I saw this,
[ http://www.twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1450554 ]And immediately recognized myself.
I've done a ton of research on this subject. My bro designs shuttles for Boeing and is a head configurator. His specialty is structures. Foam sandwich structures for craft that fly into space. We talk alot about foam sandwiches. The tolerances on these craft are alot higher than for a car, but the numbers he comes up with to guide me coencide perfectly with what's in the articles below. I've also conversed with folks from Bayer, Foamseal, Henkle and other companies on the subject. I also talked at length with Art Goldman, of Mike Kojima's article, who admitted that, his own advice to Mike K. at the time; using a 2 pounds per cubic foot foam density, the type Mike used; was "a crapshoot at best". Art recommends, as does every SAE article I've read, that one use 8 lbs per cubic foot (8PCF) or heavier for "structural" use. 8PCF is stiff stuff. This type of foam requires either a very messy bucket mix-and-dump-into-a-funnel method (no handy "frothpacks"--as they are called) or a $50,000 robotic mixture system that meters it out and shears the two materials so they froth. It is also only available in 50 gallon drums. Two 50 gallon drums, to be exact. Or in samples, if you are lucky enough to get someone who has some lying around. I have some 4 PCF, too light, and some 25 PCF, way the hell too heavy. But I plan to play with them sometime. Here's a link to some foam articles you can download and read yourself. Some of these, I paid for. You be the judge. But please, bring a brain, or have someone who's an engineer read them for you. I've even looked at other Epoxy-type foams (Henkle) that say they can stick to oily substrates, which is quite interesing. The inside of a frame rail is far from clean, and some PU foams won't stick well. [ http://www.personal.mwsmotorsports.com/z32/foam/Structural_Foam_Forum.html ] ("Body in White" refers to the entire spaceframe of the car, "Matchboxing" is what it sounds like, open a matchbox, and flex it side to side or twist it. Now, apply that to a car) You'll find, right off the bat, most of the applications are to the JOINTS, not the rails. Rule #1 of structural stiffening: If you stiffen a rail and not the joint, the rail can work the joint easier and the structure may in fact be LESS stiff overall after awhile. Or the joint may fatigue and break. Not good. Please understand, that I'm not saying you don't feel any benefit from squirting lightweight foam into your rails, but you must understand, that 99% of the benefit is a reduction in noise, and an apparent smoothing of vibration and that's it. Any perception that the car is significantly stiffer is likely in your head. There is a scientifically proven ratio of strength that a foam must have, relative to the steel skin, in order to make a sandwich that is stronger than either by itself. The 2PCF foam you can buy from Foamseal is nowhere near strong enough to do that job, and is sold by the automotive industry for NVH, not as a "structural foam".
_MWS Crash Test Dummy(tm)
"taking it on the chin so you don't have to..." "Knowledge is Power" (tm)
(the more you know, the more confused you get) Ignorance is Clarity(tm)
(at least in that case, there is one and only one route to take ;-) |
