Rigid Flexibility?

Let me clear up this apparent oxymoron. While developing an automated sun screening system there are many additional factors we must contend with, including high wind loads. The first and maybe most obvious option is to scale up the material thickness while keeping the same ration between materials. Unfortunately, we have found that this does not result in a scaled up or equivalent deflection, rather it dramatically reduces the movement. When asking how we could potentially increase the systems resistance to wind loads while still maintaining the required amount of deflection, I have turned to the light weight expanded  aluminum  hexagon core that Rigidized Metals uses in some of their products.

I originally saw potential for the implementation of this hex-core as a way to increase the panel depth  (and its rigidity) while keeping weight to a minimum and allowing for flexibility.

The first investigation utilized the hex-core for its depth, simply sandwiching it between the plastic and steel. The result was an incredibly rigid panel, even when heated. A few more tests sought to manipulate the hex-core by cutting away portions of the material to create a directional weakness while maintaining the overall rigidity. These test too remained static.

The second set of investigations allowed the hex-core to become the “control” material, replacing the metal sheet and resulting in an open faced panel. These panels more closely achieved the ratio of flexibility to rigidity that I have been seeking. When tested, none of them met our quantitative expectations for deflection. The greatest performance came from the thinnest hex-core with the largest cell size. This Hex-core uses less than half of the amount of metal as the previous 1 to 1 plastic to steel lamination while providing more rigidity.

A potential reason for the lesser deflection could be because the hex core is made out of aluminum  which has a much higher  linear coefficient of expansion, hindering its performance as a control material.

The third set of investigations introduced a new material that brought with it a new method of adhesion between the two materials; A pourable plastic that hardens in minutes. We hoped that in addition to the expanding layer of plastic on the edge of the hex-core, the plastic that entered into the bottom of each hexagon would result in numerous small local reactions that complimented and enhanced the global response. These poured panels exhibited minimal deflection however.

As promised, Eric Echert, has provided me with four different adhesive samples from one of his main vendors, 3M.  After much discussion these four different adhesives were deemed most appropriate for our use and the flexibility required.

I have laminated 5 new uniform strips (one being the traditional epoxy I have been using) to be tested side by side, allowing me to compare their reactionary performance when heated.

The recent results remain puzzling however as the adhesives provided various results depending on orientation (standing vs Hanging) rather than having one adhesive out performing the rest.

The original butterfly unit that worked surprisingly well and while common sense may suggest to go with what works, the very detailed and time consuming assembly method of this unit leaves a lot to be desired when thinking about the manufacturing process. Not to mention the small inefficiencies of this system that lead to lost kinetic energy during the actuation process. These problems have led to a series of  investigations into a more seamless construction, including attempts at a taped seam and a spray on rubber that creates a single uniform layer on top.

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