2023 Create the Future Design Contest: Manufacturing & Materials Finalist

TenseFlatables: 3D-Printed Tensegrity-Assisted Inflatable Structures

William Johnston, Dr. Bhisham Sharma
Michigan Tech University
Houghton, MI

Keeping structures lightweight without adversely affecting their functionality is a major engineering challenge. Inflatables — structures that gain their load-carrying capabilities from pressurized air within a tensioned hyperelastic skin — offer a unique solution to this problem. Although lightweight, inflatables are rarely used for engineering applications because of their inability to meet tight dimensional tolerances or sharp-edged design features.

Current fabrication methods limit inflatable designs to simple, rounded geometries and do not allow the creation of inflatables with complex topological features. The current fabrication method of fusing 2D patterns to achieve 3D post-inflation shapes precludes the fabrication of inflatables with complex post-inflation shapes. Additionally, current inflatables lack the mechanical stiffness requisite for engineering applications.

TenseFlatables solve both these issues while simultaneously simplifying the overall design and fabrication process. Each TenseFlatable has two important components: an external geometry that can be customized by the user and an internal tensegrity architecture that allows the TenseFlatable to achieve high dimensional tolerances while improving its overall load-bearing capabilities. As with traditional inflatables, TenseFlatables can be easily deflated and stowed.

“As aerospace engineers, we are continually seeking ways to decrease structural weight without sacrificing strength,” said Student Team Lead William Johnston. “The idea of TenseFlatables stemmed from our earlier efforts to devise methods for printing thin fibers and impervious hyperelastic membranes for acoustic applications. From this, it was a natural progression for us to use these methods to print lightweight inflatables for structural applications. The idea for an internal tensegrity mesh came as we tried to find ways to make inflatables dimensionally precise and stiff enough for load-bearing applications. Throughout, we focused on using 3D printing because it allows us to consolidate these features into a singular, scalable workflow,” he added.

TenseFlatables are manufactured using a patent-pending method, which uses an extrusion-based additive manufacturing technique to fabricate the flexible, airtight hyperelastic skin and the internal tensegrity mesh within a single workflow. The additive approach is significantly more efficient than the current methods that rely on form-finding complex 2D patterns before fusing them together to achieve 3D post-inflation shapes.

Reliance on an additive technique allows to customize the external shapes as well as the internal tensegrity mesh and achieve application-specific design and performance. The simplification of the design and manufacturing process makes it significantly cost and time efficient, while allowing at-scale and at-rate manufacturing of TenseFlatables via automation.

A major challenge the team faced in design and development was to identify the correct process parameters to reliably print thin skins that remain hyperelastic as well as airtight. “The layer-by-layer technique of the fused filament fabrication process typically results in inter- as well as intra-layer air gaps or porosities. Avoiding these porosities while retaining stretchability is crucial to the fabrication of robust inflatables,” said Johnston. “Another significant challenge was to ensure repeatable fabrication of cylindrical fibers that constitute the internal tensegrity mesh and to achieve a strong fiber-skin interface connection. Eventually, we were able to overcome these challenges, and we can now print complex inflatables that can be optimized to achieve desired mechanical performance,” he added.

TenseFlatables have the potential to significantly outperform conventional inflatables in their form and functionality. The ability to create lightweight structures reliant on pressurized air can enable the design of novel multifunctional technologies for use as automotive, aircraft, and spacecraft components that help reduce fuel consumption. Their deploy-and-stow ability makes them ideal for aerospace and hypersonic deployable supports and decelerators.

According to Johnston, TenseFlatables can revolutionize fields ranging from aerospace to medicine. “Their lightweight, deployable nature is ideal for aerospace components, reducing fuel consumption. Medically, they can enhance procedures like Balloon Kyphoplasty and rotator cuff surgeries. Additionally, when filled with reactive hydrogel, they’re suitable as diagnostic pills for illnesses like cancer. We are also exploring potential naval, architectural uses, and alternatives to air-based systems,” he said.

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