# Creating Mohr's strain circle from a strain rosette

## Homework Statement

A sample is put in tension and a strain rosette gives the following results: i) Calculate principal strains and poissons ratio using Mohrs strain circle.
ii) Calculate principal stresses from principal strains and poissons ratio.

## Homework Equations

Mohr's strain circle
γ = -lateral strain / axial strain
σx = E / 1 - γ2 (εx + γεy)
σy = E / 1 - γ2 (εy + γεx)
E = 210 GPa

## The Attempt at a Solution

I have drawn up Mohr's circle in autocad and found the following results. principal strains = 122.5x10-6 & -296.5x10-6

poissons ratio = -122.5 / -296.5 = 0.413 (this seems too high?)

principal stresses = σx = 11.5kPa (this is supposed to be low as the load is applied in the y direction?)
σy = -62.99MPa (should this be negative if its in tension?)

Im hoping someone can tell me if im on the right track.

Thanks in advance!

## Answers and Replies

Chestermiller
Mentor
Is this supposed to be plane stress or plane strain?

Chestermiller
Mentor

## Homework Statement

A sample is put in tension and a strain rosette gives the following results:
View attachment 231132
i) Calculate principal strains and poissons ratio using Mohrs strain circle.
ii) Calculate principal stresses from principal strains and poissons ratio.

## Homework Equations

Mohr's strain circle
γ = -lateral strain / axial strain
σx = E / 1 - γ2 (εx + γεy)
σy = E / 1 - γ2 (εy + γεx)
E = 210 GPa

## The Attempt at a Solution

I have drawn up Mohr's circle in autocad and found the following results.
View attachment 231133
principal strains = 122.5x10-6 & -296.5x10-6

poissons ratio = -122.5 / -296.5 = 0.413 (this seems too high?)

principal stresses = σx = 11.5kPa (this is supposed to be low as the load is applied in the y direction?)
σy = -62.99MPa (should this be negative if its in tension?)

Im hoping someone can tell me if im on the right track.

Thanks in advance!
I confirm your principal strains. As far as the Poisson ratio is concerned, it seems that there is not enough information provided to determine it, unless the loading is uniaxial, and the principal strain in the z direction is also 122.5E-6.