This study compares amorphous PEI, PES, PSU, and PC films co-cured as functional interlayers in aerospace-grade CFRP laminates based on HexPly® M18/1. A unified quasi-static test matrix comprising single lap shear, interlaminar shear strength, and Mode I and Mode II fracture toughness was applied to establish a directly comparable mechanical ranking. All interlayer systems preserved structural integrity, increasing single-lap shear strength by 6.2% to 13.3% to approximately 16–18 MPa. Interlaminar shear strength remained in a range of 48–59 MPa but depended on interlayer placement. Fracture testing revealed two distinct response types. PEI and PES showed the most effective toughening, with PEI reaching the highest Mode I toughness of 590 J/m² (+59.0%) and PES the highest Mode II toughness of 6180 J/m² (+518.6%). In contrast, PSU and PC exhibited poor resistance under opening-mode loading. Overall, the results demonstrate that interlayer selection governs both the fracture mechanism and the achievable damage tolerance.     «

This study compares amorphous PEI, PES, PSU, and PC films co-cured as functional interlayers in aerospace-grade CFRP laminates based on HexPly® M18/1. A unified quasi-static test matrix comprising single lap shear, interlaminar shear strength, and Mode I and Mode II fracture toughness was applied to establish a directly comparable mechanical ranking. All interlayer systems preserved structural integrity, increasing single-lap shear strength by 6.2% to 13.3% to approximately 16–18 MPa. Interlamin...     »