looking for a flexible material with memory retention 1

[conneral]

I'm looking for an injection moldable material that is flexible enough to fold easily yet retains memory of its original geometry. i.e. even if it’s stored in the folded position, it should spring back open to the flat position when released. Both Sabic and GLS have told me they don't have any products that will do this.

My problem is, i'm not sure what properties to search for or what values of those properties to search for. I'm a little rusty on the tangible meanings of the different properties. Elastic modulus? Flexural modulus?

any input on material suggestions or search strategies would be greatly appreciated.

 

[Demon3]

I think you will have to explain the part geometry better, i.e. how much folding are you expecting and how many times?

Modulus = stiffness, so it's not that

Yield Strength = force you can apply until it deforms so much it doesn't spring back (closer)

I would say the properties closest to what you need is the elastic limit, i.e. the quasi-linear part of the stress-strain curve. Unfortunately that property is not usually measured or listed but it is normally related to and significantly less than, the yield stress.

If the part will be stored folded for a longer period then creep will become important.

Another way to approach this is to look for an elastomer (rubber) with low compression set (rubber term for creep).



Chris DeArmitt

http://www.phantomplastics.com

Consulting to the plastics industry

 

[patprimmer]

Thermoplastics are subject to cold flow or creep.

The property you are looking for is elastic recovery.

Cross linked plastics perform a lot better re elastic recovery or memory.

Examples are cast polyurethane, vulcanized rubber, cross linkable polyethylene and liquid silicone rubber. The last two are injection mouldable.

Regards
Pat
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[tom1953]

Pat,
Rubber can be injection molded as well (some types more easily than others).
tom

 

[conneral]

thanks for the replies!
Chris, the part is essentially a strap ~7mm wide, 55mm long and 0.8 mm thick. the ends of the strap will be held together most of the time (bend radius no less than 2-3mm). should be good for at least 1000 cycles.

 

[btrueblood]

Sounds like a rubber band.