Injectionable Foam in a Fb Rear Bumper?

[Formerly Steve Wilkinson]

Wait a minnit. We take off the big, heavy, ugly stock bumper and put on a cute little fiberglass one, then we lie awake nights wondering how to make the fiberglass bumper big, heavy and ugly again? What am I missing here? If you wear a miniskirt, just make sure you keep your undies on.

Stephan

[jtratza]

I like the idea of filling a fiberglass bumper with foam. And I can attest from personal experience how stong a little foam can be as I recently crashed one of my road bikes in excess of 20 mph landing on my head. The helmet foam split but not the cover and all I suffered was some serious road rash. Without the helmet I'd have left what little brains I have on the road. Modern bike helmets are very thin and light but give remarkable protection. One foam I thought would work is an injection foam from Dow called Great Stuff but after reading the can it is only good up to 240 degrees. After that it can ignite. Maybe not so good near a rear muffler.

BTW spelling mistakes are perfectly readable as long as all the letters are there. According to some study/email joke I read as long as all the letters are there the mind sorts them out and reads them correctly. Thank god since I can't spell any better now then when I was in the 4th grade. A very long time ago.

[randywebb]

Hey! Those are called Utili-kilts...


"big, heavy and ugly again?"

no bigger, not appreciably heavier, and you wouldn't be able to see the "ugliness"

- this would all be in the interior concavity of the bumper -- inside the the FG shell

[Formerly Steve Wilkinson]

There's a big difference between professionally designing an energy-absorbing bumper, or bike helmet, that utilizes urethane as an absorbant and william-nilliam spraying home-insulating foam into a big round cavity.

Stephan

[geof33]

I would agree with Steve. What happens when the foam falls out? Foam needs to be bonded to the structure to allow for the energy absortion. If there are gaps and space the foam just moves out of they way of the force, it won't absorb much. If the FG bumpers could be built with an impact resistant foam core bonded into it, then we might be talking.

To be honest, once we go down the road of doing FG bumps, we pretty much make the decision that the ramifications are what they are. FG is a pretty tough material, and if the pieces are well made they will absorb a pretty good amount of force if properly installed.

[randywebb]

SW put it well and succintly.

BUT, people on this forum seem to have a lot of 'excess energy' - and why not experiment a little?

And, I am always pleased to have others test stuff on their car before I think about putting it on mine...

[dd74]

Well, I visited today with a Porsche expert who knows his stuff well enough to make a sizeable living, partly from designing race parts for our 911s. He made the following statement regarding this topic:

"All this talk of filling foam into fiberglass bumpers is ridiculous. No matter what amount of foam there is, nothing will protect the car as well as the stock bumpers."

As an example, this person compared a 5 mph impact with a 5 mph bumper as minimal, while the same speed impact to a fiberglass bumper equates to $2,000 damage to the car.

We need more cowbell, and I guess need more foam.

[island911]

dd, I think that you are missing the point. The additional foam is squirted-in to make the driver feeeeel like they've out smarted the Porsche engineers. . . and those damn ridiculus "5mph bumpers." I mean sheesh; what were those guys smoking to ruin that design, perfected back in 1972?

They must not have known about foam back then .... yeah; that's it! ... They didn't know about foam, AND they made those big bumpers just for parking-lot bumping. ..stupid porsche engineers....




I think I need a foam helmet for these threads.

Seriously, I do believe that I (or a few others here) could design a high specific toughness composite bumper. I also think it could be designed, tested and tweaked, all for about 50 grand. (on the cheap)

So; Who wants the first one?

[911pcars]

Partial view, foam bumper layer, '05 Scion TC. Probably more effective at reducing low speed collision damage.



Sherwood

[dd74]

Originally posted by island911

Seriously, I do believe that I (or a few others here) could design a high specific toughness composite bumper. I also think it could be designed, tested and tweaked, all for about 50 grand. (on the cheap)

So; Who wants the first one?

If I get two, can you throw in a crash test dummy...

[dd74]

Originally posted by 911pcars
Partial view, foam bumper layer, '05 Scion TC. Probably more effective at reducing low speed collision damage.



Sherwood

Correct, and the rest of what is seen - the body, that is, is a crumple zone. The engine probably either drops or tears away during a collision, and who knows what other safety features are engineered into this car; stuff unheard of 30+ years ago...

[Formerly Steve Wilkinson]

That's the back of a Scion.

Stephan

[dd74]

Originally posted by Formerly Steve Wilkinson
That's the back of a Scion.

Stephan

LOL! Well there you go!

[RickM]

Other than expanded bead technology, which requires expensive equipment and large quantities of matirial, this may be an option: http://www.cfoam.com/bumpers.htm

"CFOAM, because of its unique combination of high compressive strength and considerable impact absorption capacity, is an attractive material for enhanced performance bumper systems. CFOAM's cellular structure can be tailored by adjusting the cell wall thickness and pore size along one axis, resulting in a variable crush strength vs. penetration depth."

Also, from DOW:

This can be cut: http://automotive.dow.com/materials/products/strand/product.htm

And this injected: http://automotive.dow.com/materials/type/foams.htm

[island911]

Originally posted by Formerly Steve Wilkinson
That's the back of a Scion.

Stephan

Well, they have been known to go flying off the road backwards . . .oh wait ....

[island911]

Originally posted by dd74
.. .The engine probably either drops or tears away during a collision, and who knows what other safety features are engineered into this car; stuff unheard of 30+ years ago...

I think that you mean; "stuff unmarketed of 30+ years ago...

I mean, WTF . ..engine dropping? I think Volvos did that as they were coming a part; so the marketing dept decided it was a "feature" . . .a "safety feature" -wink wink.

[island911]

Originally posted by RickM
O ...high compressive strength and considerable impact absorption capacity, . . .]

Right, like I said before, you have to compress the stuff to get any performance. So what's it going to be compressing against?

[thrown_hammer]

As Rarly L8 says every time this comes up....I am safer in my car than on a motorcycle. Last time I checked motorcycle riders don't have 6 point harnesses and roll bars.

[70SWT]

I'll take the hit from the naysayers/jokesters for bringing up the spray foam idea in another thread....wouldn't think of taking credit for either the use of foam in impact resistance in general, or garage-engineering attempts to apply the principle. Although I did invent the internet, but that's another story...

Anyway, I take it for granted that a FG bumper dramatically reduces impact resistance. IOW I'd be surprised if anyone feels the FG/CF bumpers with or without modifications are even partially comparable to the stock setup in terms of impact resistance. My view as a synopsis:

Benefit of FG bumper: lighter overall weight, improved weight distribution. Risk: car may be FUBAR in a fairly minor accident; possible fire hazard if using foam? (I doubt temps will get high enough to be an issue inside the bumper). As always, the R/B ratio MAY be able to be improved.

Having accepted this risk/benefit equation: if I am going to use a FG bumper (I am), and if some foam buys even .1 mph of theoretical improved impact resistance, it sounds like a worthwhile experiment to spray a bit in. A whole can of this stuff only weighs maybe a pound or so, and a few squirts expand to fill a surprisingly large volume, so it shouldn't add measurable weight (used it before).

In terms of what it is compressed against, I am thinking in terms of it simply buying a few miliseconds of crush time as the FG bumper deforms before sheetmetal inevitably absorbs whatever degree of impact. In the right accident a millisecond or two could make a difference between degrees of damage.

[RickM]

Originally posted by island911
Right, like I said before, you have to compress the stuff to get any performance. So what's it going to be compressing against?

Not arguing the fact.


Edit: Let me clarify....All industry info describes bumper systems that make use of a flexible bumper cover, a steel bar (of some type), a honeycomb brace and foam. teh steel bar applies and disperses the impant energy more evenly to the foam. However, I can't say what is behing the bumper system. Most likely a structure which was designed together with the system.