STP787

    Study of Compression Properties of Graphite/Epoxy Composites with Discontinuities

    Published: Jan 1982


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    Abstract

    This study assesses the static compression and R=10 compression-compression fatigue properties of graphite/epoxy composites with ply drop-off discontinuities under severe operating environments, including room-temperature dry and wet, −65°F wet, and 218°F dry and wet. In 30-ply [(±45)5/016/904]C laminates two 0-deg plies or four 45-deg plies are dropped off, symmetrically, in the middle one third of the specimen thickness. Static strength and moduli of elasticity are unaffected by these discontinuities; however, some proportional limit values and Poisson's ratio values are significantly changed. At 1.25 × 106 cycles of constant frequency and amplitude fatigue, the algebraic minimum endurance limit stress level is degraded 15 to 30 percent by the two 0-deg ply drop-offs, but only 0 to 13 percent by the four 45-deg ply drop-offs, or is even increased somewhat. The endurance limits of the surviving specimens are lower than their residual strengths, which vary directly with maximum applied cyclic compressive stress up to a threshold level. Detailed data tables and plots are included.

    Keywords:

    graphite/epoxy, composite, compression, fatigue, severe environment, ply drop-off discontinuities, residual strength, mechanical properties, stress and strain, stiffness, F-N, curves, orthotropic, anisotropic, moisture and temperature effects, ϵ-, N, curves


    Author Information:

    Grimes, GC
    Engineering Specialist and Engineer, Northrop Corporation, Hawthorne, Calif.

    Dusablon, EG
    Engineering Specialist and Engineer, Northrop Corporation, Hawthorne, Calif.


    Paper ID: STP28498S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP28498S


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