Modelling of a patch repair with surface-surface contact 2

[johnnyc2]

Hi everybody,

I've been using Patran for a bit over a year and have a model of a carbon fibre aileron made out of surfaces. I have introduced a hole in to the top skin (as damage) and now I need to place a carbon fibre patch over the top to repair the damage.

To simplify the problem, imagine a flat plat with a 2inch diameter hole in it. I need to attach a 5inch diameter patch to go on top of this hole.

My problem is that I've never had to model surface-on-surface contact like this before and am unsure of which approach to take. I have received some suggestions from colleagues (using RBE2, modelling the adhesive as bricks with a surface patch on top) but nobody seems sure. I was wondering what people on here thought. Modelling of the adhesive is not necessary at this stage, but would be helpful to know how to do.

Any help would be much appreciated.

Thank you,
John

 

[Onda]

On my point of view You have two way to proceed:
the first one is, as Your colleague said, use brick elements. You should, using brick, keep aspect ratio reasonable, this force your mesh dimension to be very small.
The second way is to model the glue using CBush elements.
You should make two coincident knots in the middle of glue thickness, connect each knot to corresponding shell grid point using RBE2 and connect the two knots together with CBush.
You can find good description of the system in this site:

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

The problem of this system is that you should keep area of elements constant to use only one property on CBush. Else you should use one property for each grid point!