Stress strain and tensile strength diagram

Click For Summary

Discussion Overview

The discussion revolves around the concepts of stress, strain, and tensile strength, particularly focusing on the behavior of materials after reaching their maximum tensile strength and the phenomenon of necking. Participants explore the implications of these concepts in the context of engineering stress-strain curves versus true stress-strain curves.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that stress decreases after reaching maximum tensile strength due to necking and strain hardening.
  • One participant expresses confusion about necking and its relationship to stress and strain, asking for clarification on the concept and the term "draw ratio."
  • Another participant agrees that necking is a key factor and questions how it affects the assumptions of engineering stress-strain curves compared to true stress-strain curves.
  • Participants discuss that necking results in a non-uniform deformation in the material, leading to a reduction in cross-sectional area.
  • There is a clarification that while the load decreases on the engineering stress-strain curve, true stress continues to increase until fracture due to the actual cross-sectional area being considered.
  • One participant acknowledges a previous misunderstanding regarding the relationship between load and stress in the context of the engineering stress-strain diagram.

Areas of Agreement / Disagreement

Participants generally agree that necking plays a significant role in the behavior of materials after maximum tensile strength, but there are varying levels of understanding and clarity regarding the implications for engineering versus true stress-strain curves. The discussion remains unresolved regarding the complete understanding of these concepts.

Contextual Notes

Participants express uncertainty about specific terms and concepts, such as "draw ratio" and the implications of necking on stress-strain relationships. There are also references to corrections made by participants regarding their earlier statements.

akkshaya
Messages
4
Reaction score
0
why does stress decrease after it reaches its maximum tensile strength after its plastic range ?
 
Engineering news on Phys.org
Hi akkshaya, welcome to PF. What are your thoughts? We don't simply provide answers here, because that wouldn't help anybody learn; you have to present your own attempt at a solution.
 
Look up necking and strain hardening, that should give you the information to understand why stress reduces after UTS.
 
all i know is that its due to the necking or the neck formation .when i sarched the info , it said about two tangents and "draw ratio".. what is a draw ratio??. necking is when large amount of strain is experienced if a little stress is applied .. is this right ? am not clear in this necking concept .. can you help me out ?
 
I agree that it corresponds to necking. How does necking affect the assumptions of an engineering stress - engineering strain curve? (Hint: compare with a true stress - true strain curve.)
 
necking means your sample gets much thinner at some point than the rest. Imagine most of the cylindrical sample diameter is say 1 inch, length is 5 inches, there's a region which is 1 inch wide in the middle that's only half an inch in diameter. that region is said to show necking, deformation is not uniform in your tensile test sample.
 
thanks for the necking concept ... and i saw that true stress-true strain curve and its explanations... i still don't uderstand how the load falls off if the area of cross section decreases after the application of a lot of stress..
 
akkshaya said:
i still don't uderstand how the load falls off if the area of cross section decreases after the application of a lot of stress..

[STRIKE]The load didn't fall off! That's absolutely not what's plotted on the y-axis of an engineering stress-strain diagram.[/STRIKE]

The load decreases from its maximum point, but what is happening to the true stress (vs. the engineering stress) in the material?

EDIT: Corrected my mistake.
 
Last edited:
The load decreases if the engineering stress-strain curve y coordinate decreases.
 
  • #10
nvn said:
The load decreases if the engineering stress-strain curve y coordinate decreases.

Yep, I misspoke there, since the engineering stress is the load normalized to a constant value. Revised to draw a comparison between the engineering stress and the true stress.
 
  • #11
The load falls off because the amount of area reduction in the necking area is faster than the work hardening in the material. So although stress increases, the load still drops. Engineering stress doesn't take the area decrease into account so it shows a decrease whereas true stress relates to the actual cross section area, so it always increases until fracture.
 
  • #12
oh k now i get it .. thanx.. and also what is a "draw ratio"?
 

Similar threads

Tensile and shear capacity of metals
  • · Replies 2 ·
Replies
2
Views
3K
Extracting mechanical properties from strain-stress plot (real test)
  • · Replies 5 ·
Replies
5
Views
1K
How Do You Calculate the Stress Limit of a Spinning Flywheel?
  • · Replies 20 ·
Replies
20
Views
5K
How to plot stress-strain curve?
  • · Replies 2 ·
Replies
2
Views
4K
Need help calculating maximum stress in a bolted assembly
  • · Replies 3 ·
Replies
3
Views
2K
Why true strain is always smaller than nominal strain in tensile test?
  • · Replies 1 ·
Replies
1
Views
2K
Tensile Test of Slip Ring - Working out Tensile Strength
  • · Replies 1 ·
Replies
1
Views
2K
Spring and its shear, torsion, tensile stresses...
  • · Replies 1 ·
Replies
1
Views
2K
Understanding Yield Strength & Stress Strain Curve
  • · Replies 2 ·
Replies
2
Views
7K
Ultimate Tensile strength of ductile materials
  • · Replies 1 ·
Replies
1
Views
3K