Aluminium can be stronger than carbon fiber

Scandium would be horrible for use in a car. I will keep this as brief as possible:

I used to be a former bicycle racer and there was a time that Scandium aluminum frames were very popular. I received several of them. Understand that because aluminum has an no fatigue limit, unlike steel or carbon which have finite fatigue limits, every time the piece is stressed, it degrades. Take an aluminum paperclip and bend in back and forth and tell me how quickly it breaks. Scandium does make aluminum stronger when added but it also makes it more brittle, regardless of heat treating (which usually strengthens aluminum), especially as it is fatigued. Ultimately, all of the frames would crack after a season of use due to this.

In a car, all of these stressed parts will end up breaking very prematurely. I wouldn't buy a car with scandium in the aluminum.

And just to be clear, it wouldn't be stronger than carbon fiber on a pound for pound basis once the carbon reaches a critical mass of thickness and can be woven.

 

Thanks, guess we have the answer to that one.
Good to know.

 

+1

Helluva first post though! Cool!

[Unless he's a Scandium salesman I guess, in which case I doubt he'll be back! ]

Cheers,
Ian

 

Sorry, I was in the middle of a few things when I made that post and made something unclear.

What I meant to say is that I am a former professional cyclist . In addition to the usual bicycle racing, I used to test equipment for various manufacturers, which is why I know a little about scandium.

 

As written, there is so much wrong with this.

Wouldn't bet on it.

 

I kinda thought the same, but figured someone would be along soon with some corrections.

I don't think the aircraft boys would have stuck with it for so long if it is so terribly subject to "fatigue" for example.....

I wonder if the OP will return?.......

Cheers,
Ian

 

Aluminum has well defined fatigue limits. Further the alloy and heat treat of aluminum will impact its fatigue limits. Durability is a function of stress, or applied load. Generally speaking, the higher the load the shorter the fatigue life. True for steel and true for aluminum. Carbon is a different animal and doesn't fatigue in the same manner as metals. It is generally considered to be better in fatigue than metal.

Carbon fiber is useless for structural applications unless it is woven or layered. Have no idea what you mean by 'critical mass of thickness'. In many applications the final layered or woven product is no stronger than aluminum, has more thickness than a comparable aluminum part, but remains lighter because its density is ~55% of aluminum.

 

Guys, this was a bomb tosser. He joined yesterday, posted once and you'll never hear from him again.

That being said, Sherpa your post was very informative!

 

Dude's probably got some farms in Australia..

 

Ferrous and titanium derived alloys have a fatigue limit whereby if the stress applied does not exceed that limit, it will never reach failure. Aluminum alloys have no fatigue limit so that a number of stresses, no matter how small, will eventually cause failure. Yet you are saying this is not true. Interesting because every white paper that I was given on applied material physics disagrees with your statement. Can you tell me how my statement is false, given your open derision of my statement. And I'm sure that you'll pepper us with credentials and such about your authority but what I really want to know is how is that statement incorrect.

Lastly, you said exactly what I meant when I typed my statement about carbon fiber being pound for pound, stronger than aluminum. As long as it's not something like a small strand, and is actually weaved, layered, and properly cured, it will be stronger than aluminum for a given weight (hence my "pound for pound" statement).

 

I think he is having trouble understanding fatigue limit. When you said Aluminum has no limit, he thought it meant Aluminum will never break instead of, aluminum has no limit because any load is degrading the material eventually leading to failure.

 

Well, it doesn't have a fatigue limit, which means that every stress applied to it, regardless of how small, eventually causes failure. I didn't say it has no fatigue life, I said it has no fatigue limit. I can't believe that someone who's an expert could confuse the two.

As I said, for such condescension, I would like to see where I'm wrong. He already agreed with my statement about carbon fiber being stronger pound for pound than aluminum. Is he going disagree with my other statement and stand by his that aluminum does have a fatigue limit like steel and titanium do?

 

+1

One of the reasons the FIA (& indeed the teams themselves) are pretty "paranoid" about keeping track of CF parts.

Of course. First time I saw it "raw" (in strands) I was like "this **** is strong?"

Then we tried to break it. I became a believer.

Same with good ol' glass fiber - A "master" at laying it up would produce a part 50% lighter *and* 50% stronger than a "rookie"...... I'm sure it's different now, but I still want to believe there's some "craftsmen" out there.....

But where's the fun in that?

Seems we've got a pretty decent thread going here - Heated (yet respectful) debates are always good.

+1

I LOL'd again!

Cheers,
Ian

 

I generally think in terms of practical limits, which is how things are actually designed, versus theoretical. While aluminum doesn't exhibit a 'knee' like ferrous metals there are generally accepted runout limits. That said, I'll retract my comment about fatigue limit for as you state there is no theoretical limit. I'll also retract my statement regarding carbon, there are just too many variables to make a blanket statement with respect to real structure.

I am interested in your original comment that "Ultimately, all of the frames would crack after a season of use due to this". How many (fatigue) cycles were applied to the frames over a season? Taking a WAG assuming 8hrs/day*cadence of 150 (per minute)*365 days=2.6x10^7. That seems very conservative (as in way too high), but is not overly high for aluminum depending on stress level. So I wonder if the (bicycle) frames w/scandium alloy were designed based on static criteria versus fatigue, e.g. "hey, it is twice as strong so we can make it half as thick (and half the weight), cool" all the while neglecting that the fatigue stresses doubled which will have a huge impact on life. Designs are always a trade-off of properties, even with the myriad of (Al) alloys that don't incorporate scandium, so outright dismissal of such is disingenuous. Rocket science is one field that doesn't necessarily give a wit about endurance limit.

 

I found this video very informative when I first saw it a few years ago...and after having busted a couple drive shafts in my time.....

https://www.youtube.com/watch?v=hjErH4_1fks

 

One season varies person to person. One person could do a lot of climbing or sprinting while the other rode incredibly smooth. However, based on those of us who had the test frames, it appeared that the biggest determining factor was mileage. I broke two in one season, one after 12.5k miles and the other after 11k miles. Both broke in nearly identical places: on the drive side chain stay just behind the bottom bracket along the edge of the weld (but not on the word itself). Its possible that maybe that part was exposed to too much heat via welding but it's really just a high stressed part.

The average recreational cyclist rides 4K miles a year so a pro who rides 25k a year gets to accelerate the life cycle in real world conditions. My friends who rode in the TdF and other grand tours would get new scandium frames every 6 to 8 weeks and during a grand tour, some would have their frames changed on the rest day. They weren't going to wait for a possible failure, even though the mileage wasn't close to the 10k mark.

Again, just my experience in a real world but non aerospace environment.

 

Smith & Wesson is using an Aluminium Scandium alloy in some of their revolvers, for the frames.

The huge benefit with Carbon fiber ( and Glass fibre) reinfoced plastic is that it can be made fairly easily in complex shapes.

Searching the 'net - found some bike sites that pointed out that it oxydises as easily as Aluminium, and has a bad fatigue limit.
I searched on Scandium vs Carbon and Scandium vs Titanium.
Apparently Titanium alloys and Carbon fibre reinforced plastic are preferable for bike frames over Scandium alloys.

 

It's worth mentioning that one of the virtues of carbon fibre is the ability to design the lay-up to direct and dissipate loads through the structure in particular ways. A key benefit of this is to direct impact loads away from and around the driver cockpit zone. In general, CF allows the chassis structure to be thicker where required by local point loads (e.g. engine or suspension mounts) and thinner elsewhere. A large portion of the man-hours required to design a composite tub is taken up with the finite-element analysis needed to accomplish this. As I understand it, the design of a metal monocoque chassis cannot be approached in the same way. Of course, these things can be done to some degree with a metal tube-frame but that will be heavier than a comparable CF or metal monocoque, and you won't get the overall coverage of a fully-surfaced structure.

 

Aluminum alloys in Ferraris are a reality. The current F12, for example, is built using a dozen different aluminum alloys with some never used before in cars. I believe they know a thing or two about aluminum. CF is reserved for panels on LEs and tubs on hypercars. They have been advertising their upcoming all-in-one aluminum space frame for all front/mid engine models outside of their hypercars. We'll see.

 

Audi and Norsk Hydro know quite a bit how to build Aluminium cars. I dare say they have the best experience.

 

Here's a question for you all:

Do you not think that Ferrari (along with just about every other car/race car/engine manufacturer etc., etc.), might have specialist materials engineers who fully investigate such materials as Scandium, in order to assess its suitability for road or race car use?

Ferrari have a great deal of experience of building steel, alloy and carbon fibre based cars, and I seriously doubt that there are many materials on this planet that their engineers are not aware of that might be suitable to use.

 

strength... how strong is something... compared to what... it depends on how one defines or parses strength... a favorite is: glass is more elastic than a rubber band :=)