An Experimental Study on the Effects of Electrospun Nanofiber Interleaves on Impact Damage Response and Compression-After-Impact of CFRP Laminates

Electrospun thermoplastic nanofiber interleaving has recently been shown to significantly enhance the Mode I and Mode II interlaminar fracture toughness of carbon fiber-reinforced polymer (CFRP) laminates. This exploratory experimental study extends those observations and investigates the influence of nanofiber interleaving on the low-velocity impact damage resistance and compression-after-impact (CAI) response of multidirectional [−45/45/90/05]s CFRP laminates, with a specific focus on the effect of interlayer placement within the layup sequence. Two non-interleaved reference laminates and two interleaved laminates with different interlayer configurations (full-thickness interleaving across all interfaces vs. localized impact-side interleaving) were subjected to low-velocity drop-weight impact at an energy level of 10 J. Projected post-impact damage area and damage morphology were quantified using ultrasonic testing, followed by CAI testing to determine residual structural performance. The results, albeit on limited specimens, demonstrate that full-thickness interleaving reduced the total delamination area by 49% and maximum damage diameter by 39%, delaying the onset of unstable buckling during post-impact compressive loading. In contrast, placing interlayers exclusively on the upper/compression side yielded only a minor (~11%) reduction in delamination area. While peak impact forces and contact durations remained virtually identical across all configurations, the spatial location of the interlayers proved critical: because impact-induced delaminations in multi-directional laminates are primarily driven by flexural tension and mid-plane transverse shear, interleaving the compression-dominated surface plies provides limited protection. Overall, despite limited explanatory observations, thermoplastic nanofiber interleaving showed potential to enhance the damage tolerance and residual load-carrying capacity of CFRP structures, provided the interlayers are targeted at shear- and tension-critical interfaces within the laminate stacking sequence.