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  • 1
    Electronic Resource
    Electronic Resource
    Large field induced strain in single crystalline Ni–Mn–Ga ferromagnetic shape memory alloy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5774-5776 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A room temperature free shear strain of 5.7% is reported in a single crystal of Ni–Mn–Ga having a composition close to the Heusler alloy Ni2MnGa. A twin boundary was created in a 2 mm×2 mm×25 mm single crystal using a permanent magnet with surface field strength of about 320 000 A/m. A sharp 6.5° bend occurs in the sample at the twin boundary. The surface magnetization changes abruptly across this boundary. By moving the sample relative to the edge of the magnet, we were able to sweep the boundary back and forth along the crystal length. Surface magnetization was measured using a Hall probe and the results confirm that the easy axis is the tetragonal c axis. Powder x-ray diffraction shows that the fcc to body-centered-tetragonal bct martensitic transition of this material involved a 6% reduction of the bct cell c/a ratio, from (square root of 2) to about 1.33. The maximum achievable strain is thus estimated to be 6.2%. The twin planes in the system are the {112}bct and were observed to lie almost normal to the long axis of the sample tested. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372518
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  • 2
    Electronic Resource
    Electronic Resource
    Model for discontinuous actuation of ferromagnetic shape memory alloy under stress (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1295-1301 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic shape memory alloys have demonstrated strains up to 5% resulting from the rearrangement of crystallographic variants by twin boundary motion under an applied field. A model is proposed that describes twin boundaries moving abruptly in order to accommodate either the mechanical energy of an applied stress σε0 or the magnetic interaction energy of the applied field MsH. This model provides predictions of the materials response under both field and load. The principal conclusion of the model is that when one energy, either mechanical or magnetic, becomes larger than the other, the twins will move to abruptly rearrange the entire sample to a variant stable under the new condition. Experiments were performed to verify this model in Ni–Mn–Ga shape memory alloy. The abrupt change of the variant structure was observed experimentally although the twin boundaries only swept through limited potions of the sample. Experimental field-induced strains reached 2.2%. Samples were also tested under cycled field with constant load and showed cyclic strains of 1.5%. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1285867
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  • 3
    Electronic Resource
    Electronic Resource
    Phenomenology of giant magnetic-field-induced strain in ferromagnetic shape-memory materials (invited) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4712-4717 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic shape-memory alloys have recently emerged as a new class of active materials showing very large magnetic-field-induced extensional strains. Recently, a single crystal of a tetragonally distorted Heusler alloy in the NiMnGa system has shown a 5% shear strain at room temperature in a field of 4 kOe. The magnetic and crystallographic aspects of the twin-boundary motion responsible for this effect are described. Ferromagnetic shape-memory alloys strain by virtue of the motion of the boundaries separating adjacent twin variants. The twin-boundary motion is driven by the Zeeman energy difference between the adjacent twins due to their nearly orthogonal magnetic easy axes and large magnetocrystalline anisotropy. The twin boundary constitutes a nearly 90° domain wall. Essentially, twin-boundary motion shorts out the more difficult magnetization rotation process. The field and stress dependence of the strain are reasonably well accounted for by minimization of a simple free energy expression including Zeeman energy, magnetic anisotropy energy, internal elastic energy, and external stress. Models indicate the limits to the magnitude of the field-induced strain and point to the material parameters that make the effect possible. The field-induced strain in ferromagnetic shape-memory alloys is contrasted with the more familiar phenomenon of magnetostriction. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373136
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  • 4
    Electronic Resource
    Electronic Resource
    Field-induced strain under load in Ni–Mn–Ga magnetic shape memory materials : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7297-7299 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-crystal Ni2MnGa shows a nearly 0.2% strain under a magnetic field of 8 kOe at −8 °C. Polycrystalline samples have been prepared near stoichiometry to study the composition dependence of the magnetic and elastic properties. A narrow band of compositions has been found having a range of Curie and martensitic transformation temperatures, Tc and T0, extending to above room temperature. The compressive stress–strain characteristics in variable transverse field were studied in samples selected to have T0 just below room temperature. Stress-induced martensite was observed as expected and the magnetic field was applied under fixed load for various stresses. A transverse field of 3200 Oe caused the sample to strain under load doing work that increased up to 1.3 J/kg with increasing volume fraction of stress-induced martensite. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367758
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  • 5
    Electronic Resource
    Electronic Resource
    6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni–Mn–Ga (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 886-888 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Field-induced strains of 6% are reported in ferromagnetic Ni–Mn–Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1306635
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  • 6
    Electronic Resource
    Electronic Resource
    Physiological changes in women during exercise in cold environments (1986)
    Springer
    International journal of biometeorology 30 (1986), S. 301-306 
    Details
    ISSN: 1432-1254
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract Both the stress of exercise and the stress of a cold environment have been shown to increase the mobilization and utilization of body fat, thereby reducing body fat stores. Much of the research has been done on either rats or male human subjects. The purpose of this research was to show the physiological changes which occur to young, relatively obese, women who exercised during five consecutive days, for 200 min per day, in each of three environmental, chamber conditions: (1) warm-warm (WW), +15
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02189365
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of cold stress and exercise on fat loss in females (1986)
    Springer
    European journal of applied physiology 55 (1986), S. 610-618 
    Details
    ISSN: 1439-6327
    Keywords: Cold stress and exercise ; Women and cold stress ; Fat loss in cold
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A Latin Square design has been used to test the responses of 24 relatively fit young women to 200 minute bouts of exercise performed over 5 day trials under each of three different ambient conditions: (i) 15
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00423205
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