Shape Memory Alloys (SMA)
by Fawn
by Shan Gao, Fangbing Qiu, Woong Ki Sung
Programmable Material
A material whose properties can be programmed to achieve specific shapes or stiffnesses upon command.
Planning phase
generating creasing patterns
Optimal Planning Multi Shape Algorithm
Fabrication phase
-materialize plans with three main parts: composite sheet, thin-foil actuators and flexible electronics
Composite Sheets
- A single sheet of sixteen-layer E-glass fiber impregnated with RS-30 resin
- Has high strength, light weight, ease of machinability, material compatibility with silicone-based elastomers
- The composite cured at 140C for 4 hours
- Magnets are used to create the potential wells
- Elastomeric joints : RTV-2 GI-1100 ( need to stretch and bend)
Thin foil actuators
The researchers used (100 μm) foil Nitinol shape memory alloy (SMA) for the actuator material. The planform geometry is formed with a pulsed ultraviolet laser micromachining system. The micromachined foil is tinned, fixed in a jig to hold a desired (folded) shape, and annealed at 420° C for 30 min. This annealing process resets the undeformed martensitic state such that when unfolded, the actuator will “remember” its folded shape when heated above its transition temperature of 70° C
- Should be low profile, simple to assemble, and easy to make for mass production
- Thin fold Nitinol shape memory alloy
- 100um thick
- Annealed at 420C for 30 min to hold a desired shape
- It remember its desired shape when heated above its transition temperature of 70C
Stretchable electronics
- Bridging the elastomer flexure creases
- Should be able to bend and stretch
- The connectors are micromachined from a sheet of copper-laminated polyimide
- All actuators are grouped according to the crease plan, and each group is actuated sequentially
Limitations
- Actuator size and torque considerations
- Inability to move back to the initial flat form
- Control and coordination constraints for multiple actuators
- A finite set of shapes
Improvement
- Bidirectional actuation at each joint
- Modification of creasing patterns and the material resolution
Applications
Animated Lamps
The one above is designed by Romolo Stanco and the below was designed by a Japanese design group, Nendo. It uses shape-memory alloys to change the shape of the lamp when the lamp is on. The change is initiated with heat from the light bulb.
“Oricalco” shirt with Nitinol fabric
The sleeves fabric could be programmed to shorten immediately as the room temperature became a few degree hotter. The fabric can be screwed up into a hard ball, pleated and creased then just by a flux of hot air (even a hairdyer) pop back automatically to its former shape.
Octopus-like Soft-Robotic-Arm Freely Moving in water
Basically composed of silicone, driven by cables and shape memory alloys
See the video here:
Octopus-like Robotic Arm grasping Human Hand.avi
Suppliers
Shape memory alloys are widely available to consumers. Nickel-titanium (nitinol) alloys have been found to be the most useful of all SMAs and can be easily purchased online. Other shape memory alloys include copper-aluminum-nickel, copper-zinc-aluminum, and iron- manganese-silicon alloys. There are no hazardous health risks associated with using this material.
There are several websites where you can obtain SMA for your projects inexpensively.