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    Bearing Strength Behavior of Clearance-Fit Fastener Holes in Toughened Graphite/Epoxy Laminates

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    Laminates made of standard modulus carbon fiber in a toughened thermosetting resin matrix were tested under pin bearing conditions to determine the effects of fastener hole oversize on both 4% hole deformation strength (4% HDS) and maximum bearing stress (per ASTM D 953, Test Method for Bearing Strength of Plastics). Results indicated 4% HDS was reduced by up to 30% due to hole oversize whereas the maximum bearing stress, which results from a complicated progressive damage mechanism, was generally unaffected. Nonlinear finite element contact analyses were used to investigate the contact force distribution between the laminate and pin, both assumed to be linear elastic, and to obtain local stress field information. Maximum contact force was greatly influenced by hole oversize, ranging from 90% to 240% of the maximum calculated for a conventional cosine distribution. Significant differences in the distribution of contact force as a function of angular position were noted also. For applied loads corresponding to the experimentally determined 4% HDS, finite element stress results, used in conjunction with a ply level Hoffman failure criterion, allowed the formulation of a model that could accurately predict 4% HDS for all nominal and oversize diameters tested. The proposed model, which is a variation of the point stress characteristic distance hypothesis, reflects the nonconstant features of the Hoffman failure contour at points removed from the hole boundary.


    polymer matrix composites, toughened resin, pin bearing strength, clearance fit holes, finite element analysis

    Author Information:

    DiNicola, AJ
    Stress analysts, United Technologies-Sikorsky Aircraft, Stratford, CT

    Fantle, SC
    Stress analysts, United Technologies-Sikorsky Aircraft, Stratford, CT

    Committee/Subcommittee: D30.07

    DOI: 10.1520/STP12630S