This paper describes the application of poly(ether-block-amide) polymers, so-called Pebax, in fused filament fabrication (FFF). Pebax^® is a thermoplastic elastomer (TPE), a copolymer based on rigid polyamide and soft polyether blocks. By variation of the blocks, unique properties such as soft or rigid behaviour are tailored without additional additives and plasticisers. Pebax^®Rnew^® polyamide blocks are bio-based and made from castor beans that allow the design of sustainable applications. In this study, two types of Pebax were selected, processing parameters were characterised, filaments were extruded and applied to FFF printing, and the final mechanical characteristics were determined. Both types were suitable for FFF processing with improved process stability due to less shear thinning and good mechanical performance. The connection strength between the grades was also described in the design context for complex parts with tailored soft or hard regions. Combining the two materials in one design is a promising concept, and the adhesion strength is close to the strength in the Z-direction of the flexible Pebax^®Rnew^®35R53 grade.

Delamination is a critical failure mode in composite laminates that degrades the structural performance and load-carrying capacity. This study investigates the improvement of Mode I and Mode II interlaminar fracture toughness of carbon fiber-reinforced polymer (CFRP) laminates through the interleaving of electrospun thermoplastic nanofiber mats. Nanofiber veils were inserted between carbon fiber plies to enhance resistance to delamination under tensile opening (Mode I) and in-plane shear (Mode II) loading. The effects of nanofiber interleaving were evaluated using double cantilever beam (DCB) tests for Mode I and end notch flexure (ENF) tests for Mode II. Both tests were conducted on a symmetric quasi-isotropic laminate [-45/45/90/0₅]_s containing a thick unidirectional 0° ply at the mid-plane. Thermally induced residual stresses resulting from mismatches in ply coefficients of thermal expansion and unsymmetric arm lay-ups were accounted for in the experimental determination of fracture toughness. These stresses, generated during cooling from the cure temperature, influence the effective strain energy release rate and were included in the fracture toughness calculations to ensure accurate toughness evaluation and consistency with numerical predictions. The results demonstrate improved delamination fracture toughness, highlighting the potential of nanofiber interleaving for aerospace and wind energy applications.

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.