A combined experimental and modeling program is proposed to study the behavior of structural cables made from NiTi Shape Memory Alloy (SMA) wires. Multi-stranded SMA wires offer a convenient and cost-effective way to scale up the excellent properties of SMA wire to larger structures, but their structural behavior and scaling have not been studied in the open literature. Compared to conventional steel cable, SMA cable would have adaptive properties, i.e. thermally active in a shape memory mode and extremely resilient/dissipative in a superelastic mode. Compared to monolithic SMA bars, SMA cables would have other advantages, including: (1) more bending/torsion flexibility, which could lead to improved fatigue performance in some applications, (2) a reduced thermal lag, since the effective surface area for heat transfer would be larger for the same material mass, and (3) load carrying redundancy, leading to more graceful failure modes, less sensitivity to defects and mishandling, and better reliability. A systematic study of the thermo-mechanical behavior of SMA cables will be conducted. A hierarchy of prototype specimens (helical wires, strands, and cables) fabricated from NiTi wires will be subjected to a series of experiments over a range of temperatures and loading histories. The response of SMA cables will be compared to that of solid SMA bars and that of conventional steel cables to demonstrate their advantages and limitations. A numerical simulation tool will be developed to study the sensitivities of the behavior to geometric parameters and size of the cable. An improved recoverable strain response in shape memory and superelastic modes as well as improved response time due to reduced thermal lag will be demonstrated. SMA cables may exhibit unusual and interesting physical phenomena due to latent heat "cross-talk" between the wires/strands. They should also exhibit unusual dynamic behavior under impact loads and cyclic disturbances, and this work lays the necessary groundwork for future study of dynamical behavior.
The funding will be used to support a doctoral student who will use the proposed research as the basis for a Ph.D. dissertation. A continuing effort will be made to involve undergraduates in the proposed work, via summer internships and independent study projects. Shape Memory Alloys cables have broad potential use in the civil, transportation, biomedical, consumer, and energy sectors. In particular, the PI is associated with a newly established General Motors/University of Michigan Collaborative Research Laboratory on Smart Materials and Structures, where technology transfer from basic research to automotive applications can occur readily.
