How to demonstrate force on assembly?

Hey all,

I designed a box, which contain foam and plastic parts (total of 6 different parts for the box- 3 made of foam and 3 made of plastic) .

The box is built to contain glass ampule (medicine ampule).

I need to check at which the box will start to crack, after assembly.

How can i demonstrate forces on assembled model? i know only to do it part at a time.

Thanks  =)

Danielle Awaskar and Itai Meirovich, BGU university.