Engineering Question

[island911]

Originally Posted by AZ_porschekid

Eh practical solution. [kachi-casters]

I'm just keeping with the designer's theme here.

Next up, cross-drilled brake lines!

[gtc]

Why not just replicate the dents that are used in the factory euro crush tubes?

[Shaun @ Tru6]

Originally Posted by gtc

Why not just replicate the dents that are used in the factory euro crush tubes?

That's an option Graham. Or I could take advice from this fine fellow:

Originally Posted by gtc

This would be easy, but you would lose the impact protection that the kink near the bumper end provides. I suppose you could put some strategically placed holes in the tube to facilitate buckling in case someone nudges you.

My friend Chris just drafted this up. I like it but would be a manufacturing nightmare I think.

[Shaun @ Tru6]

These look nice. Mine will use studs.

Porsche 911 Lightweight Impact Bumper Mounts

[john70t]

Originally Posted by island911

^ ha! --not an engineered solution

I was thinking about post #2 and the near total failure of a steering column.
Aluminum doesn't give warning and it's either there or it isn't. Yeah it's a hack but wire is light.

I imagined Shawn getting a good tap in the parking lot, then driving home in heavy traffic at speed. The flex part has been broken 95%. He rolls over a pothole and the front bumper falls off and rolls under the car. Not good.

[island911]

Yeah, Aluminum doesn't have the toughness of steel.

where's my popcorn? oh..

[gordner]

what if you were to use the Al tubes to sleeve a (obviously as light as possible) steel spring to assist with the damping force? The inserted spring would both dampen the collision force and prevent the buckling from collapsing the Al tube inwards, forcing it to buckle outwards which may assist in keeping the forces in line...
I understood that the damping force in the front bumper shocks was largely due to them being fluid filled, and the metered release of the damping fluid after collision provided the damping much more than the buckle zones on the shocks. I know due to a rear end collision that I suffered in my 76 911S that this is how the rear shocks are intended to work, in my case they were not fluid filled (leaked out over time I am told) and thus the full force was transmitted to my tub after the shock tube distorted to its limit.

[aschen]

Originally Posted by Shaun 84 Targa

That's an option Graham. Or I could take advice from this fine fellow:



My friend Chris just drafted this up. I like it but would be a manufacturing nightmare I think.

you could use this basic design, but use a block of aluminum/composite honeycomb material for the collapsible bit instead of the s-shaped pieces.

This would be much easier to fab, and the honeycomb has a huge energy absorption to weight ratio

[gtc]

Originally Posted by Shaun 84 Targa

That's an option Graham. Or I could take advice from this fine fellow:

Ha, you got me!
Ok, I'm out.

[Shaun @ Tru6]

Originally Posted by aschen

you could use this basic design, but use a block of aluminum/composite honeycomb material for the collapsible bit instead of the s-shaped pieces.

This would be much easier to fab, and the honeycomb has a huge energy absorption to weight ratio

Thanks Aschen, can you describe/show the honeycomb and its orientation?

[wayner]

Why not fill the fiberglass bumper with expanding foam to absorb impact?

[Shaun @ Tru6]

I'm keeping the Al bumpers, just making them lighter.

[David]

Goofing around with FEA with a model of a 2" OD x .125" wall 6061-T6 aluminum tube with 50,000 lb slightly offset force gives this result. It doesn't really show you how it would collapse though. I'd mock up a piece, bolt it to a tree or something else that won't give and bump into with a beater truck

[scottmandue]

Originally Posted by wayner

Why not fill the fiberglass bumper with expanding foam to absorb impact?

I had the same thought...

[dad911]

3 sections of Mcmaster-Carr square 1/8 wall 1"x4" aluminum tubing, part number 88875K21, cut to the height you want (2" shown) bolted side to side to get 12" total length.

Easy to machine, drill press and a chop saw...... For proper crash testing you will need to provide me with 12 running cars....

David, you using solidworks?

[aschen]

Originally Posted by Shaun 84 Targa

Thanks Aschen, can you describe/show the honeycomb and its orientation?

Maybe something like this

McMaster-Carr

If you choose a 1" thick material, maybe you need 2-3 pieces in series. They have the loads listed so you could pick an appropriate cell density.

For example if you want the material to crumple at 500 Lbs force you might pic 4 square inches of 250 psi rated material

I would orient the material such that the long axis of the cells are parellel to the direction of travel.

You are relying on the cells buckling but they are thinwall so they will give in near rated load. The should crumple and absorb work.

[Shaun @ Tru6]

Thanks Aschen, that is very interesting. I wonder if the 8458K66 would be best. the bracket sizes are different about about 2.5x3.5 inches.

[Shaun @ Tru6]

Thank you David, and I happen to have a beater truck.

I see some testing in my future. Probably should have ordered a lot more tube.

I'm also going to try the horizontal cuts staggered around the tube. It would be much easier to produce these.

Originally Posted by David

Goofing around with FEA with a model of a 2" OD x .125" wall 6061-T6 aluminum tube with 50,000 lb slightly offset force gives this result. It doesn't really show you how it would collapse though. I'd mock up a piece, bolt it to a tree or something else that won't give and bump into with a beater truck