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Behaviour of Interface element in delamination analysis

Good morning,

I'm trying to simulate delamination with interface element, with a traction-jump law.

In order to see the Behaviour of the Interface element before the delamination occur, i introduce one interface element (8 nodes ) between two normal linear elastic solid element (quader with 8 nodes also).

I think the strain in the interface corresponds to the Jump

I have many difficulties:

  • are the strain in the bulk element different to the one in the interface element?
  • How can I compute the  stress in the Interface element!?
  • The interface element is elastic before the delamination onset , which will be the behaviour of the global system?

should i use the newton-rahpson method to solve the global system, because for the moment, only the behaviour of the interface before the delamination onset is the aim of my calculations.

I apologize for my Englisch.

Thanks in advance for any answers.



phunguyen's picture

Hi Vanez,

Your problem is 2D right? You have two 8 node quadrilateral elements and you insert an interface element between them. Why you said it is a 8 node interface element? I think it should have been a 6 node interface element.

The zero-thickness interface elements model adopt a traction-separation law. So the kinetic variable is the displacement jump and the kinematic variable is the traction. Why you asked about strain and stress of interface elements?

Above are my two cents reply.

Hi vinh phu nguyen


first, thank you for the reply Smile!

You are right, the kinematic variable is the displacement jump.

I am trying to implement a 3D problem,  and  the interface element between the two hexaeders,  has 8 nodes, 4 nodes of each hexaeder.

And i thought before the delamination onset, when the interface element is consider as elastisch, the Stress would be the same in all the three element, i mean, for the interface element, one should have traction = stress*normal.

But it is not the case.

Is there any treatment to do for the solid-elements, when inserting interface element between them?

Is it possible to consider a problem with only the interface element?

or the interface elements are only useful in association with solids element?




phunguyen's picture

The traction in the interface element follows a traction-separation law. Before onset of damage initiation, this law reads t = K [u] where [u] is the displacement jump. That explain why the traction so computed differs from the traction = stress * n.

The formulation of solid elements are simply normal, no modification when used in combination with interface elements.

Hope it was a bit of help.


Hello Phu!


thank you one more time for Reply.

 "That explain why the traction so computed differs from the traction = stress * n".

But per Definition of the Traction, one should have  traction = stress*n, and it is a little bit bizarre that the two computed values of the traction are different.

Don't you think so!!?


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