Effect of infill pattern on the mechanical properties and stress relaxation behavior of 3D printed PEEK

Polyether ether ketone is prized for its outstanding mechanical strength, biocompatibility, and high-temperature stability, which underpin its widespread use in aerospace and biomedical sectors. Additive manufacturing via fused filament fabrication brings additional benefits for polyether ether ketone components—reduced material consumption, part-level customization, and expanded geometric freedom—yet the long-term load-bearing behavior of printed polyether ether ketone remains underexplored. This study systematically evaluates how eight representative infill architectures (line, grid, honeycomb, triangular, gyroid, Hilbert-curve, concentric, and random) at ∼30% nominal relative density control both instantaneous tensile behavior and time-dependent stress relaxation. Tensile testing shows that honeycomb and grid infills consistently outperform conventional line and triangular patterns, delivering up to a 25% increase in elastic modulus and yield strength. Long-duration relaxation experiments reveal that these architectures also preserve higher residual stresses after two hours, indicating improved viscoelastic stability. Correlative micro-computed tomography imaging and finite-element modelling demonstrate that the superior performance arises from more uniform stress distributions and optimized load-transfer pathways; stress–strain responses from finite element modeling closely reproduce the experimental curves, validating the structural interpretations. Together, these results provide direct design rules for infill selection in load-bearing, long-service polyether ether ketone parts (aerospace structural components, long-term biomedical devices, seals and clamping elements) and inform international research on architected polymer mechanics by quantifying trade-offs between stiffness, strength and viscoelastic retention.