# Torsion results don't match hand-calcs

**URL:** <https://prepomax.discourse.group/t/torsion-results-dont-match-hand-calcs/1317>\
**Category:** General Questions\
**Tags:** results\
**Created:** [December 5, 2023, 1:30pm UTC](https://prepomax.discourse.group/t/torsion-results-dont-match-hand-calcs/1317 "2023-12-05T13:30:28Z")\
**Posts on this page:** 1\
**Showing post:** 16

<div class="post-metadata">

**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\
**Post date:** [December 6, 2023, 9:40pm UTC](https://prepomax.discourse.group/t/torsion-results-dont-match-hand-calcs/1317/16 "2023-12-06T21:40:45Z")

</div>

Check this thread: [Help Non Linear Aluminium FEM Beginner - #6 by FEAnalyst](https://prepomax.discourse.group/t/help-non-linear-aluminium-fem-beginner/1311/6)

Basically, you need true stress vs true **plastic** strain data points. Here you can find some helpful information, including formulas to calculate true stress/strain from engineering stress/strain and plastic strain from total strain: [https://classes.engineering.wustl.edu/2009/spring/mase5513/abaqus/docs/v6.5/books/gsx/default.htm?startat=ch05s02.html](https://classes.engineering.wustl.edu/2009/spring/mase5513/abaqus/docs/v6.5/books/gsx/default.htm?startat=ch05s02.html)

You can use a bilinear model (hardening recommended) like this, for instance:

Re ——- 0  
Rm —— A

where Re is yield strength, Rm is tensile strength (UTS) and A is elongation at failure.

Or you can specify more data points to define a while nonlinear stress-strain curve (keeping in mind what I said at the beginning about the required stress and strain measures).

> [@JKnight](#):
>
> I assume the software does linear interpolation between them.

Between them - yes. But outside of the specified data, it assumes plateau (horizontal line). You should avoid this due to potential convergence issues - do the linear extrapolation manually by specifying higher stress-strain values as the last point.

---

_[View the full topic](https://prepomax.discourse.group/t/torsion-results-dont-match-hand-calcs/1317)._