In the present study, the feasibility to achieve localized induction heating and debonding of multi-material composite structures is assessed in testing coupons prepared by Automated Fiber Placement (AFP) and extrusion-based additive manufacturing (AM) technologies. Nano-compounds of Polyether-ketone-ketone (PEKK) with iron oxide nanoparticles acting as electromagnetic susceptors have been processed in a parallel co-rotating twin-screw extruder to produce filament feedstock for extrusion-based AM. The integration of nanocomposite interlayers as discrete debonding zones (DZ) by AFP-AM manufacturing has been investigated for two types of sandwich-structured laminate composites, i.e., laminate-DZ-laminate panels (Type I) and laminate-DZ-AM gyroid structures (Type II). Specimens were exposed to an alternating magnetic field generated by a radio frequency generator and a flat spiral copper induction coil, and induction heating parameters (frequency, power, heating time, sample standoff distance from coil) have been investigated in correlation with real-time thermal imaging to define the debonding process window without compromising laminate quality. For the optimized process parameters, i.e., 2–3 kW generator power and 20–25 mm standoff distance, corresponding to magnetic field intensities in the range of 3–5 kA m⁻¹, specimens were effectively heated above PEKK melting temperature, exhibiting high heating rates within the range of 5.3–9.4 °C/s (Type I) and 8.0–17.5 °C/s (Type II). The results demonstrated that localized induction heating successfully facilitated debonding, leading to full unzipping of the debonding zones in both laminate structures. Further insight on PEKK nanocomposites debonding performance was provided by thermal, morphological characterization and non-destructive inspection via X-ray micro-computed tomography at different processing stages. The developed framework aims to contribute to the development of rapid, on-demand joining, repair and disassembly technologies for thermoplastic composites, towards more efficient maintenance, repair and overhaul operations in the aviation sector and beyond.

With an ever-increasing material and design space available for Fused Filament Fabrication (FFF) technology, fabrication of complex three-dimensional structures with functional performance offers unique opportunities for product customization and performance-driven design. However, ensuring the quality and functionality of FFF-printed parts remains a significant challenge, as material-, process-, and system-level factors introduce variability and potentially hinder the translation of bulk material properties in the respective FFF counterparts. To this end, the present study presents a methodological framework for assessing the influence of process parameters on FFF strand stability and functional performance through a systematic analysis of FFF structural elements (1D stacks of FFF strands and 3D blocks), in terms of dimensional deviation from nominal geometry and resistivity, corresponding to the printability and functionality attributes, respectively. The influence of printing parameters on strand stability was investigated in terms of dimensional accuracy and surface morphology, employing optical microscopy and micro-computed tomography (mCT) for dimensional deviation analysis. In parallel, electrical resistance measurements were carried out to assess the effect of different process parameter combinations and toolpath patterns on functional performance. In low-level structural elements, strand height (H) was found to induce the greatest influence on FFF strand dimensional accuracy and resistivity, with higher H values leading to a reduction in resistivity of up to 38% in comparison with filament feedstock; however, this occurred at the cost of increased dimensional deviation. At higher structural levels, the overall effect of process parameters was found to be less pronounced, indicating that the translation of 1D strand properties to 3D blocks is subject to a trade-off due to competing mechanisms that facilitate/hinder current flow. Overall, the proposed framework enables the quantification of the influence of process parameters on the selected response variables, contributing to the development of standard operating procedures and recommendations for selecting optimal process parameters to achieve the desired process stability and functional performance in FFF.

The increasing use of Material Extrusion (MEX) 3D printing for creating structural components has increased the need to improve the mechanical performance of the utilized materials. Herein, polyethylene terephthalate glycol (PETG) was reinforced with glass fibers, an efficient, cost-effective additive. The mechanical properties of such composites are sensitive to the printing parameters used, indicating that there is a need for systematic optimization of the printing process. This research focused on optimizing the mechanical performance of PETG/glass fiber composite parts manufactured with MEX 3D printing using a Taguchi design and a regression models (linear and reduced quadratic). The effect of raster deposition angle (RDA), nozzle temperature, layer height, and strand width on tensile and flexural properties of the composite parts was assessed. Of the four parameters, RDA was the highest ranked parameter affecting the mechanical metrics evaluated, but this was not the same for all the mechanical responses studied; the highest ranked parameter varied between the responses. Optimization resulted in significant improvements in mechanical properties; specifically, increases of 11% in tensile strength (45.5 MPa), 21% in Young’s modulus (237.75 MPa), 61% in flexural strength (89.86 MPa), and 56% in flexural modulus (1910.61 MPa). The tensile toughness improved by an impressive 92%, and the energy absorbed up to the prescribed flexural strain (in accordance with the respective standard ASTM D790) increased by 54%. The R ² values were in the range of 82%-98%, while the confirmation runs deviation was less than 5%, confirming the accuracy of the proposed optimization framework. These results provide significant process optimization guidelines for the manufacturing of PETG/glass fiber parts using MEX for structural components.