Investigating the effect of VED and lattice strut diameter on the shape memory effect of nitinol actuators

This study examines the combined effect of volumetric energy density (VED) and lattice strut diameter on the microstructure, mechanical properties, and shape memory performance of NiTi lattice structures fabricated by laser powder bed fusion (PBF-LB). Produced sample characterisation included measurement of printed part density, composition, thermal transitions, and the compressive stress-strain response. The true strain ( ε t ), elastic strain ( ε e ), residual strain ( ε r ), SME recovered strain ( ε S M E ), actuation time, and thermal field generated during loading and recovery were also examined. These sample characteristics were evaluated in relation to both the process parameters as well as the printed lattice structure geometry. Lattices with 0.5, 1.0, and 1.5 mm strut diameters were produced by VEDs ranging from 21 J/mm 3 to 83 J/mm 3 . Results reveal a strong process-geometry-property relationship. Optimum VED increased with strut diameter, resulting in relative densities of up to 99.36 %. Larger struts resulted in higher ultimate strengths however resulted in reduced SME recovered strain and slower actuation. Thinner struts provided lower load baring capability however with the benefit of greater SME recovery, larger stroke displacement, and faster actuation. The findings highlight a trade-off between strength and actuator performance and highlight the importance of considering both geometry and process parameters when designing NiTi actuators while targeting application specific properties.