Influence of magnetic field, magnetic particle percentages, and particle diameters on the stiffness of magnetorheological fluids

Abstract

Generally, variable stiffness joints of soft robots are generally fabricated using thermoplastics and elastomers due to their ability to change state from rigid to flexible and vice versa. However, these materials require a considerable amount of time to change states and are associated with other technical drawbacks. We demonstrate the instantaneous physical transformation of a Ga-based magnetorheological fluid called Gallistan from a liquid to a viscoelastic solid, and precisely controlled within milliseconds under an applied magnetic field. We studied the magnetic properties of a magnetorheological fluid by dispersing Fe particles in a Ga–In–Sn eutectic alloy. Theoretical analysis of the movement of two particles under magnetic field and typical defects in dipolar chains is studied. The experimental results showed a reversible change in Young’s modulus depending not only on the magnetic field intensity but also the percentage of magnetic particles. Thus, we confirm that the arrangement of magnetic particles transition from random distribution to stable chain structures in the magnetic field. Based on the bi-material nested cantilever beam, the variable stiffness joints can also be precisely adjusted under a magnetic field. In future, this property of the magnetorheological fluid will help develop a variable stiffness joint for soft robotics.