Tavarez

If you'd like too don't forget to answer the above poll!

I've been asking this question around lately and hopefully this thread will join all the answers. I have somewhat of a fascination with the difference in both frames, some Z owners seem to lay weight on the "superiority" of their cars over the base C6. The Frame is one of the unmodifiable aspects of our cars and I was wanting to know the true advantages Vs the true disadvantages of Aluminum Vs Steel in the C6 frame application. I know the steel frame to be undeniably stiffer than the Aluminum, not only based on the properties of Aluminum but also from a post quoting a GM engineer mentioning it was 97% as rigid as the steel frame including its magnesium fixed roof. This said, the Aluminum frame is undeniably lighter.

Browsing this forum i've learned that good Torisonal Chassis Rigidity is essential in a well handling race car. On the other hand, weight is also the enemy of a performance car. I can understand the advantages of the aluminum application in the street scenario but is the Z06 Aluminum frame really superior? For the highly stressful racecar application what do you believe to be the best choice in frames. I take notice that although the Aluminum frame is 97% as rigid, which is really close to the steel it does so with a fixed roof. In a racecar/track application the Steel frame would also be accompanied by a fixed roof. Judging that Aluminum flexes more and also has no Fatigue limit and so overtime is more prone to damage I can't seem to place it to be as superior in all extreme situations as I feel steel. Set me straight, maybe this thread will justify what I feel or give me more trust in aluminum. All my thoughts are based almost purely on speculation so once again I hope the experts chime in.

By the way I know it's rather annoying that I keep bringing this subject up regarding both cars but it's a subject I feel not only is appliable to our vehicles but all vehicles aswell as vehicles in the future. I keep dropping to PM's to certain forum members regarding this and I feel i'm somewhat bombarding with my questions so i'll leave it to this thread hopefully to help me out with all the technical aspects that I may or may not understand. I'm up for reading any technical data you provide no matter how intensive it may be. Thank you!

Steel VS Aluminum Basic Facts
http://ussautomotive.com/auto/steelvsal/basicfacts.htm

Dana Aluminum Frame Article:
http://dana.mediaroom.com/file.php/1...na_article.pdf

More Articles on AL Frame (posted on digitalcorvette)
Aluminum Now - Aluminum safer in crash tests
http://www.aluminum.org/ANTemplate.c...ContentID=9015

Automotive design
http://www.autofieldguide.com/articles/040507.html

Job Shop
http://www.jobshop.com/techinfo/pape...trusions.shtml




Supplementary Threads

Torsional Chassis Ridgidity
http://forums.corvetteforum.com/show...assis+Rigidity

Z06 Targa Discussion (some talk on frames)
http://forums.corvetteforum.com/show...1347410&page=4

C6R Frame Thread
http://forums.corvetteforum.com/show...ight=C6R+Frame

Aluminum Frame Specifications:

Specifications:

Frame Weight 285 lbs
(weight as shipped) *
Self Piercing Rivets 236
Total Laser Weld Length 14,195 mm
Combined Max Material Thickness
5.5 mm
Combined Min Material Thickness
3.5 mm

calemasters

The aluminum frame is lighter and that is why it was used on the Z06. If the 97% figure is correct, it is close to the steel frame for torsional rigidity. Keep in mind that the LS7 used in the Z06 has more torque, so the rigidity/torque ratio is less for the Z06, when compared to the C6 with steel frame and the LS2.

Which frame is better? It just depends on your set of criteria. If you want strength and rigidity and fatigue resistance, the steel is better. If you want low mass, aluminum alloy is better.

Tavarez

So would the aluminum not fare aswell in endurance racing, like the C6R?

Test Driver

Nope.

calemasters

The alumium Z06 frame will hold up fine. It is just that the steel frame has a higher limit for fatige failure.

EuroRod

Hmmmm, wonder how much trouble it would be to swap out? Guess it would have to come out the bottom, right?

Tavarez

Are the aluminum frame dimensions the same as the steel one aswell?

ronsc1985

One downside to aluminum frames is the difficulty in attaching things to it like roll bars and cages. It is doable but a major PITA and requires using equipment not ordinarily found in chassis shops. This is a big deal if you plan on doing serious modifications which bump up against the various racing organizations safety rules.

Red Shift

Most of what has been said in this thread is correct. A good way to see how that information is used in designing something is to look at bicycle frames. I don't have exact numbers at hand so I'll use ballpark figures. Aluminum is about half the density of steel, so you might think that the frame could be half the weight. Except that it's maybe 2/3rds the strength. So you have to thicken the aluminum to compensate--but not twice as thick. So your still ahead of the game...until you start to talk about fatigue. The best exammple of fatigue is breaking a coat hanger by repeaded bending. All metals have a "fatigue limit" usually expressed as a percentage of maximum strength. If the loads on the metal never pass that percentage, the metal doesn't fatigue and has an indefinite life. But the greater the amount and times you go past that limit, the sooner the metal will fail. Other than engine work, this is pretty much what airplane maintenance is all about. And that's because the fatigue limit for aluminum is a much lower percentage of max load than it is for steel. So a steel frame may be able to go to 70% of maximum load with no fatigue, but aluminum can only go to about 50%. So now our aluminum frame has to be made even thicker so the expected loads are only half of max rather than 70%. The outcome is what you see in bikes. Aluminum framed bikes have bigger, bulkier looking frames that are usually a bit lighter and a bit stiffer. But the trade-offs are so close (and for mountain bikes a little flex is a nice thing) that neither frame type has taken over. If the Z06 can drop several hundred pounds at the expense of 3% stiffness it can easily make up any losses in the turns with acceleration on the straights. But as with any high tech material, from Aluminum to carbon fiber, the attention to fatigue effects can't let up. Steel usually is a lot lower maintenance. This isn't to say that Z06 owners need to obsess over their frame life. Unless your daily commute includes the Nurburgring you probably don't ever get near the fatigue limits of that chassis.

Tavarez

How much weight did the Z06 frame shave off? Like 140?

2bubbas

The Z06 with its aluminum frame is for street bragging rights.

I doubt many Z06 will do track duty but I've been wrong once or twice in the past.

OregonC6

Interesting technical discussion. Thanks to all contributors. I think it should be remembered that the hydroformed steel frame is very innovative itself and replaces frames that were fabricated of many parts with many weaknesses and failure points.

So.....while the aluminum frame may be lighter and superior in some ways the steel is , itself, very strong and high performance.

The thing that interests me is the long term performance of the steel vs aluminum. If asked to bet I'd say the steel will fare better in the long run standing up to constant flexing without cracks or failure.....I have never heard anything about problems with C5 frames and we are approaching ten years experience with those....

and is not the C5 frame essentially the same as the C6?

D-ROCK

The aluminium frame may be at a weight advantage but as far as durability, I'm going with the steel frame. A disadvantage of aluminium is that seperate aluminium pieces cannot be welded together. While welding aluminium is not impossible, it is very difficult to achieve. One positive side to the aluminium frame is its ability to resist corrosion. All in all, as far as safety and durability, I believe the steel is better.

xs650

Steel makes more sense for most automotive frames. Designing with aluminum takes a different approach and higher level of design skill for high fatigue applications. Simply replacing a steel frame with a bit thicker wall aluminum frame isn't generally the best way to go about the job.

Aluminum can be succesfully used for structural design, but it's not cheap to design and fabricate properly and Bubba will have a tough time fixing it in his dirt floored shop.

Aircraft are one area where aluminum is a hands down favorite over steel. Aircraft structures have to be light weight and they have to have long fatigue lives. They do it through good design.

phillymike

I weld aluminum quite regularly. It is not as hard as people like to think. The days of the 1000lb TIG welder are fading as well. My Miller inverter unit, weighs about 50 lbs, runs off 120/240 and anyone who can weld steel with a oxy/actl setup can learn to weld Al in a few hours on it.

Body shops are becoming well versed in Al repair as well. Aluminum body panels are no longer limited to boutique cars like the NSX. A lot of Jaguars and even some Hondas have aluminum bodies. If a new Jag XK needs a 1/4 do you think they total the car or ship it back to the UK for repair? It's repaired more or less just like any other car. I'm not sure if the repair manuals are out for the Z06 yet, but I'm positive that the frame is FAR from disposable.


As far as strength/weight numbers some of you may be interested in taking a look at http://www.matweb.com. They have material properties for just about any alloy you can think of.

It varies by the specific alloys compared, but as a general rule Al is about 1/3rd the mass of a ferrous alloy.

LTC Z06

Aluminum took us to the moon, flies us around every day, and many combat vehicles like the M2 Bradley are made from it. They both have advantages and disadvantages, there are plenty of aluminum "frame" cars racing out there.

Tavarez

Oh that reminds me, I was curious to know what some of the more predominant aluminum frame race cars are?

Tavarez

Here's an article regarding the aluminum frame it speaksa about Dana, the company that built the new aluminum frames. Turns out they're actually idententical to the steel frames so that both cars can be put through the same assembly line.

http://dana.mediaroom.com/file.php/1...na_article.pdf

TTRotary

In fact, I cannot think of a single solitary modern-day AL-framed purpose-built race car. Nearly all Formula cars, NASCAR, Sprint, and most SCCA spec classes (F500, D-Sport, C-Sport) all use steel cage-frames with a non-structural 'Glass or AL body bolted on. The exception to this rule is the pro Formula cars like Indy, CART, F1, which all use Carbon monocoques. Formula Atlantic and Star Formula Mazda have also transitioned just recently to Carbon (the pre-2004 Formula cars were aforementioned steel).

Steel predominates for a number of reasons, which chiefly include, in order of importance: (1) cost, (2) field repairability, (3) known attributes of, (4) known behavior in crashes, (5) known endurance and (6) the SCCA and racers are never fond of fundamental, cost increasing technology. The fact is that AL requires substantially more cost to perform only incrementally better than steel, which drives costs up, which in turn is the anathema of spec / formula racing. In short, it's just not worth the bother.

That said, marques such as Ferrari did build AL framed race cars in the 50s and eraly 60s and these were considered state of the art then. Of course, Al continues to feature prominently as a performance material in components and as a reinforcement to older steel frame spec racer designs because of it's rigidity.

shopdog

They do it through frequent and extensive inspections and proactive replacement as well as through good design.

As was mentioned earlier, aluminum doesn't have a fatigue limit. That means, unlike steel, even minor stress has a cumulative effect. Steel, and most other metals, have a fatigue limit, stresses below the fatigue limit can be supported indefinitely. No so with aluminum. All aluminum structures have a finite working life.

Good design can push that working life out pretty far, and vigorous inspection programs can catch impending failures before they become catastrophic, but the one sure thing is that ultimately all aluminum structures will fail. That doesn't have to be the case with steel. If a steel structure is designed so that stresses are below the fatigue limit, a steel structure will never suffer a fatigue failure.