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Research Papers: Materials and Fabrication

Modeling the Temperature Dependence of Tertiary Creep Damage of a Ni-Based Alloy

[+] Author and Article Information
Calvin M. Stewart, Ali P. Gordon

Department of Mechanical, Materials, and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450

J. Pressure Vessel Technol 131(5), 051406 (Sep 03, 2009) (11 pages) doi:10.1115/1.3148086 History: Received September 19, 2008; Revised February 28, 2009; Published September 03, 2009

To capture the mechanical response of Ni-based materials, creep deformation and rupture experiments are typically performed. Long term tests, mimicking service conditions at 10,000 h or more, are generally avoided due to expense. Phenomenological models such as the classical Kachanov–Rabotnov (Rabotnov, 1969, Creep Problems in Structural Members, North-Holland, Amsterdam; Kachanov, 1958, “Time to Rupture Process Under Creep Conditions,” Izv. Akad. Nauk SSSR, Otd. Tekh. Nauk, Mekh. Mashin., 8, pp. 26–31) model can accurately estimate tertiary creep damage over extended histories. Creep deformation and rupture experiments are conducted on IN617 a polycrystalline Ni-based alloy over a range of temperatures and applied stresses. The continuum damage model is extended to account for temperature dependence. This allows the modeling of creep deformation at temperatures between available creep rupture data and the design of full-scale parts containing temperature distributions. Implementation of the Hayhurst (1983, “On the Role of Continuum Damage on Structural Mechanics  ,” in Engineering Approaches to High Temperature Design, Pineridge, Swansea, pp. 85–176) (tri-axial) stress formulation introduces tensile/compressive asymmetry to the model. This allows compressive loading to be considered for compression loaded gas turbine components such as transition pieces. A new dominant deformation approach is provided to predict the dominant creep mode over time. This leads to development of a new methodology for determining the creep stage and strain of parametric stress and temperature simulations over time.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Stress and temperature combinations of available creep experiments (does not include elastic strain)

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Figure 2

Creep rupture data at various temperatures (11)

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Figure 3

Single element FEM geometry used with force and displacement applied

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Figure 4

Comparison of experimental and numerically simulated creep deformation of IN617: (a) 760°C and 982°C, and (b) 871°C

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Figure 5

Temperature dependence of elastic, secondary creep, and creep damage constants of IN617

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Figure 6

Stress ratios resulting from various bi-axial (Hayhurst) stress configurations (a) 1–3σm, 2–σ1, and 3–σ. (b) All lines satisfy incompressibility and uni-axial tensile conditions. (c) all curves satisfy compressible and uni-axial tensile conditions. For all cases σz.

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Figure 7

Creep deformation predictions in tension and compression at 815.5°C for both secondary creep (dotted lines) and tertiary creep models (solid lines)

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Figure 8

Comparison of ((a) and (c)) total strain and ((b) and (d)) dominant deformation mode for ((a) and (b)) 100 MPa and 815.5°C and ((c) and (d)) 250 MPa and 649°C

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Figure 9

Contours of constant total deformation and constant deformation mode at (a) 760°C, (b) 871°C, and (c) 982°C. (Note: σ/σys is the applied stress over yield strength.)

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Figure 10

Total strain deformation maps from creep simulations

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