Aluminum Roll Bar?

[Tippy]

Aluminum alloy would still break as others have posted. Steel just keeps bending and bending without breaking......to a point.

[LJ851]

That depends a lot on the type of aluminum used.

[island911]

Originally Posted by LJ851

I don't think anyone was considering a cast aluminum rollbar.

I expect that you are focusing on his sarcasm, and not the more subtle point below that. - "It did help the rollover after all."

That is, putting weight up high does a car no performance favors. Certainly adding stiffness helps, but at what weight penalty? A 911 coupe has plenty of stiffness from the geometry. A targa or Cab uses much more steel down low to come to an acceptable rigidity... which can be improved on.

Of course you could make the aluminum thin enough (think a thin band of AL - not tubing) that the strain to failure wouldn't be reached ... but that would be ridiculously thin.(no stiffness)

So what's the OP trying to optimize? Strength, stiffness, weight? ...bling? He has a coupe for the fitment. Sounds like he's liking the thought of a no-paint solution, and yet offers "Safety is clearly the issue here." For that, clearly steel is the winner.

Side note, people confuse strength with toughness all of the time. ...and then there are issues such as strain to failure and stiffness.

[kach22i]

I did find one stainless steel roll bar (cage), a non-911 application though.

Is 304 grade stainless steel more brittle than molybdenum steel?

Is molybdenum steel more brittle than mild steel?

And where does aluminum fit into the spectrum?

TigerCage – Bolt-In Roll Cage System
TigerCage – Bolt-In Roll Cage System « Ridetech News and Information

The cage is constructed entirely from 304 grade stainless steel and requires absolutely no welding or fabricating.

Some sort of hierarchical rating system or chart of metals and their strength and other characteristics such as energy absorbing bending would be useful in any meaningful discussion.

I am by no means qualified to create such a chart, but if I find one I'll post it.

Is the statement below true?

Hypothetically...Aluminum Roll cage
http://www.jeepforum.com/forum/f12/hypothetically-aluminum-roll-cage-955970/

Aluminum will self harden over time

Post #17 is very interesting:
http://www.jeepforum.com/forum/f12/hypothetically-aluminum-roll-cage-955970/index2.html

..........if you stay below the endurance limit everything is fine.

Good discussion on topic over at Rennlist back in 2004
http://forums.rennlist.com/rennforums/964-forum/111229-heigo-rollbar-aluminum-or-steel.html

[LJ851]

This 917/10 chassis including rollbar must be a horrible idea then, being all aluminum....

[kach22i]

Originally Posted by LJ851

This 917/10 chassis including rollbar must be a horrible idea then, being all aluminum....

Beautiful, but I don't think anyone is going to be claiming that the 917 was the epitome of safety engineering.

I think it's all a matter of engineering and lifespan of the material.

If I were going to race a car for just a few years or just want to make a car safer, it seems aluminum would have a lot of advantages.

Longevity and cost is where steel takes the lead, right?

[Trackrash]

It would be interesting to know the engineering details of the 917 frame. What alloy, temper, welding details, and was the frame heat treated after welding. Some of the 917s crashed. I wander how they fared.

[kach22i]

April 6th 1970, EHRA-LESSIN (Germany)
"photographs of Carlos Ghys´ biography, part 22 = «KURT AHRENS»"

Kurt escaped unhurt from this horrible crash, aquaplaning at 250 km/hr while testing at the Volkswagen test track at Ehra-Lessin

This is what it should look like in one piece.


http://www.carlosghys.be/html/biography_ahrens.html

1970 24 HR LE MANS
Kurt giving a helping hand to his mechanics during practise.

[RSBob]

QUOTE: "Oh wait, my 35 year old Porsche 911 has aluminum bumpers both front and back."

_______________________



Yes, bumping into things is very similar to putting a vehicle on its roof - or rolling it several times in a wreck.



Aren't you the guy who attached casters with perforated-metal straps to his front pan?



Best stick to designing homes in Detroit.

Man, you are cold.

[kach22i]

Some of the boys forget to close the door after they leave PARF and a cold draft sneaks in along the floor following them.

[RedCoupe]

A little personal perspective on roll bars and roll cages: Last night I received a call from my son who is racing his Ultra-4 off road racer at Moab, UT at Easter Jeep Safari. My son is a mechanical engineer in his day job, so his racer is properly designed and has the roll cage as well as the front and rear frames constructed out of steel DOM tubing. Anyway, within sight of the finish line he did an end-over-end roll, winding up on the roof! With some assistance from another competitor, the rig was uprighted and he finished the event. After an inspection and topping up fluids, he ran and placed in the next race. Damage is minimal as no tubing is bent, dented, or misaligned. My take on all of this is that we will see and ever increasing use of aluminum and composites in our vehicles going forward, but for those of us modifying and racing our own cars without the services of a well-staffed engineering department, we need to err on the side of safety and strength.

[cgarr]

Our cage made for what our car weighs is. 1 1/2 4130 .095 wall tubing only added about 60# to the car and we are still just under 2k total. This tubing is very strong and light weight.

[TRE Cup]

FWIW: The porsche factory was selling the Tekquipment stainless roll bar for the 996 GT3. A couple people modified these for installation in a G series chassis (1978 SC i believe).

imho, an aluminum bar is not for me. At best its a cool visual accessory

[kach22i]

I talked to my brother on this topic (an engineer), he said the real weakness in using aluminum is in the welds.

The impurities introduced during the welding process could over time compromise the strength and other qualities of the material.

By contrast the 911 aluminum bumpers are not welded anywhere that I know of. Of course some people fill in where the rubber strip is and also fill in other holes, so that may change things for them.

All this talk has given me a curious thought; what if someone removing their stock aluminum bumpers in exchange for fiberglass parts attempted to recycle/reuse/modify them as roll bars? For sure it would gobble up lots of interior room and the channel shape would not be as strong as a circular section of the same amount of material (weight). However it would come at an affordable cost - free. I'm never going to try it, as some thoughts just meant to be left as thoughts.

[javadog]

A used bumper wouldn't be my first choice...

You could design an aluminum structure with the same strength or stiffness as a steel one, if you used enough material and selected an appropriate diameter and wall thickness. Whether it would be lighter or not is debateable. There's a weldable alloy sold in Japan, 7N01, that has the ability to return to near pre-weld strength through natural aging. It's around 60ksi, give or take.

JR

[kach22i]

Thank you javadog for adding some good information.

On another note; I wasn't sure what DOM steel was and how it may differ from mild steel. So I started to look up a few things and found this................

Mild Steel vs DOM | race-deZert

DOM (Drawn over Mandrel) & ERW (ElectroResistance Welded) are manufacturing methods, not grades or specific alloys of steel.

I swear I remember one Pelican forum member posting his homemade roll bar made of electrical conduit. It must have meet the regulations and requirements of what he was racing under. I do recall being put off by it though, as it looked a little too "light weight" for my taste.

[javadog]

I don't think there is a sanctioning body on Earth that would permit a roll bar to be made from electrical conduit.

JR

[kach22i]

You know, maybe it was just the mock-up now that I think about it.

It was several years ago, I'll try and find it.

[cgarr]

According to NASA rules if using ERW or DOM the tubing has to be larger for the weight vehicle that's why we went with the strongest 4130 seamless tubing and could use 1 1/2 inch which kept the weight down but still offers superior protection. And I'm not sure but they may not even allow ERW any longer?

We used conduit for the cage mockup cheap and easy to work with. Last thing you want to do is waste some expensive tubing.

[Flieger]

Originally Posted by kach22i

I talked to my brother on this topic (an engineer), he said the real weakness in using aluminum is in the welds.

The impurities introduced during the welding process could over time compromise the strength and other qualities of the material.

By contrast the 911 aluminum bumpers are not welded anywhere that I know of. Of course some people fill in where the rubber strip is and also fill in other holes, so that may change things for them.

All this talk has given me a curious thought; what if someone removing their stock aluminum bumpers in exchange for fiberglass parts attempted to recycle/reuse/modify them as roll bars? For sure it would gobble up lots of interior room and the channel shape would not be as strong as a circular section of the same amount of material (weight). However it would come at an affordable cost - free. I'm never going to try it, as some thoughts just meant to be left as thoughts.

Welding also reduces 4130's strength significantly. Which is why you have double-butted tubes on things like bicycle frames.