Why Does Mild Steel Only Have One Yield Point?

[Mattheo]

Homework Statement

I had a Young's Modulus experiment in lab. Our specimen, which was used, was mild steel. After plotting the graph I realized that there was only one yield point. However, as I read from many sources, there must be two yield points for mild steel(upper and lower). I am pretty sure that I didn't to any mistakes since the data were recorded by a computer.

Can anyone explain to me how that is possible to get a one yield point from mild steel.

Homework Equations

E = (ΔL/L)/(F/A)

The Attempt at a Solution

 

[Chestermiller]

Homework Statement

I had a Young's Modulus experiment in lab. Our specimen, which was used, was mild steel. After plotting the graph I realized that there was only one yield point. However, as I read from many sources, there must be two yield points for mild steel(upper and lower). I am pretty sure that I didn't to any mistakes since the data were recorded by a computer.

Can anyone explain to me how that is possible to get a one yield point from mild steel.

Homework Equations

E = (ΔL/L)/(F/A)

The Attempt at a Solution

Were you plotting the engineering stress strain curve (force divided by original cross sectional area) or the true stress strain curve (force divided by deformationally reduced cross sectional area)?

 

[Mattheo]

Were you plotting the engineering stress strain curve (force divided by original cross sectional area) or the true stress strain curve (force divided by deformationally reduced cross sectional area)?

Hello,

Engineering stress curve, force divided by original cross sectional area. The graph I got was exactly like this

http://www.benbest.com/cryonics/sscurve.gif


However, what I think is I should have got a graph like this with upper and lower yield points included

http://www.etomica.org/app/modules/sites/MaterialFracture/Images/SSPicture3.jpg

So there is a mistake?

 

[Chestermiller]

Hello,

Engineering stress curve, force divided by original cross sectional area. The graph I got was exactly like this

http://www.benbest.com/cryonics/sscurve.gif


However, what I think is I should have got a graph like this with upper and lower yield points included

http://www.etomica.org/app/modules/sites/MaterialFracture/Images/SSPicture3.jpg

So there is a mistake?

I don't know what to say. It's hard to argue with the data. I always tend to believe the data.

Chet

 

[Mattheo]

I don't know what to say. It's hard to argue with the data. I always tend to believe the data.

Chet

I learned that our equipment should have been more sensitive to measure the second yield point.

Cheers.