I’m very curious.
In: 141
When the outside cools rapidly it shrinks , this puts inward facing stress on the molecules
Then the molten bit inside cools and continues to do the exact same thing but pulling on a solid essentially
This causes the molecules to be under such an extreme amount of stress that the amount that can be exerted by a external force is negligible , even a bullet doesn’t impart enough force and can be shattered
However all this internal force pulls into the tail where it’s weakest , think if you had millions of ropes all being pulled to one spot. This puts a lot of stress on the tail that is really only kept together by a very thin layer this time so it’s possible to break it with a reasonable amount of force.
Once it’s broken though all that stress force has a place to go , outwards , which causes it to quite literally explode outward
It’s a similar reason structural concrete is so strong. They utilize a concept called prestressing. Keep in mind for the explanation that tension is the opposite of compression. If something has no forces acting on it, then it’s right between the both of them.
See, concrete is extremely weak in tension. You can practically pull it apart by hand. But how do we build bridges with it if it’s so weak? Well, we build them with rebar that is pulling extremely tight. Since the concrete is always being pulled in, it’s always in compression. Concrete may be a pushover in tension, but it’s incredibly strong in compression. So, we are always leveraging concrete’s natural strength by not allowing it in tension.
Prince Rupert’s drops do the same exact thing. The process of creating them makes them stupidly strong in compression in a similar way: The outside is already tight around the center when it’s first made and very hot, but then it cools down. It wants to shrink around the center but it cannot. That keeps everything in strong compression, so forces that would normally break it by pushing it into tension are absorbed, keeping the piece still overall in compression.
It’s also much easier to break if you hit it at an angle, as that causes a mix of tension and compression stresses. A hydraulic press is axially calibrated to be extremely straight, and essentially acts only in compression. This makes it perfect to show off the strength of Prince Rupert’s drops.
Side note, the tail is extremely weak! It’s a glass cannon, but the hydraulic press video shows off its absolute best-case scenario strength while hiding all of the weaknesses, like a well-engineered part!
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/
Funny. I had the prince rupert hydraulic press video in my yt recommends yesterday as well.
It’s basucally hardened glass. The big drop is almost indestructible but the small end is very sensitive and can shatter the whole thing .
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