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    Post-Impact Fatigue Response of Stitched Composites

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    The post-impact fatigue response of stitch-reinforced carbon/epoxy composite materials was evaluated. Five different material configurations, all based on a 48-ply quasi-isotropic laminate, were used in this study. Three different stitch densities and two separate resin systems were used in combination with AS4 fiber uniwoven lamina for these composites. An unstitched baseline laminate was also evaluated. After the samples were impacted using a drop tower, tension-compression fatigue tests were conducted with a 4-Hz frequency and a stress ratio of R = -5. Damage progression was monitored by radiographic techniques and extensometers mounted over the impact site. All the stitched materials developed a narrow self-similar damage zone transverse to the loading direction, which emanated from the damage site. Only very minor damage developed in the longitudinal loading direction of any of the stitched samples. While the lightly stitched tougher resin material had the best fatigue performance, a highly stitched brittle system behaved comparably. The current generation of stitched material was found to provide twice the fatigue load-carrying capability of the baseline unstitched laminate. Reinforcement was also determined to improve the impact damage tolerance of the materials while incurring no undamaged static compressive strength penalty.


    polymer matrix composite, tension-compression fatigue, impact, stitching, damage growth

    Author Information:

    Moon, DG
    Student and associate professor, Clemson University, Clemson, SC

    Kennedy, JM
    Student and associate professor, Clemson University, Clemson, SC

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP14024S