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Research Papers: Materials and Fabrication

Notch Behavior of Components Under the Stress-Controlled Creep–Fatigue Condition: Weakening or Strengthening?

[+] Author and Article Information
Jian-Guo Gong

School of Mechanical and Power Engineering,
East China University of Science
and Technology,
130 Meilong Road,
Shanghai 200237, China
e-mail: jggong@ecust.edu.cn

Fu-Zhen Xuan

School of Mechanical and Power Engineering,
East China University of Science and
Technology,
130 Meilong Road,
Shanghai 200237, China
e-mail: fzxuan@ecust.edu.cn

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received April 9, 2016; final manuscript received May 26, 2016; published online August 5, 2016. Assoc. Editor: Haofeng Chen.

J. Pressure Vessel Technol 139(1), 011407 (Aug 05, 2016) (9 pages) Paper No: PVT-16-1064; doi: 10.1115/1.4033731 History: Received April 09, 2016; Revised May 26, 2016

Notch-related weakening and strengthening behavior under creep–fatigue conditions was studied in terms of the elastic–viscoplasticity finite-element method (FEM). A coupled damage analysis, i.e., the skeletal point method for creep damage evaluation coupled with the equivalent strain range method for fatigue damage, was employed in the notch effect evaluation. The results revealed that, under the short holding time condition, a weakening behavior was observed for the notch, while a strengthening effect was detected with the increase of holding time. The difference could be ascribed to the creep damage contribution in the holding stage. The influence of stress concentration factor (SCF), stress ratio, and the maximum stress was strongly dependent on the competition of creep and fatigue mechanism.

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References

Figures

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Fig. 1

Weakening and strengthening behavior of notches under the creep–fatigue condition in terms of the experimental results of Ref. [10]

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Fig. 2

Schematic diagram of notch effect under creep/fatigue/creep–fatigue conditions

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Fig. 3

Comparison of notch effect numerically based on ASME III-NH method and experimental results under the pure creep condition

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Fig. 4

Effective stress and creep rupture life distributions of smooth and notch specimens based on ASME III-NH: effective stress [(a) smooth specimen, (b) specimen with a blunt notch (Kt = 1.13), and (c) specimen with a relatively sharp notch (Kt = 1.90)] and creep rupture life [(d) smooth specimen, (e) specimen with a blunt notch (Kt = 1.13), and (f) specimen with a relatively sharp notch (Kt = 1.90)]

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Fig. 5

Stress distributions along the path from notch center to notch root in the initial stage

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Fig. 6

Stress distributions along the path from notch center to notch root during the creep stage

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Fig. 7

Creep cracks observed in the cross section of notched specimens [2]: (a) R = 1.0 mm, σn = 400 MPa, (b) R = 0.5 mm, σn = 373 MPa, (c) R = 1.0 mm, σn = 245 MPa, and (d) R = 0.5 mm, σn = 245 MPa

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Fig. 8

Maximum principle stress distributions along with the radial direction using the Norton equation with various stress exponents

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Fig. 9

Comparison of notch effect numerically based on ASME III-NH method and experimental results under the repeated loading condition

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Fig. 10

Procedure diagram for the notch effect under creep–fatigue condition

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Fig. 11

Four notch geometries investigated in this work

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Fig. 12

A typical mesh configuration of notched component under creep–fatigue condition

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Fig. 13

Notch effect under creep–fatigue condition using the proposed method

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Fig. 14

Effect of SCF on the notch effect of notched components under the creep–fatigue condition using the proposed method

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Fig. 15

Effect of damage accumulation creteria on the notch effect coefficient (Kt = 2.76)

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Fig. 16

Effect of stress ratio on the notch effect of notched components under the creep–fatigue condition using the proposed method

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Fig. 17

Effect of maximum stress on the notch effect of notched components under the creep–fatigue condition using the proposed method

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