Superelastic response and damping behavior of additively manufactured Nitinol architectured materials

In energy absorption applications, architectured metallic materials generally suffer from unrecoverable deformation as a result of local yield damage or inelastic buckling. Nitinol (NiTi) offers recoverable deformation and energy dissipation due to its unique superelasticity, which can change the way we design and additively manufacture energy-absorbing architectured materials. The interplay between microstructure, mesoscopic deformation, and macroscopic thermomechanical response of NiTi architectured materials is still not studied in depth. In this work, NiTi architectured materials featuring anisotropic superelastic response, recoverable energy absorption and damping were successfully modeled and manufactured using laser powder bed fusion (L-PBF). Extensive numerical models demonstrated that NiTi architectured materials exhibit temperature-dependent superelasticity and effective transformation stress which can be controlled by the relative density and cell architecture. An effective transformation surface was developed based on the extended Hill's model, illustrating anisotropy is temperature-independent. Stable cyclic behavior with 2.8 % of reversible strain and damping behavior was successfully achieved in cyclic compressive tests without yielding damage or plastic buckling, which further illustrates that the progressive martensitic transformation is the main deformation and energy dissipation mechanism. A comparative study between designed herein body centered cubic (BCC) and octet structures showed that local microstructures significantly affect the deformation modes. The integrated computational and experimental study enables tailoring the superelasticity by combining structural design and microstructural control. Architectured materials designed in this study are potentially applicable as reusable impact absorbers in aerospace, automotive, maritime and vibration-proof structures.