1. Interlayer peeling: When subjected to pressure, the fiber layer of the paperboard will peel off, resulting in the reduction of the thickness and strength of the paperboard.

2. Paper indentation: When the cardboard is subjected to high pressure, the surface will be indented, which will lead to the decrease of the surface flatness of the cardboard.

3. Extrusion deformation of cardboard: When the cardboard is under great pressure, it will be extruded and deformed, thus changing the shape and structure of cardboard.

4. Broken cardboard: In extreme cases, when the cardboard can't bear the pressure, it will break or break.