Mechanical characterization of PEEK-CF/PEEK sandwich structures prepared via a combination of fused filament fabrication and epoxy post-bonding

Poly-ether-ether-ketone (PEEK) and carbon-fiber-reinforced PEEK (PEEK-CF) are examples of engineering thermoplastics with exceptional mechanical properties. In the context of Fused Filament Fabrication (FFF), the interlayer bonding between PEEK and PEEK-CF has a significant impact on the mechanical properties of printed components. Epoxy resin is used to enhance the interfacial bonding between PEEK and PEEK-CF due to its remarkable adhesive properties, while preserving the dimensional and weight attributes of the bonded sandwich structure. The application of epoxy resin as a post-processing technique enables the creation of intricate geometric designs within the bonded sandwich structures. This study presents a straightforward technique for producing sandwich structures using PEEK and PEEK-CF, followed by improving their mechanical properties through isothermal annealing. We conduct systematic single-factor experiments to explore the mechanical advantages of FFF-printed PEEK and PEEK-CF via three-point bending tests on individually printed monolithic specimens. Furthermore, mono-material specimens are bonded using epoxy resin to form dual-material bending specimens. Our findings reveal an optimal sequence: after isothermal annealing, mono-material specimens bonded with epoxy resin exhibit superior flexural strength and modulus. In addition, an in-depth examination of the meso-structure and fracture morphology of FFF-printed sandwich structures after bonding and heat treatment reveals insights into toughening and reinforcement mechanisms. This analysis is complemented by corresponding finite element simulations to validate the results. Notably, our research highlights the successful optimization of interlayer structures, facilitating the creation of sandwich structures with superior mechanical performance.