• Title/Summary/Keyword: Thermal Fatigue

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ASSESSMENT OF THERMAL FATIGUE IN MIXING TEE BY FSI ANALYSIS

  • Jhung, Myung Jo
    • Nuclear Engineering and Technology
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    • v.45 no.1
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    • pp.99-106
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    • 2013
  • Thermal fatigue is a significant long-term degradation mechanism in nuclear power plants. In particular, as operating plants become older and life time extension activities are initiated, operators and regulators need screening criteria to exclude risks of thermal fatigue and methods to determine significant fatigue relevance. In general, the common thermal fatigue issues are well understood and controlled by plant instrumentation at fatigue susceptible locations. However, incidents indicate that certain piping system Tee connections are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentations. Therefore, in this study thermal fatigue evaluation of piping system Tee-connections is performed using the fluid-structure interaction (FSI) analysis. From the thermal hydraulic analysis, the temperature distributions are determined and their results are applied to the structural model of the piping system to determine the thermal stress. Using the rain-flow method the fatigue analysis is performed to generate fatigue usage factors. The procedure for improved load thermal fatigue assessment using FSI analysis shown in this study will supply valuable information for establishing a methodology on thermal fatigue.

Thermal-mechanical Fatigue Life Prediction of 12Cr Forged Steel Using Strain Range Partitioning method (변형률분할법에 의한 12Cr 단조강의 열피로 수명예측)

  • 하정수;옹장우;고승기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.5
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    • pp.1192-1202
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    • 1994
  • Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

Thermal-Mechanical and Low Cycle Fatigue Characteristics of 12Cr Heat Resisting Steel with Hold Time Effects (유지시간 효과를 고려한 12Cr 내열강의 열피로 및 저주기 피로 특성)

  • Ha, J.S.;Koh, S.K.;Ong, J.W.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.3 no.1
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    • pp.1-12
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    • 1995
  • Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at $600^{\circ}C$ and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to $600^{\circ}C$ were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at $600^{\circ}C$ showed that the fatigue life decreased as the strain rate and frequency decreased,especially for the low strain ranges.

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Thermal Fatigue Life Prediction of Alumina by Finite Difference Model (유한 차분 모델을 이용한 알루미나의 열피로 수명 예측)

  • 이홍림;한봉석
    • Journal of the Korean Ceramic Society
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    • v.30 no.3
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    • pp.229-235
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    • 1993
  • Thermal history and thermal stress of alumina specimen, which occured from thermal shock process, were calculated by finite difference method. Stress intensity factor and crack growth in cyclic thermal fatigue were calculated from single thermal shock temperature history and thermal stress. Cyclic thermal life were estimated by bending strength after cyclic thermal shock under critical thermal shock temperature. Calculated stress intensity factor was compared with real experimental thermal fatigue life of specimen. Fatigue life until critical stress intensity factor and real experimental result were comparable.

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Analysis of Thermal Shock and Thermal Fatigue in Tool Steels for Hot Forging (열간단조 금형강의 열충격과 열피로 특성연구)

  • 김정운;문영훈;류재화;박형호
    • Transactions of Materials Processing
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    • v.11 no.1
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    • pp.61-68
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    • 2002
  • The thermal shock and thermal fatigue test has been carried out to analyze the thermal characteristics of tool steels for hot forging and the effects of mechanical properties on this study have been investigated. The resistance to thermal shock is first of all a matter of good toughness and ductility. Therefore, a proper hot-work tool steel should be characterized by high fracture strength and high temperature toughness. Based on these results, some critical temperature($T_{fracture}$) at which fracture occur can be measured to characterize the thermal resistance of the materials. During thermal fatigue tests, the thermal fatigue cracks occur because of the repetitive heating and cooling of the die surface and the thermal fatigue damage was evaluated by analyzing different number of cycles to failure. The results showed that the resistance to thermal shock and thermal fatigue were found to be favoured by high hot tensile strength and high hot hardness, and thermal resistance of SKD61 was superior to that of ESC, SKT4 and this was caused by higher mechanical properties of SKD61.

Prediction of Thermal Fatigue Life of Alumina ceramics (알루미나 세라믹스의 열피로 수명 예측)

  • 정우찬;한봉석;이홍림
    • Journal of the Korean Ceramic Society
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    • v.36 no.8
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    • pp.871-875
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    • 1999
  • Theoretical equation to calculate thermal fatigue life was derived in which slow crack growth theory was adopted. The equation is function of crack growth exponent n. Cyclic thermal fatigue tests were performed at temperature difference of 175, 187 and 200$^{\circ}C$ respectively. At each temperature difference critical thermal fatigue life cycles of the alumina ceramics were 180,37 and 7 cycles. And theoretical thermal fatigue life cycles were calculated as 172, 35 and 7 cycles at the same temperature difference conditions. Therefore thermal fatigue behavior of alumina ceramics can be represented by derived equation. Also theoretical single cycle critical thermal shock temperature difference can be calculated by this equation and the result was consistent with the experimental result well.

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Effects of Cr Content and Volume Fraction of δ-Ferrite on Thermal Cycling Fatigue Properties of Overlay Welded Heat-Resistant 12%Cr Stainless Steels (내열용 오버레이 12%Cr계 스테인레스강의 열피로 특성에 미치는 Cr 함량과 델타-페라이트의 영향)

  • Jung, J.Y.
    • Transactions of Materials Processing
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    • v.26 no.6
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    • pp.356-364
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    • 2017
  • In this study, submerged arc cladded Fe-Cr-Ni-Mo-CuWNbV-C stainless steels containing various Cr contents between 11.2 wt.% and 16.7 wt.% were prepared with fixed C content at about 0.14 wt.%. Using these alloys, changes in microstructure, tensile property, and thermal fatigue property were investigated. Phase fraction of delta-ferrite was increased gradually with increasing Cr content. However, tensile strength, hardness, and thermal fatigue resistance appeared to be decreased. When the microstructure of delta-ferrite was observed, it was revealed that the mesh structure retained up to about 15% Cr content. Although thermal fatigue resistance was almost the same for Cr contents between 11.0 and 14.5 wt.%, it was significantly decreased at higher Cr contents. This was evident from mean value of crack lengths of 10 largest ones. Evaluation of thermal fatigue resistance on alloys with various Cr contents revealed the following important results. First, the reproducibility of ranking test was excellent regardless of the number of cycles. Second, thermal fatigue resistance was increased in proportion to true tensile fracture strength values of overlay materials. Finally, the number of thermal fatigue cracks per unit length was increased with increasing true tensile fracture strength.

A study on the thermal-mechanical fatigue life prediction of 12 Cr steel (12 Cr 강의 열피로 수명단축에 관한 연구)

  • Ha, Jeong-Soo;Kim, Kun-Young;Ahn, Hye-Thon
    • Journal of the Korean Society for Precision Engineering
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    • v.11 no.4
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    • pp.114-125
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    • 1994
  • Fatigue behavior and life prediction method were presented for themal-mechanical and isothermal low cycle fatigue of 12 Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test from 350 .deg. C to 600 .deg. C and isothermal low cycle fatigue test at 600 .deg. C, 475 .deg. C, 350 .deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. Thermal-mechanical fatigue life predication was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase range partitioning method in a conservative way. By the way life prediction of thermal-mechanical fatigue by Taira's equivalent temperature method and spanning fartor method showed good agreement within out-of-phase thermal-mechanical fatigue.

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Prediction of Thermal Fatigue Life on $\mu$BGA Solder Joint Using Sn-3.5Ag, Sn-3.5Ag-0.7Cu, and Sn-3.5Ag-3.0In-0.5Bi Solder Alloys (Sn-3.5Ag, Sn-3.5Ag-0.7Cu, Sn-3.5Ag-3.0In-0.5Bi Solder를 이용한 $\mu$BGA Solder접합부의 열피로 수명예측)

  • 김연성;김형일;김종민;신영의
    • Journal of Welding and Joining
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    • v.21 no.3
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    • pp.92-98
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    • 2003
  • This paper describes the numerical prediction of the thermal fatigue life of a $\mu$BGA(Micro Ball Grid Array) solder joint. Finite element analysis(FEA) was employed to simulate thermal cycling loading for solder joint reliability. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. The results show that Sn-3.5mass%Ag solder had the longest thermal fatigue life in low cycle fatigue. Also a practical correlation for the prediction of the thermal fatigue life was suggested by using the dimensionless variable ${\gamma}$, which was possible to use several lead free solder alloys for prediction of thermal fatigue life. Furthermore, when the contact angle of the ball and chip has 50 degrees, solder joint has longest fatigue life.

Microstructure and Thermal Fatigue Properties of Flame-Sprayed Nickel-Based Coatings (니켈계 용사층의 조직 및 열피로 특성)

  • 김형준;권영각
    • Journal of the Korean institute of surface engineering
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    • v.29 no.3
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    • pp.163-175
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    • 1996
  • Flame-sprayed Ni-based coatings are investigated in order to improve the thermal fatigue properties of gray cast iron in the presence of water spraying. The results of thermal cycling tests from room temperature to $1100^{\circ}C$ indicate that thermal fatigue endurance is increased in the order of Ni-20%Cr, NiCr-6%Al, and Ni-5%Al. The thermal fatigue failure is caused by the formation of iron oxides between the coating and the substrate and then the thermal fatigue cracks have propagated either along the brittle iron oxide layer resulting in the spatting of the coatings in case of Ni-5%Al and NiCr-6%Al coatings or to the substrate resulting in the whole specimen fracture in case of Ni-20%Cr coating. It seems that the most governing factor for thermal fatigue resistance is the thermal expansion coefficient difference between the coating and the substrate. Microstructural variations before and after the tests are also discussed.

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