1. Home
  2. ⏣ General Metalworking
  3. welding aluminum
  4. Page 2

welding aluminum

I don't, but I still have a couple of Mechanics and Statics-and-Dynamics books from college, as old as I am. The formulas for moment of inertia and radius of gyration are the same but the Earth rotated the opposite way in those days, which makes it confusing.

About those tubes, Euler's formula and much of the rest are long lost in my memory, but my non-mathematical recollection of the situation is this. Increasing resistance to buckling for a given *weight* of of a given tubular material, by increasing tube diameter and thinning the walls, is self-limiting. You reach a degree of wall thinness at which the diameter (and the curvature) of the tube becomes a lesser factor and the thin walls begin to behave more like a plate loaded in compression, on edge. In other words, plate stiffness in compression-induced bending begins to cross curves with the sectional stiffness of the large-diameter tube.

Aluminum in the form of a tube, having 1/3 the density of steel and also 1/3 the stiffness (roughly), can be made larger in diameter (for the same material weight and length) because the relative wall thickness remains greater, even when the tube is somewhat larger in diameter. In other words, you can take advantage of aluminum's far greater plate stiffness, per pound of material, and, in doing so, you can increase the diameter of the tube somewhat. You can increase diameter and still have considerably thicker walls than you'd have with steel tubes of the same weight. The total effect is an increase in the radius of gyration for the aluminum tubes over the steel tubes, because of the greater diameter, before you start to cross curves with the plate stiffness of the walls.

To get back to the space frames for cars, and what I originally said about there being no theoretical advantage in performance for an aluminum-tube space frame, the things I've just said above don't change that. The performance of a space-frame car chassis is limited by stiffness, not by strength, and the actual resistance to buckling should never come into play at all, in a properly designed, fully triangulated space-frame chassis -- until you crash.

Ed Huntress

Reply to
Ed Huntress
Loading thread data ...

On Tue, 30 Nov 2004 21:05:34 GMT, Ted Edwards vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

Well all I can say is that reading these posts, my radius of gyration is becoming increasingly small, but my speed is being maintained. In the end my brain will probably exceed Yield Stress!

I do have to say that you guys may be arguing at cross purposes. I _thought_ that Ed was saying that tube stiffness is not the only thing. Wall thickness is important as well, because that will prevent buckling under certain circumstances.

I am trying to learn here, from minds that scare my dilettante little brain!

AFAICS the argument revolves around the fact that you can keep the same wall thickness or even nincrease it, using aluminium, and use a larger diameter tube to achieve the stiffness. You in fact need to do this.

Having a smaller diameter tube would presumably make a given wall thickness less likely to buckle. That feels right to me.

But would a steel tube of small diameter, having the _same weight_ as a larger tube of aluminium, have as strong a _wall_ as the alum one?

If you thinned the walls of the steel pipe, in order to allow a larger diameter for the same weight, the walls would _not_ be as strong as an aluminium tube of the same weight as the thin-walled steel one, with wall thickness strengthening as a cube of the thickness (?) while weight is linear. Looking at the wall as a bar of steel, aluminium would be stiffer than the same _weight_ bar of steel. (?????)

Hope I am saying this in a way that can be understood. trying to avoid having to learn a whole dgree's worth of engineering terms and conditions, by using gut feeling and laymen's terms.

Reply to
Old Nick

Here's the lab demo: Take a soda straw. Push on both ends. Watch what happens and write a description of it in your lab notes.

Then take an aluminum beer can. Place it on end on the floor, or on your forehead, whichever you prefer. Stomp on it. Watch what happens and write a description of it in your lab notes.

You now have completed the course in Failure Modes of Tubes of Widely Varying Proportions in Compression, and you're ready to design the Lotus 8.

Actually, Chapman already designed the Lotus 8, and wished that he hadn't. The Lotus 9 was developed into the Budweiser beer can and has changed life as we know it.

Ed Huntress

Reply to
Ed Huntress

On Wed, 1 Dec 2004 01:20:10 -0500, "Ed Huntress" vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

Peuh! Boring!

Used the straw to drink the beer. As I wanted to ensure that the test was repeatable I tried this severla tims. Now the strwa is alread bnet cause I staempd on it. I reul...re...know this nillu... nuli... makes the test not vrey god.

msorry. Faliuer mode of a diffrent sot altogether.

Sory. That's...... shoobee _differen_ sot.

no kid!??

Reply to
Old Nick

My life is forever changed because of it.

Whats a Lotus 9?

Gunner

"I mean, when's the last time you heard of a college where the Young Republicans staged a "Sit In" to close down the Humanities building? On the flip side, how many sit in's were staged to close the ROTC building back in the '60's? Liberals stage protests, do civil disobedience, etc. Conservatives talk politely and try to work out a solution to problems through discourse until they believe that talking won't work... they they go home and open the gun cabinets. Pray things never get to the point where the conservatives decide that "civil disobedience" is the next step, because that's a very short route to "voting from the rooftops" Jeffrey Swartz, Misc.Survivalism

Reply to
Gunner

AFAIK, it's a flower that grows in CHina and Japan.

Ted

Reply to
Ted Edwards

You might want to get it. It's put out by Lincolm (the welder people) and, like most of their books, is both good and cheap. As well as unusually readable theoretical stuff, there's a lot of charts, tables, worked problems and comparisons of designs.

Correct. As with most things, if you go to extremes, you get into trouble. Just where that point occurs requires working through a particular case. My point is that it is not clear that going to aluminum will improve stiffness - you need to do the calculations for a particular case.

BTW, similar considerations apply to torsion.

Ted

Reply to
Ted Edwards

And a symbol of...erm... *cough* fun :)

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

formatting link

Reply to
Tim Williams

Would I kid you? The 9-1/2 was *really* brilliant. It didn't make much of a car, because, in his never-ending quest to add lightness, he left off the wheels and seats. But it had a great sound system. It became the iPod.

Ed Huntress

Reply to
Ed Huntress

I don't know. It probably never made it off the drawing board. Or maybe it was one of the small open-wheelers.

The 8 was a one-off, a design exercise toward the purest possible space frame. It turned out to be a backfire, construction-wise, because it required a lot of add-on assemblies to be a practical car. But it raced, and it was a good one.

The 10, IIRC, was a tiny front-engined car like the 11. The Lotus 11 was a major design, one of the last of the little front-engined racing sports cars made for the 1100 cc class. Somebody is building replicas. It's a wild little thing.

Ed Huntress

Reply to
Ed Huntress

Cars? Cars????? Homebrew racing cars?????

Who the hell cares about them?????

This whole thing has been about freaking cars??????????????

Christos on a crutch...airplanes, firearms, even sail boats...but cars????????

Your kidding me...right?

Shit..they havent made a decent car since my Rambler.

Gunner

"I mean, when's the last time you heard of a college where the Young Republicans staged a "Sit In" to close down the Humanities building? On the flip side, how many sit in's were staged to close the ROTC building back in the '60's? Liberals stage protests, do civil disobedience, etc. Conservatives talk politely and try to work out a solution to problems through discourse until they believe that talking won't work... they they go home and open the gun cabinets. Pray things never get to the point where the conservatives decide that "civil disobedience" is the next step, because that's a very short route to "voting from the rooftops" Jeffrey Swartz, Misc.Survivalism

Reply to
Gunner

Well, in terms of attendance, car racing is the world's most popular professional sport.

Mostly Lotus cars.

Cars. Cars that weigh from around 800 pounds to 1,300 pounds. Really little cars. Fast little cars.

I think you mean "descent." That's how you get a Rambler started, right? It's all downhill. d8-)

Ed Huntress

Reply to
Ed Huntress

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.