Thermo-mechanical performance of FFF-printed PEEK gyroid lattice structures across the glass transition: implications for lightweight autoclave tooling

Fused Filament Fabrication (FFF)-printed polyether-ether-ketone (PEEK) Gyroid lattice structures are promising candidates for lightweight autoclave tooling, yet their thermo-mechanical behavior across the glass transition temperature (Tg ≈ 143–150 °C) remains poorly characterized. This study presents a systematic experimental investigation of FFF PEEK Gyroid lattices at three relative densities (10%, 20%, 30%) under quasistatic compressive loading at 25 °C, 140 °C, 160 °C, and 200 °C. Post-printing thermal annealing effects were quantified by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA); sustained-load stability under autoclave-representative conditions was assessed via a purpose-designed spring-loaded fixture (12 h at temperatures up to 200 °C). Annealing raised crystallinity from 12.5% to 31.7% and increased storage modulus by ~ 17%. Compressive stiffness and yield strength decreased progressively with temperature, with a sharp transition above glass transition temperature Tg consistent with DMA measurements. Higher-density lattices retained superior load-bearing capacity and dimensional stability at all temperatures. These results provide quantitative guidelines for the design of FFF PEEK tooling subjected to combined thermal and mechanical loading.