Does Poisson's ratio apply when we have no loadings?

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question4
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Does Poisson's ratio apply when we have no loadings ? For instance if we have a free rod and we increase its temperature, in order to find the change of its diameter should i say :
Δd=-v*ε_x*d, where d is the length of the diameter or Δd= α*ΔΤ*d ?
Thanks in advance.
 
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question4 said:
Does Poisson's ratio apply when we have no loadings ? For instance if we have a free rod and we increase its temperature, in order to find the change of its diameter should i say :
Δd=-v*ε_x*d, where d is the length of the diameter or Δd= α*ΔΤ*d ?
Thanks in advance.
Poisson's Ratio is stress related. If you apply a stress in a given direction causing a strain, it quantifies what happens in lateral directions in terms of expansion/contraction for a given material.

Uniformly heating (i.e. changing the temp of) a free rod is stress free.
 
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erobz said:
Poisson's Ratio is stress related. If you apply a stress in a given direction causing a strain, it quantifies what happens in lateral directions in terms of expansion/contraction for a given material.

Uniformly heating (changing the temp) a free rod is stress free.
So in order to find the change of the diameter is it enough to say that : Δd= α*ΔΤ*d ?
 
  • #4
question4 said:
So in order to find the change of the diameter is it enough to say that : Δd= α*ΔΤ*d ?
Well, I believe that formula is for ##\frac{\delta }{L} \ll 1##, but basically...yes.
 
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Welcome, @question4 ! :cool:

In practice, the linear expansion of metals is the most calculated due to its negative consequences.
Diameters of solid metal bars also grow with temperature, but that is mainly important for rings that slide tightly into cavities (like a bearing in its housing).

The diametral expansion of those rings are calculated like an unfolded section of metal expanding linearly; therefore, a coefficient of linear expansion is mostly used.

For fluids, a coefficient of volumetric expansion is used instead.

Please, see:
https://pressbooks.bccampus.ca/collegephysics/chapter/thermal-expansion-of-solids-and-liquids/

https://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html

https://www.engineeringtoolbox.com/thin-circular-ring-radius-temperature-change-d_1612.html

https://www.engineeringtoolbox.com/linear-thermal-expansion-d_1379.html

Now, when combining mechanical loads and high temperatures:

Copied from
https://en.wikipedia.org/wiki/Poisson's_ratio

"Most steels and rigid polymers when used within their design limits (before yield) exhibit values of about 0.3, increasing to 0.5 for post-yield deformation which occurs largely at constant volume."

The forging process shown in this video seem to demonstrate that any ratio (determined experimentally for metal in normal conditions) would change depending on sufficiently high applied loads and/or temperatures to the molecular bonds.

 
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This video can be helpful:
 

FAQ: Does Poisson's ratio apply when we have no loadings?

What is Poisson's ratio?

Poisson's ratio is a measure of the deformation behavior of a material when it is subjected to loading. It is defined as the negative ratio of transverse strain to axial strain. Essentially, it describes how much a material will expand or contract in directions perpendicular to the direction of loading.

Does Poisson's ratio have any meaning without applied loadings?

No, Poisson's ratio is inherently a property that describes the material's response to stress. Without any applied loadings, there are no strains to measure, and thus Poisson's ratio does not have a practical application in this context.

Can Poisson's ratio be used to predict material behavior in the absence of loading?

Poisson's ratio itself cannot predict material behavior in the absence of loading because it is specifically a measure of the relationship between strains under stress. However, it is a fundamental material property that helps in understanding how a material will behave when loads are applied.

Is Poisson's ratio relevant for unloaded materials in theoretical studies?

In theoretical studies, Poisson's ratio is relevant as a fundamental material property. It can be used in simulations and models to predict how materials will behave under various loading conditions, but it does not describe the state of the material when it is unloaded.

How is Poisson's ratio determined if there are no loadings?

Poisson's ratio cannot be determined without applying loadings. It is measured by applying a known stress to a material, observing the resulting strains in both the axial and transverse directions, and then calculating the ratio of these strains.

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