Functional behaviour of an innovative complex Nitinol structure for space applications manufactured by Selective Laser Melting

NiTi alloy is a smart material characterized by two effects, “Shape Memory Effect” and “Pseudoelastic Effect”. It is one of the most widely used Shape Memory Alloys (SMA) and its properties can be interesting for aeronautical and space applications. In particular, for the latter field, the usage of NiTi can lead to weight reduction and increased reliability, since it would eliminate the need for complex mechanisms. The Shape Memory Effect allows to use NiTi for actuation, while the Psudoelastic Effect enables the material to recover large deformations and can be employed to provide structural damping. Currently, the main limit to the widespread adoption of NiTi is its poor workability with conventional technologies, and for this reason, the development of new production technologies, such as Additive Manufacturing (AM), is of great interest to research. This work focuses on the study of the two effects of SMA in an innovative complex structure with origami geometry. The origami samples were fabricated through Laser Powder Bed Fusion (LPBF), an AM process that uses a laser beam to selectively melt layers of micrometric metal powders. The LPBF process parameters were established through a prior investigation on simple-shaped specimens aimed to guarantee the material’s performance and minimize the occurrence of defects. The studied geometry presents an intrinsic suitability for energy absorption, so when SMA are employed in the pseudoelastic regime, the material functionality increases the structural damping performances. Likewise, thanks to the shape memory effect, once the structure is heated over a certain threshold the pre-strained structure recovers its initial shape, thus obtaining a deployable structure. Thermal analysis and thermo-mechanical tests were used to investigate the overall performance of the origami structure. Once assessed the phase transformation temperatures, the structure was analysed to investigate separately the pseudoelastic and shape memory effects.