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 similar to 200-210 N (cycle I) to similar to 120-130 N (cycle III) yet maintains significantly higher energy absorption (similar to 175 mJ/g initial value) than other configurations. In contrast, NS_Spring shows lower initial strength (similar to 60 N) but smaller performance decay (similar to 32% vs similar to 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 (similar to 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.