How much force is needed to bend steel?

[Majin Gojira]

Just something I've always wanted to know, really.

Basically this is so I can quantify certain super-strong characters.

A solid rod 2 inches thick

A hollow rod 1/2 an inch thick

a Sheet 2 inches thick

A sheet 4 inches thick

6-inch thick sheet

Assume time of this is about of less than 5 seconds.

Any takers?

[PainRack]

You need to quantify strain.

THen we can apply Young modulus.IIRC,iron is 3k.(or was it 300 )

[Majin Gojira]

And that is something I know nothing about...-_-;

[BlkbrryTheGreat]

It would depend upon how long the steel rods were and how/where you applied the force/s.

[Darth Wong]

Depends on the grade of steel. Are we talking about a high-strength tool steel or armour-plate steel, standard structural steel, or shitty low-grade steel?

[Mark S]

The hollow rod, is 1/2 inch its inside diameter? outside diameter? wall thickness? If it's wall thickness, what's the outside diameter?

[SWPIGWANG]

It also depends how much you want to bend it since elastic bending is still bending.....

The question here is really torque not force...... A long enough rod/sheet would bend itself if supported incorrectly.

[Admiral Valdemar]

Maybe just using stainless steel as a basis would be simple enough... unless I forgot something about its properties, it's been years since I did design & technology.

[aerius]

There's still a million different types of stainless steels with wildly differing strengths and properties. My math is kinda crap these days and I don't remember the formulas anymore, so let's start by making some assumptions on the steel.

Let's assume heat treated 4130 since it's a pretty common steel, and we can go from there and fill out the lengths, tube diameters, and other stuff.

[Darth Wong]

There's also the length of the bar being bent, and the question of whether the superhuman in question is using a physical object to support the middle of the bar and increase his ability to apply bending moment.

[LordShaithis]

Two-foot bar, one inch in diameter, grasped from the ends and bent without use of an object in the middle. Use whatever type of steel would be most resistant to this.

[Zoink]

Two-foot bar, one inch in diameter, grasped from the ends and bent without use of an object in the middle. Use whatever type of steel would be most resistant to this.

To calculate bending of bars use:

F=Mc/I

F=Bending stress on outer fibers (lb/in^2)
M=Bending moment (in-lb)
c=distance to outer fibers from neutral axis (in)
I=Inertia (in^4, depends on shape)

c=0.5 in
I=(1/4)pi*(0.5)^4=0.049in^4

F=235 ksi (yield of AerMet 100 steel, I don't know if this is the strongest, my reference books are mostly all aerospace aluminum because that's what I work with)

therefore M=23030 in-lb (moment to deform bar w/o middle object), the force on each thumb and little finger (assume 4in wide hand) would be 5758 lb.

If you were to bend the bar over your knee, you would need to push down with a total force of 23030/12 = 1919 lb at each end (3838 lb total)

So there you go, you can run the numbers yourself if you like, because I did it rather fast during my break.

[aerius]

F=235 ksi (yield of AerMet 100 steel, I don't know if this is the strongest, my reference books are mostly all aerospace aluminum because that's what I work with)

They've got a slightly stronger version of Aermet 100 out now known as Aermet 310, but the datasheets I have don't have a specific yield strength listed, they just say it's >250ksi. I'm also kinda surprised that your reference book lists Aermet 100 yield strength at 235ksi, most sources I've seen including the manufacturer list it as >250ksi, topping out at around 260ksi (I'm somewhat obsessed with Aermet since I had a bicycle frame made out of it).

Highest yield strength steel I've found so far is Grade 18Ni(350) Maraging Steel with a yield strength of 295 ksi, I remember seeing much stronger ones somewhere but I can't find them at the moment.

[Zoink]

I'm also kinda surprised that your reference book lists Aermet 100 yield strength at 235ksi, most sources I've seen including the manufacturer list it as >250ksi, topping out at around 260ksi (I'm somewhat obsessed with Aermet since I had a bicycle frame made out of it).

The source in question was the military's aeronautical material reference book; the values have to be super conservative. Strength values are just statistical averages, usually something like "99% of the samples have a higher strength value with a confidence of 95%" (which is an "A" basis, which is the value aircraft parts are made to). In this specific case they used an "S" basis (the lowest published figure for Aermet 100) for the value because the 'A' value wasn't available .

In certain applications where failure doesn't mean catastrophic loss of life, you can use less conservative values. In a bike, the frame would probably bend (if welded correctly) and be rendered useless before snapping in two and impaling someone.