Hi all,
i'm coding a umat for hyper-viscoelastic behaviour and i wonder what formula use for the exact deformation gradient tensor F since dfgdr0 and dfgrd1 passed into the umat (according to Abaqus user subroutine reference manual 1.1.40) are a modified deformation gradients at the begining and the end of time increment respectively?
thanks in advance
It all depends upon the numerical implementation for stress and jacobian calculation in umat. for example, if the current stress state is required (after increment), dfgdr1 should be used. However, some implementation use dfgdr0 for calculation
Hi,
it depends on the algorithm you use for the stress update at finite deformations. In general, you need both dfgrd0 and dfgrd1, and no "exact" update formula is available.
Regards
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