The Effect of Particle Shape on Magnetic Field-Induced Rubber-Like Behavior of Ni-Mn-Ga/Silicone Composites

Abstract

Abstract The single crystalline of the prototype Ni-Mn-Ga ferromagnetic shape memory alloy exhibits a huge magnetic field-induced strain of 6% due to the re-orientation of twin variants. Therefore, it is promising as the magneto-driven actuator material. However, the magnetic field or mechanical stress applied along the orthogonal direction is necessary to restore the deformed bulk single crystal into the original shape. In order to avoid an application of the extra fields, the Ni-Mn-Ga particles/polymer composite is an alternative solution supported by the concept of the accumulated stress in a polymer matrix which drives a deformation recovery of the composite during switching off of the magnetic field. The objective of this study is to clarify the effect of embedded particle shape on the deformation recovery of Ni-Mn-Ga particles/silicone composites by using the finite element method (FEM) and to investigate the local stress distribution in a polymer matrix between either spherical or rectangular shape particles pairs, whereby to provide the guidelines for design/optimization of the magneto-strain-active Ni-Mn-Ga particles/polymer composites. The case studies of the simulation are divided into an isolated particle and a pair of particles, the particles being positioned either parallel or perpendicular to the applied magnetic field direction. Particularly, the simulations reveal that in case of 200 µm of the inter-particle distance in the pair of spherical particles aligned perpendicularly to the applied field, the polymer layer between particles generates the compressive recovery stress of -0.32 MPa, which is insufficient to restore the deformation of the embedded Ni-Mn-Ga particles during removal of the magnetic field. By contrast, the strain recovery effect can be achieved for the rectangular particle pairs, generating the stress concentration in a matrix of about -0.5MPa, in a similar condition and arrangement.