This image shows the self-folding process of smart shape-memory materials with slightly different responses to heat. Using materials that fold at slightly different rates is important to ensure that the components do not interfere with one another during the process. Credit: Credit: Qi Laboratory, Georgia Tech
Using components made from smart shape-memory materials with slightly different responses to heat, researchers have demonstrated 4D printing technology that allowed creation of complex self-folding structures. The technology, from Georgia Institute of Technology and Singapore University of Technology and Design (SUTD), could be used to create 3D structures that sequentially fold themselves from components that had been flat or rolled into a tube for shipment. The components could respond to stimuli such as temperature, moisture or light in a way that is precisely timed to create space structures, deployable medical devices, robots, toys and range of other structures.
The researchers used smart shape memory polymers (SMPs) with the ability to remember one shape and change to another programmed shape when uniform heat is applied. The ability to create objects that change shape in a controlled sequence over time is enabled by printing multiple materials with different dynamic mechanical properties in prescribed patterns throughout the 3D object. When these components are then heated, each SMP responds at a different rate to change its shape, depending on its own internal clock. By carefully timing these changes, 3-D objects can be programmed to self-assemble.
The patterning, done with a 3-D printer, allows the resulting flat components to have varying temporal response to the same stimuli. Examples included a mechanism that can be switched from a flat strip into a locked configuration as one end controllably bends and threads itself through a keyhole. They also demonstrated a flat sheet that can fold itself into a 3-D box with interlocking flaps. These examples all require the precise control of the folding sequence of different parts of the structure to avoid collisions of the components during folding.
“We have exploited the ability to 3D print smart polymers and integrate as many as 10 different materials precisely into a 3D structure,” said Prof Martin L. Dunn. “We are now extending this concept of digital SMPs to enable printing of SMPs with dynamic mechanical properties that vary continuously in 3-D space.”
“An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding,” the researchers said in their paper. “A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.”
APPS:eg unmanned air vehicle might change shape from one designed for a cruise mission to one designed for a dive; 3-D components designed to fold flat or be rolled up into tubes so they could be easily transported, and then later deformed into their intended 3-D configuration for use. http://www.news.gatech.edu/2015/09/21/4-d-technology-allows-self-folding-complex-objects
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