Magnetic actuation and transition shapes of a bistable spherical cap

Abstract

Multistable shells have been proposed for a variety of applications; however, their actuation is almost exclusively addressed through embedded piezoelectric patches. Additional actuation techniques are needed for applications requiring high strains or where remote actuation is desirable. Part of the reason for the lack of research in this area is the absence of appropriate models describing the detailed deformation and energetics of such shells. This work presents a bistable spherical cap made of iron carbonyl-infused polydimethylsiloxane. The magnetizable structure can be actuated remotely through permanent magnets while the transition is recorded with a high-speed camera. Moreover, the experiment is reproduced in a finite element (FE) dynamic model for comparison with the physical observations. High-speed footage of the physical cap inversion together with the FE modeling gives valuable insight on preferable intermediate geometries. Both methods return similar values for the magnetic field strength required for the snap-through. High-strain multistable spherical cap transformation is demonstrated, based on informed material selection. We discover that non-axisymmetric transition shapes are preferred in intermediate geometries by bistable spherical caps. We develop the methods for design and analysis of such actuators, including the feasibility of remote actuation methods for multistable shells.

Magneto-active elastic shells with tunable buckling strength

“…We envision that our tunable mechanism can be used to gain control on the structural life of a shell, by applying a magnetic field as critical conditions approach. More generally, we believe that the approach of coupling mechanical deformation and magnetic actuation, already successfully applied for beams 33 , 48 , 51 and films 47 , and employed here to tune the knockdown factor of shells, can be extended to modify the instabilities of other structures such as rods, plates, and non-axisymmetric shells 45 , 46 , for which research efforts are currently ongoing. We hope that the principle that we have uncovered will open an axis of tunability in the design of mechanical systems where shell buckling is harnessed as a functional mechanism 59 – 61 , to offer devices with tunable mechanical properties or behavior.…”

Static bistability of spherical caps

“…More recently, structures that are able to switch between two different configurations have attracted interest for applications in which morphing between states is desirable, for example in mechanical metamaterials and origami structures [1,7,14] or in actuators [3]. Various mechanisms have been proposed by which the system may be forced between two stable states including loading via magnetic forces [18,29], fluid flow [2,12,31], changes in lateral confinement [13,11] or, more generally, variations in the natural curvature of a structure [23,24].…”

A Kirchhoff-like theory for hard magnetic rods under three-dimensional geometrically nonlinear deformation

“…The main results of this section are Eqs. (20) and (21), that is the magnetic Kirchhoff rod equations. To arrive at this set of ODEs, in Sec.…”

“…We refer to the set of Eqs. (20) and (21) as the magnetic Kirchhoff rod equations, where the coupling between elasticity and magnetism is captured by p mag and q mag .…”

“…Interestingly, these chains posses an effective bending stiffness [16]. (iv) MREs embedded with soft-ferromagnetic particles or soft magnetic elastomer [1,4,[18][19][20][21][22][23][24][25][26][27] deform upon the application of an external magnetic field due to elasto-magnetic couplings. The magnetic particles with low coercivity dispersed in a soft matrix align themselves with the applied field, thereby forming particle chains.…”