• Title/Summary/Keyword: 참조응력

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Reference Stress Based Stress Analysis for Local Creep Rupture of a T-pipe (참조응력법에 입각한 T-배관 국부 크리프 파단 평가를 위한 응력해석 사례연구)

  • Shin Kyu-In;Yoon Kee-Bong;Kim Yun-Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.8 s.251
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    • pp.873-879
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    • 2006
  • To investigate applicability of the reference stress approach as simplified inelastic stress analysis to estimate local creep rupture, detailed finite element stress analyses of a T-piece pipe with different inner pressure and system loading levels are performed. The reference stresses are obtained from the finite element (FE) limit analysis based on elastic-perfectly-plastic materials, from which the local reference stress for creep rupture is determined from R5. The resulting inelastic stresses are compared with elastic stresses resulting from linear elastic FE calculations. Furthermore they are also compared with the stresses from full elastic-creep FE analyses. It shows that the stresses estimated from the reference stress approach compare well with those from full elastic-creep FE analysis, which are significantly lower than the elastic stress results. Considering time and efforts for full inelastic creep analysis of structures, the reference stress approach is shown to be a powerful tool for creep rupture estimates and also to reduce conservatism of elastic stress analysis significantly.

Creep Analysis of Type 316LN Stainless Steel by Reference Stress Concept (참조응력 개념에 의한 316LN 강의 크리프 해석)

  • Kim, Woo-Gon;Kim, Dae-Whan;Ryu, Woo-Seog
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.123-128
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    • 2001
  • The creep constants which are used to the reference stress equations of creep damage were obtained to type 316LN stainless steel, and their determining methods were described in detail. Typical Kachanov and Rabotnov(K-R) creep damage model was modified into the damage equations with reference stress concepts, and the modified equations were applied practically to type 316LN stainless steel. In order to determine the reference stress value, a series of high-temperature tensile tests and creep tests were accomplished at $550^{\circ}C$ and $600^{\circ}C$. By using the experimental creep data, the creep constants used in reference stress equations could be obtained to type 316LN stainless steel, and a creep curve on rupture strain was predicted. The reference stress concept on creep damage can be utilized easily as a design tool to predict creep life because the process, which is quantified by the measurement of voids or micro cracks during creep, is omitted.

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Reference Stress Based Fracture Mechanics Analysis for Circumferential Through-Wall Cracked Pipes;Comparison with Pipe Test Data (참조응력 개념을 이용한 원주방향 관통균열 배관의 파괴역학 해석;실배관 실험 데이터와의 비교)

  • Huh, Nam-Su;Shim, Do-Jun;Kim, Yun-Jae;Kim, Young-Jin
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.389-396
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    • 2003
  • This paper presents experimental validation of the enhanced reference stress based J estimates for circumferential through-wall cracked pipes, recently proposed by authors. Using the pipe test data for circumferential through-wall cracked pipes, the predicted fracture initiation and maximum moments according to the proposed enhanced reference stress method are compared with experimental ones as well as predictions from the R6 method. The results show that both the R6 method and the proposed method give conservative estimates of initiation and maximum moments for circumferential through-wall cracked pipes, compared to experimental data. For longer cracks, the proposed method reduces conservatism embedded in estimated J according to the R6 method, and the resulting predictions are less conservative, compared to those from the R6 method. For shorter cracks, on the other hand, the proposed method reduces possible non-conservatism embedded in estimated J according to the R6 method, and the resulting predictions are slightly more conservative.

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Reference Stress Based Fracture Mechanics Analysis for Circumferential Through-Wall Cracked Pipes - Comparison with Pipe Test Data - (참조응력 개념을 이용한 원주방향 관통균열 배관의 파괴 역학 해석 - 실배관 실험 데이터와의 비교 -)

  • Huh, Nam-Su;Shim, Do-Jun;Kim, Yun-Jae;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.4
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    • pp.638-646
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    • 2003
  • This paper presents experimental validation of the enhanced reference stress based J estimates for circumferential through-wall cracked pipes. recently proposed by authors. Using the pipe test data for circumferential through-wall cracked pipes, the predicted fracture initiation and maximum moments according to the proposed enhanced reference stress method are compared with experimental ones as well as predictions from the R6 method. The results show that both the R6 method and the proposed method give conservative estimates of initiation and maximum moments for circumferential through-wall cracked pipes, compared to experimental data. For longer cracks, the proposed method reduces conservatism embedded in estimated J according to the R6 method, and the resulting predictions are less conservative, compared to those from the R6 method. For shorter cracks, on the other hand, the proposed method reduces possible non-conservatism embedded in estimated J according to the R6 method, and the resulting predictions are slightly more conservative.

Creep Analysis of Type 316LN Stainless Steel Using Reference Stress (참조응력을 이용한 316LN 스테인리스강의 크리프 해석)

  • Kim, Woo-Gon;Ryu, Woo-Seog
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.10
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    • pp.2122-2129
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    • 2002
  • Creep damage using a reference stress(RS) was analyzed for type 316LN stainless steel. The generalized K-R equation was reconstructed into the RS equation using a critical stress value $\sigma$. The RS equation was derived from the critical stress in failure time $t_f$ instead of material damage parameter $\omega$, which indicates the critical condition of collapse or approach to gross instability of materials during creep. For obtaining the reference stress, a series of creep tests and tensile tests were conducted with at 55$0^{\circ}C$ and $600^{\circ}C$. The stress-time data obtained from creep tests were applied to the RS equations to characterize the creep damage of type 316LN stainless steel. The value of creep constant r with stress levels was about 18 at 55$0^{\circ}C$ and 21 at $600^{\circ}C$. This value was almost similar with r = 24 in the K-R equation, which was obtained by using damage parameter $\omega$. Relationship plots of creep failure strain and life fraction $(t_f /t_r)$ were also obtained with different λ values. The RS equation was therefore more convenient than the generalized K-R equation, because the measuring process to quantify the damage parameter $\omega$ such as voids or micro cracks in crept materials was omitted. The RS method can be easily used by designers and plant operator as a creep design tool.

Reference Stress Based J-Integral Estimates Along the Semi-Elliptical Surface Crack Front (반타원 표면균열 선단을 따른 참조응력 기반의 J-적분 예측)

  • Kim, Jin-Su;Shim, Do-Jun;Kim, Yun-Jae;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.6
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    • pp.701-708
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    • 2004
  • This paper discusses applicability of the enhanced reference stress method to estimate J-integral along the semi-elliptical surface crack front. It is found that angular variations of normalized J­integral are strongly dependent on the geometry, loading mode and loading magnitude. As application of the reference stress approach to semi-elliptical surface cracks implies proportional increases in the normalized J-integral, the present results pose a question in applicability of the reference stress approach. However, investigation of the error in the estimated J-integral in the present work suggests that the enhanced reference stress approach, recently proposed by authors, provides an effective engineering tool fur estimating crack driving force along the semi-elliptical surface crack front.

Engineering J-Integral Estimation for Internal Axial Surface Cracks in Cylinders (II) -Optimised Reference Stress Based Estimation- (실린더에 존재하는 축방향 표면균열에 대한 공학적 J-적분식 (II) - 최적참조응력에 기초한 방법-)

  • Kim, Jin-Su;Kim, Yun-Jae;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.11
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    • pp.2442-2449
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    • 2002
  • This paper provides an reference stress based J estimation equation fur cylinders with finite internal axial surface cracks under internal pressure. In part 1, the J estimation equation based on deformation plasticity using Ramberg-Osgood (R-0) materials is proposed. In this paper, the developed CE/EPRI -type solutions ale then re-formulated based on the reference stress concept. Such a re-formulation provides a simpler equation for J. estimation are then further extended to combined internal pressure and bending. The proposed reference stress based J estimation equation is compared with elastic-plastic 3-D FE results using actual stress-strain data for a Type 304 stainless steel. Good agreement between the FE results and the proposed reference stress based J estimations provides confidence in the use of the proposed method to elastic -plastic fracture mechanics of pressurised piping.