Adhesive Joint Modeling: Joining shell elements 1

[anants]

Hi

I'm a new user of ANSYS and I was wondering if someone could help me with a question I had. I am trying to model a structure which involves adhesive joints (graphite bonded to glass shells) and am having trouble modeling this.

The adhesive thickness in my model is small (10micron) with the upper adherend being glass (200microns thick) and the lower adherend being graphite. I have been trying to model the graphite as a solid volume and the adhesive and glass with shell elements.

My question is essentially- what is the best way of joining together these three entities, i.e the botton surface of the glass elements to the top surface of the adhesive elements, and the bottom of the adhesive shell to the top area of the graphite solid? What would a convenient way of joining these be?

Anant

 

[Drej]

I've come across this problem before, and there is a specific way that you should address it, at least according to the experts in the field. I would say first of all that you should take a look at this article "Finite Element Modeling of an Adhesive Bonded Joint" By Farhad Tahmasebi:

http://femci.gsfc.nasa.gov/adhesive/

This seems to be the definitive reference for the bonded modelling joint. In addition, from your description I would say that you may have modelled your problem in the opposite sense to which this guy proposes, although you're most definitely on the right track. Let me know how you get on with it.

-- drej --


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[anants]

Drej

Thanks very much for the heads up - It certainly looks to be a good way of incorporating the adhesive properties into the model. Reading the article led me to another quick question which perhaps someone can throw some light on.

When connecting a shell to a solid I've seen people suggest using rigid links between nodes of the sholid and shell, using contact elements and using DOF constraints to bind them together. Would anyone have an opinion on which is the best way or alternatively guide me to a discussion of this issue.

For example, when modeling a joint with a thin bond line; if you wanted to compare results incorporating the adhesive and without what would be a smart way of connecting the upper shell adherend to the lower solid?

Thanks again for the reply.

 

[Drej]

Yeah, the DOF mismatch between shells and solids is/can be a pain. Whenever I've come across this phenomena in the past I've always used either constraints (CE) or contact ("bond" them together using CONT174 and TARG170 elements) to tie the two together. However, each method only works for certain cases, for example the CE method is the best for when the shell was joined perpendicular to the solid. I think in your case the shell and solid are parallel, and in fact could share coincident nodes(?). If that's the case you wouldn't need to use any constraints to tie the two together, since this job would be done by the coincident nodes of the shell and the solid. The shared translational DOFs should be sufficient for transfer of load. If you're expecting large bending deformations locally, simply refine the mesh accordingly. As long as your mesh is fine enough, you would get transfer of the bending DOF into the solids.

Cheers,

-- drej --


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