Thermally conditioned aerospace-grade carbon fiber reinforced polyether ketone ketone composites: Structure, impact response, and thermomechanical performance

Carbon fiber-reinforced high-performance thermoplastic composites have recently become an efficient alternative for aerospace engineering applications. However, the temperature sensitivity of semi-crystalline carbon fiber/polyether-ketone-ketone (CF/PEKK) polymers revealed the necessity of investigating their performance in service conditions. This study aims to evaluate the effect of extreme service conditions on thermomechanical performance and fracture characteristics of CF/PEKK composite laminates. For this, aerospace-grade composite laminates were manufactured with the automated fiber placement process and were exposed to extreme service temperatures of -50 & DEG;C (Conditioned I), 180 & DEG;C (Conditioned II), and initially 180 & DEG;C following -50 & DEG;C (Conditioned III), simulating critical service temperature ranges in aerospace applications. According to impact tests, the energy absorbance of CF/PEKK composites decreased in all thermal conditioning scenarios by up to 25%. Additionally, Conditioned I samples represented relatively low glass transition temperature and degree of crystallinity compared to the control samples; however, Conditioned II and Conditioned III samples exhibited an opposite behavior. Dynamic mechanical analysis (DMA) investigations revealed a 13% reduction in the storage modulus for all thermal conditionings. While CF/PEKK composites represented ductile/brittle behavior at room temperature and high/low conditioning temperatures, their brittleness increased at -50 & DEG;C, and the structure became ductile at 180 & DEG;C. This study confirms that DMA is a powerful tool for determining the glass transition temperature for fiber-reinforced composites with higher sensitivity and accuracy than DSC.