Passive vibration damping with magnetostrictive composite material

摘要

This paper describes evaluation of an autonomous-material system tailored for free-layer vibration damping of structural elements. The magnetostrictive particulate composite (MPC) material described has moderate stiffness and minimal temperature and frequency dependence. The composite is created by curing Terfenol particles {Tb_((1-x))Dy_(x)Fe_(2), 0.2 < x < 0.7} in a thermoset polymer resin system; during curing, the material is subjected to a constant magnetic field. The cured MPC, under vibratory loading, dissipates energy through hysteresis due to domain-wall motion within the particles. The material has an uncommon combination of stiffness and damping, with modulus near that of fiberglass and loss factor similar to many rubber formulations, and the material exhibits vibration damping capability over wide temperature and frequency ranges. Challenges for design are the material's load-dependent damping capacity and its low ultimate strength. The MPC damping mechanism is predictable, and a finite element modeling approach was validated by test. Material evaluation was performed with direct measurements of modulus and loss factor. Both composite and monolithic Terfenol samples were built and tested. Measurements of the MPC formulations showed loss factors of up to 0.1 are achievable. Off-stoichiometric samples, with higher levels of Terbium (Tb) content compared to the standard Terfenol composition, were found to have even higher damping, with peak damping observed at Tb 0.5. Loss factors approaching 0.3 were measured in monolithic, off-stoichiometric material samples. The damping is load-dependent, moderately dependent on temperature, and relatively insensitive to loading frequency. A prototype flexure with MPC damping, based on the patented SoftRide design used for whole-spacecraft vibration isolation, was built and tested. Damping and stiffness matched predictions with a finite element model of the MPC-damped SoftRide isolator.