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
This paper focuses on understanding and developing a new approach to dampen MEMS structures using both
experiments and analytical techniques. Thin film Nitinol and thin film Terfenol-D are evaluated as a damping solution
to the micro scale damping problem. Stress induced twin boundary motion in Nitinol is used to passively dampen
potentially damaging vibrations. Magnetic domain wall motion is used to passively dampen vibration in Terfenol-D.
The thin films of Nitinol, Nitinol/Silicon laminates and Nitinol/Terfenol-D/Nickel laminates have been produced using
a sputter deposition process and damping properties have been evaluated. Dynamic testing shows substantial damping
(tan &dgr;) measurable in each case. Nitinol film samples were tested in the Differential Scanning Calorimetry (DSC) to
determine phase transformation temperatures. The twin boundary mechanism by which energy absorption occurs is
present at all points below the Austenite start temperature (approximately 69°C in our film) and therefore allows
damping at cold temperatures where traditional materials fail. Thin film in the NiTi/Si laminate was found to produce
substantially higher damping (tan &dgr; = 0.28) due to the change in loading condition. The NiTi/Si laminate sample was
tested in bending allowing the twin boundaries to be reset by cyclic tensile and compressive loads. The thin film
Terfenol-D in the Nitinol/Terfenol-D/Nickel laminate was shown to produce large damping (tan &dgr; = 0.2). In addition to
fabricating and testing, an analytical model of a heterogeneous layered thin film damping material was developed and
compared to experimental work.
Thin film Nitinol is evaluated for a new damping solution to microscale damping. In this study, thin film Nitinol was mechanically tested under steady and cyclic tensile loads in a DMA Q800 load frame to determine stiffness and hysteric losses (tan δ = 0.17). A method of determining the damping properties of a multilayered laminate was derived and evaluated using measured and predicted values of Nitinol film damping. Hysteretic loss of tan δ = 0.76 was predicted for a tensile/compressive loading of a film indicative of loading in a MEMS structure. Damping in a silicon/Nitinol laminate using the tensile/compressive loading film damping prediction was calculated to be tan δ = 0.127.
Magnetostrictive particulate composites promises to be a revolutionary new damping solution with possible loss factors similar to current viscoelastic systems but coupled with a significantly higher modulus ~ 10GPa. Magnetostrictive particulate composites fabricated from Terfenol-D (TbxDy1-xFe1.92) particles and epoxy resin, were mechanically tested under cyclic compressive loads in an MTS load frame to determine hysteric losses, from which an approximate tanδ was derived to quantify damping performance. DMA results on the same composites corroborated the MTS results. Various off-stoichiometric compositions of Terfenol-D were studied with varying Tb composition of x = 0.35, 0.4, 0.45, 0.5, 0.75 and 1.0. Results indicated better damping with higher Tb compositions peaking at Tb=0.5.
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