• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.407-416
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• 2010

A new tunnel auxiliary method is proposed in this paper which utilizes the concept of cavity expansion for tuunel reinforcement by forming an umbrella arch on the roof of tunnel. When an inflatable pipe is inserted and expanded by pressure in the bore hole of umbrella arch, the ground around the bore hole can be compacted so that the stress condition above the tunnel perimeter is favorably changed. In order to verify the reinforcement effect of new concept, pilot-scale chamber test, trapdoor test and numerical analysis were performed and compared. In pilot-scale chamber test, three types of inflatable pipes are tested to verify the capability of expansion, and the results arc compared with analytical results obtained by applying cavity expansion theory and with results obtained from finite clement analysis, and the experimental results showed agreeable matches with analytical and numerical ones. Numerical analysis of a tunnel and trapdoor test applied with the inflatable pipes are also performed to figure out the reinforcement effect of the proposed techniques, and the results implied that the new method with 3 directional inflatable pipe (no pressure to downward direction) can contribute to reduce tunnel convergence and face settlement.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.315-316
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• 2003

차량의 통행이 빈번한 기존 아스팔트 도로는 연속적인 차량의 하중에 의한 스트레스로 하중을 받을 때마다 아스팔트도로 층의 강도와 안정성이 떨어지면서 균열이 발생하고 이 균열이 아스팔트 도로 상층부까지 전달되는 반사균열이 발생한고, 열팽창과 수축의 반복에 기인하는 상부의 아스팔트 층의 피로에 의한 균열이 발생한다. 따라서 아스팔트 도로의 반사균열을 억제하고, 아스팔트의 소성변형에 의한 rutting현상을 억제하여 아스팔트의 도로보수 주기를 연장하여 도로상에서의 잦은 보수에 의한 자동차의 정체현상을 줄이고 도로유지에 소요되는 비용을 절감하기 위해서 아스팔트 도로를 설치할 때 아스팔트를 보강시켜주는 geogrid의 사용이 보편화 되고 있다. (중략)

• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.49-60
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• 2010

Semiconductor packages are increasingly moving toward miniaturization, lighter and high performance. Futhermore, packages become thinner. Thin packages will generate serious reliability problems such as warpage, crack and other failures. Reliability problems are mainly caused by the CTE mismatch of various package materials. Therefore, proper selection of the package materials and geometrical optimization is very important for controlling the warpage and the stress of the package. In this study, we investigated the characteristics of the warpage and the stress of several packages currently used in mobile devices such as CABGA, fcSCP, SCSP, and MCP. Warpage and stress distribution are analyzed by the finite element simulation. Key material properties which affect the warpage of package are investigated such as the elastic moduli, CTEs of EMC molding and the substrate. Geometrical effects are also investigated including the thickness or size of EMC molding, silicon die and substrate. The simulation results indicate that the most influential factors on warpage are EMC molding thickness, CTE of EMC, elastic modulus of the substrate. Simulation results show that warpage is the largest for SCSP. In order to reduce the warpage, DOE optimization is performed, and the optimization results show that warpage of SCSP becomes $10{\mu}m$.

• Toxicological Research
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• v.13 no.1_2
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• pp.1-21
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• 1997

염증반응이란 우리 신체에 외부 물질이 침입했을 경우 대처하는 정상적인 현상이다. 외부에서 물리, 화학, 생물학적 물질에 노출되었을 경우 혈관이 팽창하고, 비특이적 면역반응이 시작된다. Selectin, integrin, immunoglobulin superfamily와 같은 adhesion molecule에 의해 macrophage 및 neutrophil과 같은 leukocyte의 반응을 촉진하기 위해 exudation이 일어나고 침입 부위에 모여 hyperemia가 발생된다.(Govan 등, 1995)

• The Journal of Engineering Geology
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• v.12 no.1
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• pp.95-109
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• 2002

A significant question is what role does newly-formed expansive mineral growth play in the premature deterioration of concrete. These minerals formed in cement paste as a result of chemical reactions involving cement paste and coarse/fine aggregate. Petrographic observations and SEM/EDAX analysis were conducted in order to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from lowa concrete highways that showed premature deterioration. Formation and expansive mechanisms involved in deterioration were Investigated. Brucite, Mg(OH)$_2$, is potentially expansive mineral that farms in cement paste of concretes containing reactive dolomite aggregate as a result of partial dedolomitization of the aggregate. No cracking was observed to be spatially associated with brucite, but most brucite was microscopic in size and widely disseminated in the cement paste of less durable concretes. Expansion stresses associated with its growth at innumerable microlocations may be retrieved by cracking at weaker locations in the concrete. Ettringite, 3CaO.Al$_2$O$_3$.3CaSO$_4$.32$H_2O$, completely fills many small voids and occurs as rims lining the margin of larger voids. Microscopic ettringite is common disseminated throughout the paste in many samples. Severe cracking of cement paste causing premature deterioration is often closely associated with ettringite locations, and strongly suggests that ettringite contributed to deterioration. Pyrite, FeS2, is commonly present in coarse/fine aggregates, and its oxidation products is observed in many concrete samples. Pyrite oxidation provides sulfate ions for ettringite formation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.24-31
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• 2002

The effects of vortex generators, in the form of small delta-shaped tabs or thin tapes at an axi-symmetric supersonic nozzle exit, on the characteristics of supersonic jet flowfields are investigated by Schlieren images and Pitot-tube measurements. Small tabs as small as 1 % of the nozzle exit area can introduce streamwise vortices and produce a significant effect on the jet flowfield downstream of the nozzle. The effect is stronger for the cases of under-expanded jet than over- and perfect-expanded cases, introducing a larger flow entrainment. The effects of the angle of tabs with respect to the flow direction are also investigated, and for over-expanded jet cases, it is found that the tabs bended toward upstream can weaken the interaction strength and remove the Mach disc in the jet flowfield. Introduction of small proturbances inside the nozzle surface by attachment of thin tapes is also found to change the pressure distribution in the circumferential direction of the flowfield. Its effect is also found to be dependent on the jet expansion ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.79-84
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• 2005

An experimental investigation for impingement of under-expanded, axisymmetric jets on a flat plate has been conducted, and the surface pressure, the adiabatic wall temperature distributions on the plate have been measured in detail. For the explanation on the wall temperature distributions, the total temperature distributions along a free jet have also been measured with total temperature probes. In this study, the under-expansion ratio and the nozzle-to-plate distance have been considered as experimental parameters. Depending on nozzle-to-plate distances, different distributions of adiabatic wall temperature are shown by the energy separation at a jet edge and a impinged surface. Also, the recovery factor on a stagnation point decreases significantly due to the isolation of fluid particles in a central region.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2008.11a
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• pp.914-917
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• 2008

This paper was to discuss the case and cause of debonding defect of wood floor board in apartment house by investigating actual survey. Most frequent defect in wood floor board was debonding of floor board. Scratch, gap and crack of floor board were also found in floor board installment work. Causes of debonding of floor board is shrinkage of cement mortar beneath floor board and expansion of floor board. Haste in floor board work did not provide enough time to dry cement mortar fully, which led to continue to dry after the installment of floor board. It caused moisture movement toward wood floor board. Accordingly, Before floor board work, careful consideration on moisture condition of cement mortar and enough curing time to eliminate the effect of moisture are taken into.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.6
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• pp.702-708
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• 2016

The torque converter is deformed according to the rotating speed and control pressure when engine power is transferred to the transmission. This deformation, which is called ballooning phenomenon, occurs mainly at the outer side by the centrifugal force of the automatic transmission fluid (ATF) and the control pressure from the valve body. Although the torque converter is slightly deformed when rotating, the ballooning phenomenon affects fluid performance, efficiency and durability. Thus, expansion characteristics analysis is important in determining torus size, control pressure and structure. In this paper, an analysis equation and FEM model was developed to investigate the expansion characteristics. Using this model, structural analysis was performed to investigate the relationships between deformation and the torus diameter. The results were confirmed by comparing with the test results.

• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.201-207
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• 2015

In this paper, a series of experiments was conducted to evaluate the resistibility of carbonation and freeze-thawing damage of the high-volume blast furnace slag concrete using expancel, the expandable microsphere, and ERCO, emulsified refine cooking oil. The concrete mixture of 0.45 water-to-binder ratio with 60% of blast furnace slag was evaluated for carbonation, freeze-thawing resistibility, SEM, and porosity. According to the previous research, replacing ERCO contributes on improving carbonation resistibility with capillary pore filling effect by soap foaming reaction of ERCO while significantly decreased freeze-thawing resistibility. To improve this decreased freeze-thawing resistibility, expancel was used, and thus freeze-thawing resistibility was improved as the replacement ratio of expancel was increased. It is considered that the selective volume shrunken effect of expancel due to the external pressure and decreased air void spacing factor due to expancel.