I have a simple hollow shaft that is subjected to axial load and torque Fy and a torque My respectively. | Fy=-25000 lbs v My=48000 in*lb --------- | | | | | | | | | | | | | | | | | | | | | | | | | | | |

------Fixed-------->X

I am forgetting something about the principal (max/min) stresses and strains and how to convert between them. My calculations for the shaft shown above are given below. Area, A=2.3 in^2 Polar Moment, J=1.754 in^4 Modulus, E=29e6 psi Shear Modulus, G=11.4e6

- Calc for Axial Load Stress, Sy=-10870 psi Strain, ey=Sy/E=-374e-6

- Calc for Torque Shear Stress, Tau=29070 psi Shear Strain, exy=Tau/G=2550e-6
- Calc Max and Min STRAIN using Mohr's Circle, ex=0 emax=-374/2 + sqrt( (374/2)^2 + (2550/2)^2 )=1102e-6 emin=-374/2 - sqrt( (374/2)^2 + (2550/2)^2 )=-1476e-6

- Calc Max and Min STRESS using Mohr's Circle Smax=24100 psi Smin=-35000 psi.

Finally, my question (if you've read this far). Why, or how can I convert between the principal stresses to get the principal strains?

We are doing a strain gage application and I am saying we will read emax and emain(1102 and -1476). Another guy is using the principal stresses, dividing them by the elastic modulus and saying we will read those strains (831 and -1207).

Who is correct?

Thank You for your help...and patience.