DSTRAN in UMAT with nonlinear geometry

Dear Colleagues,

I have done some analysis with nonlinear geometry. I use quadratic 3D solid elements. I have learned the way to calculating DSTRAN and DROT from ABAQUS documentation as follows:

ΔF*F (t)= F (t+dt)ΔF=ΔV*ΔR

DSTRAN=ln(ΔV)

DROT=ΔR

where F (t)=DFGRD0 and F (t+dt)=DFGRD1.

I have calculated DSTRAN and DROT by DFGRD0 and DFGRD1 by the above equations. The problem is what I get is different from that computed by ABAQUS which is passed into UMAT subroutine. The maximum relative error in some component of strain increment can exceed 10%. Does anyone know the exact way to calculating the strain increment in ABAQUS? Any help will be appreciated.

Thanks in advance!

Email: hanshiwei1987@gmail.com