A Theoretical Study on the Transient Morphing of Linear Poroelastic Plates

Based on their shape-shifting capabilities, soft active materials have enabled new possibilities for the engineering of sensing and actuation devices. While the relation between active strains and emergent equilibrium shapes has been fully characterized, the transient morphing of thin structures is a rather unexplored topic. Here, we focus on polymer gel plates and derive a reduced linear model to study their time-dependent response to changes in the fluid environment. We show that independent control of stretching and bending deformations in stress-free conditions allows to realize spherical shapes with prescribed geometry of the mid-plane. Furthermore, we demonstrate that tensile (compressive) membrane stresses delay (accelerate) swelling-induced shape transitions compared to the stress-free evolution. We believe that these effects should be considered for the accurate design of smart systems and may contribute to explain the complexity of natural shapes.

Micromechanics Study on Actuation Efficiency of Hard-Magnetic Soft Active Materials

Hard-magnetic soft active materials have drawn significant research interest in recent years due to their advantages of untethered, rapid and reversible actuation, and large shape change. These materials are typically fabricated by embedding hard-magnetic particles in a soft matrix. Since the actuation is achieved by transferring the microtorques generated on the magnetic particles by the applied magnetic field to the soft matrix, the actuation depends on the interactions between the magnetic particles and the soft matrix. In this paper, we investigate how such interactions can affect the actuation efficiency by using a micromechanics approach through the representative volume element simulations. The micromechanics reveals that particle rotations play an essential role in determining the actuation efficiency, i.e., the torque transmission efficiency. In particular, a larger local particle rotation in the matrix would reduce the effective actuation efficiency. Micromechanics simulations further show that the efficiency of the torque transmission from the particles to the matrix depends on the particle volume fraction, the matrix modulus, the applied magnetic field strength, as well as the particle shape. Based on the micromechanics simulations, a simple theoretical model is developed to correlate the torque transmission efficiency with the particle volume fraction, the matrix modulus, as well as the applied magnetic field strength. We anticipate this study on the actuation efficiency of hard-magnetic soft active materials would provide optimization and design guidance to the parameter determination for the material fabrication for different applications.

Electromechanical Control and Stability Analysis of a Soft Swim-Bladder Robot Driven by Dielectric Elastomer

Compared to the conventional rigid robots, the soft robots driven by soft active materials possess unique advantages with their high adaptability in field exploration and seamless interaction with human. As one type of soft robot, soft aquatic robots play important roles in the application of ocean exploration and engineering. However, the soft robots still face grand challenges, such as high mobility, environmental tolerance, and accurate control. Here, we design a soft robot with a fully integrated onboard system including power and wireless communication. Without any motor, dielectric elastomer (DE) membrane with a balloonlike shape in the soft robot can deform with large actuation, changing the total volume and buoyant force of the robot. With the help of pressure sensor, the robot can move to and stabilize at a designated depth by a closed-loop control. The performance of the robot has been investigated both experimentally and theoretically. Numerical results from the analysis agree well with the results from the experiments. The mechanisms of actuation and control may guide the further design of soft robot and smart devices.