• Title, Summary, Keyword: Thermal Stress

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Thermal Stress Simulation of Mass Concrete Using Thermal Stress Device

  • Amin, Muhammad Nasir;Kim, Jin-Keun
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.474-477
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    • 2006
  • To predict thermal stress independent of uncertain material properties of early age concrete, such as elastic modulus and creep, thermal stress device is used. In order to verify the application of various degree of constraint in the thermal stress device, a series of experiments were performed on mass concrete followed by numerical simulation. The application of various degrees of constraint can be achieved by using constraint frame material with different thermal expansion coefficient, length, and cross sectional area. Temperature development in the real structure has been simulated using temperature and humidity control chamber. The results from experiments and numerical analysis show that the thermal stresses estimated from simulation agree well with the general stress variations in the real structure even though the properties of concrete are uncertain.

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Synthesis of Epoxy Functional Siloxane and its Effect on Thermal Stress

  • Hyun, Dae-Sup;Jeong, Noh-Hee
    • Journal of the Korean Applied Science and Technology
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    • v.26 no.4
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    • pp.379-384
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    • 2009
  • Epoxy resin based encapsulants are widely used in semiconductor packaging applications. Epoxy resin based encapsulants are often subject to crack or delamination during the reliability test due to the thermal stress caused by high modulus nature of epoxy resins. Epoxy functional siloxanes are often added into epoxy resin to reduce the modulus so that the thermal stress can be reduced. Epoxy functional siloxanes, additives for reduced modulus, were synthesized and added into the curable epoxy resins. The modulus and the coefficient of thermal expansion (CTE) were also measured to investigate the thermal stress and to see whether the epoxy functional siloxane adversely affects the CTE or not. As a result, around 26% to 72% of thermal stress reduction was observed with no adverse effect on CTE.

Effect of Thermal Cycle on Strength of Ceramic and Metal Joint (세라믹/금속접합재의 강도에 미치는 열사이클 영향)

  • 박영철;오세욱;김광영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.7
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    • pp.1664-1673
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    • 1994
  • As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.

Stress Analysis of the Micro-structure Considering the Residual Stress (잔류응력을 고려한 미세구조물의 강도해석)

  • 심재준;한근조;안성찬;한동섭
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.820-823
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    • 2002
  • MEMS structures Generally have been fabricated using surface-machining, but the interface failure between silicon substrate and evaporated thin film frequently takes place due to difference of linear coefficient of thermal expansion. Therefore this paper studied the effect of the residual stress caused by variable external loads. This study did not analyzed accurate quantity of the residual stress but trend for the effect of residual stress. Several specimens were fabricated using other material(Al, Au and Cu) and thermal load was applied. The residual stress was measured by nano-indentation using AFM. The results showed the existence of the residual stress due to thermal load. The indentation area of the thermal loaded thin film reduced about 3.5% comparing with the virgin thin film caused by residual stress. The finite element analysis results are similar to indentation test.

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Study for thermal stability of Liquid Crystal Device (액정 소자의 열적 안전성에 관한 연구)

  • Lee, Sang-Keuk;Hwang, Jeoung-Yeon;Seo, Dae-Shik;Lee, Joon-Ung
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.9-12
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    • 2004
  • In this study, we investigated about electrooptics characteristic of three kind of TN cell on the polyimide surface. Monodomain alignments of thermal stressed TN cell over temperature of liquid crystal isotropic phase were almost same that of no thermal stressed TN cells. However, the thermal stressed TN cell have many defects. Also, threshold voltage and response time of thermal stressed TN cells show same performances of no thermal stressed TN cells. There were little changes of value in these TN cells. However, transmittances of TN cells on the polyimide surface decrease with increasing thermal stress time. Finally, the residual DC voltage of the thermal stressed TN cell on the polyimide surface show decrease of characteristics as increasing thermal stress time. Therefore, thermal stability of TN cell was decreased by high thermal stress for the long times.

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Study for Thermal Stability of Liquid Crystal Device (액정 소자의 열적 안전성에 관한 연구)

  • 이상극;황정연;서대식;이준웅
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.4
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    • pp.439-442
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    • 2004
  • In this study, we investigated about electrooptics characteristic of three kinds of TN cell on the polyimide surface. Monodomain alignments of thermal stressed TN cell over temperature of liquid crystal isotropic phase were almost the same as that of no thermal stressed TN cells. However, the thermal stressed TN cells have many defects. Also, threshold voltage and response time of thermal stressed TN cells show the same performances as no thermal stressed TN cells. There were little changes of value in these TN cells. However, transmittances of TN cells on the polyimide surface decrease with increasing thermal stress time. Finally, the residual DC voltage of the thermal stressed TN cell on the polyimide surface shows decrease of characteristics as increasing thermal stress time. Therefore, the thermal stability of TN cell was decreased by high thermal stress for the long times.

Thermal Stress Evaluation by Elastic-Creep Analysis during Start-up of Boiler Header (보일러 헤더 기동시의 탄성 크리프 해석에 의한 열응력 평가)

  • Shin, Kyu-In;Yoon, Kee-Bong
    • Journal of the Korean Society of Safety
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    • v.24 no.2
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    • pp.17-22
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    • 2009
  • Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.

Thermal Shock Stress Intensity Factor and Fracture Test (열충격 응력세기계수와 파괴실험)

  • 이강용;심관보
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.1
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    • pp.130-137
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    • 1990
  • Thermal shock stress intensity factor for an edge-cracked plate subjected to thermal shock is obtained from Bueckner's weight function method. It is shown that thermal shock stress intensity factor has maximum values with variation of time and crack length and that there is most dangerous crack length. By comparing thermal shock stress intensity factor with fracture toughness, the fracture time and critical temperature difference due to thermal shock are determined theoretically. Under constant thermal shock temperature difference, and increase of crack length is shown to increase fracture time. The theoretical fracture time is compared with experimental value measured by acoustic emission method with soda lime glass.

Residual DC characteristic on Twisted Nematic Liquid Display on the Polyimide Surface by the Thermal Stress (열적 stress에 의한 폴리이미드 표면에서의 TN-LCD의 잔류DC 특성)

  • Bae, Yu-Han;Hwang, Jeoung-Yeon;Kim, Jong-Hwan;Mun, Hyun-Chan;Han, Jung-Min;Kim, Young-Hwan;Seo, Dae-Shik
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.498-501
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    • 2004
  • In this study, the threshold voltage and the response time of thermal stressed TN-LCDs showed the same performances on no thermal stressed TN-LCDs. There was little change of value in TN cells. Also, the transmittances of TN-LCDs on the rubbed PI surface were almost same while increasing thermal stress time. However, the thermal stability of TN cell was decreased by the high thermal stress for the long duration. Residual DC was decreased as the thermal stress increases. Especially, when TN cell was stressed more and more by heating, residual DC was changed a lot. As a result, the residual DC property of LCD in projection TV is affected very much by heating.

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A study on the flow and thermal analysis of the hot gas casing of gas turbine (가스 터빈 Hot gas casing에 대한 유동 및 열응력 해석)

  • Choi, Young-Jin;Lee, Young-Shin;Kim, Jae-Hun;Park, Won-Seek;Kim, Hyun-Soo
    • Proceedings of the KSME Conference
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    • pp.557-561
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    • 2004
  • The hot gas casing of gas turbine has operated high temperature and thermal gradient. The structure safety of hot gas casing will be highly depend on the thermal stress. In this paper, flow and thermal stress analysis of hot gas casing is carried out using ANSYS program. The obtained temperature data by flow analysis of hot gas casing apply the load condition of the thermal analysis. The thermal stress analysis is carry out the elastic-plasticity analysis. The pressure, temperature and velocity of the flow and thermal stress of the hot gas casing are presented.

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