Passive Structural Vibration Damping with Ferromagnetic Shape Memory Alloys

The proposed Phase I will explore the application of composites of polymer and ferromagnetic shape memory alloys (FSMAs) to passive structural vibration damping. The large hysteresis present in the stress-strain behavior of NiMnGa, a ferromagnetic shapememory alloy (FSMA), and other shape memory alloys (SMAs) suggests that both FSMAs and SMAs have the potential to dissipate mechanical energy more effectively than piezoelectrics, viscoelastic materials (VEMs) or Terfenol-D. However, FSMAs, unlike SMAs,allow harvesting a portion of the vibrational energy as usable electrical energy. Further, an external field can be applied to vary the stiffness of the FSMA composite. In principle, stress variations in the FSMA spanning more than ¿10 MPa can be coupledto twin boundary motion-induced deformations of several percent, representing a mechanical loss of order 1 MJ/m3 and a loss tangent in excess of 0.5. The Phase I will combine fabrication, test, and design tasks, in order to rapidly assess the merits andchallenges of proceeding further: (1) fabrication of composite polymer-NiMnGa samples, (2) static and dynamic testing of the samples, and (3) design of practical concepts for applying FSMAs to a structure. We will fabricate and test samples of NiMnGacomposite with various degrees of particle alignment, easy axis orientations, and fill factors with the intent of maximizing vibration damping. The program will conclude with identification of practical means for applying FSMAs to a representative trussstructure during the Phase II and estimation of the resulting damping. Wind, earthquakes, accelerations and reciprocating and rotating machinery represent disturbances that can force undesired and potentially destructive oscillations in both ground- andspace-based equipment: bridge trusses, towers, civil structures, buildings, industrial equipment, space station, launch vehicles, etc. Materials that more effectively damp vibration than existing polymer-based VEMs offer a promising means for attenuatingthese oscillations, reducing both design, construction and life-cycle costs for these structures.