A question about crystal plasticity, UMAT and ABAQUS

Hi all,

I'm a PhD student and a new member here. My thesis is about “modeling the mechanical behavior of a Ti-alloy microstructure in dwell-fatigue using cellular automata”. I'm using MATLAB to develop a program that allows me to simulate the mechanical behavior of a microstructure by crystal plasticity theory. In general, my program has to do the jobs of ABAQUS and its UMAT at the same time. So, I’m trying to translate a UMAT in MATLAB. For this purpose, I read some UMATs but I have some problems because some information in UMAT will be calculated in ABAQUS and I'm not sure if I know how ABAQUS do that and how I can do it in MATLAB?

In my program, I try to calculate the shear stress of each slip system but I obtain very high value (the problem). I think it is because of the way that I calculate F0 and F1 (DFGRD0 and DFGRD1 in ABAQUS respectively). I don't know how ABAQUS calculate these values and who can I calculate them correctly by a time integration process in MATLAB.

Can you help me to solve this problem please?

In the attached file you can find the detail of the calculation.

Thank you and sorry for my poor English, I'm studying in a French university.