Magnetic-field-induced bending and straining of Ni–Mn–Ga single crystal beams with high aspect ratios

Abstract

a b s t r a c tSmall monocrystalline beams of the magnetic shape-memory alloy (MSMA) Ni-Mn-Ga, with a square 1Â1 mm 2 cross section and length between 2 and 10 mm, with the 10M martensite structure and all faces parallel to {100}, were subjected to rotating magnetic fields while being held at one end. The beams deform by both magnetic-field-induced straining (MFIS) and magnetic-torque-induced bending (MTIB), in directions parallel and perpendicular to the beam's longitudinal axis, respectively. With the field parallel to the beam axis, the beams were straight and short. Upon field rotation, the beam elongated and bent in the direction of the field. When the field reached 90°, the beam deflected rapidly and took a bent shape oriented in the opposite direction. Upon further field rotation, bending strain and axial strain decreased until the beam was short and straight again with the field at 180°. With an increase in beam aspect ratio, the bending component increases while the total axial strain remains constant. MTIB -a natural but so far neglected response of long MSMA samples exposed to a transversal magnetic fieldoccurs during switching of current linear (one-dimensional) actuators, thus causing friction losses, wear, and fatigue. However, MTIB provides the opportunity to actuate high aspect ratio MSMA continuously and smoothly in all directions (in three dimensions), thus mimicking slender biological actuating structures such as microorganism flagella tails and fins of fish, heart valves, leaves and petals of plants, and wings of birds or insects.

Localized deformation in Ni-Mn-Ga single crystals

“…1 Exhibiting magnetic field induced strains of up to 12%, 2 Ni-Mn-Ga is a promising material for use as the active element in actuating devices. [3][4][5][6][7][8] Ni-Mn-Ga's shape change is accommodated by growth, through twin boundary motion, of martensite variants preferentially aligned with the applied magnetic field. The twinning stress necessary to initiate magnetic field induced twin boundary movement in Ni-Mn-Ga has been shown to be as low as 0.05 MPa.…”

Ni–Mn–Ga Single Crystal Exhibiting Multiple Magnetic Shape Memory Effects

“…Preparing suitable twin structure can be challenging in bulk but it seems nearly impossible for thin films. The domain engineering must solve how to form and modify twin boundary pattern for given purpose/applications (actuating, damping, shape morphing [46,47], energy harvesting [17] and similar). This is particularly challenging for miniaturization.…”

Superelasticity by reversible variants reorientation in a Ni–Mn–Ga microwire with bamboo grains

“…A 1 T magnetic field caused the wire to bend to a surface strain of 1.5%, and during field rotation, the wire deflected back and forth by reversible twinning, an effect called magnetic-torque-induced bending (MTIB). Further investigation of the relative importance of MFIS and MTIB has been recently carried out in monocrystalline, martensitic Ni-Mn-Ga beams (with a square 1 Â 1 mm 2 cross section and length varying between 2 and 10 mm) subjected to a rotating magnetic field [22].…”