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11 July 2002 AC magnetic-field-induced strain of single-crystal Ni-Mn-Ga
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The dynamic field-induced strain response at 2Hz is reported for a ferromagnetic shape memory alloy (FSMA), Ni49.8Mn28.5Ga21.7. For the d31 actuation mode, longitudinal strain response was measured as a function of longitudinally applied bias stress and transverse applied field. Under a 1.5MPa compressive bias stress, dynamic strains of 2.6% were achieved at fields of 6 kOe. However, dynamic field-induced strain is largely blocked under a compressive bias stress of 4.2MPa. The 'coercive field' hysteresis in the field versus strain loops was observed to be as low as 100kA/m at 1.5MPa and increase linearly at greater stresses. Peak piezomagnetic d31 coefficients measured from these field versus strain loops approached 1.3 X 10-7 m/A. Dynamic stress versus strain loops were recorded for compressive bias stresses from 0 to 4.2MPa. Stiffnesses of approximately 40MPa in the active twinning stress range were recorded, and the stiffness approached 5 times the twinning stiffness beyond the twinning range. The mechanical loss measured in stress versus strain loops, when normalized to the output strain, resulted in a linear increase of 6.84 kJ/m3 per MPa bias stress. Current investigations are attempting to isolate the factors that contribute to the extraordinary behavior exhibited in these properties of the Ni-Mn-Ga system.
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Christopher P. Henry, Jorge Feuchtwanger, David Bono, Robert C. O'Handley, and Samuel M. Allen "AC magnetic-field-induced strain of single-crystal Ni-Mn-Ga", Proc. SPIE 4699, Smart Structures and Materials 2002: Active Materials: Behavior and Mechanics, (11 July 2002);

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