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    The Effect of Resin Toughness and Modulus on Compressive Failure Modes of Quasi-Isotropic Graphite/Epoxy Laminates

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    Compressive failure mechanisms in quasi-isotropic graphite/epoxy laminates were characterized for both unnotched and notched specimens and also following damage by impact. Two types of fibers (Thornel 300 and 700) and four resin systems (Narmco 5208, American Cyanamid BP907, and Union Carbide 4901/MDA and 4901/mPDA) were studied. The widely used T300/5208 served as the baseline composite system. For all material combinations, failure of unnotched specimens was initiated by kinking of fibers in the 0° plies. A major difference was observed, however, in the mode of failure propagation after the 0° ply failure. In laminates made with Narmco 5208 resin, the 0° ply failure was immediately followed by delamination and catastrophic failure of the specimen. In BP907 resin, the fiber kinking was well contained without delamination, and still allowed further increase of load. The remaining two resins lay in their resistance to delamination between BP907 and Narmco 5208. The strength of quasi-isotropic laminates in general increased with increasing resin tensile modulus. The laminates made with Thornel 700 fibers exhibited slightly lower compressive strengths than did the laminates made with Thornel 300 fibers. The notch sensitivity as measured by the hole compressive strength was lowest for the BP907 resin and highest for the 5208 resin. For the materials studied, however, the type of fiber had no effect on the notch sensitivity. The area of impact damage was smallest for the BP907 resin. The 4901 resins were comparable to the 5208 resin in their impact resistance. Of the two fiber types, the T700 fiber consistently gave smaller damage area. The strength reduction after impact could be explained from the impact damage area and the unnotched strength.


    graphite/epoxy composites, quasi-isotropic laminates, compressive failure, fiber kinking, delamination, impact damage, resin modulus, notch sensitivity

    Author Information:

    Sohi, MM
    Graduate student and professor, Center for Composites Research, Washington University, St. Louis, MO

    Hahn, HT
    Graduate student and professor, Center for Composites Research, Washington University, St. Louis, MO

    Williams, JG
    Aerospace engineer, NASA Langley Research Center, Hampton, VA

    Committee/Subcommittee: D30.01

    DOI: 10.1520/STP24370S