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    Strength of a Thick Graphite/Epoxy Rocket Motor Case After Impact by a Blunt Object

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    NASA is developing graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the space shuttle. They are wet-wound with AS4W graphite fiber and HBRF-55A epoxy. The membrane region is about 36 mm (1.4 in.) thick. A study was made to determine the reduction in strength of the FWC caused by accidental damage from low-velocity impacts. Two 76.2-cm (30-in.) diameter by 30.5-cm (12-in.) long cylinders were impacted every 5 cm (2 in.) of circumference with impactors of various masses having a 1.27-cm (0.05-in.) radius indentor affixed to the end. The impacters represented tools and equipment dropped from various heights. One cylinder was empty, and the other was filled with inert propellent. Five-cm (2-in.) wide test specimens were cut from the cylinders. Each was centered on an impact site. The specimens were X-rayed and loaded to failure in uniaxial tension. The strengths and depths of impact damage were analyzed in terms of maximum impact force. Rigid body mechanics and the Hertz law were used to derive an equation for impact force in terms of kinetic energy and the masses of the impacter and target. The depth of damage was predicted in terms of impact force using Love's solution for pressure applied on part of the boundary of a semi-infinite body. The predictions of damage depth were reasonably good. Damage depths increased with increasing impact force, and strengths decreased with increasing impact force. The strengths were reduced by as much as 37% without visible surface damage. Even the radiographs did not reveal the nonvisible damage.


    graphite/epoxy composites, filament winding, motor case, impact damage, resid-ual strength

    Author Information:

    Poe, CC
    Senior research engineers, NASA Langley Research Center, Hampton, VA

    Illg, W
    Senior research engineers, NASA Langley Research Center, Hampton, VA

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP10025S