<scp>UV</scp> ‐Accelerated Aging Behavior and Residual Strength Modeling of FDM‐Printed CF/PEKK Composites

ABSTRACT Fused deposition modeling (FDM)‐printed carbon fiber‐reinforced polyetherketoneketone (CF/PEKK) composites represent promising lightweight structural materials for ultraviolet (UV)‐exposed service environments. Nevertheless, their UV‐induced degradation mechanisms and residual strength evolution remain poorly understood. Herein, FDM‐printed CF/PEKK composites were subjected to UVA‐340 accelerated aging for up to 480 h. Changes in mass, tensile strength, flexural strength, and interlaminar shear strength were quantified, and the underlying degradation mechanisms were investigated. After 480 h of UV exposure, average mass losses reached 0.0478, 0.0565, and 0.132 g cm −2 for tensile, flexural, and interlaminar shear specimens, with the corresponding strength reductions of 7.65%, 13.72%, and 18.12%, respectively. UV exposure induced surface defect accumulation, fiber exposure, and photo‐oxidative degradation of the PEKK matrix, accompanied by the formation of oxygen‐containing species and a decrease in crystallinity from 24.12% to 17.79%. Thermal stability decreased slightly, whereas the intrinsic thermal transition temperatures changed only marginally. A simplified residual strength model captured the monotonic degradation trends of all three mechanical properties under the present aging condition. These results indicate that UV damage is primarily surface‐localized but sufficient to degrade interfacial integrity and mechanical properties, providing essential insights for durability assessment of FDM‐printed CF/PEKK composites under UV exposure.