STP948

    Determination of Crack Propagation Directions in Graphite/Epoxy Structures

    Published: Jan 1987


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    Abstract

    This paper presents the results of an investigation into the fracture surface characteristics of delaminations in graphite/epoxy composite materials. Relationships between fracture surface features and imposed singular failure conditions are illustrated for tension (Mode 1) and shear (Mode 2) loading. Interlaminar tension fractures were generated utilizing a double cantilever beam geometry. Interlaminar shear fractures were generated utilizing an end-notch flexural geometry. In both cases controlled crack initiation and progression were produced between various cross-ply orientations. Interlaminar tension fracture features are illustrated showing a relatively flat surface morphology and river markings resulting from microplane coalescence. The direction of coalescence is shown to correspond to the direction of propagation. Fractures produced by interlaminar shear exhibit numerous epoxy platelets (hackles) oriented perpendicular to the direction of resolved tension at the crack tip. These platelets were found to occur predominantly on one fracture surface, where the direction of applied shear coincided with the direction of propagation. The overall relationship of each of these features with fiber orientation is reviewed and its value in postfailure identification of crack directions and load states presented.

    Keywords:

    fractography, composite materials, graphite/epoxy, fracture, crack propagation, failure analysis, delamination


    Author Information:

    Smith, BW
    Supervisor—Metals and Finishes and materials engineer, The Boeing Commercial Airplane Co., Seattle, WA

    Grove, RA
    Supervisor—Metals and Finishes and materials engineer, The Boeing Commercial Airplane Co., Seattle, WA


    Paper ID: STP25619S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP25619S


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