Optimizing Thickness and Interlayer Placement of Electrospun TPU Nanofibrous Membranes for Enhanced Interlaminar Performance and Impact Resistance in CFRP Laminates

Carbon fiber reinforced polymer (CFRP) composites exhibit outstanding in-plane mechanical properties but suffer from poor interlaminar fracture toughness and low-velocity impact resistance due to inherent resin-rich interlayer regions. To address these limitations, this study introduces electrospun thermoplastic polyurethane (TPU) nanofibrous membranes as interlayer toughening agents in CFRP laminates. The effects of TPU membrane thickness (10, 30, and 50 μm) and insertion position (fully, top, middle, and bottom interlayers) on interlaminar fracture toughness, flexural strength, interlaminar shear strength (ILSS), and impact resistance were systematically investigated. Results demonstrate that increasing TPU membrane thickness enhances Mode I (70.6% improvement at 50 μm) and Mode II (32.4% improvement) interlaminar fracture toughness. These improvements can be ascribed to the fact that during the curing process, TPU has the ability to melt and blend with the epoxy resin, thereby improving the interface bonding performance between the resin and the fibers. Moreover, during the crack propagation process, the TPU-resin mixture undergoes plastic deformation, which consumes a greater amount of energy. However, excessive thickness reduces flexural strength by 14.6% due to inhibited fiber bridging. Low-velocity impact tests reveal that fully toughened laminates exhibit the highest damage resistance, reducing delamination area by 53.6% and improving residual compressive strength by 17.7% compared to unmodified laminates. Middle and top regional toughening configurations outperform that of bottom, highlighting the critical role of interlayer placement. These findings underscore the potential of TPU nanofibrous membranes as a scalable solution for enhancing CFRP interlaminar mechanical and impact resistance properties in aerospace and automotive applications. © 2025 Society of Plastics Engineers.