Thermal Degradation Effects on Consolidation and Bonding in the Thermoplastic Fiber-Placement Process

Effects of elevated temperature exposure during thermoplastic fiber placement on bonding and consolidation are investigated experimentally for AS 4/ polyetherketoneketone (PEKK) composite. Coupons of 24 layers are consolidated on the University of Delaware Center for Composite Materials (UD-CCM) fiber- placement robot at deposition rates of 20 and 40 mm/s over a range of process temperatures (700-900 degC, with 50 deg C increments). The main torch and preheater distances and the compaction force are held constant for all coupons. Two competing mechanisms governing strength buildup are considered: (1) polymer bonding and (2) degradation. Coupons are sectioned, and one-half of each coupon is reconsolidated in a hot press at conventional processing conditions (i.e., 30 min at 370 deg C and 0.70-MPa pressure) in order to remove any effect of poor consolidation on strength. Void content of the robot-consolidated panels is measured. Short-beam shear (SBS) tests are performed on the specimens cut from each coupon. Strength and void-content measurements for robot-consolidated panels are presented to illustrate the effect of processing parameters on product quality. Results of the SBS strength tests performed on reconsolidated coupons indicate that there is significant decrease in the strength of coupons consolidated at 20-mm/s deposition rate and high torch temperatures, possibly due to polymer degradation, whereas approximately the same value of reconsolidated strength is measured for the 40-mm/s deposition rate, suggesting that polymer degradation is insignificant at that rate. Effects of void content on SBS tests are discussed.Army Research Lab Aberdeen Proving Ground is the author of 'Thermal Degradation Effects on Consolidation and Bonding in the Thermoplastic Fiber-Placement Process' with ISBN 9781423551928 and ISBN 1423551923.