Shape memory alloys are metals which can exhibit pseudoelastic behaviour, allowing them to achieve significant strains under load with minimal plastic deformation. For metamaterials and programmable materials with a higher stiffness than polymers and a greater recoverable strain than typical metals, this pseudoelastic beahaviour is helpful. Nickel Titanium (NiTi) represents the most common shape memory alloy due to its functional stability. The fabrication of complex 3D structures made of NiTi cannot be realized using conventional manufacturing techniques, which is why additive manufacturing techniques are employed to create meta- or programmable materials.

We present delicate NiTi structures, manufactured by Laser Powder Bed Fusion (LPBF), with pseudoelastic properties in the as-built state by using adapted scanning strategies [1] and seek the way of manufacturing programmable materials made of NiTi. In this study, we show the compression behaviour of NiTi lattice structures, with an unit cell design inspired by an auxetic structure, of which one demonstrates a rise in stiffness in the pseudoelastic region (Fig. 1). The stiffness jump is due to the insertion of a design feature within the unit cell. In comparison, the equivalent structure without the design feature does not show the change in stiffness behaviour (Fig. 1). Compression tests conducted parallel to the building direction indicate that the materials can endure approximately 30 % effective strain without failure. Further compression illustrates gradual strut failure. We compare microscopic analyses with CT data of the as-built and compressed state and present results on step-by-step μCT scans during compression.