SYMPOSIA PAPER Published: 01 January 2000
STP13416S

Prediction of S-N Fatigue Curves Using Various Long-Crack-Derived Δ Fatigue Crack Growth Curves and a Small Crack Life Prediction Model

Source

In this study, stress-life (S-N) fatigue curves are predicted for high-strength aluminum alloy 7055 for open-hole specimens at two stress ratios, R = 0.1 and 0.5, and smooth specimens at R = 0.1 using the small-crack growth model of Brockenbrough et al. [1,2] and closure-free FCG curves obtained from long-crack tests by the following methods: (1) high R testing at R = 0.7; (2) constant Kmax testing at Kmax of 11 and 24.7 MPa√m; (3) a ΔKeff curve obtained at the appropriate stress ratio (R = 0.1 or 0.5) by the ASTM method; and (4) a ΔKeff curve obtained at the appropriate stress ratio by the adjusted compliance ratio (ACR) method. The predictions were compared to experimental S-N fatigue data. The objective of the study was to determine which method of obtaining closure-free FCG curves from long-crack tests provided the best estimates of fatigue life for the three combinations of specimen type and stress ratio in conjunction with the small-crack growth model employed. The ΔKeff curves obtained by the ACR method yielded the closest and most consistent fatigue predictions for all three conditions. This was attributed to this method being able to account for Kmax sensitivity of fatigue crack growth rates in aluminum alloys that could not be accounted for by the other methods.

Author Information

Brockenbrough, JR
Alcoa Technical Center, Aluminum Company of America, Alcoa Center, PA
Bray, GH
Alcoa Technical Center, Aluminum Company of America, Alcoa Center, PA
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Details
Developed by Committee: E08
Pages: 388–402
DOI: 10.1520/STP13416S
ISBN-EB: 978-0-8031-5418-6
ISBN-13: 978-0-8031-2617-6