Development of variable topology programmable surfaces capable of altering their shape, functionality, or mechanical properties in response to change in operational conditions would improve fluid surface interactions, human-computer interactions, and a broad range of mobility applications. Programmable active surfaces and volumes present significant implications for improving energy efficiencies, actuation displacements, and force distribution. Active knits are hierarchical actuation architectures composed of a continuous network of organized loops of shape memory alloy (SMA) wire that generate complex motions and large actuation forces upon thermal actuation. The knit architecture incorporates two unique unit cells- the knit and purl loops, which are distinguished by the position of the ridge on the pattern (rear ridge for knit loop, forward ridge for purl loop). A variety of knit patterns can be created by altering the distribution of knit and purl loops across the wales (columns) and courses (rows) of the structure. The kinematic behavior of SMA knitted structures is affected by adjacent loops (above, below, left, and right) resulting in 16 independent unit cells that define the geometry of the system. This project derives homogenous active knit patterns using unique SMA knitted cross topology elements (KCTE) to study kinematic actuation motions of 2D planar textile surfaces to 3D out of plane topologies.  The design, manufacture and modeling framework of three dimensional, programmable, multifunctional knitted surfaces and volumes that facilitate complex shape changes is introduced. The out-of-plane motion of the surfaces is recorded using Digital Image Correlation (DIC) and Marker Tracking. The effect of each cross-topology element on the acquired shape is then assessed to identify the isolated kinematic behavior of individual KCTE’s. A segment superposition modeling approach is used to develop simple mechanical models for unit cells which are superimposed to predict the global performance of the knitted structures.  Development of a design tool capable of forward and inverse design is introduced to 1) predict the performance and shape changes of KCTE assembled knitted patterns which actuate from planar to 3D forms and 2) enable the synthesis of any desired 3D programmable structure. This research establishes a foundation for a new class of programmable surfaces that exhibit large spatially distributed deformations on actuation as a result of the distinctive design of knitted patterns.


Kinematic Synthesis of Knitted Shape Memory Alloy Programmable Structures

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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