Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

New Methods for Automated Fatigue Crack Growth and Reliability Analysis

[+] Author and Article Information
R. Craig McClung

Southwest Research Institute,
P.O. Drawer 28510,
San Antonio, TX 78238
e-mail: craig.mcclung@swri.org

Yi-Der Lee, Michael P. Enright, Wuwei Liang

Southwest Research Institute,
P.O. Drawer 28510,
San Antonio, TX 78238

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 18, 2012; final manuscript received November 27, 2013; published online January 30, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(6), 062101 (Jan 30, 2014) (7 pages) Paper No: GTP-12-1174; doi: 10.1115/1.4026140 History: Received June 18, 2012; Revised November 27, 2013

A new methodology has been developed for automated fatigue crack growth (FCG) life and reliability analysis of components based on finite element (FE) stress and temperature models, weight function stress intensity factor (SIF) solutions, and algorithms to define idealized fracture geometry models. The idealized fracture geometry models are rectangular cross sections with dimensions and orientation that satisfactorily approximate an irregularly-shaped component cross section. The fracture model geometry algorithms are robust enough to accommodate crack origins on the surface or in the interior of the component, along with finite component dimensions, curved surfaces, arbitrary stress gradients, and crack geometry transitions as the crack grows. Stress gradients are automatically extracted from multiple load steps in the FE models for input to the fracture models. The SIF solutions accept univariant stress gradients and have been optimized for both computational efficiency and accuracy. The resulting calculations are used to automatically construct FCG life contours for the component and to identify hot spots. Finally, the new algorithms are used to support automated probabilistic assessments that calculate component reliability considering the variability in the size, location, and occurrence rate of the initial anomaly; the applied stress magnitudes; material properties; probability of detection; and inspection time. The methods are particularly useful for determining the probability of component fracture due to fatigue cracks forming at material anomalies that can occur anywhere in the volume of the component. The automation significantly improves the efficiency of the analysis process while reducing the dependency of the results on the individual judgments of the analyst. The automation also facilitates linking of the life and reliability management process with a larger integrated computational materials engineering (ICME) context, which offers the potential for improved design optimization.

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Grahic Jump Location
Fig. 1

Example of the plate model for a surface crack where the plate orientation is defined by tangency to the component boundary

Grahic Jump Location
Fig. 2

(top) Example of the plate model for an embedded crack where the orientation is defined by tangency to the nearby boundary; (bottom) example of the plate model for an embedded crack where the orientation is defined by a significant stress gradient

Grahic Jump Location
Fig. 3

Schematic illustration of the plate sizing algorithm

Grahic Jump Location
Fig. 4

Example of the plate model for a surface crack on a nonstraight boundary (convex above the crack and concave below the crack)

Grahic Jump Location
Fig. 5

(top) Hoop stress contour plot for part of an axisymmetric ring disk geometry; (bottom) corresponding FCG life contour plot. Red indicates the highest stresses and the lowest FCG lifetimes.

Grahic Jump Location
Fig. 6

(top) Hoop stress contour plot for part of an axisymmetric impeller geometry; (bottom) corresponding FCG life contour plot

Grahic Jump Location
Fig. 7

Stress contours (top), life contours (middle), and risk contours (bottom) for combined bulk residual stresses and spin pit fatigue stresses based on a manufacturing process simulation



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