Interlayer bonding strength of 3D printed PEEK specimens

Recent advances in extrusion-based filament 3D printing technology enable the processability of high-performance polymers. Poly(ether ether ketone) (PEEK) is an important group of high-performance polymer that has been widely used in aerospace, automotive, and biomedical applications. The interlayer bonding strength of 3D printed PEEK is crucial for load-bearing applications, yet studies on 3D printed PEEK are sparse due to processing challenges. In this study, the three-point flexural test is used to study the interlayer bonding strength of 3D-printed PEEK specimens with respect to the printing process parameters, including nozzle temperature, print speed, layer height, and wait-time. A design of experiment (DOE) approach is developed to study correlations between printing parameters and the end-use properties, including flexural stress (σf) and strain at break (εf), flexural modulus (Ef), and crystallinity (χ). Our results show that the nozzle temperature, layer height, and wait-time significantly affect the interlayer bonding strength, with nozzle temperature being the most influential parameter to enhance interlayer bonding strength indicated by a significant increase in σf, εf, and χ. Thermal annealing post-printing is shown to increase the degree of χ and Ef, yet its effect on interlayer bonding strength is minimal, indicating that the interlayer bonding strength is primarily determined during the printing process. This study demonstrates the use of a three-point flexural test integrated with a versatile and robust DOE approach to study the interlayer bonding strength of PEEK to reduce product development time while improving mechanical properties.