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### Course: Class 11 Physics (India)>Unit 13

Lesson 1: Stress, strain, and modulus of elasticity

# Stress vs strain curve

What happens if you stretch something beyond its elastic limits? In this video, we will explore the regions beyond the elastic limits. We will take a steel rod and keep stressing it until it breaks. We will draw a graph of stress vs strain and explore all the different regions of it.  Created by Mahesh Shenoy.

## Want to join the conversation?

• here we can see that hooke's law has limitations..is there any alternate law which overcomes hooke's law? like bohrs atomic model overcomed rutherfords model.
• Among stress and strain which quantity is independent and dependent??
• stress is always dependent on how the system (or body) is constrained (resisted from accelerating). strain is however independent of this.. It is possible to have strains without stress too..
• What happens if we graphed the steel bar's stress for the neck as well? Would it instead shoot straight up?
• probably. Until the fracture point i think it would still keep increasing
• Hey! Why is the yield point beyond proportionality limit?
(1 vote)
• steel still retains its original configuration when stressed beyond the proportionality limit. this happens till yielding sets in (yield point). however the stress beyond proportionality limit varies non linearly vs strain. This gap is usually very small.
• So point A is called proportional limit point, is the point above any applied stress doesn't obey linear stress-strain behavior (Hooke's Law). And the elastic limit or yield point is the point where a combination of elastic and plastic behavior is still there (although it's not in the plastic region) so according to ASKLAND BOOK at that point the departure of the plastic behavior is noticeable unlike Proportional limit where the plastic behavior is on a microscopic level.

So know my question is: why he said if the stress that is applied on the specimen is between both proportional limit point and yield point will return fully as if it's elastic ?! I think that is wrong. Since there is also plastic behavior (small) beside the elastic the specimen will retain but some deformation will be there isn't it ?
• No real body is perfectly elastic.
Even within the proportional limit, there will be microfractures (minute).
So, there will be some degree of deformation if a body is strained.
It's just that within B, the material can return to its original dimensions without undergoing a noticeable plastic (permanent) deformation.
Think about a rubber band, it loses elasticity after being used frequently even if strained below the strain corresponding to the yield point.
(1 vote)
• why if the strain increasing and the stress is decreasing?
• rewatch the video, he explains it.
timestamp:
if you don't get it let us know
(1 vote)
• Let's say I have 2 materials,
ultimate tensile strength of A is greater than that of B,
but, the region of plastic deformation of A is lesser than that of B.
Isn't A stronger than B?

P.S: my teacher said B is stronger cuz the area under the graph is larger. How does that make sense?
i.e., if A was diamond and B steel (as in the video), diamond is definitely stronger.
(1 vote)
• How do I calculate the material thickness needed for a given metal, in
the cylindrical part of the internal combustion chamber?
(1 vote)