New Structural Forms of Shape Memory Alloys

NiTi shape memory alloys (SMA) have been in commercial use for a variety of applications and have achieved commercial success especially in the biomedical sector for stents, guidewires, and other devices. Built-up shape memory alloy (SMA) architectures offer significant design flexibility to achieve adaptive properties in previously vacant design regimes. Two new SMA structural classes, multi-strand SMA cables and low-density SMA honeycombs, will be presented. Structural cables made from superelastic NiTi wires have unusual properties and the potential for new adaptive structures. Advantages over monolithic SMAs include increased bending flexibility and fatigue performance, energy absorption and damping, reduced thermal lag, redundancy, and design flexibility. Low-density NiTi shape memory alloy honeycombs were fabricated using a new Nb-based brazing method that demonstrate enhanced shape memory and superelastic properties under in-plane compression. A ten-fold increase in macroscopic strain recovery, compared to monolithic SMAs, is demonstrated. Such adaptive, light-weight cellular structures present interesting possibilities for the design of new architectures and novel applications. An overview is presented of ongoing work to address the multi-scale stability and design of superelastic, thin-walled, SMA honeycombs.