Thermo-mechanical Study on Auxetic Shape Memory Periodic Open Cellular Structures—Part II: Mechanical and Shape Memory Properties

Abstract

This study explores the potential of periodic open cellular structures (POCS) that combine the auxetic and the shape memory effect (SME) with the aim of enhancing heat transfer in catalytic tubular reactors. On the one hand, these structures exhibit a negative Poisson's ratio, contracting perpendicular to the load axis under compression, driven by the rotation of nodes generating complex stress fields. On the other hand, the shape memory alloy (SMA) Nitinol (NiTi) with a reversible strain of up to 8% produced via electron beam powder bed fusion (PBF-EB) shows extraordinary material properties with a high degree of freedom in structure design. The study conducts finite element method simulations and experiments to design POCS with tailored properties. Compression tests on less expensive Ti-6Al-4V POCS compared to NiTi POCS validate the simulative parameter study applied to fabricate novel auxetic hexagonal reentrant structures from NiTi with a unique stacking order and curved struts. The aim of this part of the study is to offer a pathway to design a NiTi auxetic POCS based on validated simulations. Further, it explains the interactions between geometrical parameters and mechanical properties of cellular reentrant NiTi structures. An optimized auxetic NiTi POCS achieved a Poisson's ratio of −1.