next iteration values

[ashu28]

Hi!
Does it matter in a UMAT, whether I define Jacobian at the start of the UMAT or after all the calculations?
Is it likely to affect DFGRD values at that and the next iteration?

I would really appreciate if you can please tell
Also how does ABAQUS calculate next oteration DFGRD values given Jacobian,DFGRD0, DFGRD1 and Stresses at previous iteration?

Ashu

[Harryboy]

To me it makes more sense to compute the Jacobian after the computation, since
quantities from the computations are needed in the Jacobian. An example is
classic J_2 plasticity where that plastic multiplier will enter the computation
of the Jacobian.
However, it is possible to used a Jacobian that is not a result from a exact
linearision (an example is the continuum tangent, i.e. a linearision without
using the specific choice of integration method for the constitutive equations).
The use of such Jacobian will affect the rate of convergence, so it is in deed
recommended to use a Jacobian resulting from a exact linearision.

To answer your second question, the "new" deformation gradient will be affected by
the computation of the Jacobian, since it will affect the displacement
increment and thereby the deformation gradient.
How this is done can be found in many textbooks.

Best regards and best of luck
Harryboy