STP1360

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

    Published: Jan 2000


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    Abstract

    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.

    Keywords:

    fatigue, fatigue crack growth, effective stress intensity, crack closure, life prediction, modeling, aluminum alloys


    Author Information:

    Brockenbrough, JR
    Engineering associate and technical specialist, Alcoa Technical Center, Aluminum Company of America, Alcoa Center, PA

    Bray, GH
    Engineering associate and technical specialist, Alcoa Technical Center, Aluminum Company of America, Alcoa Center, PA


    Paper ID: STP13416S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13416S


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