STP937

    The Effect of Matrix Toughness on Delamination: Static and Fatigue Fracture Under Mode II Shear Loading of Graphite Fiber Composites

    Published: Jan 1987


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    Abstract

    Both the static and fatigue behavior of delaminations subjected to pure Mode II shear loading were investigated using end-delaminated flexure specimens. By carrying out the constant amplitude sine-wave fatigue tests at fatigue load ratios (R) of R = 0 and R = −1, the importance of shear reversal was evaluated. The effect of improved matrix toughness on the Mode II properties was determined by testing four different graphite fiber composite systems having widely different Mode I fracture energies. The results indicated that the benefits of improved matrix toughness on the composite properties were less under Mode II loading than under Mode I and were reduced further still, or eliminated entirely, under Mode II fatigue conditions. It was found also that full shear reversal had an accelerating effect on the Mode II fatigue crack growth rates, especially at low values of ΔGII. These findings are discussed in terms of the failure mechanisms taking place. The significance of the results to damage tolerance and long-term durability design considerations are also addressed.

    Keywords:

    delamination, shear, fracture, fatigue, growth rate, toughness, graphite fiber


    Author Information:

    Russell, AJ
    Research scientist and composite group leader, Defence Research Establishment Pacific, F.M.O., Victoria,

    Street, KN
    Research scientist and composite group leader, Defence Research Establishment Pacific, F.M.O., Victoria,


    Paper ID: STP24383S

    Committee/Subcommittee: D30.04

    DOI: 10.1520/STP24383S


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