- #1
koolraj09
- 166
- 5
Hi guys. Just out of curiosity I want to know that why the concept of stress evolved? Why do we need stress?
Click For Summary
Discussion Overview
The discussion revolves around the concept of stress in materials science and engineering, exploring its definition, significance, and the rationale behind its formulation. Participants engage in a variety of perspectives regarding the physical interpretation of stress, its utility in material behavior, and the implications of viewing stress as a hypothetical quantity.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants inquire about the necessity of the concept of stress and its evolution over time.
- One participant suggests that stress is defined as internal restoring force per unit area, questioning the reasoning behind this definition.
- A participant recalls that stress was developed to describe a field of force applied to particles, integrating to provide a uniform description of force application.
- Another participant argues that stress is not a hypothetical quantity, comparing it to pressure and emphasizing its role in describing material behavior independent of object shape.
- One contribution highlights that stress is useful for determining material strength and behavior under load, with examples related to Young's modulus and material failure points.
- A participant suggests viewing stress as force per molecule, linking it to molecular bond breaking during material failure.
- Another viewpoint presents stress as a means to compare different geometries and materials under load, aiding in material selection for applications.
- Some participants express differing opinions on whether stress can be considered hypothetical, with one asserting that it cannot be directly measured, while another counters this claim.
- A participant draws an analogy between material stress and stress experienced in human contexts, suggesting that the inability to see stress does not negate its existence.
- One participant challenges the understanding of stress by questioning the definitions of force and area in the context of internal forces within a body.
Areas of Agreement / Disagreement
Participants exhibit a range of views on the nature of stress, with no consensus reached regarding its classification as a hypothetical quantity or its fundamental significance in material science. The discussion remains unresolved with multiple competing perspectives presented.
Contextual Notes
Some claims rely on specific definitions of stress and its measurement, which may not be universally accepted. The discussion includes assumptions about the visibility and measurability of stress and strain, as well as the implications of these characteristics on the understanding of material behavior.
- #2
Studiot
- 5,440
- 11
To make lazy students work and explain what they mean?
- #3
koolraj09
- 166
- 5
I'm talking about stress=F(force)/A(area).
Why is it that stress has to be defined the way it is...i.e internal restoring force per unit area?? Why did the researchers put it that way? I'm interested is in the physical significance of stress(since stress is a hypothetical quantity).
Why is it that stress has to be defined the way it is...i.e internal restoring force per unit area?? Why did the researchers put it that way? I'm interested is in the physical significance of stress(since stress is a hypothetical quantity).
- #4
tygerdawg
- 285
- 81
<time travel back 30 years to my Advanced Machine Design class in graduate school...bzzzzzt! 
>
I vaguely recall that the concept of stress was developed to describe a field of force applied to particle: dF/dA. It integrated to F/A. It was a useful concept because it allowed one to derive high-order equations that provided a uniform description of how force was applied to objects.
Hope this helps. Like I said, it was long time ago. I also learned that most of the equations used by engineers in common practice are chock-full of estimations that eliminate the higher-order equation components. What's a few percent of error between friends anyway?
<back to future/present day...bzzzzt!
>
>I vaguely recall that the concept of stress was developed to describe a field of force applied to particle: dF/dA. It integrated to F/A. It was a useful concept because it allowed one to derive high-order equations that provided a uniform description of how force was applied to objects.
Hope this helps. Like I said, it was long time ago. I also learned that most of the equations used by engineers in common practice are chock-full of estimations that eliminate the higher-order equation components. What's a few percent of error between friends anyway?
<back to future/present day...bzzzzt!
>- #5
AlephZero
Science Advisor
Homework Helper
- 6,999
- 299
I'm not sure why you call stress a hypothetical quantity. It's no more hypothetical than pressure (and the units are the same, of course).
Stress is useful for describing how different materials behave, in a way that is independent of the shape of particular objects made form the materials. For example Young's modulus (stress / strain ) describes how rigid or "stretchy" different materials are. If the stress is higher than the elastic limit for a material, it will not return to its original shape when you remove the loads that caused the stress. If the stress is higher than the "ultimate stress", the material will crack or break.
As a simple example, the force needed to break a piece of wire depends on the material it is made from, and also on the thickness of the wire, but the stress needed to break it only depends on the material. The same stress level will also break a cantilever beam, or a plate, or anything else made from the same material.
Stress is useful for describing how different materials behave, in a way that is independent of the shape of particular objects made form the materials. For example Young's modulus (stress / strain ) describes how rigid or "stretchy" different materials are. If the stress is higher than the elastic limit for a material, it will not return to its original shape when you remove the loads that caused the stress. If the stress is higher than the "ultimate stress", the material will crack or break.
As a simple example, the force needed to break a piece of wire depends on the material it is made from, and also on the thickness of the wire, but the stress needed to break it only depends on the material. The same stress level will also break a cantilever beam, or a plate, or anything else made from the same material.
- #6
jack action
Science Advisor
- 3,584
- 9,999
From Wikipedia:
Instead of looking at it as force per unit area, look at it as force per molecule. Stress is useful to determine how strong a material is. When a part breaks under a certain force, we actually break the molecular bonds between the particles. The greater the area of the fracture, the higher the number of molecules, the greater the force needed.
Instead of looking at it as force per unit area, look at it as force per molecule. Stress is useful to determine how strong a material is. When a part breaks under a certain force, we actually break the molecular bonds between the particles. The greater the area of the fracture, the higher the number of molecules, the greater the force needed.
- #7
Vadar2012
- 208
- 1
I like to think of stress as way of comparing how different geometries and materials act under the applied load. This let's me decide on the best geometry and type of material to use for the intended application.
- #8
koolraj09
- 166
- 5
Hi AlephZero...
I think stress as a hypothetical quantity because we can't see or directly measure it!
On the other hand we can see/measure strain.
I think stress as a hypothetical quantity because we can't see or directly measure it!
On the other hand we can see/measure strain.
- #9
Vadar2012
- 208
- 1
koolraj09 said:
How does that make it hypothetical? Considering the definition of the word, it doesn't make any sense to me.
You might not see the affects of the load on the material, but you can see what's applying a force to it and the material itself. What about Reynolds number and the lift coefficient, do you think they're hypothetical too?
- #10
TheSymbol
- 11
- 0
What my experience says is Stress is the resistant provided by the material. Hence the name. It something like the stress/tension that is present in our body/mind too. Just because you can't see or measure it does it mean its not present. I just gave a rough analogy here.
Hope this helped :) :shy:
Hope this helped :) :shy:
- #11
Studiot
- 5,440
- 11
@koolraj
You said stress = force/area..
What force? what area?
When you first start considering internal forces within a body it is tempting to try to continue to work in force terms only , as you did with forces between bodies.
However try to explain why an auto tyre (which is round off the vehicle) has the shape it does and describe what forces are acting and over what areas in terms of forces.
Then you will see the need for the stress concept.
You said stress = force/area..
What force? what area?
When you first start considering internal forces within a body it is tempting to try to continue to work in force terms only , as you did with forces between bodies.
However try to explain why an auto tyre (which is round off the vehicle) has the shape it does and describe what forces are acting and over what areas in terms of forces.
Then you will see the need for the stress concept.
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