Specimens of the neat epoxy and the two composites were subjected to static flexural tests and to dynamic compression tests at various strain rates from 10^{- 3} to 105 s^-1. In tension, as loaded in the flexural tests, both composite materials failed at the interfaces between the aluminum particles and the epoxy. Relative to the composite containing the larger (H3) particles, the composite containing the smaller (H2) particles exhibited lower flexural failure stress (see figure). It has been conjectured that this difference could be attributable to the difference in the number of particles per unit volume or to the greater oxide component in the smaller particles.

In the compression tests, the smallerparticle composite proved to be consistently stronger than the larger-particle composite. This difference is attributed to the greater number of particles per unit volume and the consequent greater constraint on the flow of epoxy in the smaller-particle sample. The differences in the compression and tension behaviors of these materials have been interpreted as signifying that the particle/matrix interfaces are weak, relative to the matrix.

In addition, as part of a continuing effort to develop constitutive equations for composite materials like these, data from the dynamic compression tests of the neat epoxy were compared with predictions of the Hasan-Boyce model — a theoretical model that has been shown to fit experimental data fairly well in prior studies of epoxies. The data and the predictions of the model were found to be in qualitative agreement. At the time of reporting the information for this article, an effort to optimize the parameters of the model for the epoxy used in this study was in progress.

This work was done by Jennifer L. Jordan, D. Wayne Richards, and Jonathan E. Spowart of the Air Force Research Laboratory, and Brad White and Naresh N. Thadhani of the Georgia Institute of Technology.

AFRL-0048

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High-Strain-Rate Tests of Epoxy/Aluminum-Powder Composites (reference AFRL-0048) is currently available for download from the TSP library.

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