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    A Comparison of Several Mechanical Tests Used to Evaluate the Toughness of Composites

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    A variety of mechanical tests are in use to evaluate the “toughness” of finished composite parts. These include compressive strength after impact, critical Mode I strain energy release rate (GIc), edge delamination GIc, and damage area generated after impact. While much data has been generated on these, and other “toughness” tests, it has usually been gathered at a variety of locations using different variations on a given test, with few materials being subjected to more than one or two of these tests. All of these factors combine to make it difficult to compare different composite matrices on an equal basis, or to predict how neat resin mechanical properties will translate to a composite structure.

    This paper discusses the results of a study comparing the neat resin and composite mechanical properties of a variety of thermoset matrices. Both single and dual matrix (“interleaved”) composite systems were studied. Comparisons of composite test data have shown large differences between the various toughness tests, with improvements in one test not necessarily being reflected in the others. For example, the effect of interleafing two resin matrices of vastly different strain capabilities results in significant increases in impact related tests, with much smaller changes in GIc.

    This study involved mechanical testing of several thousand coupons. Analysis of the results has shown that a strong relationship exists, albeit not a perfect one, between neat resin and composite properties.


    advanced composites, aerospace composites, toughened composites, epoxy matrix composites, hybrid composites, composite epoxy resins, toughened epoxy resins, dual matrix epoxy resins, toughness mechanical tests, test correlations, impact resistance, crack propagation, neat resin mechanical tests, shear mechanical tests

    Author Information:

    Hirschbuehler, KR
    Product development engineer, American Cyanamid Co., Havre de Grace, MD

    Committee/Subcommittee: D30.05

    DOI: 10.1520/STP24371S