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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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On the Measurement of Residual Stresses in Aluminum Alloy Parts Fabricated by Precision Metal Mold Casting (정밀금형 알루미늄 합금 주물에서의 잔류응력 측정에 관한 연구)

  • Kim, Chae-Hwan;Mun, Su-Dong;Gang, Sin-Il
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.23 no.11 s.170
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    • pp.2087-2095
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    • 1999
  • One of the main causes of unwanted dimensional changes in precision metal mold casting parts is excessive and irregular residual stresses induced by temperature gradients and plastic deformation in the solidifying shell. Residual stresses can also cause stress cracking, and lower the fatigue life and fracture strength of the casting parts. In the present study, aluminum alloy casting system with metal mold equipped with electrical heating elements and water cooling units was designed and the casting specimens were produced to quantify the effects of different cooling conditions on the development of residual stresses. The layer removal method was used to measure the biaxial residual stresses in casting specimens produced from the experiments. The experimental results agreed with Tien-Richmond's theoretical model for thermal stress development for the solidifying metal plate.

Development and Sensitivity Analysis of Life Estimation Program for Turbine Rotors (터빈로터 수명예측 프로그램의 개발 및 민감도 분석)

  • Park, Jae-Sil;Seok, Chang-Sung;Suh, Myung-Won;Hong, Kyung-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.10 s.181
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    • pp.2654-2663
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    • 2000
  • Steam turbine rotors are the most critical and highly stressed components of a steam power plant; therefore, the life expectancy of the turbine rotor is an important consideration for the safety of a steam power plant. The objective of this paper is to develop a life estimation program for turbine rotors for all possible operating conditions. For this purpose, finite element analysis was carried out for four normal operating modes (cold, warm, hot and very hot starts) using ABAQUS codes. The results are made into databases to evaluate the life expenditure for an actual operating condition. For any other possible abnormal operating condition, the operating data are transmitted to the server (workstation) through a network to carry out finite element analysis. Damage estimation is carried out by transmitting the finite element analysis results to the personal computer, and then the life expectancy is calculated.

A study on the cracking mechanism of the welded parts in steel structures for the use of low temperature and high pressure (저온, 고압력용 강재 구조물의 용접부균열 발생과 그 대책에 관한 연구)

  • 김영식;배차헌;구자영
    • Journal of Advanced Marine Engineering and Technology
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    • v.9 no.4
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    • pp.328-338
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    • 1985
  • When the low temperature service steels are used as materials for welded structure, some problems-brittleness and weld cracking, etc.-occur in welded part due to the change of mechanical and metallurgical characteristics resulted from the thermal cycle during the welding procedure. In this study, the experiments were conducted to investigate the change of mechanical and metallurgical characteristics of the welded part for the low temperature and high pressure service steels. Moreover, the Static and Dynamic Implant Test Method was introduced to this study in order to find out the mechnism of weld cracking. In addition, the fracture toughnesses of welded bond were inspected under the various low temperature environments. Main results obtained are as follows; 1) The effect of the hydrogen on the fatigue characteristics of the weld bond can be estimated by the new self-contrived Dynamic Implant Test equipment. 2) The fine micro-structure and low hardness in the heat affected zone can be obtained by the small heat input multi-pass welding. 3) The susceptibility of the delayed cracking is largely affected by the condition of used electrode. 4) The transition temperature of the fracture surface in weld bond appears to be higher 20 .deg. C than that in base metal.

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The Study of Heat Resistant Aluminum Alloy with CrW Homogeneous Solid Solution (CrW 전율고용체 첨가 내열 알루미늄 합금에 관한 연구)

  • Kim, Jin-Pyeong;Sung, Si-Young;Han, Beom-Suck;Kim, Sang-Ho
    • Journal of Korea Foundry Society
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    • v.33 no.3
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    • pp.122-126
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    • 2013
  • Recently, heat-resistant aluminum alloy has been re-focused as a downsizing materials for the internal combustion engines. Heat-resistant Al alloy development and many researches are still ongoing for the purpose of improving thermal stability, high-temperature mechanical strength and fatigue properties. The conventional principle of heat-resistant Al alloy is the precipitation of intermetallic compounds by adding a variety of elements is generally used to improve the mechanical properties of Al alloys. Heat resistant aluminum alloys have been produced by CrW homogeneous solid solution to overcome the limit of conventional heat resistant aluminum alloy. From EPMA, it is found that CrW homogeneous soild solution phases with the size of 50100μm have been dispersed uniformly, and there is no reaction between aluminum and CrW alloy. In addition, after maintaining at high temperature of 573 K, there is no growth of hardening phase, nor desolved, but CrW still exists as a homogeneous solid solution.

Infrared Thermography Characterization of Defects in Seamless Pipes Using an Infrared Reflector

  • Park, Hee-Sang;Choi, Man-Yong;Park, Jeong-Hak;Lee, Jea-Jung;Kim, Won-Tae;Lee, Bo-Young
    • Journal of the Korean Society for Nondestructive Testing
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    • v.32 no.3
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    • pp.284-290
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    • 2012
  • Infrared thermography uses infrared energy radiated from any objects above absolute zero temperature, and the range of its application has been constantly broadened. As one of the active test techniques detecting radiant energy generated when energy is applied to an object, ultrasound infrared thermography is a method of detecting defects through hot spots occurring at a defect area when 15~100 kHz of ultrasound is excited to an object. This technique is effective in detecting a wide range affected by ultrasound and vibration in real time. Especially, it is really effective when a defect area is minute. Therefore, this study conducted thermography through lock-in signal processing when an actual defect exists inside the austenite STS304 seamless pipe, which simulates thermal fatigue cracks in a nuclear power plant pipe. With ultrasound excited, this study could detect defects on the rear of a pipe by using an aluminium reflector. Besides, by regulating the angle of the aluminium reflector, this study could detect both front and rear defects as a single infrared thermography image.

The Study on the Microstructure and Mechanical Properties of the Nodular Indefinite Chilled Iron Containing Ni (Ni 함유 NICI(Nodular Indefinite Chilled Iron)의 미세조직과 기계적성질에 관한 연구)

  • Baek, Eung-Ryul;Oh, Seok-Jung;Villando, Thursdiyanto
    • Journal of Korea Foundry Society
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    • v.26 no.4
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    • pp.180-183
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    • 2006
  • The effects of adding Ni on microstructure and mechanical properties of Nodular Indefinite Chilled Iron (NICI) were studied. Thermal fatigue, hardness, tensile properties, wear resistance, are very important factors for NICI used for hot working roll and wire rod mill. The results show that addition 4% nickel has changed pearlite to bainite. Bainite matrix is superior to pearlite matrix on wear resistance, hardness and strength and will increase performance lifetime of NICI conventional roll material. Based in the bainitic microstructure, hardness and tensile property increase up to 48 HRc and 72kg/mm2, respectively.

Research on safety assessment and application effect of nanomedical products in physical education

  • Zhuli Li;Song Peng;Gang Chen
    • Advances in nano research
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    • v.15 no.3
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    • pp.253-261
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    • 2023
  • This study investigates the application of nano-composite materials in physical education, specifically focusing on improving the performance of sports hall flooring. The research centers on carbon nanotube reinforced polyvinyl chloride (PVC) composites, which offer enhanced mechanical properties and durability. The incorporation of carbon nanotubes as reinforcements in the PVC matrix provides notable benefits, including increased strength, improved thermal stability, electrical conductivity, and resistance to fatigue. The key parameters examined in this study are the weight percentage of carbon nanotubes and the temperature during the fabrication process. Through careful analysis, it is found that higher weight percentages of carbon nanotubes contribute to a more uniform dispersion within the PVC matrix, resulting in improved mechanical properties. Additionally, higher fabrication temperatures aid in repairing macroscopic defects, leading to enhanced overall performance. The findings of this study indicate that the utilization of carbon nanotube reinforced PVC composites can significantly enhance the strength and durability of sports hall flooring. By employing these advanced materials, the safety and suitability of physical education environments can be greatly improved. Furthermore, the insights gained from this research can contribute to the optimization of composite material design and fabrication techniques, not only in the field of physical education but also in various industries where composite materials find applications.

Convergent Investigation through Durability Analysis at the Seam of Railroad Track by Season (계절별 기차선로 이음새에서의 내구성 해석을 통한 융합적 고찰)

  • Oh, Bum-Suk;Cho, Jae-Ung
    • Journal of the Korea Convergence Society
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    • v.11 no.4
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    • pp.189-193
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    • 2020
  • In this study, the structural analysis of the track was performed according to the gap between the rails due to thermal expansion by the frictional contact between the wheels of the train in motion. The equivalent stress and total deformation at the condition for which the gap between joints are wide as the winter condition (model B) can be seen to happen more than at the summer condition (model A) in which the joints are narrow. If the results of this study are applied to the design of railway tracks, it is thought to be highly useful in preventing fatigue failure and increasing its durability. By applying the durability analysis at the seam of railroad track by season, this investigation result is seen to be favorable as the convergent research applied to the aesthetic design.

Evaluation of Structural Integrity and Leakage for a Gas Turbine Casing (가스터빈 케이싱의 구조안전성 및 누설 평가)

  • Seo, Hee Won;Ham, Dong Woo;Kim, Kyung Kook;Han, Jeong Sam
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.4
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    • pp.347-354
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    • 2016
  • Because typical gas turbine systems have frequent startup and shutdown operations, it is likely to cause cracks at the gas turbine casing and gas leakages at casing flanges due to thermal fatigue and embrittlement. Therefore, the evaluation of structural integrity and gas leakage at the gas turbine casings must be performed. In this paper, we have evaluated the structural integrity of the turbine casing and bolts under a normal operation in accordance with ASME B&PVC and evaluated the leakage at casing flanges by examination of contact pressure calculated using the finite element analysis. Finally, we propose a design flow including finite element modeling, the interpretation and evaluation methods for gas turbine casings. This may be utilized in the design and development of gas turbine casings.

Defect Detection of the Wall Thinning Pipe of the Nuclear Power Plant Using Infrared Thermography (적외선열화상을 이용한 원자력발전소 감육 배관의 결함 검출)

  • Kim, Kyeong-Suk;Chang, Ho-Sub;Hong, Dong-Pyo;Park, Chan-Joo;Na, Sung-Won;Kim, Kyung-Su;Jung, Hyun-Chul
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.2
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    • pp.85-90
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    • 2010
  • The infrared energy is emitted in the infrared wavelength range that corresponds to the surface temperature of a object which has temperature that is over the absolute the temperature(OK). The infrared thermography (IRT) is a non-destrnctive testing method that provides thermal video for the user in real-time by converting the infrared quantity that is detected by the infrared detector into temperature. The pipes of nuclear power plant(NPP) could be thinned by the corrosion and fatigue and the defect could lead to a big accident. For this reason, the effective non-destructive testing method is necessary. In this study, the relationship between the measured temperature and the defect depth or size of NPP pipes were recognized and that was applied to detect the wall thinning defects of NPP pipes.