STP580

    Reducing Variability in Composite Tensile-Strength Properties

    Published: Jan 1975


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    Abstract

    Variability in composite tension-test values limits the application of advanced composite materials to structural design loads far below the capabilities inherent to the reinforcing fibers. Failure probabilities of boron and graphite filaments on the low-strength side of the skewed distribution contribute to composite fracture initiation early in the loading cycle. Dispersion in composite test values at these low levels imposes restrictions on allowable design values to conform to the minimum in the test data population. Prestressing the prepreg materials affects a fiber strength property improvement by prebreaking the filaments at the defect sources of low load failure. Increases in “B” design allowable levels for boron and graphite-epoxy material systems are shown to relate to reductions in fiber strength dispersions accompanied by increases in the average values. Projections of composite “B” allowables to 297 ksi are made for defect-free filaments.

    Keywords:

    composite materials, mechanical properties, prestressing, failure, boron, graphite, epoxy resins, variability


    Author Information:

    Mills, GJ
    Assistant for technical planning, senior engineer, and research associate, Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.

    Brown, GG
    Assistant for technical planning, senior engineer, and research associate, Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.

    Waterman, DR
    Assistant for technical planning, senior engineer, and research associate, Northrop Research & Technology Center, Northrop Corp., Hawthorne, Calif.


    Paper ID: STP32319S

    Committee/Subcommittee: D30.07

    DOI: 10.1520/STP32319S


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