# Looking for a certain flexible material

1. Feb 19, 2016

### Infinitybyzero

I'm working on making a little gadget for myself and am in need of a material that meets the following criteria:

1) non toxic
2) can double over on itself and return to it's original position*
3) rigid enough to avoid plastic deformation at maximum design deflection*
4) can be obtained in "sheet form" in which many of the same sized pieces can be cut

*the ratio of (distance from bending edge to fold)/(material thickness) would be, at the very highest, 100. For example, if you folded an (0.1mm thick) 8.5x11 sheet of paper into a 8.5x5.5 pamphlet, the ratio I'm describing is (5.5*25.4)/.1 = 1,400.

Anyways, I would like some suggestions for materials that are linearly elastic within the criteria.

Thanks!

2. Feb 19, 2016

### Staff: Mentor

How sharp does the bend have to be?
Paper would satisfy the criteria easily if the bending radius (or even the circumference) can be 100 times the thickness.

Any other requirements, like forces involved?

3. Feb 19, 2016

### Infinitybyzero

It needs to be very durable and springy. Some forms of sheet metal would probably work, but I don't think that's the type of material I'm looking for. It needs to be able to return to a perfectly flat surface, even after thousands of times bent from flat to the configuration below.

4. Feb 19, 2016

### rbelli1

Nitnol is one of the most bendy materials that fit your description that I can think of and that needs about 20T radius. Could you join two sheets together with some sort of elastomer?

BoB

5. Feb 19, 2016

### Infinitybyzero

I certainly could, but then it comes down to how thin can I tangibly get the sheet. It could be as thin as 1/32" but I'm not sure. I'm looking for it to be bendable by hand, but not so much that you could easily accidentally bend it too far (hence safely elastic doubled over).

6. Feb 20, 2016

Staff Emeritus
A bend radius of 2T is very, very, very small. I doubt this is possible. You are talking strains in the neighborhood of 1.2.

7. Feb 20, 2016

### rbelli1

What is the application?

BoB

8. Feb 20, 2016

### Infinitybyzero

Flexible surface cleaner. I know the first thought is "why not just use a cloth or rag"? Well, the rigidity is of paramount importance to my application.

If we assume I need a thickness T, could I do two layers of, say 0.4T with a 0.2T elastomer between them, like recommended?

9. Feb 20, 2016

### rbelli1

10. Feb 20, 2016

### Infinitybyzero

Not quite the right application. Sorry, I'm being intentionally vague because there's a very specific application I'm looking at and might monetize it later.

The entire material needs to be flexible, not just two plates attached by an elastomer hinge. While that does solve the issue I'm looking at, I'm pretty sure the specific functionality I'm looking for goes away.

11. Feb 20, 2016

### rbelli1

It seems that the material you are looking for has two properties that are in direct opposition to each other.

If you made a thin plastic pillow you could deflate it for folded storage and then lay it flat and re-inflate it for use. The surface would not be flat as there would be a dimple at each place the two surfaces were bonded together. Think inflatable mattress. Would that work?

BoB

12. Feb 22, 2016

### Infinitybyzero

I understand what you're saying, but what would you think about this? Could I make a springy enough elastomer hinge to create the range of motion I need (shown below)?

13. Feb 22, 2016

### rbelli1

Yes. That is what I was suggesting with the hinge. You would get it to lie flat with both panels' surfaces touching if the shape of the hinge was designed correctly. If you went with minimal hinge material then the far edge would touch and the hinge would bulge slightly holding the panels at a small angle.

BoB