[{"type":"speech","title":"A thermo-magneto-mechanical free energy model for Ni-Mn-Ga single crystals","issued":{"date-parts":[["2007"]]},"author":[{"family":"Morrison","given":"P."},{"family":"Seelecke","given":"S."},{"family":"Krevet","given":"B."},{"family":"Kohl","given":"M."}],"note":"Materials Research Society Fall Meeting, Boston, Mass., November 26-30, 2007","abstract":"A Thermo-Magneto-Mechanical Free Energy Model for NiMnGa Single Crystals. Phillip\nMorrison1, Stefan Seelecke1, Berthold Krevet2 and Manfred Kohl2; 1Department of\nMechanical and Aerospace Engineering, North Carolina State University, Raleigh, North\nGermany.\nThe paper extends the authors\u2019 recent model for one-dimensional rate-dependent magnetomechanical behavior of NiMnGa single crystals to account for temperature-dependent effects\nincluding austenite\/martensite and ferro-\/paramagnetic phase transitions. The magnetomechanical model consists of a constitutive Helmholtz free-energy landscape constructed for\na meso-scale lattice element with strain and magnetization as order parameters. This twodimensional energy landscape includes three paraboloidal wells representing the two easyaxis and one hard-axis martensite variants relevant for the one-dimensional case. Phase\ntransformations resulting from applied stresses and magnetic fields follow from a system of\nevolution laws based on the Gibbs free energy equations and the theory of thermallyactivated processes. The phase fractions subsequently determine the macroscopic strain\nand magnetization of a sample of NiMnGa by a standard averaging procedure. To account\nfor phase transitions to austenite, additional wells representing the stable states of austenitic\nNiMnGa are added to the Helmholtz energy landscape. The transition from ferromagnetic to\nparamagnetic states is modeled as a second-order transformation. The temperature\nevolution of the sample follows from an energy balance equation, incorporating joule heating,\nheat transfer with the environment, and latent heats of transition between martensite and\naustenite, thus accounting for a full thermo-magneto-mechanical coupling.","kit-publication-id":"230070566"}]