New question #692166 on Yade:
https://answers.launchpad.net/yade/+question/692166

Hi, 

I got a question about the engineering strain and logarithmic strain in 
triaxial compression test.  

For example, for one model I have (in which the axial loading is along 
y-axis.), I got:

Before deviatoric loading, the position of top wall and bottom wall is 
(0.035,0.14,0.035) and (0.035,0,0.035) respectively (i.e., height of 0.14), and 
the triax.strain=(0,0,0). 

The final position of top wall and bottom wall is (0.035,0.12,0.035) and 
(0.035,0,0.035) respectively. The  -triax.strain=(-0.08,0.15,-0.08) at final 
state.

So the engineering strain is (0.14-0.12)/0.14=0.143 according to the height 
change of the sample. 
However, since triax.strain returns the logarithmic strain, it means that the 
logarithmic strain is 0.15 in axial direction (y direction). And from [1], the 
corresponding  engineering strain is exp(0.15)-1=0.16

My question is why the engineering strain obtained from the two ways are 
different from each other. Do I misunderstand something?

Thanks
Leonard
[1]https://answers.launchpad.net/yade/+question/660034

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