STP1044

    Interlaminar Fracture Toughness of Thermoplastic Composites

    Published: Jan 1989


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    Abstract

    Edge delamination tension (EDT) and double cantilever beam (DCB) tests were used to characterize the interlaminar fracture toughness of continuous graphite-fiber composites made from experimental thermoplastic polyimides and a model thermoplastic. Residual thermal stresses, known to be significant in materials processed at high temperatures, were included in the edge delamination calculations. In the model thermoplastic system (polycarbonate matrix), surface properties of the graphite fiber were shown to be significant. Critical strain energy release rates for two different fibers having similar nominal tensile properties differed by 30 to 60%. The reason for the difference is not clear. Interlaminar toughness values for the thermoplastic poly-imide composites (LARC-TPI and polyimidesulfone) were 400 to 700 J/m2. Scanning electron micrographs of the EDT fracture surfaces suggest poor fiber/matrix bonding. Residual thermal stresses account for up to 32% of the strain energy release in composites made from these high-temperature resins.

    Keywords:

    thermoplastic-matrix composites, interlaminar fracture, fiber/matrix interface, edge delamination, double cantilever beam, polyimide composites, carbon fiber


    Author Information:

    Hinkley, JA
    Chemical engineer and chief scientist—Materials Division, NASA Langley Research Center, Hampton, VA

    Johnston, NJ
    Chemical engineer and chief scientist—Materials Division, NASA Langley Research Center, Hampton, VA

    O'Brien, TK
    Senior scientist, U.S. Army Aerostructures Directorate, Hampton, VA


    Paper ID: STP24606S

    Committee/Subcommittee: D30.06

    DOI: 10.1520/STP24606S


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