Shock-absorbent material?

[elementcollector1]

I'm wondering how best to make a material, say a thin bar, that has very good shock-absorbing properties and low mechanical stress. I was thinking a layered mix of fiberglass and carbon fiber, bound together by resin, and I was wondering what some more experienced engineers would think of this.

[Externet]

Search for sorbothane products. Their main site has some and applications too.

[elementcollector1]

Not quite what I had in mind, but it'll work very well nonetheless.

EDIT: Checked the site, and I would have to call for pricing nonetheless. Where do you order this stuff cheap? There must be some sort of Chinese manufacturer somewhere... Everywhere I look a 12"-12"-1/8" sheet is around $25 at the cheapest!

 

Back to my original question: Just how shock-resistant is a mixed-layer composite of fiberglass, carbon fiber and resin? Would it be better in terms of absorbance to just use one or the other? Does the resin factor in?

Edited August 29, 2013 by elementcollector1

[Externet]

From experience, it is a product that perfoms. If its price is justified, depends on your application you did not expose.

 

Sheets of different dimensions show at ----> http://www.ebay.com/bhp/sorbothane-sheet ; but you never mentioned size you want.

 

Plain consumer insoles of gel or sorbothane seem more expensive than sheets. Shock "resistant" and shock absorbent are different animals, and simple to do a test, with the materials you mention, or a sandwich of those fancy gels. A plain lead bar can do wonders too.

[elementcollector1]

My application is an experiment to see if this stuff will cushion shock to an appreciable level while being dropped from different heights. For example, if I were to wrap an egg in a quarter-inch thick layer so that the egg couldn't move on its own, and dropped the setup from 50 feet up, I would hope that the egg remains intact. If this works, I'd like to see if this applies to humans, e.g. if a human could survive falling from higher distances with a thick pad of this stuff and a few other bracers on.

 

This is why I mentioned the carbon-fiber/fiberglass setup - my hope is that this would be a sort of leg brace that would also absorb the shock (there might be pads of sorbothane on this as well). I was inspired by the carbon-fiber flat pieces that are attached to an amputated leg - apparently with two of these, humans can jump/fall 15/20 feet and not be hurt.

 

My best bet right now would be to conserve on the sorbothane until it's only where it's needed, and instead place rubber padding everywhere else.

[Enthalpy]

Carbon fibre is exactly what one should avoid to absorb shocks. Glass fibres aren't good neither. You might try aramide fibres, but they're good only to spread a very local impact as a bullet-proof vest.

 

The real material to absorb shocks is polyurethane. Most resistant, little rebound. If for some reason its shape does not fit you need, you may try a polyamide rope, but it absorbs only one shock through irreversible strain.

 

Instead of a material, you may consider a component called a hydraulic shock damper. Highly predictable, more compact than polyurethane.

[elementcollector1]

Carbon fibre is exactly what one should avoid to absorb shocks. Glass fibres aren't good neither. You might try aramide fibres, but they're good only to spread a very local impact as a bullet-proof vest.

 

The real material to absorb shocks is polyurethane. Most resistant, little rebound. If for some reason its shape does not fit you need, you may try a polyamide rope, but it absorbs only one shock through irreversible strain.

Very odd. If you look up 'powerbocking', most of the stilts used there are either carbon fiber or fiberglass. Additionally, prosthetics are leaning more and more towards carbon fiber (and also titanium) nowadays, with some interestingly superhuman side effects (faster run speed, higher jump, etc.)

 

Additionally, I found out about 'leaf springs', which seem to be very similar to the goal I'm trying to accomplish. They're made of high-carbon steel, and you'd think that would transmit mechanical energy rather than absorb it.

 

According to my research, sorbothane is polyurethane, just a different form. This makes sense, as the video from the original site states that it was developed from an existing polymer to simulate human skin (which is apparently very good at dampening and absorbing shocks).

[Enthalpy]

You have to decide if you want to absorb the shock or to rebound.

 

As a strong absorber, polyurethane is the best - though Viton for instance rebounds less.

[elementcollector1]

If I had to choose, I would say absorb, although rebound works as well. The point is that the force doesn't reach what's being shielded/cushioned by the substance.

[Enthalpy]

PU then.

It's also more compact for the same energy than an elastic material.

Different hardnesses exist, but apply badly to computations at shocks, because speed changes radically how elastomers behave, and because we use them in a nonlinear mode. One has to experiment, with fast cameras or accelerometers.