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Novel structure makes foam material crush and shear proof

10 April 2015

UC Santa Barbara materials scientist, Jonathan Berger has developed a structured foam material that resists both crushing and shearing forces.

A 3D-printed model of the foam's cellular structure reveals ordered cells in two basic shapes that contribute to its low density and high stiffness (photo: Sonia Fernandez)

Called Isomax, this material could be easily manufactured and, with fairly minor tweaks, changed to emphasize different properties to function in various ways without sacrificing its structural integrity.

According to Berger, the Isomax foam, in comparison to other similar engineering materials, has the highest stiffness to lightness ratio, resisting crushing and shearing forces that would buckle and flatten denser, heavier materials.

Key to the technology behind Isomax is its geometry. The foam has an ordered topology of regularly occurring cells featuring two basic shapes — the triangle and the cross. Taken into three-dimensional space, the cells look like contiguous pyramids — some with three diagonal faces and a base; or four diagonal faces reinforced with diagonal intersecting 'walls' in their interiors that resemble the insides of wine cases.

Each shape was chosen because of its unique properties. The intersecting walls of the three-dimensional cross shape are ideal for resisting perpendicular crushing forces, while the pyramidal shapes, long known for their stability, resist shearing forces. Combined in a repeating pattern, these cells are made to withstand forces from all directions while maintaining the foam’s low density, making it ideal as a structural material.

“Because it has certain symmetries and alignments and achieves the theoretical bounds for stiffness, there is no other material like it,” claims Berger.

The foam can be used as a functionally graded material, useful in situations in which one part of an object must have different physical properties than another. For instance, a hip replacement must be stiff enough to provide shape and support, while the surface that comes in contact with the pelvis would ideally be soft and flexible enough to allow for weight bearing without grinding away at the socket.

“We can make the walls of the cells thicker and denser at one end and then thinner at the other end,” Berger says. The walls could be removed to leave a lattice structure that could serve as a replacement for knees or other bones that have to provide structure while allowing for blood flow, he added.

Isomax’s low density for its stiffness means that things made from it require less material for the desired amount of strength. Using the material in certain objects, such as vehicles, could make them more energy efficient, and the foam’s regularly repeating cellular structure makes it simple to manufacture and scale to demand.

Isomax is in the early stages of development, but Berger is preparing it for the market through Nama Development, a company he formed with the help of UCSB’s Technology Management Program.


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