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Tailoring of material architectures in three-dimensions enabled by additive manufacturing (AM) offers the potential to realize bulk materials with unprecedented properties optimized for location-specific structural and/or functional requirements. Here we report tunable energy absorption characteristics of architected honeycombs enabled via material jetting AM. We realize spatially tailored 3D printed honeycombs (guided by FE studies) by varying the cell wall thickness gradient and evaluate experimentally and numerically the energy absorption characteristics. The measured response of architected honeycombs characterized by local buckling (wrinkling) and progressive failure reveals over 110% increase in specific energy absorption (SEA) with a concomitant energy absorption efficiency of 65%. Design maps are presented that demarcate the regime over which geometric tailoring mitigates deleterious global buckling and collapse. Our analysis indicates that an energy absorption efficiency as high as 90% can be achieved for architected honeycombs, whereas the efficiency of competing microarchitected metamaterials rarely exceeds 50%. The tailoring strategy introduced here is easily realizable in a broad array of AM techniques, making it a viable candidate for developing practical mechanical metamaterials.

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Thermally activated shape memory polymers (SMP) are typically programmed by initially heating the material above the glass transition temperature (Tg), deforming to the desired shape, cooling below Tg and unloading to fix the temporary shape. Though this approach is employed in small‐scale applications, the process of deforming at high temperatures becomes a time, labor, and energy expensive process while applying to large structures (e.g. deployable space structures). The reversible plasticity shape memory (RPSM) property provides an alternate programming approach wherein the material is plastically deformed to a temporary shape at temperatures well below the transition temperature, preferably at room temperature. This paper aims to study the advantages of RPSM programming under bending and torsional deformations in multi‐walled carbon‐nanotube (MWCNT) reinforced epoxy nanocomposites. The samples are characterized for their thermal, morphological, and mechanical properties. The shape recovery behavior under various deformation modes is studied in detail. The effect of deformation level, relaxation time, and thermo‐mechanical cycles are also studied. All samples show excellent shape memory properties under all deformation modes and programming conditions. As a result, it is demonstrated that the RPSM programming can be used as an effective and a simplified alternative to conventional shape memory programming. POLYM. ENG. SCI., 58:E189–E198, 2018. © 2018 Society of Plastics Engineers

Thermally activated shape memory polymers are typically programmed by initially heating the material above the glass transition temperature (Tg), deforming to the desired shape, cooling below Tg, and unloading to fix the temporary shape. This process of deforming at high temperatures becomes a time-, labor-, and energy-expensive process while applying to large structures. Alternatively, materials with reversible plasticity shape memory property can be programmed at temperatures well below the glass transition temperature which offers several advantages over conventional programming. Here, the free, partial, and fully constrained recovery analysis of cold-programmed multi-walled carbon nanotube–reinforced epoxy nanocomposites is presented. The free recovery analysis involves heating the temporary shape above Tg without any constraints (zero stress), and for fully constrained recovery analysis, the temporary shape is held constant while heating. The partially constrained recovery behavior is studied by applying a constant stress of 10%, 25%, and 50% of the maximum recovery stress obtained from the completely constrained recovery analysis. The samples are also characterized for their thermal, morphological, and mechanical properties. A non-contact optical strain measurement method is used to measure the strains during cold-programming and shape recovery. The different recovery behaviors are analyzed by using a thermo-viscoelastic–viscoplastic model, and the predictions are compared with the experimental results.

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