Dear All,

     In ABAQUS manual, it is said for hyperelastic material, it is better to define it by stretch tensor U. But if I need to use deformation gradient F in the material model directly, I need to rotate the stress back to corotational frame. How should I do that?  Should I make a polar decomposition of F=R*U first, and then apply Rt*S*R? or I can use the relative spin increment already provided to do that? If so, how?

     Also, an alternative method I think is that I can rotate the deformation gradient to corotational frame  first, and then calculate the stress based on tranformed deformation gradient. Is that right?

Hi

I’m trying to develop a VUMat routine so I’ve already
started to learn its features. I recently got this problem that what exactly
the variable stepTime means! I created a model with 3 steps including the initial
step and I coded my routine somehow that when the stepTime is equal to 0 it
prints something into a file. Surprisingly only once in whole analysis the
stepTime would be 0 and that’s exactly at the beginning of the analysis when
totalTime is in fact 0. Could anyone please explain why this happens?

Thanks

I have noticed that a lot of people are using UMAT and VUMAT material model
subroutines for their researches. However, most of these subroutines do not
find their way to free code market and remain in the hands of the developers.
Therefore, a lot of wheel re-inventing has to be done by other people. Since
development and testing of a material subroutine takes a damn long time, I
think it is a good idea if each of us can share the subroutines she has
developed with the others. I know that a couple of subroutines are publicly
available and many other people also know that. Please comment about less-known
freely available subroutines.

I have noticed that a lot of people are using UMAT and VUMAT material model
subroutines for their researches. However, most of these subroutines do not
find their way to free code market and remain in the hands of the developers.
Therefore, a lot of wheel re-inventing has to be done by other people. Since
development and testing of a material subroutine takes a damn long time, I
think it is a good idea if each of us can share the subroutines she has
developed with the others. I know that a couple of subroutines are publicly
available and many other people also know that. Please comment about less-known
freely available subroutines.