Question for you Mech Engineering guys/gals

[IveGotTheBlues]

Ok so I'm in the Computer Science/Engineering field. But I remember from my Physics classes in school, graphing the Stress v Strain curve for materials. It was like a section on properties of materials.

Anyhow, I remember that the graphs had a general look depending on the material. The graph was linearly increasing until it's yield point. Then it became parabolic until each material had a rupture point.

Well, I had a debate with my younger brother, who is an Iron Worker. He bends a lot of metal for a living, machining different metals for companies to utilize in the construction of things (buildings, walls, etc).

Debate was that metal cannot snap. It only bends. Basically, if you take a rod of metal, apply opposing pressue to both ends, it will keep bending until it folds. He says it's impossible to snap.

Logically, I felt that everything can snap because I thought every material had a rupture point on the Stress v Strain curve.

What is the answer?

 

[Misquamarauder]

You're both right.
You: Everthing does have a "snap" point where Stress/Strain curves intersect.
He: Real world, you can fold a piece of metal in half and it won't break. OTOH, if you bend a 6" machinist's scale, it'll snap.

Size, material ducility, and various other properties go into the mix, but in the end, I'd say you are the most correct.

 

[IveGotTheBlues]

You're both right.
You: Everthing does have a "snap" point where Stress/Strain curves intersect.
He: Real world, you can fold a piece of metal in half and it won't break. OTOH, if you bend a 6" machinist's scale, it'll snap.

Size, material ducility, and various other properties go into the mix, but in the end, I'd say you are the most correct.

Ok. The way I interpreted his arguement is that I agree that you can fold/bend metal. That pretty obvious because there are many applications for bending metals. I mean.. all of us have exhaust on our cars.

However, he said it's IMPOSSIBLE for it to snap. Since everything has a rupture point on the curve as you suggest, that means all metals should be POSSIBLE to snap.

So, by contradiction, his argument is incorrect because all metals can snap according to the curve.

Or are you saying that depending on the many variables, there are some metals which ARE impossible to snap?

 

[SecondhandSnake]

Theohetically, every metal will eventually snap. Even the most ductile metals have a rupture point eventually. Think about it, after the elastic zone you have the plastic zone, then what? Rupture.

Where you get into a grey area is the semantics used, particularly "snap" and "bend." Technically speaking yes, they'll yield before they rupture, so you could say they'll bend before snapping.

I don't think there's a material out there that won't snap eventually. There's a fixed ultimate strength, so you just need to exceed that.

Of course that's assuming I'm understanding correctly. It's a bit of a strange argument.

 

[IveGotTheBlues]

Theohetically, every metal will eventually snap. Even the most ductile metals have a rupture point eventually. Think about it, after the elastic zone you have the plastic zone, then what? Rupture.

Where you get into a grey area is the semantics used, particularly "snap" and "bend." Technically speaking yes, they'll yield before they rupture, so you could say they'll bend before snapping.

I don't think there's a material out there that won't snap eventually. There's a fixed ultimate strength, so you just need to exceed that.

Of course that's assuming I'm understanding correctly. It's a bit of a strange argument.

Haha. Yes it is a strange arguement.

He has never taken a physics class. As far as science, he only believes what he sees. And obviously because a metal will bend before snapping and there isn't really a practical application to snap metal, he thinks metal can only bend.

From his point of view, he has never seen metal snap because all he does is bend metal.

 

[Blown_By_You]

I see 2 and 1/4 chrome steel snap all the time on peoples weld tests.. That would be a fail.
As an Iron worker, your brother would only be working with mild carbon steel, which is very soft and will not break, but get into something harder, like T22, or something that has been hardened or heat treated, and bet your ass it will break

 

[motoman991]

Your brother is dumb.

 

[Blown_By_You]

Mild Carbon tube test.. Bends nicely