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.

中文翻译：

---

磁场、磁性粒子百分比和粒子直径对磁流变流体刚度的影响

通常，软机器人的可变刚度关节通常使用热塑性塑料和弹性体制造，因为它们能够将状态从刚性变为柔性，反之亦然。然而，这些材料需要相当长的时间来改变状态，并且还存在其他技术缺陷。我们展示了一种名为 Gallistan 的基于 Ga 的磁流变流体从液体到粘弹性固体的瞬时物理转变，并在施加的磁场下在几毫秒内精确控制。我们通过将 Fe 颗粒分散在 Ga-In-Sn 共晶合金中来研究磁流变流体的磁性能。研究了磁场下两个粒子的运动和偶极链中典型缺陷的理论分析。实验结果表明，杨氏模量的可逆变化不仅取决于磁场强度，还取决于磁性颗粒的百分比。因此，我们确认磁性粒子的排列从磁场中的随机分布转变为稳定的链结构。基于双材料嵌套悬臂梁，变刚度接头也可以在磁场下进行精确调整。将来，磁流变流体的这种特性将有助于开发用于软机器人的可变刚度关节。基于双材料嵌套悬臂梁，变刚度接头也可以在磁场下进行精确调整。将来，磁流变流体的这种特性将有助于开发用于软机器人的可变刚度关节。基于双材料嵌套悬臂梁，变刚度接头也可以在磁场下进行精确调整。将来，磁流变流体的这种特性将有助于开发用于软机器人的可变刚度关节。