High energy absorption in bulk ferromagnetic shape memory alloys (Ni50Mn29Ga21)

Mechanical testing of a bulk, single-crystal sample of Ni50Mn29Ga21 produced large hysteresis loops indicating the potential for the material to be used as a damper. Damping capacity was measured as a function of energy absorbed by the material relative to the mechanical energy input to the system. Tan 8, the tangent of the phase lag between stress and strain, was calculated and shown to increase as a function of maximum strain level. Five strain levels were evaluated (1%, 2%, 3%, 3.5%, and 3.7%) with tan delta values increasing from 0.6 at 1% strain level to 1.1 at 3.7% strain level. The secant modulus of these curves was also evaluated at each strain level to characterize the sample in terms of both damping and stiffness. The maximum secant modulus of 285 MPa occurred at the 1% strain level and decreased to 56 MPa at 3.7% strain. Examining the stress and strain values in the time domain reveals a varying time lag and thus the reported values for tan delta are considered an average measure of the material's damping capacity.