Bi-Directional Origami-Inspired SMA Folding Microactuator

Abstract

We present the design, fabrication, and characterization of single and antagonistic SMA microactuators allowing for uni- and bi-directional self-folding of origami-inspired devices, respectively. Test devices consist of two triangular tiles that are interconnected by double-beam-shaped SMA microactuators fabricated from thin SMA foils of 20 µm thickness with memory shapes set to a 180° folding angle. Bi-directional self-folding is achieved by combining two counteracting SMA microactuators. We present a macromodel to describe the engineering stress–strain characteristics of the SMA foil and to perform FEM simulations on the characteristics of self-folding and the corresponding local evolution of phase transformation. Experiments on single-SMA microactuators demonstrate the uni-directional self-folding and tunability of bending angles up to 180°. The finite element simulations qualitatively describe the main features of the observed torque-folding angle characteristics and provide further insights into the angular dependence of the local profiles of the stress and martensite phase fraction. The first antagonistic SMA microactuators reveal bi-directional self-folding in the range of −44° to +40°, which remains well below the predicted limit of ±100°.

Microelectronic Morphogenesis: Smart Materials with Electronics Assembling into Artificial Organisms

“…Additionally, self-folding structures can be introduced into the body in compact forms and then triggered to unfold to perform intricate surgical procedures with minimal invasiveness. [71,72] In the current Perspective, we identify that such folding can now be Figure 2. Architectural encoding of cell units for natural and artificial organisms.…”

“…Additionally, self‐folding structures can be introduced into the body in compact forms and then triggered to unfold to perform intricate surgical procedures with minimal invasiveness. [ 71,72 ] In the current Perspective , we identify that such folding can now be placed under autonomous on‐board electronic control, to create soft structures with programmable flexibility and shapes, which will further expand the boundaries of design and material science toward morphogenetic control.…”

Actuation for flexible and stretchable microdevices

“…Mechanical strain-based actuation utilises mechanical forces to bend, 125 twist, 126 and stretch 47 microdevices to achieve specific functions. Actuation is entirely based on stretching 47 or combining electric fields, [127][128][129][130] magnetic fields, 131 and temperature sources 132,133 to generate displacements and forces.…”

Vectorized MATLAB Implementation of the Incremental Minimization Principle for Rate-Independent Dissipative Solids Using FEM: A Constitutive Model of Shape Memory Alloys

“…The performance of the complete FEM computational tool is now demonstrated in the example of the bending of a beam. Beams manufactured from shape memory alloys have been intensively investigated due to their superb actuation and energy harvesting capabilities [42][43][44]. Although analytical models can be very useful for quick concept validation and preliminary design studies [45][46][47], full-scale FEM simulations are often indispensable in detailed studies [42,44,48,49], since they are not constrained by assumptions on a particular geometry, material response, boundary conditions, etc.…”

“…Beams manufactured from shape memory alloys have been intensively investigated due to their superb actuation and energy harvesting capabilities [42][43][44]. Although analytical models can be very useful for quick concept validation and preliminary design studies [45][46][47], full-scale FEM simulations are often indispensable in detailed studies [42,44,48,49], since they are not constrained by assumptions on a particular geometry, material response, boundary conditions, etc. The simulated problem mimics a simple beam with a rectangular cross-section (with its width being half of the height) loaded at both ends and supported in the middle so that bending is invoked.…”