A Prince Rupert's drop looks like a glass tadpole from a beginner's crafts festival, but it's so strong it can take a hammer hit without breaking. That would be impressive enough, but if you break its tail, which can be done with finger pressure, the drop explodes into powder. The reason for this has mystified scientists for 400 years, but a team from Purdue University, the University of Cambridge, and Tallinn University of Technology in Estonia finally has an answer.
[...]Focusing on the head of the drop instead of the tail, the current study found that the compressive stresses in the glass are about 50 tons per square inch, which gives it the strength of some steels. According to the team, this is because the outside of the drop cools faster than the inside. This turns the outside into a layer of powerful compressive forces pushing inward. These are balanced out by the tensile or pulling forces inside the drop.
So long as these forces remain in balance, the drop remains stable and can withstand tremendous punishment. Normally, because glass is a supercooled liquid rather than a solid, any cracks in the surface propagate at the speed of sound through a glass object, breaking it.
But in a Prince Rupert's drop, the interface between the inner and outer regions deflects the forces sideways, so the crack can't propagate. However, if the tail is broken, The shallow cracks in the tail shoot parallel to the axis of the drop, deep into the head, and into the interface. The damage is so great that the balanced forces are released, causing the drop to explode.
(Score: 3, Informative) by wonkey_monkey on Saturday May 13 2017, @09:37AM (1 child)
The article makes it sound like we had no idea what was going on until now, which isn't true. It was known it was down the cooling, the inside contracting as it cooled while the outside had already solidified, and the breaking that tail allowed cracks to propagate which released the tension in the head and caused it explode.
systemd is Roko's Basilisk
(Score: 3, Informative) by Rosco P. Coltrane on Saturday May 13 2017, @04:18PM
It hasn't be a mystery at all for a long time: the study of Prince Rupert drops is what led to the development of safety glass - which works exactly the same way.
(Score: 2) by Unixnut on Saturday May 13 2017, @09:43AM (7 children)
I didn't even know of the Prince Rupert's drop until now, let alone the how and why of its properties. Amazing! Thanks for the article, learned something new :)
(Score: 5, Informative) by c0lo on Saturday May 13 2017, @10:25AM (6 children)
Crushed in a press [youtube.com] - 20 tons to crush it (given the contact surface, I don't want to think of the pressure, in 10-100 Giga-Pascals range for sure).
Indentation left in the steel plate used as support before crushing.
170,000 FPS - the drop resists a full metal jacket .38 Magnum special at point-blank range [youtube.com]
when defeated by a rifle bullet [youtube.com] it emits light by triboluminescence. Survives a grazing blow from an AK-47.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by kaszz on Saturday May 13 2017, @01:47PM (4 children)
I'll hope someone tries to make a gigantic prince Rupert drop. It would be interesting to see how it decomposes.
Thinking of something with a 0.5 meter diameter or so.
(Score: 2) by Scruffy Beard 2 on Saturday May 13 2017, @03:57PM (2 children)
That would be a bomb; only less safe to handle.
(Score: 2) by kaszz on Saturday May 13 2017, @04:32PM
From the high speed footage I have seen. The drop essentially just cracks. It doesn't seem to explode really. Regardless it's possible to use robots etc to handle it safely.
(Score: 3, Informative) by c0lo on Saturday May 13 2017, @10:07PM
The maximum energy it will hold is limited upwards by the energy required to melt it - it's all mechanical energy, no chemical reactions takes place.
Somehow, I don't think it will be that much.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by c0lo on Saturday May 13 2017, @10:12PM
Mmm... I don't think the process scales up that well.
Think volcanic rock from underwater volcanoes - I don't hear about any rocks on Hawaiian beaches exploding.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by fubari on Sunday May 14 2017, @04:16PM
Some more cool super slow motion video @ Smarter Every Day: Prince Ruperts Drop [youtube.com].
Worth watching, they explain why calling it an explosion is reasonable (mechanical vs. chemical energy). They observed that the speed of the failure front at a bit over 1 mile per second (3,708 mph). Fun stuff.
(Score: 2) by kaszz on Saturday May 13 2017, @01:30PM (1 child)
50 tons per square inch = 77.5 MPa.
Same ballpark as pressure at 6500 meters under the ocean or a bullet chamber during firing.
(Score: 2) by iWantToKeepAnon on Saturday May 13 2017, @03:00PM
Funny you should say that Smarter Every Day has a series of videos [youtube.com] where he fires higher and higher caliber bullets at Prince Rupert Drops
"Happy families are all alike; every unhappy family is unhappy in its own way." -- Anna Karenina by Leo Tolstoy