STP743

    Fracture Control in Ballistic-Damaged Graphite/Epoxy Wing Structure

    Published: Jan 1981


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    Abstract

    This paper describes the development of a graphite/epoxy wing skin configuration capable of sustaining limit load following damage from a 23-mm high-explosive (HE) projectile impact. The skin configuration incorporates information learned in sawcut and ballistic fracture testing, and consists of a ±45 graphite/epoxy laminate with integral spanwise and chordwise crack-arresting pads formed by adding 0-deg glass/epoxy between the plies of graphite/epoxy. The ±45-ply orientation provides enhanced battle damage tolerance because of its higher residual strain-to-fracture capability relative to quasi-isotropic 0/±45/90 laminates. This permits developing the full load-carrying capability of the spar chords before unstable crack propagation can occur in the damaged skin. The 0-deg glass/epoxy was added to further enhance this capability, and concentrated into pads to avoid undesirable ballistic damage augmentation caused by the glass fibers, and to provide a controlled failure mode under blast pressures. The optimum graphite-to-glass ratio and the required width of the crack-arresting pads were determined using a new analysis method for predicting fracture in laminates containing high-strength 0-deg fibers. The effectiveness of the damage tolerance concept was demonstrated by firing a 23-mm HEI projectile into the tension surface of a full-scale wing-box test component loaded in combined bending and torison. Following damage, limit load was achieved as a result of successful crack arrestment.

    Keywords:

    cracking (fracturing), fracture (materials), advanced fiber composites, ballistic damage, impact strength, military aircraft, antiaircraft projectiles, high-explosive projectiles, tensile strength, fracture strength, ballistics, residual strength


    Author Information:

    Avery, JG
    Manager, Survivability/Vulnerability, technical analyst, and senior specialist engineer, Boeing Military Airplane Co., Research and Engineering, Seattle, Wash.

    Bradley, SJ
    Manager, Survivability/Vulnerability, technical analyst, and senior specialist engineer, Boeing Military Airplane Co., Research and Engineering, Seattle, Wash.

    King, KM
    Manager, Survivability/Vulnerability, technical analyst, and senior specialist engineer, Boeing Military Airplane Co., Research and Engineering, Seattle, Wash.


    Paper ID: STP28806S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP28806S


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