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TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

Convergent Zone-Refinement Method for Risk Assessment of Gas Turbine Disks Subject to Low-Frequency Metallurgical Defects

[+] Author and Article Information
Harry R. Millwater

Department of Mechanical Engineering,  The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, 78249harry.millwater@utsa.edu

Michael P. Enright

Reliability and Material Integrity, Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX, 78228menright@swri.org

Simeon H. K. Fitch

 Mustard Seed Software, 1634 Brandywine Drive, Charlottesville, VA, 22901simeon.fitch@mseedsoft.com

J. Eng. Gas Turbines Power 129(3), 827-835 (Sep 15, 2006) (9 pages) doi:10.1115/1.2431393 History: Received March 08, 2005; Revised September 15, 2006

Titanium gas turbine disks are subject to a rare but not insignificant probability of fracture due to metallurgical defects, particularly hard α. A probabilistic methodology has been developed and implemented in concordance with the Federal Aviation Administration (FAA) Advisory Circular 33.14-1 to compute the probability of fracture of gas turbine titanium disks subject to low-frequency metallurgical (hard α) defects. This methodology is further developed here to ensure that a robust, converged, accurate calculation of the probability is computed that is independent of discretization issues. A zone-based material discretization methodology is implemented, then refined locally through further discretization using risk contribution factors as a metric. The technical approach is akin to “h” refinement in finite element analysis; that is, a local metric is used to indicate regions requiring further refinement, and subsequent refinement yields a more accurate solution. Supporting technology improvements are also discussed, including localized finite element refinement and onion skinning for zone subdivision resolution, and a restart database and parallel processing for computational efficiency. A numerical example is presented for demonstration.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Fracture mechanics model using a rectangular plate overlaid on an axisymmetric finite element model

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Figure 2

Univariant stress gradient

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Figure 3

Selection of zones for refinement using risk contribution factors; red (gray) zones indicate RCF greater than 5%

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Figure 4

Schematic of zone subdivision: parent zone (left) divided into four subzones (right) about stress centroid of parent

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Figure 5

Example of finite element subdivision in support of zone refinement

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Figure 6

Example of onion-skinning algorithm applied to a single finite element

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Figure 7

Three-dimensional idealized impeller finite element model

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Figure 8

(a)–(d) Sequence of zone refinement iterations for impeller rotor disk model and (e)–(h) sequence of zone refinement iterations for impeller rotor disk model

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Figure 9

Iteration results showing the convergence in risk versus the number of zones (old and new)

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