# yade-users team mailing list archive

## Re: Strain compution in Triaxialstresscontroller

```Hi,

There is several definitions of strain, see for instance the page

http://en.wikipedia.org/wiki/Deformation_(mechanics)

If I'am right (but please verify to be sure):

** Log means ln (natural logarithm),

** The way to compute strains in Yade is valid for large strains (or
large transformations), whereas the definition
epsilon=(length-length0)/length0 is valid under the hypothesis of small
strains.

** compare the results given by ln(length/length0) and
(length-length0)/length0, it is quasi the same for strains lower than
20% to 30%, when strains become too much important
(length-length0)/length0 is no longer valid.

Best

Luc

> Hi everyone
> These days I'm a little puzzled with the strain compution in
> TriaxialstressController.cpp ,just as follows:
>
> strain[0] = Mathr::Log(width0/width);//Eq(1)
> strain[1] = Mathr::Log(height0/height);//Eq(2)
> strain[2] = Mathr::Log(depth0/depth);//Eq(3)
> volumetricStrain=strain[0]+strain[1]+strain[2];//Eq(4)
>
> IIRC,Log means not log10 but ln as usual .Is it right?
> Eq(1 to 3) is different from the common compution of strain like:
> epsilon=(length-length0)/length0
> and, in PFC3D manuals(V3.0)->users' guide->problem solving with pfc3d
> Page 47, I found another Eq for strain compution:
> epsilon=(L-L0)/((L0+L)/2)
> Are the 3 methods all right? They're designed for different fields?
>
> Thanks for any suggestion.
> Regards.
> Zhang Lin
> 　　　　　　　　xtss_0002@xxxxxxxxxxxx
> 　　　　　　　　　　2008-11-25
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________

--
Luc Sibille

Université de Nantes - Laboratoire GeM UMR CNRS

IUT de Saint Nazaire
58, rue Michel-Ange - BP 420
44606 Saint-Nazaire Cedex, France

Tel: +33 (0)2 40 17 81 78

```