Very interesting comments. I have not been able to look at your images, for some reason I dont have permission to reach the jpg-files.
Here are a few more questions/comments:
(1) What density did you use?
(2) You said that you got perfect agreement for the 1 element case. What loading conditons did you try? Did you try both uniaxial and shear?
(3) I am surprised that you did not get the same answer for the 4-element case. Did you try uniaxial loading for the 4-element case? Do you get the same answer as for the 1-element case?
It sounds like you pretty close to getting it right 🙂
I run the 1 element case again, and found consistent results for uniaxial tension. For some reason I thought Ive got fit results for simple shear, but this run shows there still is problem with simple shear of 1 element.
So I should not conclude 1 element test is good. Sorry for that.
I am sending bunch of plots to your email box with the cae file. NH.for is the NH model VUMAT subroutine downloaded from this website.
Based on your comments I wanted to make sure that the vumat worked as I though that it should. To verify that this was the case I ran a number of validation experiments with the VUMAT and I got the following results:
âž¡ For uniaxial tension, I get very similar results using these methods:
* Closed-form analytical solution,
* ABAQUS/Explicit with one 3D element using the vumat,
* ABAQUS/Explicit with one 3D element using the built-in NH model,
* ABAQUS/Explicit with one axisymmetric element using the vumat,
* ABAQUS/Explicit with one axisymmetric element using the built-in NH model,
* ABAQUS/Explicit with 4x4x4 3D elements using the vumat
See the following figure
[img] [/img]
âž¡ For simple shear, I get very similar results using these methods:
* Closed-form analytical solution,
* ABAQUS/Explicit with one 3D element using the vumat,
* ABAQUS/Explicit with one 3D element using the built-in NH model,
Due to the deformation state, I get a slightly different stress response for the following two methods:
* ABAQUS/Explicit with 4x4x4 3D elements using the vumat,
* ABAQUS/Explicit with 4x4x4 3D elements using the built-in NH model
Although these two methods are different than the one element case, they are both consistent.
See the following figure
[img] [/img]
These results seem to indicate to me that the vumat is working correctly 😀
1) The results should be qualitatively similar for plane strain elements. The call structure for axisymmetric and plane strain elements are the same with regard to the vumat (ndi=3, nshr=1).
2) There should be no problem to go to 500% strain. The vumat will behave the same.
3) As far as I know, it it not necessary to make the vumat behave in a certain way for the first time increment. The given vumat works as it is.
If you want, you can try out the response at larger deformations, etc.
