Calculating Poisson's Ratio and Modulus of Elasticity for a Solid Cylinder

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Discussion Overview

The discussion revolves around calculating Poisson's ratio and the modulus of elasticity for a solid cylinder, specifically a circular cross-section tie rod under load. Participants explore the necessary definitions and formulas related to strain and stress, as well as the implications of given measurements.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • Scott seeks assistance in calculating Poisson's ratio for a solid cylinder, noting the lack of specific force values in the problem statement.
  • Some participants inquire about the availability of stresses or strains, and whether elastic or bulk modulus values are provided.
  • Scott later provides the full problem statement, which includes specific measurements for length and diameter changes under load.
  • There is a discussion about the definition of strain, with participants emphasizing the need to calculate both axial and lateral strains using the provided measurements.
  • One participant clarifies that the strain formula involves change divided by the original dimensions, prompting further discussion on unit consistency.
  • A later reply introduces a related problem involving the modulus of elasticity, questioning whether normal strain corresponds to axial strain and how to calculate normal stress.

Areas of Agreement / Disagreement

Participants generally agree on the definitions and formulas needed for calculating Poisson's ratio and modulus of elasticity, but there is no consensus on the specific calculations or interpretations of the problem details.

Contextual Notes

Participants express uncertainty regarding the application of formulas and the need for consistent units. There are unresolved questions about how to approach the calculation of normal stress and its relationship to the undeformed diameter.

Who May Find This Useful

This discussion may be useful for students or individuals working on problems related to material properties, specifically in the context of mechanics of materials and structural analysis.

bono141
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Hi, I am new to this so bear with me,

I'm stuck on a question, basically, i need to work out the poissons ratio for a solid cylinder 140mm dia by 4.0m long to find out if it's steel or aluminium. I know the formula for poisson ratio is lateral strain / axial strain. The question states that there is a force acting on the cylinder but gives no values, how would I go about working out the poisson's ratio? Any help would be much appreciated.

Many Thanks
Scott.
 
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Does the problem provide stresses or strains, and the elastic or bulk modulus?

One would need to know the axial and lateral strains, or a force/stress.

Please write the problem as given.
 
the whole question

A circular cross section tie rod located in a structure has a diameter of 140mm and a length of 4.0m. If under load the length increases by 1.2mm and the diameter decreses by 0.11mm, identify the relationship between lateral and transverse strain and determine the value of poisson's ratio.

I have no idea how to go about completing this one. Any help would be greatly appreciated.
 
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What is the definition for strain? You have two things you need to calculate in order to calculate Poisson's Ratio, the axial strain and the lateral strain. You are given all of the pieces of the two parts. What two numbers will make up the axial strain? What two numbers will make up the lateral strain?
 
continued...

the strain formula is: change divided by original

the 4.0m & 1.2mm increase is for the lateral strain and the 140mm and 0.11mm decrease is for the axial strain i beleive.
 
Right. Now just make sure you are dealing with the same units for each number. Either m or mm, it doesn't matter, just make sure you use only one.
 
Okay I know this thread is so old now, but I'm working a similar problem and its also asking for me to find the modulus of elasticity.

I know the basic formula for it is normal stress divided by the normal strain.

So I'm thinking the normal strain is the same as the axial strain?
Also when it says the normal stress does that mean I calculate the Initial stress with the undeformed diamter or do i calculate both of them and just use the difference of the two?
 

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