Looking for a material

Hi Everyone,

This bord has been very helpful to me in the past for identifying materials. This time, I have a really tough one!

I am looking for a material to make a flexible, impact resistant rod out of. The approximate dimensions of the rod are 2- 5 mm (.08-.2") diameter, and about 300 mm (12") long. The rod will have to support a load, no more than a small set of keys. The problem is that the rod will be positioned in a place where it can easily be run into by other objects and therefore can easily be damaged.

Here are the materials I have tried so far:
Carbon fiber: Excellent support for the weight, but not flexible enough.
Fiberglass: Breaks too easily
Nylon: Good impact resistance, but not rigid enough to hold the weight.
Stainless steel: Too rigid

If any of you guys have any ideas of materials/ composites I could try, I would love to hear from you.

Thanks for reading this post!

Sure a SS rod could be used if you find the right thickness. It’s not that rigid if thin. You might poke your eye out though :slight_smile:

Or how about some sort of nylon/TPU?


this site is great for fun materials and experimentation…http://www.inventables.com/

Carbon fiber thinner, spring steel, bamboo. Nylon and almost all thermoplastics will “creep” get lower and lower under the same load.

Metal spring material is the most conventional material used in your application.

Weight-for-weight, tube is “stronger” in torsion than solid rod … a generalization of course; driven by wall thickness, the material itself, etc.

But 5mm is p-r-e-t-t-y small… and with a diameter-to-length ratio of 60:1 you’re asking for a lot, especially if you are also asking it to be able to bend back on itself as you depict in your sketch.

Maybe some kinda plastic like glass filled Delrin or Torlon, but that stuff is expensive. Nxakt 's spring steel sounds like a good idea but maybe put some sleeve tubing on the outside, I dunno :confused: .

  • 1 Spring steel…

If carbon is too stiff and fiberglass not strong enough, have you tried Kevlar?

If it can easily be run into by other objects, you may want to coat it with a rubber or something so that neither the impacter nor impactee get hurt (im thinking dip molding or a rubber sheath?)

Regarding the material, I agree with steel. However depending on the potential for corrosion (or surface scratches if you decide not to cover it with an elastomer), you may want to go towards a stainless variety instead of spring steel.

google ‘300 vs 400 stainless steel’ or ‘austentic vs martensitic stainless steel’ to dig in more.

Yes, aside from material selection you should consider optimizing rod cross section shape or extrusion profile. ‘I’ beam, ‘T’ shape or ‘star’ type pattern can provide rigidity you need in a flexible material. Co-extrusion - plastic over metal substrate - is also an option.

I’d agree with Earthman. If stainless steel is too rigid and nylon is too soft, I’d try a glass-filled nylon. Should stiffen the nylon by up to a factor of 2.

Hi Everyone,

Thanks for all the help! I have just laid up a fiberglass/carbon composite that seems to be working quite well.

You guys are definitely right. We have found that the shape is equally, if not more important than the material to control the bend characteristics.

Once again, thanks everyone for the help!

McMaster-Carr offers “spring-back” stainless steel wire in 12" lengths in variety of diameters (not sure which one you’d need to support the weight).

Here’s a link: McMaster-Carr