What kind of interaction to use?

[mdama]

Hello
I am trying to push the material by an indenter as you see here (

https://www.dropbox.com/s/v9yqi2qfpg84gil/1.PNG?dl=0)

but after a while, the extruded rectangular ribs are coming out of the plane (

https://www.dropbox.com/s/y9hlib5d1rck0nf/2.PNG?dl=0).

The ribs and the planes are one part(single part) . What kind of interaction should I use to avoid this?

Thanks