Cyclic Loading and Thermal Activation on the Shape Memory Performance of 3D-Printed PLA Cellular Structures

This study investigates the cyclic behavior and thermally activated recovery of FDM-printed PLA cellular structures, with a focus on the role of activation strategy in controlling short-term cyclic response and environmental impact. Seven architectures were initially screened, and Leaf_Spring and NS_Spring were selected based on energy absorption and structural integrity. These were tested over three loading–recovery cycles using hot water and localized hot air, with performance evaluated through Specific Energy Absorption (SEA). Results show that localized activation improves consistency of cyclic response: hot-air-treated samples exhibit a 9–11% increase in SEA across cycles compared to hot-water activation, while reducing geometric degradation induced by hydrostatic effects. For the Leaf_Spring structure, maximum force decreases from ~200–210 N (cycle I) to ~120–130 N (cycle III) yet maintains significantly higher energy absorption (~175 mJ/g initial value) than other configurations. In contrast, NS_Spring shows lower initial strength (~60 N) but smaller performance decay (~32% vs ~42%). Localized heating improves performance by preserving load-bearing regions and limiting damage through controlled softening. Life cycle assessment (LCA) shows reduced Human Health impact due to the smaller heated volume (~14%), with trade-offs depending on energy efficiency and scale. Overall, the results demonstrate that thermal activation mode, structural architecture, and relative density act as coupled design variables governing short-term cyclic behaviour and sustainability in 4D-printed shape memory metamaterials. These findings provide quantitative preliminary design insights for the design of reusable and energy-efficient lattice structures.