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Research Papers: Materials and Fabrication

An Anisotropic Creep Damage Model for Anisotropic Weld Metal

[+] Author and Article Information
S. Peravali, T. H. Hyde

School of M3, University of Nottingham, University Park, Nottingham NG7 2RD, U.K

K. A. Cliffe

School of Mathematical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK

S. B. Leen

School of M3, University of Nottingham, University Park, Nottingham NG7 2RD, UKsean.leen@nottingham.ac.uk

J. Pressure Vessel Technol 131(2), 021401 (Dec 09, 2008) (8 pages) doi:10.1115/1.3007429 History: Received May 24, 2007; Revised December 17, 2007; Published December 09, 2008

Past studies from creep tests on uniaxial specimens and Bridgman notch specimens, for a P91 weld metal, showed that anisotropic behavior (more specifically transverse isotropy) occurs in the weld metal, both in terms of creep (steady-state) strain rate behavior and rupture times (viz., damage evolution). This paper describes the development of a finite element (FE) continuum damage mechanics methodology to deal with anisotropic creep and anisotropic damage for weld metal. The method employs a second order damage tensor following the work of Murakami and Ohno (1980, “A Continuum Theory of Creep and Creep Damage  ,” Creep in Structures, A. R. S. Ponter and D. R. Hayhurst, eds., Springer-Verlag, Berlin, pp. 422–444) along with a novel rupture stress approach to define the evolution of this tensor, taking advantage of the transverse isotropic nature of the weld metal, to achieve a reduction in the number of material constants required from test data (and hence tests) to define the damage evolution. Hill’s anisotropy potential theory is employed to model the secondary creep. The theoretical model is implemented in a material behavior subroutine within the general-purpose nonlinear FE code ABAQUS (ABAQUS User’s Manual, Version 6.6, 6006, Hibbitt, Karlsson and Sorenson, Inc., Providence, RI). The validation of the implementation against established isotropic continuum damage mechanics solutions for the isotropic case is described. A procedure for calibrating the multiaxial damage constants from notched bar test data is described for multiaxial implementations. Also described is a study on the effect of uniaxial specimen orientation on anisotropic damage evolution.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Area reduction on principal planes of damage (12)

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Figure 2

Tetrahedron showing the current damaged configuration and the fictitious strain-equivalent undamaged configuration (13)

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Figure 3

Anisotropic creep damage predictions for uniaxial specimens machined at different orientations relative to the welding direction

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Figure 4

Dimensions of axially loaded creep test specimens (mm)

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Figure 5

Comparison of anisotropic UMAT and isotropic UMAT predictions for isotropic creep and damage for aged CrMoV parent metal at 640°C

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Figure 6

Accumulation of damage component, ω22 with varying α1 and α2=0.45 for stress levels of 100MPa

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Figure 7

Effect of nominal stress level and variation in α2 on accumulation of (a) ω11 and (b) ω22 damage components, for Case 1 specimen at α1=0.59

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Figure 8

Damage component contours corresponding to approximate failure time for Case 1 specimen with α1=0.59 and α2=0.2 for an applied nominal stress of 100MPa

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Figure 9

Damage component contours corresponding to the approximate failure time for the Case 2 specimen with α1=0.3 and α2=0.45 for an applied nominal stress of 100MPa

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Figure 10

Effect of nominal stress level and variation in α1 on accumulation of (a) ω11, (b) ω22, and (c) ω33 damage components, for Case 2 specimen at α2=0.45

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