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Research Papers

Mechanism Based Creep Model Incorporating Damage

[+] Author and Article Information
Nicola Bonora, Luca Esposito

Department of Mechanics, Structures and Environment (DiMSAT), University of Cassino, Via G. Di Biasio 43, 03043 Cassino (FR), Italy

J. Eng. Mater. Technol 132(2), 021013 (Feb 22, 2010) (7 pages) doi:10.1115/1.4000822 History: Received March 19, 2009; Revised November 16, 2009; Published February 22, 2010; Online February 22, 2010

The increasing demand of reliable creep design for very long lives (exceeding 100.000 h), as those for high stress-low temperatures and high temperature-low stress regimes, requires a model formulation capable to account for the nonlinearity in the stress dependence of the logarithm of the creep rate as a result of the combination of both diffusional and dislocation type creeps. In this paper, a creep model, where the effect of mechanism change has been accounted for through an explicit dependence of the creep exponent n on stress, has been proposed. The model has been also extended, incorporating damage processes and characteristics of tertiary creep stage, adopting a time independent damage formulation proposed by the authors. An application example of the proposed approach to high purity aluminum is given.

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Figures

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Figure 1

Comparison of total dislocation density in Fe-3%Si (data from Barrett and Nix, 1965) and present model as a function of applied creep stress. The representation of data in the semi-ln plot emphasizes the nonlinearity of the trend and the good agreement with the proposed formulation.

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Figure 2

Comparison of the present model solution for the normalized average dislocation velocity and the solution based on diffusion controlled process of jog dragging

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Figure 3

Comparison of the average dislocation velocity in Fe15Cr25Ni and the proposed model as a function of the applied creep stress (15)

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Figure 4

Deformation mechanism map for pure aluminum with average grain size d=10μ.

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Figure 5

Activation energy as a function of temperature for pure Al (1)

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Figure 6

Comparison of experimental data relative to 99.99% pure Al and present model. Dashed line is relative to the calculated solution for zero threshold stress.

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Figure 7

Comparison of the predicted creep curves and experimental data for 5N pure aluminum at 293 K and two different stress levels

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