Modelling Crack Growth in the Life Assessment of Elevated Temperature Components

Abstract:

Modelling of Creep Crack Growth (CCG) using analytical and numerical methods is relevant to life assessment procedures of components operating at elevated temperatures. This paper compares an analytical crack prediction and a numerical based virtual CCG technique used in fracture mechanics components with sample experimental results. Two approaches are presented. First the well developed strain exhaustion model called the NSW and the modified NSW-MOD models which predict plane stress/strain bound crack initiation and growth rates for engineering alloys and the second a damage-based approach used to numerically predict the crack propagation rate in Finite Element models of fracture mechanics specimens. The results from both methods are correlated against an independently determined C* parameter. As an example the NSW and the extended NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions for two steels at Carbon-Manganese steel tested at 360 oC and a weld 316H stainless steel at 550 oC. For values of C* within the limits of the present creep crack growth data presented the plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model.

• Periodical: Key Engineering Materials (Volumes 348-349)
• Pages: 709-712
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.348-349.709
• Online since: September 2007
• Authors: Kamran M. Nikbin
• Keywords: Creep Crack Growth, Creep Deformation, Fracture Mechanic, Incubation Period, Lifetime Assessment, Residual Stress

References

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[11] Yatomi, M., Nikbin, K. M., Virtual Methods in Creep Crack Growth Predictions in Welded Components, IOM conference on welded structures, London April 22-24 th , (2007).

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[10] [3] [10] [4] FEM, Plane stress FEM, Plane strain NSW, Plane stress NSW, Plane strain da/dt, (mm/h) C*, (J/m.

DOI: 10.1002/nme.1620231005

[2] h) Band for Experimental CT data εf = 18 % ∆ < 0. 5 . Band for Experimental CT data.

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[10] -1 10-4 10-3 10-2 10 -1 100 101 102 103 104 FEM, Plane stress FEM, Plane strain ext_NSW, Plane stress(θ = 0) ext_NSW, Plane strain(θ = 0) da/dt, (mm/h) C*, (J/m 2h) εf = 18 % ∆ < 0. 5 . Figure 1: Comparison between FE prediction and experimental data for C-Mn steels at 360 o C with (a) NSW model and (b) NSW-MOD where εf = 18% and n = 10 were used [5].

DOI: 10.1002/nme.1620231005

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[10] [0] [10] [1] [10] [2] [10] [3] da/dt (mm/h) C* (J/m 2h) NSW, Plane stress NSW, Plane strain Experimental data band for C(T) specimens.

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[10] [0] [10] [1] [10] [2] [10] [3] FE, Plane stress FE, Plane strain NSW-MOD, Plane stress NSW-MOD, Plane strain da/dt (mm/h) C* (J/m.

[2] h) Figure 2 Comparison between a) NSW and b) NSW-MOD predictions with the experimental results for 316H stainless steel at 550 o C. Where εf = 10% and n = 10 were used [11] (a) (b) (a) (b).