Consolidation of aerospace-grade high-temperature thermoplastic carbon fiber composites via nano-engineered electrothermal heating

Abstract

A carbon nanotube (CNT) electrothermal heater is shown to enable consolidation of high-temperature thermoplastic composite laminates for the first time, leveraging the CNT film's stable operation in air above 500 degrees C. This out-of-oven (OoO) conductive heating method without applied pressure (i.e., vacuum bag only) is used to process aerospace-grade carbon fiber/polyether ether ketone (PEEK) composite prepreg, which requires heating to 380-400 degrees C and is normally processed with significant applied pressure (similar to 2 +/- 1 MPa) via a hot-press or autoclave. Micro-computed tomography verifies that the processed laminates exhibit low porosity of <= 0.1 vol%, which more than meets the desired target of <1 vol% voids. A range of thermophysical (including degree of crystallinity) and mechanical (interfacial shear strength and bending) tests show equal or improved properties vs. both hot press and autoclave processing. The CNT heaters in the OoO approach are observed to most closely match the desired processing cycle, with the observed benefit of being the only process studied to hit the target range of % crystallinity. The energy consumption comparison indicates a 98% energy saving of the CNT heater compared to the hot press. This study demonstrates autoclave-quality processing of high-temperature thermoplastic composite structures via conformal CNT heaters that can be fabricated efficiently and effectively in an out-of-autoclave (OoA) process.