| Abstract: | Thermoplastic composites in general have been found to display improved resistance to impact damage over their thermosetting counterparts. However, in earlier work, we presented data that suggested that in poly(etheretherketone) (PEEK) based composites, damage tolerance may be adversely affected if cooling rates are too slow in the processing of these parts. In this work, ultrasonic C-scan and compression-after-impact testing were implemented on PEEK APC-2 plaques cooled at three different cooling rates, in addition to toughened epoxy and bismaleimide plaques processed conventionally as a comparison. It was found that the damaged areas as measured ultrasonically varied significantly between the PEEK samples cooled at different rates, and that under the slowest cooling conditions, the damaged areas approached those of the thermosetting systems tested. However, because compressive strengths before impact were found to be greater on slow cooling, the differences in compression-after-impact were less dramatic than one would have expected from the C-scan results alone. Variations in crystallinity as well as spherulite size were the source for the differences in damaged areas as well as in compressive strength. |
