A sharper knife can puncture a surface with less force than a dull knife, presumably because a sharp knife has greater pressure than a dull knife for the same force.
I suspect that pressure alone isn't what we need for puncturing; e.g. if I apply the same pressure as the knife uniformly over a large area, I might not puncture the surface. Presumably I need some sort of minimum tension in the surface for it to tear after deforming under the pressure, or something like that, but I'm not sure what. How would you build a simple model for puncturing?
For a specific example, just imagine puncturing the leather on a couch, I guess.