according to aspect ratio values of polyethylene fibers, and the compressive strength and tension tests were performed. Test results showed that the effect of aspect ratio of fiber on the compressive strength was negligible and the tensile strength, ductility, and number of cracks of the mixture including the fiber with high aspect ratio were higher than those of the mixture including the fiber with low aspect ratio. On the other hand, the crack spacing and crack width were low in the mixture including the fiber with high aspect ratio.

Fabrication and application of high-aspect-ratio microchannels using laser-induced etching (레이저유도 에칭을 이용한 고세장비 마이크로채널 가공 및 응용)

  • Oh Kwang-H.;Lee M.K.;Kim S.G.;Lim H.T.;Jeong S.H.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2006.05a
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    • pp.659-660
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    • 2006
  • High-aspect-ratio(max. 12.5) microchannels with excellent surface quality and good shape uniformity have been realized utilizing laser-induced etching technique. Etch width and depth variations depend largely upon process variables such as laser power and etchant concentration. Etchant concentration in association with viscosity also influence on the cross-sectional profile of the channels. The optimum process conditions for the fabrication of high-aspect-ratio microchannels applicable to micro thermal devices are demonstrated.

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Experimental study on micro-hole drilling with high aspect ratio using picosecond laser (피코초 레이저를 이용한 고세장비 미세 홀가공의 실험적 연구)

  • Oh, Bukuk;Kim, Jongki;Kim, Dooyoung;Lee, Seungkey;Jeong, Soohoa;Hong, Michael
    • Laser Solutions
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    • v.18 no.2
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    • pp.11-13
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    • 2015
  • Pressure-drop in a micro-channel is critical when a hole diameter is less then 100um with the high aspect ratio, more than 40. To minimize these pressure loss for micro-channel applications is important and there would be the best hole diameter, taper angle, and their combinations. In this work, the parametric study for laser drilling of anodized material is conducted to obtain the micro-channel hole with high aspect ratio.

Compressive and Flexural Behavior of High-Strength Concrete Incorporating Different Types of Hooked-End Steel Fibers (강섬유 특성에 따른 고강도 콘크리트의 압축 및 휨 거동)

  • Jeong, Woo-Jin;Jin, Ai-Hua;Yun, Hyun-Do
    • Journal of Korean Association for Spatial Structures
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    • v.23 no.2
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    • pp.69-78
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    • 2023
  • This paper investigates the effects of aspect ratio and volume fraction of hooked-end normal-strength steel fibers on the compressive and flexural properties of high-strength concrete with specified compressive strength of 60 MPa. Three types of hooked-end steel fibers with aspect ratios of 64, 67 and 80 were considered and three volume fractions of 0.25%, 0.50% and 0.75% for each steel fiber were respectively added into each high-strength concrete mixture. The test results indicated that the addition of normal-strength steel fibers is effective to improve compressive and flexural properties of high-strength concrete but fiber aspect ratio had little effect on the modulus of elasticity and compressive strength. As steel fiber content and aspect ratio increased, flexural beahvior of notched high-strength concrete beams was effectively improved.