Influence of Cooling Rate on Residual Strain Evolution and Interlaminar Properties in Thermoplastic Composites With Embedded FBG Monitoring

ABSTRACT This study utilizes fiber Bragg grating (FBG) sensors to monitor the real‐time evolution of residual strain in thermoplastic composite structures during the hot‐press forming process under different cooling rates. Three representative structures—pure polyether ether ketone (PEEK) resin, carbon fiber‐reinforced polyether ether ketone (CF/PEEK) composites, and aluminum alloy/carbon fiber‐reinforced polyether ether ketone (AL/CF/PEEK)—were investigated. Differential scanning calorimetry (DSC) was employed to analyze the influence of crystallization temperature on the final residual strain. Double cantilever beam (DCB) and short beam shear (SBS) tests were conducted to evaluate the interlaminar fracture toughness and shear resistance of fiber–fiber and fiber–metal interfaces at different cooling rates. The results demonstrate that cooling rate modulates the crystallization morphology of the thermoplastic matrix, thereby influencing material performance. In the CF/PEEK system, a faster cooling rate reduced crystallinity, leading to decreased residual strain and enhanced interlaminar toughness and shear strength. However, in the AL/CF/PEEK system, excessive cooling rates compromised cooling uniformity, increased residual strain, and deteriorated interlaminar performance. The findings reveal that the residual strain in high‐performance thermoplastic structures is governed by both resin crystallization and interlayer cooling uniformity, which ultimately determine interlaminar mechanical properties.