Offering high strength, excellent corrosion and fatigue resistance, and most importantly, an ability to recover their original shape after being subjected to large deformations, shape memory alloys (SMAs) are among the most promising “smart” materials for structural applications. Due to their unique thermomechanical properties and phase transformations, SMAs can recover from large strains (6-8%) by temperature increase – known as shape memory effect – or load removal – known as superelasticity effect. Such characteristics make the superelastic SMAs particularly suitable for self-centering applications, e.g., in self-centering braces, beam-to-column connections, and dampers.
As part of his postdoctoral research, Dr. Salehi has been working on the design and testing of an innovative class of self-centering dampers incorporating SMAs, termed SMA-Based Multi-Ring (SBMR) dampers. These devices consist of at least two concentric rings, namely, a superelastic (SE) ring and a supplemental energy-dissipating (ED) ring. The SE ring(s) is made of a superelastic SMA, such as an austenitic NiTi alloy and is primarily intended to provide an SBMR damper with self-centering. The ED ring(s) is made of a metal of high damping capacity, e.g., mild steel and an martensitic NiTi alloy, and is intended to supplement the moderate energy dissipation provided by the flag-shaped hysteretic response of the SE ring(s). Due to their special configuration, SBMR devices may absorb energy under both tension and compression (without buckling) and can be employed in both unidirectional and multidirectional fashions (for example, via a cross-bracing system).
Dr. Salehi recently evaluated the general performance and the optimal designs of SBMR dampers with various configurations through 3D finite element modeling in Abaqus – part of this study has been published here. In addition, four SBMR devices of various configurations are currently being tested under quasi-static and dynamic loading to examine their feasibility and to further validate their numerically-predicted performances. The results of the experimental program will be reported in the near future.