Hi Amique Ukani!

DSTRAN ist the increment of strain. This means DSTRAN is the difference between the strains at the end and at the beginning of the increment. In the case of small deformation analysis you may use the linear strain tensor. For large deformations, STRAN refers to the logarithmic strain.

DFGRD1 is the deformation gradient at the end of the increment, while DFGRD0 is the deformation gradient at the beginning of the increment.

For explanations of different strain measures and the deformation gradient, I advice to read either the ABAQUS theory manual or the English version of Wikipedia. But I try to give a short explanation here:

The linear strain epsilonij is 1/2 * (dui/dxj + duj/dxi), where u are displacements and x are the coordinates. All strain measures are symmetric matrices.

The deformation gradient tensor Fij is dui/dxj + I, where I is the identity matrix. The deformation gradient is in general not symmetric.

The logarithmic strain (so called Hencky strain) is obtained from the deformation gradient F by first using the polar decomposition F = U*R into a symmetric stretch tensor U and a rotation matrix R, and then constructing E = ln(U).

best regards

Martin Lederer