You're going to love this playlist from Practical Engineering [1]. Grady explains all of this much better than I could. The second video explains reinforcement and the fifth explains pre-stressing.
Also interesting that "All the frameworks used USB drives as the physical transmission medium to transfer data in and out
of the targeted air-gapped networks. We have not found any case of actual or suspected use of covert physical transmission mediums,
such as acoustic or electromagnetic signals."