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Published on May 11th, 2017 | By: April Gocha, PhD

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Glass goes ballistic: What happens when you shoot a bullet at Prince Rupert’s drops?

Published on May 11th, 2017 | By: April Gocha, PhD

[Image above] Credit: SmarterEveryDay; YouTube

 

 

About three years ago, I shared a fascinating video that showcased the impressive strength of Prince Rupert’s drops. These glass drop structures have some incredible materials properties that highlight the fact that glass isn’t just a brittle, easily broken material.

 

That video, made by YouTube channel SmarterEveryDay, showed how strong these glass structures are at their head, but how fragile the structures can be when their tail is distorted.

 

Prince Rupert’s drops are formed by dropping hot molten glass into cold water, a technique that develops opposing forces of high compressive strength on the outside—making the head incredibly strong—and high tensile strength on the inside—making the tail incredibly sensitive.

 

Because of those opposing forces, a minor distortion to a drop’s tail causes the whole structure to explode with surprising force. At 100,000 frames per second, that explosion looks like a psychedelic glass confetti explosion.

 

Breaking a Prince Rupert’s drop unleashes a glass confetti explosion. Credit: SmarterEveryDay; YouTube

 

The reason why these explosions put on such a psychedelic show is that cracks race from the tip to the head of a Prince Rupert’s drop at speeds in excess of 4,000 mph, according to previous work.

 

Now, Purdue researchers have taken a deep dive to decipher more of the science behind the incredible strength found at the head of Prince Rupert’s drops.

 

Using a technique called integrated photo elasticity—which uses a polarized filter to visualize stress distribution in a material—the researchers calculated compressive stresses of around 50 tons per square inch in the head of Prince Rupert’s drops, making them as strong as steel, according to a Purdue press release.

 

For more about the long history and incredible science of Prince Rupert’s drops, check out this great video from Purdue Engineering.

 

The Purdue scientists published their findings, “On the extraordinary strength of Prince Rupert’s drops“, in Applied Physics Letters (DOI: 10.1063/1.4971339).

 

So Prince Rupert’s drops are strong—but are they strong enough to survive being shot with a high-speed bullet at point-blank range?

 

Lucky for us, SmarterEveryDay host Destin wondered the same thing. The channel recently posted a series of new videos exploring the limits of strength of Prince Rupert’s drops in the face of some serious ammunition spewed from progressively bigger guns.

 

Before you watch the videos below, however, make a prediction—which will win, bullet or glass? The Purdue research above might give you a clue.

Credit: SmarterEveryDay; YouTube

 

Because several of the bullets in the original video are lead-tipped, Destin ups the ante in the next video by taking aim with a series of full metal jacket bullets, which speed at even higher velocities from a 0.22 Magnum and a 0.38 Special.

Credit: SmarterEveryDay; YouTube

 

Bigger guns, you say? You got it in this next video. Just don’t miss the triboluminescence.

Credit: SmarterEveryDay; YouTube

 


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