>> “Magnetomechanical characterization and unified energy model for quasistatic behavior of ferromagnetic shape memory Ni-Mn-Ga” appeared in Smart Materials and Structures

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This paper presents an overview of the characterization and modeling of single crystal ferromagnetic shape memory Ni–Mn–Ga. A continuum thermodynamics model is presented which describes the magnetomechanical characterization of single crystal Ni–Mn–Ga for the following behavior: (i) sensing effect; (ii) actuation effect; (iii) blocked force (stress generation). The thermodynamic potentials, namely the magnetic Gibbs energy and the Gibbs energy, are obtained from the Helmholtz energy in order to arrive at the set of required independent and dependent variables; the potentials include magnetic energy consisting of Zeeman, magnetostatic and anisotropy components, and mechanical energy consisting of elastic and twinning components. Mechanical dissipation and the microstructure of Ni–Mn–Ga are incorporated in the continuum model through the internal state variables volume fraction, domain fraction, and magnetization rotation angle. The constitutive response of the material is obtained by restricting the process through the second law of thermodynamics. The model requires only seven parameters identified from two simple experiments. Several interesting characteristics of Ni–Mn–Ga are examined in concert with the magnetomechanical characterization.

 

N.N. SARAWATE and M.J. Dapino, “Magnetomechanical characterization and unified energy model for quasistatic behavior of ferromagnetic shape memory Ni-Mn-Ga,” Smart Materials and Structures, Vol. 19, 035001, 22 January 2010.

>> “Dynamic model for a displacement amplified magnetostrictive driver for active powertrain mounts” appeared in Smart Materials and Structures

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A magnetostrictive actuator with a hydraulic displacement amplification mechanism is designed to be used as a driver in active engine mounts. The dynamic response of the actuator is quantified in terms of the output displacement and the magnetostriction. Eddy current losses are modeled as a one-dimensional magnetic diffusion problem in cylindrical coordinates. The Jiles–Atherton model is used to describe the magnetization state of the material as a function of applied magnetic fields. Magnetostriction, which is modeled as a single-valued function of magnetization, provides an input to the mechanical model describing the system vibrations. Friction at the elastomeric seals is modeled using the LuGre (Lund–Grenoble) friction model for lubricated contacts. Results show that the model accurately describes the dynamic behavior of the actuator up to 500 Hz. An order analysis of the data and calculated responses shows that the model describes the fundamental and higher-order spectral components generated by the device.

 

S. CHAKRABARTI and M.J. Dapino, “Dynamic model for a displacement amplified magnetostrictive driver for active powertrain mounts,” Smart Materials and Structures, Vol. 19, 055009, 2010.

>> “Dependence of magnetic susceptibility on stress in textured polycrystalline Fe81.6Ga18.4 and Fe79.1Ga20.9 Galfenol alloys” appeared in Applied Physics Letters

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Magnetization and magnetostriction measurements in constant tension and compression as a function of applied magnetic field are reported for ⟨100⟩ oriented, textured polycrystalline Fe81.6Ga18.4 and Fe79.1Ga20.9 Galfenol alloys. The susceptibility change with stress, or sensitivity, is maximum at zero field for both alloys. The greatest sensitivity is observed for the 18.4 at. % Ga alloy between −10 and +20 MPa, where domain wall motion dominates. The sensitivity is greater for the 20.9 at. % Ga alloy than for the 18.4 at. % Ga alloy below −15 MPa (domain rotation region). The difference in behavior is attributed to a difference in the anisotropy coefficient.

 

A. MAHADEVAN, P. EVANS, and M.J. Dapino, “Dependence of magnetic susceptibility on stress in textured polycrystalline Fe81.6Ga18.4 and Fe79.1Ga20.9 Galfenol alloys,” Applied Physics Letters, Vol. 96, Issue 1, 012502, 5 January 2010.