h a l f b a k e r yI like this idea, only I think it should be run by the government.
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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.
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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. |
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// Plutonium might have greater impact resistance // |
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Yes, right up to the point where it gets compressed that little bit too much, into supercriticality ... |
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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. |
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// lung full of cyanide gas // |
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That's polyurethane ..... but yes, polystrene fumes are not pleasant. |
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The extra strength bits would be in a sills and passenger cell and not the crumple zones. |
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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. |
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Bumpers are made this way. |
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Not sure what you're expecting to get from the polystyrene. |
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If you're after crumpling resistance due to incompressibility, foam is not the answer. Water would be better. |
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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. |
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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. |
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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. |
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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. |
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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. |
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A higher density foam of blown epoxy sounds like a better medium. |
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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. |
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The filling is to control the compressive forces on the structure when it is experiancing a bending force. |
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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. |
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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. |
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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. |
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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. |
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[+] for this side implementation, [-] for the original. |
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//The frame box sections that surround the passenger area// |
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Not aware of any that do.... |
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//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. |
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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. |
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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. |
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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. |
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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. |
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Probably help with impact dynamics also. Well, it'd help YOU at least... |
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I thought that the sills, posts and some
other body sections were basically box
sections, albeit formed by folded sheet? |
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[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. |
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...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!!! |
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// your brain gets smacked into your skull // |
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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..... |
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// wibble, tin foil hats, brain waves, wooo!!! // |
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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 ! |
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I was intimating that the vastly increased mass would reduce your deceleration during an accident, which is very much the case. |
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Calling anything monocoque a "box section" is a bit of of a bastardisation - normally box section is RHS. |
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If you really want an impact resistant car, I recommend building the entire hoopy out of tungsten. |
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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. |
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Unless you roll over. Then you get squished. |
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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. |
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