How to convert Abaqus logarithmic strains to deformation gradient in global/local axis?

[Waqas Rashid]

Hi everyone,
If I have material orientation in global axis (i.e. X,Y,Z) and I apply biaxial stretch in Abaqus using single element, I get same deformation gradient analytically and Abaqus (transformed logarithmic strains into stretches etc.). Attached in case 1.
If material orientation of X-Y makes 30 degrees with global axis (i.e. X,Y ) and I apply biaxial stretch in Abaqus using single element, I get different deformation gradients analytically and Abaqus (although I am using all the necessary transformations). Attached in case 2.
The idea behind was to make sure that strains from Abaqus are either in global axis or local axis (in the direction of material orientation).
If someone knows where I am making mistake let me know. Thanks.

 

[FEA way]

Which material model are you using in Abaqus ? Maybe you will find the source of this difference by requesting more output from Abaqus. It offers output variables even for quantities such as principal stretches and deformation gradient. And you could transform the results to a different coordinate system to make comparisons easier.

 

[Waqas Rashid]

I am using Fung model in which I also wrote script. This method looked simple for me because I conpared both results when both orientations were same and results matched.