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  • Title/Summary/Keyword: Thermal-mechanical Fatigue

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A study on the shape optimization of ship's bellows (선박용 벨로우즈의 형상최적화에 관한 연구)

  • Kim J.P.;Kim H.S.;Kim H.J.;Cho W.S.;Jeh S.B.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.06a
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    • pp.1303-1306
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    • 2005
  • The mechanical properties of bellows, such as the extensibility and the strength can be changed depending on the shape. For the shipbuilding material, it is favorable that the fatigue life is long due to the elastic property and the reduction of thermal stress in piping system. Nowadays, the domestic production and design of bellows are based on the E.J.M.A Code. Therefore, the design standard is in need because of much errors and lack of detailed analysis. In this study, it is attempted to find out the optimal shape of U-type bellows using the finite element method. The effective factors, mountain height, length, thickness, and number of mountains and the length of joint are considered and the proper values are chosen for the simulation. The results shows that if the number of mountains are reduced, the volume decreases while the stress increases. However, the number of mountains are increased, the volume increases above the standard volume and the stress obviously increases. In addition, the effect of the thickness of bellows on the stress is very large. Both of the volume and stress are decreasing at a certain lower value region.

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Characterization of Surface treatment for Mold materials using optical system of laser heat treatment (레이저 열처리 광학계를 이용한 금형소재의 표면 열처리 특성)

  • Shin, Ho-Jun;Yoo, Young-Tae;Shin, Hyung-Heon;Ro, Kyoung-Bo
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.1542-1547
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    • 2007
  • Laser surface treatment technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for mold parts. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with a uniform hardness. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser surface treatment for the case of SKD61 steel and SCM4 steel. From the results of the experiments, it has been shown that the maximum average hardness is approximatly 700780 Hv when the power, focal position and the travel of laser are 1,095 W, 0mm and 0.3 m/min, respectively. In samples treated with lower scanning speeds, some small carbide particles appear in the interdendritic regions. This region contains fine martensite and carbide in proportions which depend on the local thermal cycle.

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Heat Treatment Characteristics of a Press Draw Mold by Using High Power Diode Laser (고출력 다이오드 레이저를 이용한 프레스 드로우금형의 열처리 특성)

  • Hwang, Hyun-Tae;So, Sang-Woo;Kim, Jung-Do;Kim, Young-Kuk;Kim, Byeong-Hun
    • Journal of the Korean Society for Heat Treatment
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    • v.22 no.6
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    • pp.339-344
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    • 2009
  • Recently, Laser surface treatment technologies have been used to improve wear charactenitics and fatigue resistance of metal molding. When the laser beam is irradiated on the surface and laser speed is appropriate, the laser focal position is rapidly heated and the thermal energy of surface penetrates the material after irradiation, finally imbuing it with a new mechanical characteristic by the process of self-quenching. This research estimates the material characteristic after efficient and functional surface treatment using HPDL, which is more efficient than the existing CW Nd:YAG laser heat source. To estimate this, microstructural changes and hardness characteristics of three parts (the surface treatment part, heat affect zone, and parental material) are observed with the change of laser beam speed and surface temperature. Moreover, the depth of the hardened area is observed with the change of the laser beam speed and temperature. From the results of the experiments, it has been shown that the maximum hardness is approximately 788Hv when the heat treatment temperature and the travel speed are 1150 and 2 mm/sec, respectively.

Material & Structural Characteristics of Composite Material Flexible Propeller (복합재료 유연 프로펠러의 재료 및 구조적 특성 연구)

  • Lee, Sang-Gab;Hwang, Jeong-Oh;Byun, Joon-Hyung
    • Journal of the Society of Naval Architects of Korea
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    • v.46 no.2
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    • pp.203-217
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    • 2009
  • The researches on the development of composite material propeller with outstanding damping effects have been actively attempted for the reduction of radiation noise of underwater vehicle propeller. Composite material suitable for the flexible propeller has the following advantages, such as high specific strength and specific stiffness, low thermal expansion coefficient, high resistance against environmental deterioration, low possibility of corrosion due to cavitation, nonoccurrence of rapid fracture due to fatigue, easy molding of complicated shape, easy repair maintenance and low production costs, etc. For the confirmation of optimal fiber array structures of composite material for the production of the flexible propeller blades, in this study, mechanical characteristics of its specimens according to materials were obtained and structural characteristics of propeller blade were also examined according to materials and stacking fiber arrays.

Effect of Tempering on the Mechanical Properties of Martensitic Stainless Steels Fabricated by Centrifugal Casting (원심주조한 마르텐사이트 스테인레스강의 기계적 성질에 미치는 템퍼링 영향)

  • Bae, Eun-Jae;Baek, Eung-Ryul;Ahn, Jong-Heon
    • Journal of Korea Foundry Society
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    • v.28 no.3
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    • pp.113-118
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    • 2008
  • A new approach of producing martensitic structure for guide-roll materials was developed using centrifugal casting instead of classic overlay welding process. Centrifugal casting offered a simpler process, fewer defects and even microstructures. Especially in terms of thermal fatigue cracking which usually occurs in the HAZ of welding beads of used continuous caster guide roll materials made by overlay welding process. A typical tensile strength of 1,600 MPa was obtained by this process and was higher than typical tensile strength(8001,200MPa) with overlay welding technique. Tempering at 400550C for 2 hrs was observed to have significant precipitate hardening effect which increases strength and elongation. Nitrogen content from the Cr-N input in the casting process was found to have positive contribution to decrease the volume fraction of δ-ferrite which directly corresponds to increasing strength of the roll materials.

Effect of Heat Treatment on the Martensitic Transformation and Tensile Deformation Behavior in Ti-Ni-B shape Memory Alloy (Ti-Ni-B 형상기억합금의 마르텐사이트변태 및 인장변형거동에 미치는 열처리의 영향)

  • Lee, O.Y.;Park, Y.K.;Ahn, H.K.
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.1
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    • pp.75-83
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    • 1995
  • The purpose of this study is to investigate the effect of heat treatments on the martensite transformation and tensile deformation behavior in Ti-Ni-B alloys with various boron concentration. Three types of heat treatment are given to the specimens; i) solution treatment ii) aging iii) thermo-mechanical treatment. In solution treated specimens. R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic transformation has been formed at a boron content of 0.2at % and the Ms temperature has been decreased with the increasing of boron content. However. It has not been affected by aging, while that of thermo-mechanically treated specimens has been remarkably increased in the vicinity of recrystallization temperature. The thermo-mechanically treated specimen has showed a good thermal fatigue characteristics, shape memory effect and superelasticity in comparison with the solution treated specimen.

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A Study on the Real-Time Temperature and Concentration Measurement of Combustion Pipe Flow Field (연소 배관 유동장의 실시간 온도, 농도 측정에 관한 연구)

  • Hong, Jeong Woong;Yoon, Sung Hwan;Jeon, Min Gyu
    • Journal of the Korean Society of Visualization
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    • v.20 no.2
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    • pp.86-92
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    • 2022
  • Pipe failure due to thermal fatigue and environmental regulations are increasing the importance of pipe monitoring systems in industrial plants. Since most pipe monitoring systems are focus on external crack inspected, it is necessary to temperature and concentration measuring monitoring system inside the pipe. These systems have spatial uncertainty due to sample inspection by one-point measurement. In addition, real-time measurement is not possible due to the limitation of time delay due to contact measurement. In this study, CT-TDLAS (Computed tomography-Tunable diode laser absorption spectroscopy) apply to overcome the limitations of existing methods. Lasers exhibiting an absorption response at a wavelength of 1395 nm were arranged in a lattice pattern on measuring cell. It showed that the inside of the pipe changed to an unstable combustion state over time.

Occupational Hazards in Firefighting: Systematic Literature Review

  • Maria F. Cuenca-Lozano;Cesar O. Ramirez-Garcia
    • Safety and Health at Work
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    • v.14 no.1
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    • pp.1-9
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    • 2023
  • Background: Firefighting involves exposure of firefighters to risks related to this activity, serious injuries, and occupational diseases are recorded. There are other consequences such as thermal and emotional stress. This systematic review is proposed in order to analyze the risks and consequences faced by these workers and thus provide elements to improve safety management systems in institutions. Method: A descriptive observational study of systematic literature review on the risks and consequences of exposure to firefighters' activity was proposed, and the information was analyzed and described based on the available data and according to the variables determined. Results: The studies showed data on mechanical, physical, chemical, psychosocial risks, workers' perception and resilience, and epidemiological data. Information related to firefighters' activity on falls and slips, exposure to noise, and high concentrations of carbon monoxide is detailed. In addition, the relationship between burnout, cognitive, and physical fatigue as adverse effects on health and performance is mentioned. Conclusions: Among the preventive measures, the use of personal protective equipment is suggested, incorporation in prevention programs of information on exposure to risk factors, as well as the implementation of models that can predict the perception of workers, additionally, the generation of management systems with safety climate models for fire departments.

Numerical study on two-phase flow instability in multi-parallel channels of helical-coiled once-through steam generator of lead-cooled fast reactor

  • Guan-Hua Qian;Ya-Nan Zhao;Xu Wang;Peng-Cheng Zhao;Jin-Sen Xie;Tao Yu
    • Nuclear Engineering and Technology
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    • v.56 no.11
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    • pp.4895-4904
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    • 2024
  • The helical-coiled once-through steam generator (H-OTSG) has the advantages of compact structure and strong heat transfer ability, and is appropriate for lead-cooled fast reactor. The two-phase flow instability may cause mechanical vibration and thermal fatigue of heat transfer tube bundles, posing a serious threat to the safe operation of the H-OTSG. In this work, the secondary side of the H-OTSG characterized as multi-parallel channels is modeled by RELAP5/MOD3.4 code, and the oscillation behavior during start-up and the influence of structural and operating parameters on system stability are studied based on time-domain method. The results indicate that the pressure, flow rate, and temperature of the secondary fluid exhibit density wave oscillations at the heating section in a (n-2,2) pattern. In addition, increasing inlet throttling, reducing outlet throttling, controlling subcooling within an appropriate range and avoiding operation under low loads are all beneficial for improving the system stability of the helical-coiled once-through steam generator.

A Study on the Mechanical Properties of AC8A/Al2O3 Composites. (용탕단조법에 의한 AC8A/Al2O3 복합재료의 기계적 성질에 관한 연구)

  • Kim, Ki-Bae;Kim, Kyoung-Min;Cho, Soon-Hyung;Yoon, Eui-Park
    • Journal of Korea Foundry Society
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    • v.11 no.6
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    • pp.475-481
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    • 1991
  • In this study the fabrication technology and mechanical properties of AC8A/Al2O3 Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/Al2O3 composistes without a porosity and the break of preform were fabricated at the melt temperature of 740C, the preform temperature of 500C, and mold temperature of 400C under the applied pressure of 1200kg/cm2 as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/Al2O3 composites was not increased linearly with Al2O3 volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/Al2O3 composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/Al2O3 composites was decreased with Al2O3 volume fraction and the sliding speed at both room temperature and 250C and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% Al2O3 composities was obtained the value of 1.65cm3/cm at sliding speed of 1.14m/sec as compared with about 3.0×108cm3/cm hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of Al2O3 composites was observed to a type of abrasive wear by the SEM view of wear surface.

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