I’m very curious.
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Introduction: a Prince Rupert’s drop is a drop of molten glass which is quickly quenched in water. This forms a teardrop-shaped object which is extremely tough in the bulb, but if you crack the tip, the entire thing shatters.
ELI-5:
* Glass is a ceramic, which means that the material tends to form microcracks (instead of atoms sliding, like in metals).
* When you pull the crack apart (tension), this causes the cracks to grow uncontrollably and shatter. If you push the cracks together (compression), the cracks can’t grown.
* The quenching process creates a compressive layer at the surface, which offsets any tensile force that you apply. If you hit it with a hammer, you need to hit it hard enough to overcome the compressive force pushing cracks together.
ELI-15
* The defining property of glass is that the atoms are arranged randomly. In most materials, pretty much every atom is the same distance apart from it’s neighbors. In glass, because of the random bonding, some atoms can be closer together than other atoms. We would generally expect, because of thermal expansion, hot parts of glass to have farther atomic separation than cold parts of glass.
* When the glass is molten, all the atoms are hot and have a far atomic separation. When this hot glass is quenched, the outside layer immediately shrinks. However, the inside layer has not had time to shrink. This creates a compressive layer on the outside, and a tensile layer on the inside
* As long as the compressive layer isn’t penetrated, the teardrop won’t break. If you can get a crack into the tensile layer, however, those tensile forces will rip the crack open at the speed of sound, shattering everything.
* Because the tail is very thin, the compressive layer is also thin. So it’s easy to crack into the tensile layer at the tail, and then the crack propagates up the teardrop and shatters it.
For ELI-Undergrad, here’s a nice article with diagrams
https://msestudent.com/prince-ruperts-drops-the-exploding-glass-teardrop/
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