STP636: Notched and Unnotched Fatigue Behavior of Angle-Ply Graphite/Epoxy Composites

    Ramani, SV
    Research scientist and chief, Materials and Physical Sciences Branch, National Aeronautics and Space Administration, Ames Research Center, Moffett Field, Calif

    Williams, DP
    Research scientist and chief, Materials and Physical Sciences Branch, National Aeronautics and Space Administration, Ames Research Center, Moffett Field, Calif

    Pages: 20    Published: Jan 1977


    Abstract

    The axial fatigue behavior of both notched and unnotched graphite/ epoxy composites has been studied as part of a continuing research investigation. In unnotched studies, conducted on a [0/±30]3s AS/3501 laminate, S-N (Δσ-log Nf) curves were determined for various stress ratios R using simply supported test specimens. Specimens were fatigue tested up to 5 × 106 cycles. Apparent fatigue limits (defined as stress amplitude at 5 × 106 cycles) in tension-tension (T-T) and compression-compression (C-C) cycling occurred at about 60 percent of the respective static strengths. The overall results were expressed in the form of a constant life diagram (that is, a Goodman diagram) showing the relationship between mean stress and stress amplitude. The diagram shows a linear relationship and illustrates a skew-symmetry in fatigue life caused by the relatively low compressive strength of the unrestrained test specimens used. In effect, a maximum in stress amplitude occurs at a positive value of the mean stress. Results of this study are of significance in situations where structural members are buckling or crippling critical in design.

    Keywords:

    composite materials, graphite/epoxy composites, angle-ply, residual strength, unnotched fatigue behavior, cyclic tests, damage accumulation, notched fatigue behavior, Goodman diagram


    Paper ID: STP27968S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP27968S


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