An experimental investigation on the tensile properties of PEEK-PEI sandwich structures prepared via fused filament fabrication

High-temperature-resistant thermoplastics, e.g., Polyetheretherketone (PEEK) and Polyetherimide (PEI), exhibit much more superior material properties than conventional plastics. They are recently becoming favorable feedstock materials in Fused Filament Fabrication (FFF) 3D printing applications, which yields a low-cost and high-efficient approach providing complex parts and tooling. This paper fabricates the PEEK-PEI combined sandwich structures by properly alternating the fed material during FFF processes, aiming to combine the benefits of both materials. This is considered one of the first few attempts to prepare high-performance thermoplastics-based sandwich samples via the FFF method. The specimens are designed as three-layer and five-layer sandwiches (i.e., each “layer” contain a unique material). In addition, the printed samples are post-processed via a thermal annealing treatment. Experimental results show that the sandwich specimens exhibit higher surface quality than independently printed PEEK materials. The PEI material can be printed in 100% infill density in sandwich structures, while it can be rarely printed independently with infill densities exceeding 40%. Annealing may not enhance the mechanical properties of sandwich specimens while stabilizing their mechanical performances. Under the same PEEK/PEI volumetric ratio (i.e., 1:1), increasing the number of alternating stack layers improves the tensile strength of the sandwich specimens by up to 17%. The sandwich printing method is also cost-effective, such that the five-layer sandwich specimen provides competitive tensile performance as compared to the virgin PEEK material. At the same time, its cost is only ∼60% of all-PEEK specimens.