Simulated Impact Damage in a Thick Graphite/Epoxy Laminate Using Spherical Indenters

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Abstract
The extent of fiber damage due to low-velocity impacts was determined for a 36-mm(1.4-in.)-thick graphite/epoxy laminate. The impacts were simulated by quasi- statically pressing spherical indenters against the laminates. Indenters of several diameters were used. The laminates were cut into smaller specimens, each containing a test site. The specimens were pyrolyzed to remove the epoxy, and the plies were separated and examined to determine the extent of fiber damage. Broken fibers were found in the outermost layers directly beneath the contact site. The locus of broken fibers resembled cracks. The cracks, which were more or less oriented in the direction of the fibers in the neighboring layers, initiated when the contact pressure exceeded a critical value. However, damage did not become visible on the surface until the pressure exceeded an even higher level. The maxi mum length and depth of the cracks increased with increasing contact pressure and in denter diameter. The length and depth of the cracks were predicted using theory of elas ticity and maximum stress criteria. The predictions and measurements were in good agreement.

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