Processing and Property Comparison of High-Temperature Carbon/BMI Composites

Bismaleimide (BMI) resins are commonly used in advanced carbon composites for their high service temperature and excellent mechanical properties. In this study, two different BMI resins were compared: 1) formula RS-8HT, a high-cure temperature resin requiring pressurized consolidation, and 2) formula BMI-2, a lower cure temperature resin compatible with vacuum bag only fabrication. The objective was to identify a suitable high-temperature resin system for hybrid aerospace gear application, however, these materials are applicable to a variety of hot-zone parts. Laminates were fabricated from each resin type and characterized by their fiber volume fraction, compression strength vs. temperature, and glass transition temperature (Tg). Optical microscopy was performed to verify laminate quality. It was found that the carbon/RS-8HT laminates were prone to thermally-induced cracking, especially during post-cure. Carbon/BMI-2 laminates were found to attain a high degree of cure and high Tg from a realtively low temperature cure, without crack development. Additionally, the fiber volume fraction of the carbon/BMI-2 laminates, which were fabricated by a vacuum bag only process, were similar to that of the autoclave-processed carbon/RS-8HT laminates.