• Title/Summary/Keyword: High temperature fatigue

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A Study on the Fatigue Behaviors of Cr-Mo-V Alloy for Steam Turbine at High Temperature Difference (터빈용 Cr-Mo-V강의 고온 환경변화에 따른 피로거동에 관한 연구)

  • Song, Sam-Hong;Kang, Myung-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.173-179
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    • 1997
  • The high temperature fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely used as thermal power plant turbine materials for examination fatigue behavior of materials in power plants which have been operated for long periods. The fatigue tests at high temperature were performed at the various temperature and applied stress. The results obtained are summarized as follows : The fatigue crack length increases and the fatigue life decreases with temperature and applied stress according to the same number of stress cycle. The fatigue crack propagation and the fatigue life were much influenced by temperature and applied stress.

High Temperature Fatigue Behavior of A356 and A319 Heat Resistant Aluminum Alloys (A356 및 A319 내열 알루미늄 합금의 고온 피로 변형 거동)

  • Park, Jong-Soo;Sung, Si-Young;Han, Bum-Suck;Jung, Chang-Yeol;Lee, Kee-Ahn
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.467-469
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    • 2009
  • In this study, fatigue samples were prepared from cylinder head parts that are actually used in domestic (A) and foreign (B) automobiles; high-temperature, high-cycle, and low-cycle fatigue characteristics were then evaluated and compared. A study on the correlation between the microstructural factor and high temperature fatigue characteristic was attempted. The chemical compositions of the heat resistant aluminum alloys above represented A356 (A) and A319 (B), respectively. The result of the tensile strength test on material B at $250^{\circ}C$ was higher by 30.8MPa compared to material A. On the other hand, elongation was 8.5% higher for material A. At $130{\circ}C$, material B exhibited high fatigue life given high cycle fatigue under high stress, whereas material A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility is increased, material A demonstrated higher fatigue life. Through the observation of the differences in microstructure and the fatigue fracture surface, an attempt to explain the high-temperature fatigue deformation behavior of the materials was made.

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Mechanical Properties of Hot Working Die Steel and Fatigue Analysis Model of Casting Mold (열간 금형재의 기계적 성질과 주조금형 피로해석모델)

  • 여은구;황성식;이용신;곽시영;김정태
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2003.06a
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    • pp.405-408
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    • 2003
  • Generally, the life of casting mold is limited by fatigue fracture or dimensional inaccuracy originated from wear in high temperature. Although recent research of metallic materials in high temperature fatigue have been much accomplished, many studies on brittle material as a die steel in high temperature fatigue does not have been reported. Especially, the study on the fatigue behavior over the transformation temperature is not studied sufficiently because of its difficult analysis and experiment. Therefore, reliable results of brittle material in high temperature fatigue behavior are needed. In this paper, stress-strain curves and stress-life curves in die STD61 steel are carefully examined between room temperature and 90$0^{\circ}C$, as the basic experimental data are used to predict from fatigue life of casting mold.

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A Study on the Shot Peening on the High Temperature Fatigue Crack Propagation (쇼트피이닝 가공된 스프링강의 고온 피로균열진전 평가)

  • 박경동;정찬기;하경준
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.10a
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    • pp.264-268
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    • 2001
  • In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, low temperature and high temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room, and high temperature at $25^{\circ}C,\; 50^{\circ}C, \;100^{\circ}C,\; 150^{\circ}C,\; and\; 180^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range $\DeltaK_{th}$ in the early stage of fatigue crack growth (Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

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A Study on the Fatigue Crack Propagation Behavior of Cr-Mo-V Alloy with Micro Defects at High Temperature. (미소 원공결함을 갖는 Cr-Mo-V강의 고온피로 크랙전파거동)

  • Song, Samhong;Kang, Myungsoo
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.12
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    • pp.70-77
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    • 1996
  • Fatigue tests were carried out at high temperature on a Cr-Mo-V steel in order to assess the fatigue life of components used in power plants. The characteristics of high temperature fatigue were divided in terms of cycle-dependent fatigue and time-dependent fatigue, each crack propagation rate was examined with respect to fatigue J-integral range, .DELTA. J$_{f}$and creep J-integral range, .DELTA. J$_{c}$. The fatigue life was evaluated by analysis of J-integral value at the crack tip with a dimensional finite element method. The results obtained from the present study are summarized as follows : The propagation characteristics of high temperature fatigue cracks are determined by .DELTA. J$_{f}$for the PP(tensile plasticity-compressive plasticity deformation) and PC(tensile plasticity - compressive creep deformation) stress waveform types, and by .DELTA. J$_{c}$for the CP(tensile creep- compressive plasticity deformation) stress waveform type. The crack propagation law of high temperature fatigue is obtained by analysis of J-integral value at the crack tip using the finite element method and applied to examine crack propagation behavior. The fatigue life is evaluated using the results of analysis by the finite element method. The predicted life and the actual life are close, within a factor of 2.f 2.f 2.

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A Study on the High Temperature Fatigue Behavior of Hot Forging Die STD61 Steel (STD61 열간 금형강의 고온피로거동에 관한 연구)

  • 여은구;이태문;이용신
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.711-714
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    • 2002
  • Although recent research of metallic materials in high temperature fatigue have been much accomplished, many studies about brittle material as a die steel in high temperature fatigue does not have been reported. Especially, the study on the fatigue behavior over the transformation temperature is not studied sufficiently because of its difficult analysis and experiment. Therefore, reliable results of brittle material in high temperature fatigue behavior are needed. In this paper, stress-strain curves and stress-life curves in die STD61 steel at 700 and 900 are carefully examined, as the basic experimental data are used to predict from fatigue life over 700.

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An Effect of Compressive Residual Stress on a High Temperature Fatigue Crack Propagation Behavior of The Shot-peened Spring Steel (압축잔류응력이 스프링강의 고온환경 피로크랙 진전거동에 미치는 영향)

  • Park, Keyoung-Dong;Jung, Chan-Gi
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.05a
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    • pp.117-124
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    • 2002
  • The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular, manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures($100^{\circ}C,\;150^{\circ}C,\;180^{\circ}C$) was investigated with considering fracture mechanics. So, we can obtain followings. (1) Compressive residual stress is decreased in high temperature, that is, with increasing temperature. (2) The effect of compressive residual stress on fatigue crack growth behavior in high temperature is increased below ${\Delta}K=17{\sim}19MPa\sqrt{m}$. The fatigue crack growth rate is increased with increasing temperature. The fatigue life is decreased with increasing temperature. (3) The dependence of temperature and compressive residual stress on the parameters C and m in Paris' law formed the formulas such as equations (3),(4),(5),(6),(7),(8),(9),(10). (4) It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

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High Temperature Fatigue Strength of the Welded Joint in Exhaust System (배기계 용접이음의 고온피로강도)

  • Chu, Seok-Jae;Lee, Han-Yong;NamKoong, Kyu-Wan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.11
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    • pp.1028-1034
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    • 2008
  • The exhaust systems are usually subjected to vibration or shock at high temperatures. The high temperature fatigue tests of the exhaust systems are rarely performed in domestic industries due to limited number of test facility and high test costs. In this paper, the high temperature fatigue test of some part of the exhaust system, not the whole system, is carried out. The resonator located at the central range is heated in the cylindrical electric furnace and the alternating load is applied on the end of the pipe welded to the resonator. The high temperature fatigue strength of the welded joint is obtained. The location of the fatigue crack is different to that in room temperature.

An Investigation on the Shot Peening on the Low.High Temperature Fatigue Crack Propagation (쇼트피이닝 가공된 스프링강의 저.고온 피로균열진전 평가)

  • 박경동;정찬기
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • 2001.11a
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    • pp.65-70
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    • 2001
  • In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, low temperature and high temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room, low temperature and high temperature at $25^{\circ}C$, -3$0^{\circ}C$, -5$0^{\circ}C$, -7$0^{\circ}C$, -10$0^{\circ}C$ and 5$0^{\circ}C$, 10$0^{\circ}C$ , 15$0^{\circ}C$, 18$0^{\circ}C$ and in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range $\DeltaK_{th}$ in the early stage of fatigue crack growth (Region I ) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

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Temperature-dependence of Mechanical Properties of Die Steel STD61 (금형강 STD61의 온도에 따른 기계적 성질의 변화)

  • 여은구;이용신
    • Transactions of Materials Processing
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    • v.13 no.5
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    • pp.435-440
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    • 2004
  • The temperature in hot forming of metallic materials, such as hot extrusion and hot forging, ranges from $300^{\circ}C$ to $900^{\circ}C$. Correspondingly, the die also exhibits high temperatures close to that of a work piece and its life is limited generally by high temperature fatigue. Thus, the analysis of high temperature fatigue would need the mechanical properties over the wide ranges of temperature. However, very few studies on the high temperature fatigue of brittle materials have been reported. Especially, the study on the fatigue behavior over such transition temperature regime is very rare. In this paper, the stress-strain curves and stress-life curves of a die steel such as STD61 are experimentally obtained. The wide ranges of temperature from $300^{\circ}C$ to $900^{\circ}C$ are considered in experiments and the transition temperature zone is carefully examined.