• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.107-115
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• 2006

A challenging topic was and still is the failure behavior of concrete beams without shear reinforcement. In spite of substantial experimental and theoretical efforts in the past, the mechanism of shear failure is not entirely understood. ALWAC is of importance to the current construction industry. Most of present concrete research focuses on high performance concrete, by which in meant a cost effective material that satisfies demanding performance requirements, including durability. The advantages of ALWAC are its reduced mass and improved thermal and acoustic insulation properties, while maintaining adequate strength. In spite of these advantages, its ultimate failure behavior has not been well defined for adequate design process. This paper will investigate mainly the shear behavior of reinforced ALWAC beam without web reinforcements numerically with experimental evidences.

• Progress in Superconductivity and Cryogenics
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• v.25 no.4
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• pp.70-74
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• 2023

The Small Punch Test (SPT) was developed to evaluate the softening and embrittlement of materials such as power plants and nuclear fusion reactors by taking samples in the field. Specimens used in the SPT are very thin and small disk-shaped compared to specimens for general tensile test, and thus have economic advantages in terms of miniaturization and repeatability of the test. The cryogenic SPT can also be miniaturized and has a significantly lower heat capacity than conventional universal test machines. This leads to reduced cooling and warm-up times. In this study, the cryogenic SPT was developed by modifying the existing room temperature SPT to be cooled by liquid nitrogen using a super bellows and a thermal insulation structure. Since the cryogenic SPT was first developed, basic experiments were conducted to verify the effectiveness of it. For the validation, aluminum alloy 6061- T6 specimens were tested for mechanical properties at room and cryogenic temperature. The results of the corrected tensile properties from the SPT experiment results were compared with known room temperature and cryogenic properties. Based on the correction results, the effectiveness of the cryogenic SPT test was confirmed, and the surface fracture characteristics of the material were analyzed using a 3d image scanner. In the future, we plan to conduct property evaluation according to the development of various alloy materials.

• Clean Technology
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• v.28 no.4
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• pp.301-308
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• 2022

Since nanoporous silica aerogel was first synthesized in 1931, its potential as an ultra-lightweight superinsulation material has been steadily attracting attention. Silica aerogel is the best thermal insulation material to date. However, the potential applications of this lightweight material have so far been hindered by its inherent fragibility and brittleness arising from its ultra-porous nature. Although the monolithic form of silica aerogel has the best ultra-lightweight superinsulation properties, it cannot be used in this form. Instead it is used in the form of powders, particles, and blankets. However, these forms still have shortcomings. Silica aerogel is most widely applied in the form of a fiber-reinforced aerogel blanket, but this form is likely to generate dust when handled. Although silica aerogel particles have been proven to be non-toxic to humans, dust formation remains a major barrier to the widespread application of silica aerogel blankets. This paper will investigate the unique properties of silica aerogel and determine what fields it can be used in or potentially be used in due to its unique properties. In addition, we will review the important advances in silica aerogel synthesis technology and its commercialization so far, and then consider the problems that exist for its widespread commercialization in the future and how to overcome them.

• Current Research on Agriculture and Life Sciences
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• v.33 no.2
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• pp.41-47
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• 2015

This study calculated the overall heat transfer coefficient (U-value) of greenhouse covering materials with thermal screens using a simulation model and then estimated the validity of the calculated results by comparison with measured values. The U-value decreased gradually as the thickness of the air space between the double glazing increased, and then remained essentially constant at thicknesses exceeding 25 mm. The U-value also increased with the difference in temperature between the inside and outside of the hot box. The vigorous convective heat transfer between two plastic films caused unsteady heat flow and then created a nonlinear temperature distribution in the air space. The distance did not affect the U-value at distances of 50~200 mm between the plastic covering and thermal curtain. The numerical calculation results, with and without sky radiation, were in accord with the experimental results for a $30^{\circ}C$ temperature difference between the inside and outside of the hot box. In conclusion, a reliable U-value can be calculated for a temperature difference of $30^{\circ}C$ or more between the inside and outside of the hot box.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.223-229
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• 2015

Surface modification is a technology to form a new surface layer and overcome the intrinsic properties of the base material by applying thermal energy or stress onto the surface of the material. The purpose of this technique is to achieve anti-corrosion, beautiful appearance, wear resistance, insulation and conductance for base materials. Surface modification techniques may include plating, chemical conversion treatment, painting, lining and surface hardening. Among which, a surface modification process using electrolytes has been investigated for a long time in connection with research on its industrial application. The technology is highly favoured by various fields because it provides not only high productivity and cost reduction opportunities, but also application availability for components with complex geometry. In this study, an electrochemical experiment was performed on the surface of 5083-O Al alloy to determine an optimal electrolyte temperature, which produces surface with excellent corrosion resistance under marine environment than the initial surface. The experiment result, the modified surface presented a significantly lower corrosion current density with increasing electrolyte temperature, except for $5^{\circ}C$ of electrolyte temperature at which premature pores was created.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.81-88
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• 2020

Flight data recorder is a equipment that records data required for investigation of aircraft accidents and should be developed in compliance with the ED-112A standard. Unlike general data storage device, flight data recorder must be able to recover data after an aircraft accident, requiring a housing and a memory board to protect data in extreme environments. To attain this performance, we designed a housing that can withstand the test by analyzing the physical environment of the impact, shear/tensile, penetration resistance and static crush test of the crash survival test and minimized the size and weight compared to the existing one in consideration of the installation of the aircraft in this paper. Insulation material and thermal block material were applied to endure high and low temperature fire so that the internal temperature does not rise above 150℃ even in 260℃, 10 hour environment. In addition, the memory board is designed to minimize the size and we devise a hoping programming method to prevent continuous data loss of more than 16 seconds. Through this, Crash protected memory module that satisfies ED-112A was completed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.114-119
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• 2013

The present study tested 5 concrete mixes to develop reliable mixing proportions for the sustainable alkali-activated(AA) foamed concrete as a thermal insulation material for the floor heating system of buildings. The AA binder used was composed of 73.5% ground granulated blast-furnace slag, 15% fly ash, 5% calcium hydroxide, and 6.5% sodium silicate. As a main variable, the unit binder content varied from $325kg/m^3$ to $425kg/m^3$ at a space of $25kg/m^3$. The test results revealed that AA foamed concrete has considerable potential for practical applications when the unit binder content is close to $375kg/m^3$, which achieves the minimum quality requirements specified in KS F 4039 and ensures economic efficiency. In addition, lifecycle assessment demonstrated the reduction in the environmental impact profiles of all specimens relative to typical ordinary portland cement foamed concrete as follows: 99% for photochemical oxidation potential, 87~89% for global warming potential, 78~82% for abiotic depletion, and 70~75% for both acidification potential and human toxicity.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.21 no.3
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• pp.139-145
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• 2011

Objectives: This investigation is purposed to evaluate the airborne asbestos concentrations in the public buildings having asbestos containing materials(ACMs) in Seoul. Methods: The Seoul Metropolitan Government carried out an asbestos survey to the city-owned public buildings to identify the level of risk exposure, classified into low, moderate and high risk. To evaluate the airborne concentration of asbestos, 11 sampling sites in ten buildings based on the survey were selected. The air samples from the eleven sites were analyzed by Phase Contrast Microscopy(PCM) and Transmission Electron Microscopy (TEM), and compared the analytical results from the both. Results: 1. The airborne fiber concentrations by PCM were less than the detection limit($7f/mm^2$) in 9(82%) out of 11 sampling sites. The highest concentration was 0.0043 f/cc, but it was below the guideline value for indoor air quality(0.01 f/cc), proposed by the Ministry of Environment, Korea. 2. In two sampling sites, having moderate risk level, the chrysotile was identified and showed it's concentrations of 0.0102 s/cc and 0.0058 s/cc, less than $5{\mu}m$ lengths. 3. The ACMs identified in the two sampling sites were a packing material(65% of chrysotile) in mechanical area and a thermal system insulation(5% of chrysotile) in a boiler room. Having more possibility of asbestos emission in the mechanical area, it would be required to set up and carry out the asbestos management plan. Conclusions: Based on the result of this study, the airborne asbestos concentrations in the public buildings with ACMs were generally lower than the guideline value for indoor air quality. There are widespread concerns about the possible health risk resulting from the presence of airborne asbestos fibers in the public buildings. Most of the previous studies about airborne asbestos analysis in Korea were performed based on PCM method that asbestos and non-asbestos fibers are counted together. In the public and commercial buildings, having ACMs, it is suggested that the asbestos be analyzed by TEM method to identify asbestos due to concerns about asbestos exposure to workers and unspecified people.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.543-551
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• 2006

Cold-formed steel studs that are being used as load-bearing members of wall panels for steel houses have a problem with their insulation due to the heat bridging of their web. Some additional thermal insulating materials should be used. To solve this problem, the new-concept hybrid stud, which consists of a galvanized steel sheet (t = 1.0 m - 12.0 m) and a GFRP panel (t = 4.0-6.0 mm), has recently been developed. An investigation on the structural behavior and the strength capacity of this new hybrid stud has been conducted so that it can be used in load-bearing wall panels of residential buildings. This paper describes the axial compression-torsion test results of the hybrid studs under both axial compression and torsion using ATTM. The main factors of the test were the stud length, the magnitude of the initial compressive force, and the loading method of the monotonic or cyclic loading. The torsion was applied increasingly while the initial compression was kept constant to the failure of the hybrid section. The advanced analysis results obtained form the finite element procedure that considered the material properties of the high-strength galvanized steel and the GFRP were compared with the test results for verification.