What Is the Correct Way to Calculate Poisson's Ratio?

In summary, Poissons ratio is a measure of the ratio between lateral strain and axial strain. In the given example, the correct calculation for Poissons ratio is ((2/30) / (-5/100))*-1 = 1.4, as the change in height was caused by a compressive load. This follows the standard convention of considering compressive loads as negative.
  • #1
tomtomtom1
160
8
Hello all

I was hoping someone could help clarify Poissons ratio.

I understand that it is Lateral Strain / Axial Strain but I wanted to understand it in the context of an example.

The question is:-
At 5kN compression load
Original Depth = 30mm
Change in Depth = 2mm
Original Height = 100mm
Change in height= 5mm

I would calculate Poissons ratio by doing the following:-

((2/30) / (5/100))*-1 = -1.4

However I have been told that this is wrong and the correct answer should be:-

((2/30) / (-5/100))*-1 = 1.4

Why is it -5?

I am assuming that the height was reduced by 5mm due to the compression then this is what makes it a negative is this correct?

Thank you.
 
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  • #2
The standard convention is that tension loads are positive and compressive loads are negative.
 

What is Poisson's Ratio?

Poisson's Ratio is a dimensionless material property that describes the relationship between a material's lateral and axial strains when it is under stress.

Why is Poisson's Ratio important in material science?

Poisson's Ratio is important in material science because it provides insight into a material's stiffness, strength, and deformability. It also helps engineers and scientists understand how materials will behave under different types of stress and loading conditions.

How do you calculate Poisson's Ratio?

Poisson's Ratio is calculated by dividing the negative lateral strain of a material by its corresponding axial strain. This ratio can be determined experimentally through various mechanical tests or it can be estimated using theoretical models.

What is a typical value for Poisson's Ratio?

Poisson's Ratio can range from 0 to 0.5, with most materials having a value between 0.2 and 0.3. However, the actual value can vary greatly depending on the type of material, its microstructure, and the testing conditions.

How does Poisson's Ratio affect the behavior of materials?

Poisson's Ratio affects the behavior of materials by determining how they will deform under stress. Materials with a high Poisson's Ratio will tend to contract laterally when stretched, while materials with a low Poisson's Ratio will expand laterally. This can impact the strength, stiffness, and stability of a material under different types of loading.

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