Why Does Mild Steel Only Have One Yield Point?

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Discussion Overview

The discussion revolves around the observation of a single yield point in mild steel during a Young's Modulus experiment, contrasting with the expectation of two yield points (upper and lower) based on various sources. Participants explore the implications of this observation, questioning the nature of the stress-strain curve plotted and the sensitivity of the measuring equipment.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that their experiment yielded only one yield point for mild steel, despite expectations of two, and seeks an explanation for this discrepancy.
  • Another participant questions whether the graph plotted was based on engineering stress or true stress, suggesting this could influence the observed yield points.
  • A participant confirms that the graph plotted was indeed the engineering stress curve, which may not show the lower yield point.
  • There is a suggestion that the equipment used may not have been sensitive enough to detect the second yield point.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons behind the observation of a single yield point. Multiple views remain regarding the nature of the stress-strain curve and the adequacy of the measuring equipment.

Contextual Notes

Participants express uncertainty about the implications of using different types of stress calculations and the sensitivity of the equipment, which may affect the results. There is no resolution on whether a mistake was made in the experiment.

Mattheo
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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

 
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Mattheo said:

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)?
 
Chestermiller said:
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?
 
Mattheo said:
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
 
Chestermiller said:
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.
 

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