Effect and mechanism of thermal aging on mechanical properties of continuous carbon fiber‐reinforced PEEK composite laminates

Abstract Continuous carbon fiber‐reinforced poly(ether‐ether‐ketone) composites (CCF/PEEK) are widely used in aerospace. However, long‐term service to elevated temperatures induces material aging in CCF/PEEK composite structures, significantly reducing their load‐bearing capacity. In this paper, the mechanisms of thermal aging effects on the mechanical properties of CCF/PEEK composites were investigated. Mechanical performance experiments were conducted on three‐point bending, short beam shear, and double cantilever beam specimens after accelerated aging in the range of 250–300°C. The evolution mechanism of crystallization behavior and aging characteristics was revealed through differential scanning calorimetry and thermogravimetric analysis. The results indicated that thermal aging primarily impacted the mechanical properties of CCF/PEEK composites through changes in crystallization and interfacial properties, which were highly sensitive to aging temperature, particularly with crystallization exhibiting temperature−/time‐ dependent behaviors during aging. The thermal aging environment promoted the growth and perfection of the crystals. However, at higher temperatures, further aging caused cross‐linking and degradation, resulting in a significant decrease in crystallinity following an initial increase. Moreover, the rate of oxidation and decomposition of the sizing agent escalated with increasing aging temperature, which led to a significant decline in interfacial properties. Generally, thermal aging at 250°C contributed to the improvement of bending and interlaminar shear properties of the composites. However, at 300°C, a significant decrease in both bending and interlaminar shear properties, as well as mode‐I interlaminar fracture toughness. Highlights The effect and mechanism of thermal aging on the mechanical properties of continuous carbon fiber‐reinforced poly(ether‐ether‐ketone) composites are investigated within the temperature range of 250–300°C. Thermal aging significantly influences the mechanical properties of the composites primarily by inducing alterations in both crystallization and interfacial properties. The differential scanning calorimetry (DSC) experimental results reveal that the crystallization of the PEEK matrix exhibits temperature−/time‐ dependent behaviors during thermal aging. Further aging at 300°C induces oxidation and decomposition of components such as sizing agents, resulting in interfacial debonding. The experimental results indicate that aging at 250°C is conducive to improving the mechanical properties and thermal stability of the composites.