I propose that a motor cars steel or aluminium box sections be filled with expanded polystyrene to increase the strength. In a crash test I would expect such a vehicle to perform better.
The polystyrene would have to be injected to completely fill each void for best effect and each void be sealed after.-- Pat-O-Cake, Jan 10 2008 It might increase the rigidity of the car sections, which isn't what is wanted at all. Modern car bodies are design to crumple and deform (which absorbs impact energy) right up to the point where they'd start squashing the passengers. Also polystyrene is quite nasty in the event of a fire.-- hippo, Jan 10 2008 // Plutonium might have greater impact resistance //
Yes, right up to the point where it gets compressed that little bit too much, into supercriticality ...-- 8th of 7, Jan 10 2008 You'd be better filling the sections with a liquid to disperse the impact....(NO NOT CUSTARD) Polystyrene also releases some unsavory chemicals when burning - fancy a lung full of cyanide gas? Not a good idea I'm afraid.-- xenzag, Jan 10 2008 // lung full of cyanide gas //
That's polyurethane ..... but yes, polystrene fumes are not pleasant.-- 8th of 7, Jan 10 2008 The extra strength bits would be in a sills and passenger cell and not the crumple zones.-- Pat-O-Cake, Jan 10 2008 Also the polystyrene hermetically sealed in each box section thus it is very unlikely to rip open and make a fire risk or melt away due to oil/petrol corrosion.-- Pat-O-Cake, Jan 10 2008 Bumpers are made this way.-- RayfordSteele, Jan 10 2008 Not sure what you're expecting to get from the polystyrene.
If you're after crumpling resistance due to incompressibility, foam is not the answer. Water would be better.
If you're after energy absorbtion - you're on the right track but I really think polystyrene will be too weak. A higher density foam (there are a lot to choose from, one of the blown epoxies is probably the ticket, or a low density rubber foam) would be better.
If you're after increased tensile/bending resistance of the section, poly won't do much for you. Once again, think about a structural blown epoxy, or something like that. The effect will be minimal, either way, and as has been stated before, if it's crash performance you're after, stiffening the members isn't really the goal.
Lastly, //and each void be sealed after// - with what? I gather you're thinking about some kind of constant-volume reinforcement - in which case you're probably suggesting to weld up the section. HOw well do you think the polystyrene inside will stand up to the heat of welding? ditto for if you ever need to do any chassis repairs, heat up bolts to loosen them, etc.
Anyhoo, not sure this is going to do what you think it will. If you explain to us exactly what you expect the foam to do - ie increase stiffness, absorb energy, etc, you might get some more meaningful discussion.-- Custardguts, Jan 10 2008 Also note, even if the sections are sealed before the crash, there's a good chance they'll be unsealed afterwards. Violent impact tends to do that, you know.-- 5th Earth, Jan 11 2008 who said helium?-- po, Jan 11 2008 A higher density foam of blown epoxy sounds like a better medium.
The idea is to have the the cars integral roll cage parts of its structure re-enforced. The frame box sections that surround the passenger area.
The filling is to control the compressive forces on the structure when it is experiancing a bending force.
The idea came from the fact that if you bend a metal tube that is empty it is difficult to bend initially but after a dent is formed on the inside of the bend it bends further very easily and seems to loose all strength thereafter.
Fill the tube and control the way the dent forms and you are required to use more force to increase the bend you dont get the sudden loss of strength of the tube.-- Pat-O-Cake, Jan 11 2008 Fill it with something stiff and you'll certainly increase the resistance to local buckling; the effect should be more pronounced as the diameter of the tube increases, thus the local radius of curvature increases. Not sure what filler you'd need to have a relevant effect; as mentioned above the forces are pretty huge.-- david_scothern, Jan 11 2008 If a car was to plummet into a body of water, the foam could help keep the car afloat a bit longer, increasing the odds that a trapped driver will be able to exit the car before it sinks.
[+] for this side implementation, [-] for the original.-- Giblet, Jan 12 2008 //The frame box sections that surround the passenger area//
Not aware of any that do....-- Custardguts, Jan 13 2008 //if you bend a metal tube that is empty it is difficult to bend initially but after a dent is formed on the inside of the bend it bends further very easily // The idea is sound, but I agree that you won't get much benefit from a foam filling.
Consider a tube that's being compressed axially (ie, end-to-end). Initially, there is no deformation and resistance to compression is very high. The tube then starts to buckle, with the first signs of oil-can failure (one side of the tube starts to kink inwards). Initially, this deformation is very slight - only a percent or so of the tube's diameter. Under these conditions, most foams will provide very little resistance to compression, and will give easily, so the initial deformation is not resisted.
Once you have that initial few-percent of deformation, everything runs away. The forces driving further buckling become huge very quickly - a deformation of a few percent means that the compressive forces at the crease become almost as large as the axial forces. Once things get to this stage, no foam is going to help.
In other words, the basic problem is that foam is no good at resisting the initial, very slight buckling that triggers the catastrophic collapse of an axially- compressed tube or box section.-- MaxwellBuchanan, Jan 13 2008 You could, of course, fill the "box sections" (of which I really don't think there are any in most cars except large 4wd's with seperate chassis, but I digress) with more steel. Nothing like solid bar for resisting axial compression.
Probably help with impact dynamics also. Well, it'd help YOU at least...-- Custardguts, Jan 13 2008 I thought that the sills, posts and some other body sections were basically box sections, albeit formed by folded sheet?-- MaxwellBuchanan, Jan 13 2008 ..yet barely dented it.-- MaxwellBuchanan, Jan 13 2008 [custardguts] It would help your car, but not you. If your car is rigid, then the impact shock travels through it and arrives at you undiminished, whereupon your brain gets smacked into your skull, hard. Deformation of your vehicle is required for your own safety.
...plus, it keeps the profits of the insurance companies nice and high. And the oil companies (somehow?). It's all a conspiracy, I tell you - burn water instead, it's cleaner and gives hundreds of miles per gallon, wibble, tin foil hats, brain waves, wooo!!!-- david_scothern, Jan 14 2008 // your brain gets smacked into your skull //
Hah hah, but [custardguts] has thought of that one ..... he has had his brain removed ...... keeps it in a jar somewhere, as far as we can tell.....
// wibble, tin foil hats, brain waves, wooo!!! //
Don't be afraid .... resistance is futile .... take that tin foil off you head ..... let us in ...... we mena you no harm.... well, not very much harm.... well, probably quite a bit of harm actually........ oh all right then, a lot of harm ! JUST TAKE THE DAMN FOIL HAT OFF !-- 8th of 7, Jan 14 2008 I was intimating that the vastly increased mass would reduce your deceleration during an accident, which is very much the case.
Calling anything monocoque a "box section" is a bit of of a bastardisation - normally box section is RHS.-- Custardguts, Jan 14 2008 If you really want an impact resistant car, I recommend building the entire hoopy out of tungsten.
Yes, it will be heavy. Gas mileage probably won't be the best. But since in most impacts the heavier vehicle "wins," there is a better than fair chance that whatever the impact, you're going to win.
Unless you roll over. Then you get squished.-- elhigh, Jan 22 2008 This has been done before. I remember '90s era Australian Fords had foam-filled A-pillars, to increase rigidity of same. The technology was dropped; I don't know why.-- sstvp, Dec 11 2009 random, halfbakery