An in‑depth study of a thin‑wall origami‑inspired NiTi structure fabricated through laser powder bed fusion

This study aims to advance the field of additive manufacturing of NiTi shape memory alloys by providing a comprehensive functional analysis of a complex NiTi structure fabricated using laser powder bed fusion. While most of the literature on additive manufacturing of NiTi has been focused on the pseudoelastic effect, this research explores both pseudoelastic and shape memory effect. The selected geometry is origami inspired with wall thickness of 0.45 mm. Samples were fabricated through an AM400 of Renishaw starting with a NiTi powder with 50.8 at. % of Ni and followed a double-stage heat treatment, at 950 °C for 5.5 h and 450 °C for 15 min. The heat-treated cells were characterized to assess at first the phase transformation temperatures through thermal analysis and then both the pseudoelastic and the shape memory effects (analyzing both free and under load shape recovery), with maximum load ranging from 600 to 1500 N for pseudoelasticity, from 600 to 1000 N for free shape recovery and from 600 to 1200 N for actuation tests. Actuation tests were conducted by heating the loaded samples from room temperature to 85 °C and from Mf to 85 °C, thereby examining the material’s actuation response with the cold phase corresponding to the R-phase and martensite phase, respectively. Results were promising for all the tests performed. The pseudoelastic response highlights a loss factor of 0.0263 under the load of 1200 N. Moreover, maximum strokes of approximately 3 mm and 3.2 mm were observed in free shape recovery and actuation tests, respectively. Finally, it was found that the proposed origami-inspired structure, featuring two distinct shaped zones with varying rigidity, offers the advantage of preventing abrupt collapse and fracture during failure tests.