STP937: Influence of the Resin on Interlaminar Mixed-Mode Fracture

    Johnson, WS
    Senior research engineer and NRC resident research associate, NASA Langley Research Center, Hampton, VA

    Mangalgiri, PD
    Senior research engineer and NRC resident research associate, NASA Langley Research Center, Hampton, VA

    Pages: 21    Published: Jan 1987


    Abstract

    Both literature review data and new data on toughness behavior of seven matrix and adhesive systems in four types of tests were studied to assess the influence of the resin on interlaminar fracture. Mixed-mode (that is, various combinations of opening Mode I [GI] and shearing Mode II [GII]) fracture toughness data showed that the mixed-mode relationship for failure appears to be linear in terms of GI and GII. The study further indicates that fracture of brittle resins is controlled by the GI component, and that fracture of many tough resins is controlled by total strain energy release rate GT. Regarding the relation of polymer structure and the mixed-mode fracture: high Mode I toughness requires resin dilatation; dilatation is low in unmodified epoxies at room temperature/dry conditions; dilatation is higher in plasticized epoxies, heated epoxies, and in modified epoxies; modification improves Mode II toughness only slightly compared with Mode I improvements. Analytical aspects of the cracked lap shear test specimen were explored. Geometric nonlinearity must be addressed in calculating the GI/GII ratio. The ratio varies with matrix modulus, which in turn varies with moisture and temperature.

    Keywords:

    interlaminar fracture toughness, adhesives, double cantilever beam specimen, edge delamination tension specimen, cracked lap shear specimen, end notched flexure specimen, mixed-mode fracture, strain energy release rate, bonded joints, composites


    Paper ID: STP24384S

    Committee/Subcommittee: D30.06

    DOI: 10.1520/STP24384S


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