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mart1975
30-04-2008, 13:48
what can i use to reconstruct the front and rear crashbars? ive got some kevlar and fibreglass strand, will this used in box contruction be good enough?
what i mean is casting the shape from the original but adding vertical flat pieces of kevlar into the inside.

it still sounds unsafe though if you consider that more recent cars have plastic type crash bars (my old pug 406 for example) it may not be so bad.

MartG
30-04-2008, 14:07
I think the modern plastic ones absorb energy through deformation ( much like the old steel ones do ) but something made of fibreglass/Kevlar will shatter instead - I don't think that absorbs as much impact energy, but I could be wrong

superchargedsam
30-04-2008, 14:30
Bullet proof vests were made from kevlar but if you imagine being shot with it on its still gonna hurt as the impact is shared over all local strands to the impact so if you made it all from kevlar you may be ok, but not fibreglass as it has no real means of tranmitting the impact as it will just break as the glass strands are not that long as they are chopped and crossed. Alot of the new modern bumpers rely heavily on the foam behind them to spread the force of impact so it is not absorbed all in one place like it would be with kevlar.

mart1975
30-04-2008, 14:35
thanks, so kevlar alongside fibreglass weave could possibly be substantial?

jasper
30-04-2008, 18:31
Is this a road or track car? A lot of the MR racers are ditching them to save weight. Have you asked on the forums to see if they still have the originals?

mart1975
30-04-2008, 18:35
its mainly for the road, i want to be able to construct something as strong as the original really. saying that, most front bumpers are made of rust anyway 8O

mart1975
30-04-2008, 18:36
jasper, im not looking to repair one but remake one from lightweight materials.

jasper
30-04-2008, 18:37
Right, I'm with you now.

jasper
30-04-2008, 18:41
How strong is that expanding foam? Just fill the whole bumper with it....?

mart1975
30-04-2008, 18:52
not strong but it may help stop the bumper crushing in, some foam materials are very good at this.
you might be onto something there.

sixafterfour
01-05-2008, 05:41
if you make a sandwhich panel with say 4 layers of kevlar and F/G then 2cm of foam and then another 4 layers of kevlar and f/g you would create a very strong panel (assuming you use proper techniques)

a foam layer will increase strength 6-9 times, and stiffness by around 35 times.

HOWEVER, i would consider ditching them. I would think that any accident in an mr2 would be enough to write it off completely. Anyways, say if your v6 mr2 got into an accident, buying another mr2 would cost you probably 500 pounds (with a dead motor) and then probably a weekend or two transfering over everything to the new car.

But if you are worried about safety, i'd ditch them, make an aluminum rollcage, still shed some pounds and i'd still feel safer. that what i am doing.

mart1975
01-05-2008, 08:17
thanks for the info, well ive modified the front of the car for the hood vent, where the steel used to be corigated it is now flat which makes it considerably weaker, so having no bumper there really wouldnt be much between my legs and any object in a collision.

i like the sandwich idea, the foam that is used in the aw11 bumpers would be good for this. any idea what kind of foam this is?

sixafterfour
01-05-2008, 15:33
no, not sure
however make sure if you do this use an epoxy resin, a polyester resin will end up melting the foam.

mart1975
01-05-2008, 16:15
ah ok, im finding it difficult to get hold of epoxy tbh, (ill have to travel into birmingham for that stuff) if i cannot find any ill use high density foam once the resin has cured.
its going to have to be made in 2 parts anyway so it wont be a problem doing it this way, ill then fix them together with tiger seal.

ive ordered the fibreglass weave so i can get on with them soon.

sixafterfour
02-05-2008, 01:30
Bonding them all together at one time yields the best results,
if you *have* to do it in two parts i'd suggest scuffing the bonding surfaces with 80grit sanding paper and then cleaning them off really well with a solvent that doesn leave a residue (methyl ethyl ketone for example) and a clean cloth.

Use pressure!! Clamps, sand bags, even duct tape to apply pressure.

mart1975
02-05-2008, 08:20
thanks, that tiger seal (windscreen adhesive) is amazingly strong stuff though, as you said scuffing the bonded surface, then adding the adhesive, theres no way itll come apart.
i can use tiger seal on the high density foam to bond it to the set composite too.
part of the mould has been curing over night, ill apply another layer later today, then hopefully 1 half of the mould will be ready by tuesday (hopefully) its so cold here it takes things ages to cure.

sixafterfour
02-05-2008, 10:17
you have an electical blanket? toss one of those over top of it

nik
02-05-2008, 10:52
i would advise against using composites for a bumper bar..theyre just not designed to be strong in that way..
the advantage of steel is that it is bolted to the chassis so in a collision will deform and transfer engergy into the rest of the car, decelerating the vehicle during the collision and using up energy in an efficient manner..
if you have a rigid composite bar up front, in the event of an impact it will shatter locally and then and lose the ability to transfer energy to chassis..basically become useless at the initial moment of impact..
this is my opinion at least..go with steal for the sake of a few kilos..

mart1975
02-05-2008, 12:51
i know exactly what you are saying nik and it makes total sense, however ive seen composites used on factory cars, like the 406 for example.
i guess though the difference with that is 2 steel petruding poles go through it at each end so they would be dragged through the composite in a collision. the mounting points on the aw11 made from composite would simply snap off.

im going to have to look at that.