Ford F-150

The 3/16" 6061 T6 skid plate on the old Datsun 510 rally car took one heck of a beating and didn't show a dent, while friends with heavier steel plates had them all mangled in one season. It was a bugger to get bent to the correct shape to fit in the first place - much more difficult than the thinner and heavier steel plates. It had no compound curves to add stifness either.

With aluminum you need to make it stout enough that it doesn't move, because ANY movement causes stress fatigue - unlike steel where as long as you don't excede the elastic limit the stress does not build up

And mine is how will they hold up to all the deicing chemicals spread willy-nilly on our roads all winter long?

I think the electric vehicles are going to have problems due to the salt and cold too. Only time will tell I guess...

Heck they can't even keep their brake-lines from rusting through in the rust belt. NHTSA says that people have to wash their vehicles more often...

Hmmm....not quite. True fatigue occurs at cyclic loadings somewhat below the yield strength of any common structural metal. The differences between steel fatigue and aluminum fatigue have to do with the "endurance limit" of steel. Below certain levels of loading, steel will not fatigue.

That's not true for aluminum. Somewhere in the range of 10^6 and 10^7 cycles, steel's tendency to break from fatigue flattens out. With aluminum, the curve never flattens. Even small loads, repeated often enough, will cause aluminum (or copper) to break from fatigue.

But all of this occurs at loadings lower than the yield strength of the material.

These two Wikipedia descriptions are pretty good, and succinct:

Or, if you're in need of a good read, here's ASM's discussion:

Very likely it was the lack of curves that gave you better performance. My description above may have led to the wrong conclusion: it's a LACK of locally-stiffening compound curves that allows the sheet to spring away and avoid a dent, if the impact has a sufficiently short travel. In other words, a short, sharp blow will allow a flat plate to spring away, but a curved panel puts up local resistance surrounding the impact and the result is that the impact overloads the yield stength of the panel in that local spot. Curved panels make the material stiffer but also more prone to dent.

Your skid plate probably was stiffer and almost certainly stronger, at T6, than the thinner steel plates. But, being flat, the panel as a whole could spring away from an intrusion by a rock. The steel, having lower stiffness and strength, was simply overloaded at the point where it would bottom on a rock.

Or something like that.

Probably much better than steel. They make salt water workboats out of

Stiffness in bending varies with the cube of thickness. Strength is proportional to the thickness _squared_. For simple cases and for the sake of rough comparisons, anyway.

Ah, right, Ned. Thanks. I always forget that because I'm almost always looking at stiffness.

Aluminum boats are primarily 5000 series alloys because of corrosion resistance. Next in line of importance is the welding of it doesn't have the same weakening effect in the HAZ that it does on 6000 series alloys. Eric, from Whidbey Island, where lots of aluminum boats are built, and where I deal a lot with aluminum boat builders. Eric

Braggart!

David

Oh, jesus. No, not that kind of stiffness. Chassis stiffness. Tool stiffness -- and not that kind of tool, either. Whipped egg-white stiffness. You know. d8-)

• 1 phil k.

I don't mean to be a killjoy here, but I can't imagine what these things are going to cost!

They start at $25,000.

-jsw

They start around $26,000 and go north, fast.

They're already on the market, Richard. You can check out the actual prices.

Well, I hate to harp on Aluminum, but let see here: The quote "Flammability of Aluminum" turns up 25,300 search results. The quote "Flammability of Steel" turns up only 10 search results.

Try taking a piece of aluminum sheet and see if you can start a fire with it.

When you get frustrated, come on back and we can talk about why that happened.

I think you need to do a little further checking, especially regarding the cause of fires from aluminum wiring -- since you apparently are an electrician.

In such a fire, the aluminum wire doesn't burn. It starts a fire in the surrounding material through one of two causes: a high-resistance overheating, caused by loosening of the connection (aluminum's thermal expansion rate makes it unsuitable for use with conventional wiring connections); or from arcing caused by "micro-fretting" of the aluminum. If you're involved in electrical wiring for buildings, you should know this.

The flammability of aluminum, contrary to popular mythology, is very low. The flammability tests performed at atmospheric pressure, in air, consistently show that it won't sustain a fire. The flammability tests you're probably seeing are conducted in pure oxygen at pressures above atmospheric.

Aluminum powder is combustible and explosive. Wrought or cast aluminum is not. The British warship that burned in the Falkland Islands war, the Sheffield, did not have an aluminum superstructure, contrary to ill-informed media reports. It was steel. And it did not burn. Diesel fuel is what burned.

The video of a Ford truck prototype burning, that someone posted here yesterday, apparently do not show the aluminum burning. It shows the vinyl "disguise" cover burning, and burning of the plastics and probably some fuel, but the aluminum just melted into a heap.

So be careful about the ideas you're promoting about aluminum burning.

I do not think that means very much. I did a search on " Flammability of water " and got 6,470,000 search results. Do you think that water is much more flammable than steel?

Aluminum powder will burn fairly easily, but if you use a oxy acet torch on aluminum , you just get blobs of melted aluminum. Steel on the other hand can be cut with a oxy acet torch.

Dan