SCIENTIFIC AND APPLIED ASPECTS OF FERROMAGNETIC SHAPE MEMORY ALLOYS

The underlying mechanisms responsible for the giant magnetic or mechanical field-induced-strains in the Ni- Mn-Ga ferromagnetic shape memory alloys are briefly discussed. The fundamental aspect is illustrated by experimental data related to the lattice instability and composition dependence of magnetization alongside literature results. An implementation of Ni-Mn-Ga single crystal as a strain sensor is described

Modeling, Prototyping, and Testing of Helical Shape Memory Compression Springs With Hollow Cross Section

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of mechanical actuation are the low mechanical bandwidth (up to a few Hertzs) and the unsatisfactory stroke (several millimeters). This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with a hollow section. The hollow spring is modeled, then it is constructed, and finally it is tested in compression to compare its performances with those of a spring with a solid cross section of equal stiffness and strength. Emptied of the inefficient material from its center, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less) than its solid counterpart. These results demonstrate that helical springs with a hollow construction can be successfully exploited to build SMA actuators for higher operating frequencies and improved strokes

Modelling, prototype construction and testing of helical shape memory springs with hollow cross-section

Shape memory alloys (SMAs) are used in many applications as actuators. The main drawbacks that limit the use of the SMAs in the field of micro-actuation are the low bandwidth and the unsatisfactory stroke. This paper contributes to enhancing the performances of SMA actuators by proposing a new SMA helical spring with hollow section. The hollow spring is modelled, then it is constructed and finally it is tested, comparing its performances with those of a spring with solid cross-section of equal stiffness and strength. Emptied of the inefficient material from its centre, the hollow spring features a lower mass (37% less) and an extremely lower cooling time (four times less). These results demonstrate that helical springs with hollow construction can be successfully exploited to realize SMA actuators with high bandwidth and stroke. Copyright © 2009 by ASME

Properties of Sputter-Deposited Ni–Mn–Ga Thin Films

Sub-micrometer Ni–Mn–Ga films on MgO(0 0 1) single-crystalline wafers have been prepared by radio-frequency magnetron sputtering. The structural and magnetic states of the as-received (quasi-amorphous phase) and annealed (highly ordered martensitic phase at T = 300 K) films have been examined by X-ray diffraction, and measurements of resistivity and magnetization. The annealed films demonstrate a transformation behavior typical for the bulk and show a thickness dependence of the magnetic properties