Prince Rupert's Drop: Resist Hammer Blow, Yet Shatter With A Twitch

Have you ever heard of an object which is as fragile as glass but as indestructible as a tank? Last week I came across one such wonder of science which can be broken with an ease of twitch but can take the blow of the hammer. Of course, it all depends on placement of force.


Prince Rupert's Glass drop has an impossible property. Researches were carried out in the 20th and 21st centuries to understand the reasons that why the drop has contradictory properties. But the history of the drop can be traced back to 1660 that is more than 350 years from now when Prince Rupert of the Rhine, brought them to England, thus got the name.  They were studied by the Royal Society, and the principles behind the unusual properties might have probably led to the development of the process to produce toughened glass, which was patented in 1874. although they were reportedly being produced in the Netherlands earlier in the 17th century and had probably been known to glass makers for much longer. - Wikipedia

The reason for the popularity of the drops are two unusual mechanical properties - The tail for the drop is extremely fragile part of it. It is so fragile that mere twist to break the very furthest end of the tail will make the whole drop disintegrate with an inward explosion. The process is so fast that it cannot be captured with the normal camera with even slow-motion capture settings. Some of the enthusiast could capture the action at high speed cameras with frame rate of more than 150,000 frames per second that is whopping 4687 times faster than normal 32 frames per second capture rate of the camera. However, the other part of the drop is a bulbous head. The drop shape head has an integrity which can withstand compressive forces of up to 15,000 newtons (3,400 lb.). That means that striking a hammer on the head of this glass drop wont impact it.

I thought that producing such object with very seemingly impossible properties may require very sophisticated tools and technology. But on thinking further, from the perspective that Prince Rupert's drops are around from early 17th century or earlier, I realized that it cannot be very complicated or cutting-edge technology required to create it. The process is very simple, is to just drop the molten glass drops in to freezing water. The result, on dropping molten glass which has temperature of more than 650 Degree Celsius. into ice cold water will rapidly cools which is also called quenching in mechanical engineering, solidifies the glass from the outside inward.


The outside inward cooling creates some amazing effects. The super cold water rapidly cools down the outermost layer of the drop which is in directly touch with it and have lesser effect to the inner layers of the drop to the least at the core of the drop. what it means is the outermost layers of the glass cools off much quickly than the inner layers. The outer layer getting cold will try to shrink and create compression on inner layer while inner layer tries to expand will be in state of tension.

This rapid cooling of outer layer and solidifying it almost instantly will lock the layer creating compressible stress which is opposed by an equally strong inner layer with tensile stress.

Thus, during the act of breaking it the compression stress created in the layers counter acts the blow. The only way to break it to get past the compression barriers, with force even higher than compression stress or snapping the thin end as due to thin layers it is much easier to break past it.

One of the applied use of this phenomenon is the tempered glasses. The tempered glasses have high compressive and tensile strength. You will see the glass shatter instead of cracks like in cars window except windshield to shatter.

Prince Rupert's Drop is truly a wonder of nature for which you can expect the unexpected. I would like to create and shatter some of them one day.


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credits
Data
            Wikipedia - https://en.wikipedia.org/wiki/Prince_Rupert%27s_Drop
    Quora - https://www.quora.com/Is-there-a-simple-explanation-as-to-why-the-Prince-Ruperts-drop-is-so-strong-If-so-what-is-it/answer/Arun-Krishna-2?share=6d705e0f&srid=LLYH

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https://www.youtube.com/watch?v=SrLfShIPYko

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