Compressive failure of a unidirectional carbon-epoxy composite at high strain rates
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REFERENCES
Fig. 1—The original scanning electron micrograph of the surface morphology of the eutectic Co-Sn alloy solidified from an undercooled state, showing that the particulate phase embeds into the continuous matrix phase, which consists of a typical anomalous eutectic grain. The regular lamellae grow from the periphery of each anomalous gain and form a radiated structure.
Reference 17 and Figure 3 in Reference 9, and that of the undercooled Co-Sn eutectic alloy in Figure 1, have revealed clearly that at least one phase in the anomalous eutectics is continuous. In addition, by successive polishing of the Ni-Sn eutectic sample and then examining parallel sections, Kattamis and Flemings[3] confirmed that both eutectic phases were continuously interconnected along a polyhedral network. Surface observations and cross-sectional confirmation after the successive polishing indicate that each eutectic phase in the anomalous eutectics is continuous rather than independent spherical grains resulting from fragmentation. This continuous morphology is consistent with the growth mode for the anomalous eutectic formation in Reference 17. Finally, it is worth noting that Kattamis and Flemings did not point out the detailed scope within which a polyhedral network is continuous. Based on independent colonies with clear contacting boundaries, as evidenced in References 10 through 12 and 17, we propose that the scope where a polyhedral network is continuous is only confined within one eutectic colony. Different eutectic colonies may have different crystallographic orientations because they originate from independent nuclei in an undercooled eutectic melt. In conclusion, we have analyzed the free growth of a single eutectic colony in the unconstrained solidification of undercooled eutectic melts. There have been many uncertainties that differ greatly from that in directional solidification. This makes it senseless to correlate the lamellar spacing vs a certain melt undercooling in free growth and may yield significant discrepancies if it is arbitrarily measured. It is evident that discussions and conclusions based on the lamellar spacing measurement under the free growth condition, more specifically, the application of the fragmentation model to account for the anomalous eutectic formation, should be further deliberated with great care. One of the authors (ML) is grateful to the Japan Society for the Promotion of Science for offering a JSPS fellowship. We also thank Drs. K. Nagashio and Z. Jian for many stimulating discussions and valuable suggestions. 1396—VOLUME 34A, JUNE 2003
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