• Title/Summary/Keyword: Exposure to High Temperature

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Effects on Tensile Strength of Base and Weld Metal of Ti-6Al-4V Alloy in Short Time Exposure to High Temperature (Ti-6Al-4V 합금의 단시간 고온 노출 시 모재 및 용접부의 인장강도 특성)

  • Chae, Byoung-Chan
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.4
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    • pp.413-421
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    • 2014
  • Since the structural temperature of a flight vehicle flying at high speed rises rapidly due to aerodynamic heating, it is necessary for optimum structural design to obtain proper material properties at high temperature by taking into account of its operational environment. For a special alloy, analysis data on strength change due to exposure time to high temperature are very limited, and most of them are for an exposure time longer than 30 minutes for long term operations. In this study, base and weld metal samples of Ti-6Al-4V alloy had been prepared and high temperature tensile tests with induction heating were performed, and then high temperature strength characteristics and strength recovery characteristics through cooling have been analyzed. Pre-tests to determine maximum heating rate were performed, and response characteristics for temperature control were confirmed. As a result, high temperature tensile strength appeared to be lower than that of room temperature, but it was higher than that of high temperature of 30 minite exposure listed in MMPDS. In strength recovery through cooling Ti-6Al-4V alloy has shown higher recovery rate compared with other alloys.

Optical Microscopic Image Analysis for Damaged GFRP Rebar by Alkali and High Temperature Exposures (알칼리와 고온노출에 의한 GFRP 보강근 손상에 대한 현미경분석 연구)

  • Bae, Jung-Myung;Moon, Do-Young;Park, Cheol-Woo;Park, Young-Hwan
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.2
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    • pp.53-59
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    • 2017
  • In this experimental study, the characteristic of damages on GFRP rebar exposed to high temperature only and immerged in alkaline solution after the exposure to high temperature was analyzed through microscopic image analysis. The found microcrack and pores in resin matrix were quantitatively compared if there was effect of pre-exposure to high temperature. The damages, such as microcrack and pores in resin matrix, by alkali exposure were mainly found in rebar surface. On the other hand, the pores caused by high temperatures were extensively found in a section and had greater width than those caused by the alkali exposure. In results of the quantitative comparison, the accumulated length and widths of microcrack and pores in resin matrix in pre-exposed GFRP rebar to high temperature were respectively 1.5 and 1.4 times of those in the GFRP rebar only immerged in alkali solution. Therefore, the deterioration of resin matrix by the alkali exposure could be accelerated due to the pre-exposure to high temperature.

A Comparison of Residual Tensile Properties of GFRP Reinforcing Bar at High Temperature and after Exposure to High Temperature (고온과 고온노출 후 GFRP 보강근의 잔존인장성능 비교)

  • Kim, Seongdo;Moon, Doyoung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.1
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    • pp.77-84
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    • 2015
  • Tensile tests were conducted on the GFRP reinforcement exposed to high temperature. The exposure condition for this study was below $200^{\circ}C$ for about 3 minutes. This conditioning is minor compared with that presented in experimental program conducted by other researchers. The residual tensile strength and elastic modulus of GFRP reinforcing bars at high temperature and after exposure to high temperature were compared. In results, tensile properties were decreased at high temperatures, but those after exposure to high temperature were recovered to pre-heating level almost completely. These results could be valuable for evaluating GFRP reinforced structure damaged by fire accident.

Characteristics and Health Status of Outdoor Workers Exposed to High Temperature (우리나라 고온 노출 야외작업자의 특성과 건강수준)

  • Lee, Bokim
    • Korean Journal of Occupational Health Nursing
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    • v.31 no.2
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    • pp.95-103
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    • 2022
  • Purpose: This study aims to identify general, workplace, and health-related characteristics of outdoor workers exposed to high temperatures, and to compare the risk of disease according to outdoor high temperature exposure. Methods: This secondary analysis study used the 5th Korean Working Conditions Survey (2017) to identify 4,915 outdoor workers exposed to high temperatures. Results: Outdoor workers exposed to high temperatures were mostly male, elderly, less educated, and daily contract workers. Most of them were engaged in agriculture, forestry and fishing, and construction industries. About 40~50% of them complained of musculoskeletal pain and overall fatigue. The results showed that high temperature exposure increased the risk of illness (hearing problem, skin problem, backache, muscular pains in upper and lower limbs, headache/eyestrain, injuries, depression, and overall fatigue) among workers. Conclusion: High temperature exposure might increase the risk of illness among workers. The results of this study demonstrated that the outdoor workers should be protected from high temperatures.

The Effect of Thermal Exposure on the Microstructural Evolution and Tensile Properties in Cast Hastelloy X (Hastelloy X 주조재의 열간 노출에 따른 미세조직 및 인장 특성 변화)

  • Choi, Baig Gyu;Kim, In Soo;Do, Jeonghyeon;Jung, Joong Eun;Jung, In Yong;Hong, Hyun Uk;Jo, Chang Yong
    • Journal of Korea Foundry Society
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    • v.37 no.5
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    • pp.139-147
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    • 2017
  • Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

The Canopy Transparency Coating Study of Cockpit Temperature Effect Verification (조종실 온도 영향성 검증을 위한 캐노피 투명체 코팅 연구)

  • Nam, Yongseog;Kim, Taehwan;Kim, Yunhi;Woo, Seongjo;Kim, Myungho
    • Journal of Aerospace System Engineering
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    • v.2 no.2
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    • pp.42-45
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    • 2008
  • Under the non-operating exposure condition in the hot area, the T-50 cockpit temperature is expected over the requirement according to T-50 environmental criteria. So it is necessary to protect the cockpit from the high temperature condition during the non-operating exposure because the high temperature of the cockpit may result in the cockpit equipment malfunction. In this study, the transparency coating is selected as the method for protecting the cockpit from the high temperature exposure and analyzed the effect on the cockpit heat load attenuation. Some kinds of cockpit coating were reviewed and selected and the analysis was performed about the effect before and after coating application under 1% hot day condition based on the T-50 FSD hot soaking test data. The result of analysis show transparency coating is so effective to attenuate the heat load of T-50 cockpit.

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Evolution of Microstructure and Mechanical Properties of a Ni Base Superalloy during Thermal Exposure (니켈기 초내열합금의 열간노출에 따른 미세조직 및 기계적 특성 변화)

  • Kim, In-Soo;Choi, Baig-Gyu;Jung, Joong-Eun;Do, Jeong-Hyeon;Jung, In-Yong;Jo, Chang-Yong
    • Journal of Korea Foundry Society
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    • v.36 no.5
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    • pp.159-166
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    • 2016
  • The microstructural evolution of a cast Ni base superalloy, IN738LC, has been investigated after long term exposure at several temperatures. Most of the fine secondary ${\gamma}^{\prime}$ particles resolved after 2000 hour exposure at $816^{\circ}C$. At higher temperatures of $871^{\circ}C$ and $927^{\circ}C$, secondary ${\gamma}^{\prime}$ resolved after 1000 hours of exposure, and cuboidal primary ${\gamma}^{\prime}$ grew with exposure time. During the thermal exposure, ${\sigma}$ phase formed at all tested temperatures, and ${\eta}$ phase was observed around interdendritic regions due to carbide degeneration. The influence of microstructural evolution during thermal exposure on the mechanical properties has been analyzed. The effects of ${\gamma}^{\prime}$ particle growth are more pronounced on the high temperature creep properties than on the room temperature tensile properties.

Critical Temperature for Inter-Laminar Shear Strength and Effect of Exposure Time of FRP Rebars (FRP 보강근의 계면전단강도에 대한 임계온도와 노출시간의 영향)

  • Moon, Do-Young
    • Journal of the Korea Concrete Institute
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    • v.25 no.1
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    • pp.45-51
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    • 2013
  • Short beam tests of GFRP and CFRP specimens exposed to high temperature were conducted to measure the inter-laminar shear strength. For the phase I test, the exposure time and temperature were varied to measure reduction in the strength due to the applied conditions. As a results, the critical temperature was found to $270^{\circ}C$ for the both FRP reinforcements. The high temperature, which causes 50% loss of inter-laminar shear strength, is defined as the critical temperature in this study. It should be noted that the critical temperature for the inter-laminar shear strength is mainly dependent on resin properties not on fiber type. In the phase II test, the effect of exposure time was investigated at intervals of 0.25hour for the critical temperature. All test results demonstrate that the exposure time effect is not significant compared to the maximum exposure temperature, but it is not negligible and, moreover, is significant at the critical temperature.

Analysis of RC Columns under High Temperature (고온에 노출된 철근콘크리트 기둥의 거동 해석)

  • 이지웅;홍성걸
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.11a
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    • pp.625-628
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    • 2003
  • This paper presents the behaviors of reinforced concrete columns under high temperature. When columns are exposed high temperature, temperature distribution of a section becomes nonlinear and it is calculated by using finite difference method(F.D.M). The interaction curves show the strength of columns at various exposure times. The strength of columns decreases according to the increase of the exposure time and the decrease of concrete cover.

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Residual Stress on Concentric Laminated Fibrous Al2O3-ZrO2 Composites on Prolonged High Temperature Exposure

  • Sarkar, Swapan Kumar;Lee, Byong Taek
    • Korean Journal of Materials Research
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    • v.23 no.9
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    • pp.531-536
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    • 2013
  • This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.