When and where the stress objective rates are used in ABAQUS software?
Hi everyone,
I have a question about the objectivity tensor in ABAQUS software. Below is my question.
The principle of objectivity demands that the constitutive equations involve objective tensors only. Needless to say, because of the arbitrary time dependence, many tensors in the ordinary sense are not objective tensors. To achieve the requirement of objectivity, we introduce the objective stress rates, such as A Truesdell stress rate of the Cauchy stress;B Truesdell stress rate of the Kirchhoff stress;C Green-Naghdi rate of the Cauchy stress;D Green-Naghdi rate of the Kirchhoff stress;E Jaumann rate of the Cauchy stress;F Oldroyd stress rate;
And so on, there may be an infinite variety of objective stress rates as variety of Lie derivative.Then my question is when and where the objective stress rate is used in ABAQUS simulation? Since only Jaumann rate and Green-Naghdi rate of Cauchy stress are used by ABQUS UMAT and VUMAT, is there a possibility of using other stress rates in ABAQUS by user subroutine?
Thank you.
Shunlai
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You can convert between different rate forms
Hi Shunlai,
I think the way abaqus treat stress/strain rate is more or less determined by its corotational local coordinate system. So direct implementation of orther rate forms are not so easy. But if you have a constitutive relation in the form of one type of stress/strain rate, you can easily convert it into the rate form used by Abaqus.
If not so straightforward to convert analytically, you can treat it as following. Expand everything around the current configuration, and neglect all higher order terms in the increment of strain/displacement. By doing that, the constitutive relation is a small-deformation relation, and the rate forms do not really matter, since the rigid-body rotation is already taken care of by abaqus, before passing into UMAT/VUMAT
Hope this helps.
Wei
Hi Shunlai, ABAQUS
Hi Shunlai,
ABAQUS will use objective stress rate when you activate the large deformation or finite strain option.
It is possible to use other stress rates in ABAQUS, but you should store the stress matrix to the state variable matrix.
Plz avoid updating the stress matrix given by ABAQUS when you use the objective stress rates other thanJauman or Naghdi rate.
Good luck.
Wang