Injectionable Foam in a Fb Rear Bumper?
 

Reading a couple of threads on the durability/impact resistance of a fb bumper in a low velocity impact - say 5 to 10 mph - there was a suggestion to use the spay/in/on expanding foam to add an extra measure of cushion. I realize it is no panacea or substitute for metal but would like a little extra margain. I was thinking that the foam could be sprayed into the rear bumber overriders areas. The weight would be minimal but my fear is that the muffler temperature well exceeds the max temp limit of 240 degrees F upper limit for the product - even if there was an airspace between the muffler and the product.

Any thoughts? One I have is to drill a couple of 3" holes behind the plate to aid in hot air venting as well as to partially relieve the air pressure created when at speed (since the bumper tends to act like a cup).

There is plenum-rated fire-retardant sealing foam available that won't char under direct impingement of a propane torch flame ...

My thoughts along the line of improving FG bumpers include 'internal' added strips of 1/8" x 2" mild steel ... bonded in place and covered by 8 - 10 Kevlar cloth layers using epoxy resin.

Not much real hope if a three-ton SUV 'bunts' you out of its' way ...

Warren is right. Just add layers inside if you want strength. The stronger you make that area, the more the energy will be spread out to other areas. Keep that in mind as you taper off the the build-up of the layers.

I don't know if you'd have to use the steel, but it can't hurt. Kevlar and epoxy by themselves are stronger. Carbon fiber is another one.

But foam is the cheapest.

Both ideas sound promising. But who is willing to test crash the final product? Not I. :D

Rick - any idea how much weight you're talking about?

You could come up with a crash test for the foam itself. Wrap some fiberglass in a tube, fill it with the foam, let it set, and then drop something heavy on it. You could try a few different foams to see which minimizes the damage the most.

Warren,

Where can that foam be found? And some steel wrapped reinforcement is a very good idea. Will have to check out clearences, etc. Thanks for the good ideas.

Why not go with Zekes idea of using Kevlar or just go with the foam? I have no experience with kevlar (only experience with carbon fiber is from bikes) but sounds better than using steel. Before I added steel I'd think a strip of more of aluminum would beef things up. At some point the added weight would approach the stock bumper.

Wow - my bike helmet semi-joke sorta took off....

OK, first - save your time and contact the folks who make bike helmets and get info from them. Also, contact Snell, and the racing/mo'cycle manfs.

BTW, it is possible to foam metals -- Al is one. I don't know if it is commercially available tho. It should be a lot better with the forces involved in car crashes.


Finally, go tear apart a Honda Insight. They tried to make it as safe as possible and a slight as possible. And it is Siechiro Honda's company... People who value light wt. for sports cars, should pay a lot of attention to where light wt. engineering and design money is going -- and this is into elec. cars and hybrids...

Using pieces of large cell styrofoam inside the bumper might make a big difference as well. If you pull the bumpers front and rear from a late model Honda Civic there are large molded styrofoam pieces that fill the void behind the bumper. The ticket is energy absorption (as well as distribution) and having something to suck up even a little impact would go a long way. About a year ago I was at a complete stop in my 2000' Civic Si coupe for a pedestrian in a crosswalk. I was rear-ended at approx. 30-35 mph by a woman who never touched her brakes (she was reaching for a water bottle in the passenger footwell). I got hit, took a good shot and got some whiplash, but drove the car home albeit a little messed up. The front end of her Buick Riviera was totally destroyed, deployed both airbags, totally thrashed. My bumper came off, the foam was destroyed, but I gotta believe it helped. If I had something like a Ruf style fiberglass bumper, I would try some long strips cut from styrofoam sheet (maybe the pink stuff from Home Depot for insulating walls?), as thick as I could find to fill the void. I'd glue them together and bond or glue them to the back of the car or bumper. I might also wrap them in something so the possibilty of it squeaking was eliminated.

Just my 2 cents...

You really need to look at how the bumper is mounted first. IF it is solidly mounted to the body you have to ask yourself what part of your car do you want taking the load. If it is mounted to bumper shocks or a similar arrangement, then that mounting area is going to need some help. A lot of these bumpers are "flange mounted" along their top edge, that is going to need some serious re working as well. A nice strong bumper is not much good if it just going to get torn off its mounts.

Jeff

Let's face it. Nothing is gonna be as good as Honda engineering. Total calculated, even distribution from many angles.

In our case, just the hollow glass shape ain't bad for what it is. You make the thing too strong and you will find a complete intact bumper somewhere in your fan and shroud.

That having been said, I used to strengthen fiberglass molds with a hokey arrangement of glassed over cardboard ribs ala a honeycomb. That would provide some crush zone before the energy started in on the tub.

I'm sure the way the early long hood cars were put together (notice I didn't say "designed"), there is some "crush," albeit with a lot of $$$ damage. At that point in history, there was a push (oh, man, pardon the pun) to make cars survive a 5 MPH hit w/o damages totalling a certain amount. CARS and insurance are what they were concerned with in those days. So, we got the bellows bumper.

Then, the lawsuits and Ralf Naders of the world took control and the occupants became the subject of the studies. The less damage became a byproduct.

Many car makers use some type of styrofoam (are there different types?) in polyurethane bumpers along with a honeycomb plastic brace. The spray foam may not be as uniform in make-up and it may take quite a bit to fill the bumper.

That said, what are you trying to protect? The FG bumper will likely be history even with a light impact and the foam will do little with a high speed hit. Polyurethane would be an ideal material even if more expensive and harder to work with.

Any industrial or commercial building supply should have the foam ... it is used extensively in commercial buildings these days. Here is one source:

http://www.fomofoam.com/Fire-Foam1.html

Usage of thin layers of carbon fiber would not help much in bumper areas ... it disintegrates far too easily ... ever seen the way a CART or F1 car proceeds to 'rapid disassembly' in an accident???

Jeff is quite right that the bumper needs to be analyzed as a total energy-management system!

Kevlar, on the other hand is very tough and tear-resistant, and would be very useful to spread the load and keep the fiberglas from emulating the CF behavior of CART cars! The shell of a Fg bumper needs to be reinforced to the point that it is capable of acting as a single, structural beam in an accident. I am surprised that Ruf never developed a reinforced bumper with some degree of crashworthiness. So far, the aftermarket bumpers seem to be intended to save weight for racing applications, and significant strength for street applications has been completely ignored!

For '74 - '89 cars ... it seems to me that the RS 3.0 style, fabricated of 80% Kevlar/20% steel, and completely enclosing a foam 'chamber' ... would be an optimal design!

The foam would seem to be a good idea to add to an existing FG bumper ... as long as there is sufficiently strong attachment area and force distribution into the chassis and at the outer points of contact ... where the foam is 'contained' between two force/impact distribution areas. Spreading out the load to as much area as possible is how the styrofoam works, and careful design details are needed to make a similar homemade solution that would be effective! Think about San Francisco taxicab bumpers from the mid-60s [long before the laughable impact bumper standards of the mid 70s on cars took effect] ...

Spreading out the load to as much area as possible is how the styrofoam works...

It also absorbs some energy as the foam structure is destroyed and turned into powder.


To re-emphasize, not all foams are going to be equally effective. Somewhere engineers have designed foam that is best for energy absorbtion... we just have to find it...

Randy, afaik, honeycomb, either arimd or aluminum, are going to give much better energy absoption (by weight) than any foam.

Also, I'll throw out; foams will perform in compression .. .. not so much in tension/flexural.

Tom makes an excellent point: "At some point the added weight would approach the stock bumper."

arimd ?

aramid (?)

Sound like when your done, you have a bumper that will weigh more then the stock one. What advange, other then looks, would you have then.

yes Randy. and "absorption" not "absoption"

Ive been leaving off letters, trranspossiing htem, and just sloppy all a round typing lately. --sorry

at least i went back and put a cap on your "R" .. out a respect. ;)

It will be a "one use" bumper. .. .like a dixie-cup. .. a cool look'n dixie-cup. :cool:

thx - I'm feelin' kinda lowercase today anyway... must be the late season rain...