Is the head of a Prince Rupert drop completely unbreakable, or is there a force strong enough to break it?

MaggieG 5

I saw the portrait of Prince Rupert in the National Portrait gallery recently and thought he was rather a dish. Why do you want to drop his head, Liz? BTW what's a Prince Rupert drop, Liz? Oct 02 03, 3:18 PM

elizabethmc

It's a drop of glass which is cooled really quickly in cold water or oil, making the outside cool quicker than the inside. They are tadpole shaped, and if you bang the head, it doesn't break, but if you snip the bottom it shatters into tiny little pieces of glass. They were discoverd in the 17th century! Oct 02 03, 3:36 PM

BreakIt

Yes the head can be broken in a couple of ways. You can impact it with a sharp hardened point, like a tungsten carbide scribe and hammer. Or, more to your question, there is a force needed to break this. That force is one that exceeds the strength of the glass (~10,000 psi) + reversing the compressive stresses which can run almost 1/4 the way through on all surfaces. Said another way, highly tempered glass products can be more than 4X in strength than the original, so an estimate is that the force would need to exceed 40,000 psi. Translated to the typical size glass drop the load/weight needed would be about 20,000 pounds. So not unbreakable, no such glass exists to date. Jun 23 06, 1:33 PM