Journal Published Online: 25 August 2016
Volume 5, Issue 3

A Methodology for Partitioning Residual Stress Effects From Fatigue Crack Growth Rate Test Data



This paper described an improved fatigue crack growth rate (FCGR) material characterization process that partitioned residual stress effects from the material “true” FCGR behavior, leading to FCGR design curves that are free of residual stress bias. The material used in the program had high residual stress intentionally introduced. Two test methods from the literature were used to characterize the material: the adjusted compliance ratio (ACR) test method for closure correction, and the crack compliance test method for measuring the stress-intensity factor due to residual stress (Kres). Both test methods operated independently on compliance data collected during FCGR tests. Two independent data reduction methods were used to analyze the FCGR data. In the first, the closure corrected ACR data were combined with the Kres data using a power law relationship to normalize the curves into a residual stress free “master” curve, which was then transformed into a more traditional closure free ΔKeff curve. In the second, the Kres data were used in a superposition approach along with a closure model to reduce the data directly to the closure free ΔKeff curve. The two ΔKeff curves were shown to be in good agreement. The closure model was also used to reintroduce the stress ratio effect to generate the familiar da/dNK family of design curves that were free of residual stress bias. Validation examples were included where curves for the material with high residual stress were compared with data from similar material that had minimal residual stress, and those results were in good agreement. A summary of fatigue crack growth life predictions was also included to show that when residual stress effects are removed from FCGR characterization data and reintroduced in the fatigue life analysis, fatigue life is predictable within the usual 2x scatter factor for damage tolerance analysis.

Author Information

James, M.
Alcoa Technical Center, New Kensington, PA, US
Maciejewski, K.
Alcoa Technical Center, New Kensington, PA, US
Wang, G.
Alcoa Technical Center, New Kensington, PA, US
Ball, D.
Lockheed Martin Aeronautics Company, Fort Worth, TX, US
Bucci, R.
1005 Harbor Avenue SW, Unit# 500, Seattle, WA, US
Pages: 21
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Stock #: MPC20150062
ISSN: 2165-3992
DOI: 10.1520/MPC20150062