Interface Elements

[Nish]

Dear Feap community,

I am going to implement a 2D interface element with a bilinear cohesive zone material law. The element is a 4 node element with 2 degrees of freedom in x and y direction.
Can I use a 2D solid element and add a new user material model or should I create a new element? which one is better choice from the computational point of view?

Regards
M.Ranjbar

[mehrangh2016]

You can implement the UEL (user element) for the cohesive elements and call the related material constants in your input file. However, from the computational point of view, it does not look to be any main difference between these two alternatives you have mentioned. I think, writing individually UMAT (user material) and UEL can simplify your job. Instead of this choice, you can do easily in your UEL what you want to do in your UMAT.

Regards,

[Prof. R.L. Taylor]

M. Ranjbar,

It is not feasible usually to use the solid element.  A cohesive model may work off the difference in displacements between the two edges of the interface and solid elements may not compute the correct deformation measure.

Thus, I would recommend you write a user element that has the correct kinematics, including the ability to have zero thickness.

[Nish]

Thank you for considering my question.

[Nish]

Dear FEAP group,

If a user element can be used in conjunction with a user material model:
in elmt01 subroutine, material properties should be derived from d(*) or from ud(*)
or maybe somewhere should copy ud(*) to d(*)?

Regards

[Prof. R.L. Taylor]

The ud(*) properties are actually available from d(*).

ud(1) is located at d(ndd-nud+1), and the parameters are in cdat1.h

[Nish]

Thank you prof. Taylor for considering my questions.

when I print "uprm+1"  in inmate.f,     it is 302

when I print  "ud(1)"     in umati01.f    it is 7 (in agreement with inp file data)

when I print d(302) after calling inmate.f in elmt01.f, it is not equal to 7 and is 0.00

I am confused

[Prof. R.L. Taylor]

Can you post the input file, the umat routines and the element so we can find the difficulty location?

[Nish]

Here you go

Note: I have no umatl input file, I implement the material behavior totally in elmt01.

[Prof. R.L. Taylor]

I do not see where you are trying to access the "ud" input values.  Also the input file yo provided does not input any of the "ud" values.  What do you want us to reply based on this posting?

[Nish]

Dear prof. Taylor,

thank you.
I could find the reason, I didn't put the print command after calling inmate.
sorry for bothering you with this question.

[Nish]

Dear FEAP community,

In the time of creating a new element (user element),
Should some considerations take out for the case of applying displacement on a node? (DISP command in inp file)
or just residual and stiffness matrix components are enough for both force or displacement loading?(FORCE,DISP)
I mean does external loading style(force or displacement) affect on our element subroutine or not?

Regards

[Prof. R.L. Taylor]

Yes, the loading type has different depends on the developments in your elements.

Force loading requires that the residual vector be correct, however, the tangent matrix can be approximate provided the solution converges.

Displacement loading (non-zero) uses the tangent matrix to compute the "effective forces" on adjacent nodes to the boundary caused by the displacement.  Normally, this action is applied only in the first iteration of each step and uses the tangent matrix from the converged solution at the last load step.  Thus, it is a much more sensitive action.  If convergence occurs all should be o.k. provided once again the residual is correctly computed.

One can follow the steps used in the solution by looking at the module ./program/pform.f

[Nish]

Many thanks prof. Taylor for the reply.

[Nish]

Dear FEAP community,

At first, I hope health and peace for all of you in such a challenging time for all people around the world,

I wanted to know, Is it possible to use a user element with a FEAP element and assemble them together?

I have implemented an interface elements which is successful in all patch tests when I use it alone, but when I assemble it with FRAME elements, strange results appear.
Is there some more possible consideration in element implementation in this case ?

my element routine is attached in the case of necessity.

Regards
M R