An experimental implication of long-term hot-wet-aged carbon fiber/polyether ketone ketone composites: The impact of automated fiber placement process parameters and process-induced defects

Abstract

During the service life of aerospace-grade composites, process parameters and process-induced defects may become crucial. Most studies in this field have mainly focused on the relationship between process-induced defects and mechanical performance. However, the potential impact of process parameters and process-induced defects on the service life of composites serving under severe service conditions has received little attention. In this work, the effects of hydrothermal conditioning on the mechanical performance of carbon fiber/polyether ketone ketone (CF/PEKK) composites are examined, along with the correlation between automated fiber placement (AFP) process parameters and process-induced defects. For this, gap and overlap defects integrated CF/PEKK laminates were exposed to a long-term (90 days) hot-wet aging environment to simulate the actual service conditions. Defect-induced composite samples reached saturation point at the end of 30 days with a mass gain of 0.2 wt%. The aging process resulted in an increase in the degree of crystallization by almost 14% without a change in the chemical structure, indicating the postcrystallization of the PEKK matrix. Even though the thermo-mechanical performance diminished (~25%) with the aging process, storage modulus was slightly affected by process parameters and process-induced defects. Considering the flexural and shear test results after the aging process, the impact of gap and overlap defects on the service life of AFP composites can be minimized with higher compaction forces (600 N) and lower lay-up speeds (0.1 m/s).