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JMarsa
07-13-2005, 07:53 AM
My next project is going to be a lightweight Model A based autocross/track car. I'm researching if it would be possible to run a aluminum chassis like the Boyd Coddington Aluma-Tub (http://www.streetrodderweb.com/features/0408sr_alumatub/) where they built the chassis from 3/16 wall 5052 (I don't know the spec H32, H34, H36, or H38).

I'd like feedback if you feel this alloy/gauge is sufficient for a sub 2000lb car and input on the grades or other alloy suggestions. I don't know the spec for the new ZO6 vette alum chassis but I know it's 4MM (.1574803 inch) which is close to 5/32 (the steel C6 chassis wall is 3MM). If anyone knows the ZO6 alloy spec that would help too as I'm sure GM has already done the math :)

Thanks,

--JMarsa

Matt@RFR
07-13-2005, 11:18 AM
Consult a qualified mechanical engineer. They don't come cheap, but guessing at something like this will get you killed. I have no comment beyond that.

censo69
07-13-2005, 02:41 PM
I'm a mechanical engineer and by no means would I feel confident in trying to work out those calculations to give you an exact awnser. But just going off what the Chevy is using may not be the best idea either the corvette gains a lot of it torisional and structural rigidity from numerous areas alowing them to use lighter / thinner materials. Some are: The frame rails are hydroformed if you got one of those in your garage im comming over. Also the floor boards are made from some composit balsa that gives rigidity.
I seriously doubt that the car will be unsafe using the materials that boyd used, wether or not the car will be torsionally rigid enough for you get the maximum usage of your suspension in autocrossing is a different ball game. Most of the rigidity will come from your design and welds not the material.
What are some of the specs on the materials you were thinking of using I can compare them to some spindle designs I have at work and let you know.

JMarsa
07-13-2005, 06:02 PM
No material specs as of yet. I'm at least a year away, but that's the way I am, I do alot of research and try to prevent throwing time and $$ in the wrong direction. I'm just getting started on this and this is the first place I've looked for advice. I was hoping for more insight on material selection here. Along the lines of..."I'd use 6061-T6 over 5052-H32 <insert resons here>..." I'll do my homework before I put anyone at risk. I'm actually more concerned about metal fatigue and cracking than anything else.

Assuming I take the Boyd approach, 5052 seems to be most popular in temper H3 = Strain-hardened and stabilized and is commonly available in temper hardness designations:

H_2 1/4 hard
H_4 1/2 hard
H_6 3/4 hard
H_8 Full hard

Any education anyone can offer me regarding hardness? I understand the concept, but how does it come into play for chassis design?

Thanks,

--JMarsa

Norm Peterson
07-14-2005, 07:09 AM
I don't know if you are envisioning welding this together or not, but when I was working in a shipyard and designing aluminum superstructure stuff for the Navy, we always assumed an allowable stress equal to that of annealed material. Hot work does that, and the 100% efficient double fillet welds in aluminum were huge. We didn't get involved with welding stuff like 6061-T6, although other industries apparently consider that a weldable alloy. That was back in the 70's, so I'm not sure just what alloys we did use without searching through some old notes. Some 54xx, as I recall.

No other quickie answers, but since aluminum has a Young's modulus that's only 1/3 that of steel, designing for equivalent stiffness will end up requiring bulkier members, especially if you're looking for all that stiffness with minimal weight (otherwise, why bother with aluminum?). So will the requirements of the lower annealed stress, if you're welding. As has been already mentioned, fatigue will have to be considered. And buckling, if the panel b/t ratio gets too high.

Do-able? Certainly. Is the engineering going to be complex? Without a doubt. You might try to find out what the builders of the A-Mod Phantom cars have done and/or used as a design envelope (OTOMH, the Modified forum at sccaforums.com is probably your best bet).

Norm

parsonsj
07-14-2005, 11:36 AM
When I was doing my uprights for my front suspension, I got some cautionary tales of the problems with aluminum. One thing I was told is what Norm just said: you need to build to the annealed strength. Welding and fatigue will both return aluminum alloyes to that.

I weld 6061 all the time, but it seems more prone to cracking, if my multiple attempts at welding fuel tanks is any guide. My fully skinned 5052 tanks have done fine, but my hybrid (with 6061) tanks have had trouble passing pressure testing.

jp

MuscleRodz
07-14-2005, 09:26 PM
If you plan on auto X'ing this, I would steer way clear of aluminum chassis. Absolutely no saftey in it or strength. You would be miles ahead money and frustration wise to buy some premade boxed steel rails to your specs. There is too many guys doing it. All of Boyd's aluminum cars will see very few street miles and never see a track. The new C6 and the is hydroformed aluminum with millions of dollars of research to keep you safe in a wreck. Sounds cool, but I would highly advise against it.

Mike

Matt@RFR
07-14-2005, 11:00 PM
The new C6 and the is hydroformed aluminum with millions of dollars of research to keep you safe in a wreck.

And if you do wreck it and bend the frame? It's an automatic total. You can't bend aluminum twice.

MuscleRodz
07-15-2005, 07:16 AM
If you are dead set on aluminum rails, I would use no less than 1/4" plate, weld in "O" or normalized condition, and then have them heat treated. You will also have to make a fixture to hold the rails during heat treat to keep them from warping. I would also use a certified welder for saftey reasons.

Mike

Norm Peterson
07-15-2005, 08:00 AM
Actually, for as non-traditional an approach as this already appears to be, there's no engineering reason that you couldn't go to riveted construction and anodized sheet and open the door to all sorts of other possibilities.

David Pozzi can probably fill in with some information regarding riveted aluminum construction and long term durability.

Another wrinkle might be to use a combination of rivets and structural adhesives.

Norm

JMarsa
07-16-2005, 07:55 AM
Thanks everyone for your responses. Sorry about the delay to respond.

Matt, check out this link, it's for GM Service Technical College (STC) specifically for C6 structural repair:

http://www.i-car.com/html_pages/training_programs/oem_training/gm_training.html

This link has some basic info on the C6 aluminum chassis: http://www.i-car.com/html_pages/about_icar/current_events_news/advantage/advantage_online_archives/2005/062705.html

Mike, when you say "O" or normalized condition" do you mean 5052-0? (as opposed to 5052-H32)

Here's some more info I found on possible about possible grades:

http://www.aircraftspruce.com/catalog/mepages/aluminfo.php

"5052 This is the highest strength alloy of the more common non heat-treatable grades. Fatigue strength is higher than most aluminum alloys...It may be drawn or formed into intricate shapes and its slightly greater strength in the annealed condition minimizes tearing that occurs in 1100 and 3003...."

"5083 & 5086 For many years there has been a need for aluminum sheet and plate alloys that would offer, for high strength welded applications, several distinct benefits over such alloys as 5052 and 6061. Some of the benefits fabricators have been seeking are greater design efficiency, better welding characteristics, good forming properties, excellent resistance to corrosion and the same economy as in other non heat-treatable alloys. Metallurgical research has developed 5083 and 5086 as superior weldable alloys which fill these needs. Both alloys have virtually the same characteristics with 5083 having slightly higher mechanical properties due to the increased manganese content over 5086. Applications: unfired pressure vessels, missile containers, heavy-duty truck and trailer assemblies, boat hulls and superstructures"

Anyone have any experience like John with 5052 vs. 5083 and 5086? These seem like the best grades to research. I appreciate everyone’s input and advice. So "to build to the annealed strength" means to the properties of the alloy after it's "being worked" is complete and it's in it's final annealed and heat treated state?

Regards,

--JMarsa

MuscleRodz
07-16-2005, 02:27 PM
Mike, when you say "O" or normalized condition" do you mean 5052-0? (as opposed to 5052-H32)

Here's some more info I found on possible about possible grades:

http://www.aircraftspruce.com/catalog/mepages/aluminfo.php

"5052 This is the highest strength alloy of the more common non heat-treatable grades. Fatigue strength is higher than most aluminum alloys...It may be drawn or formed into intricate shapes and its slightly greater strength in the annealed condition minimizes tearing that occurs in 1100 and 3003...."

"5083 & 5086 For many years there has been a need for aluminum sheet and plate alloys that would offer, for high strength welded applications, several distinct benefits over such alloys as 5052 and 6061. Some of the benefits fabricators have been seeking are greater design efficiency, better welding characteristics, good forming properties, excellent resistance to corrosion and the same economy as in other non heat-treatable alloys. Metallurgical research has developed 5083 and 5086 as superior weldable alloys which fill these needs. Both alloys have virtually the same characteristics with 5083 having slightly higher mechanical properties due to the increased manganese content over 5086. Applications: unfired pressure vessels, missile containers, heavy-duty truck and trailer assemblies, boat hulls and superstructures"

Anyone have any experience like John with 5052 vs. 5083 and 5086? These seem like the best grades to research. I appreciate everyone’s input and advice. So "to build to the annealed strength" means to the properties of the alloy after it's "being worked" is complete and it's in it's final annealed and heat treated state?

Regards,

--JMarsa
"O" is the nomenclature for the strenght of the alloy, and can be applied to any alloy, ie. 3003-O, 5052-O, 6061-O, etc. "O" is soft, and H32 is what is considered "half-hard", and is still malable and would not provide much strength. Non-treatable alloys come in O, H14, and H32. Treatable alloys have a "Tx", ie. T3, T4, T6, etc, to designate the hardness of the alloy. 5083 and 5086 are not alloys that I am familiar with.

For frame rails which will be under considerable stresses during turning, accelleration, and braking, I would use a heat treatable alloy. If you form in "O" or normalized condition, it will be easy to fabricate bends and radius'. Once assmebled, install them in a heat treating fixure and heat treat. It would probably be as good as an unboxed rail at least. Just figure the cost to do in aluminum correctly over steel will be exponetionally (sp?) different.

In the vintage aircraft world which I am familiar with, 3003 is great for making engine cowling, hot rod hoods, stuff with low stresses that need alot of forming. 5052 is mainly used for aircraft fuel tanks, aluminum tubing for fuel line, etc. 6061-T6 is used in structural locations.

Mike

David Pozzi
07-16-2005, 05:37 PM
I wouldn't use 5052 in an aluminum "tub" structure unless I were making a smaller complicated part that had some sharp bends. 6061 is the main alloy used in aluminum monococue sports-racers. Of course most of them are built in Gt Britain and they have different alloys. I beileve L72 is the one used, but I might be wrong.

6061 is easily cracked when bends are made, you need to make large radius bends.
2024 is stronger but cracks even more easily, I've seen it used but only on very flat panels.

The only reasion I can think of for boyd using 5052 is better formability with less cracking risk. The more the alumium is hammered on, the stiffer, and harder it get's unless it's annealed. If you are set on a "T" why not a track T with some structure?

Avoid welding it if at all possible, use rivets, adhesives and bolts. Most sports-race car tubs use steel bulkheads with sheet aluminum skin riveted/glued on.

The Ford GT is made from welded aluminum extrusions. There is probably an SAE paper written on it and available from the SAE website.