Posted on 05/09/2017 10:39:25 AM PDT by Red Badger
Prince Rupert’s drop.
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(Phys.org)—Researchers have finally answered a question that has stumped scientists since the early 1600s: Why are the heads of tadpole-shaped pieces of glass called "Prince Rupert's drops" so strong?
In the 17th century, Prince Rupert from Germany brought some of these glass drops to England's King Charles II, who was intrigued by their unusual properties. While the head of the drop is so strong that it can withstand the impact of a hammer, the tail is so fragile that bending it with your fingers will not only break the tail, but cause the entire droplet to instantly disintegrate into a fine powder.
Prince Rupert's drops are easily made by dropping red hot blobs of molten glass into water. Although researchers have tried to understand what causes the unusual properties of these drops for many years, it was not until recently that modern technology has allowed researchers to thoroughly investigate them.
In 1994, S. Chandrasekar at Purdue University and M. M. Chaudhri at the University of Cambridge used high-speed framing photography to observe the drop-shattering process. From their experiments, they concluded that the surface of each drop experiences highly compressive stresses, while the interior experiences high tension forces. So the drop is in a state of unstable equilibrium, which can be easily disturbed by breaking the tail.
One open question, however, is how the stresses are distributed throughout a Prince Rupert's drop. Understanding the stress distribution would help to more fully explain why the heads of these drops are so strong.
To do this, Chandrasekar and Chaudhri began collaborating with Hillar Aben, a professor at Tallinn University of Technology in Estonia. Aben specializes in determining residual stresses in transparent three-dimensional objects, such as Prince Rupert's drops.
Fringes throughout a Prince Rupert’s drop indicate residual stresses. Credit: Aben et al. ©2017 American Institute of Physics ==============================================================================================================================
In the new study published in Applied Physics Letters, Aben, Chandrasekar, Chaudhri, and their coauthors have investigated the stress distribution in Prince Rupert's drops using a transmission polariscope, which is a type of microscope that measures the birefringence in an axi-symmetrical transparent object, such as a Prince Rupert's drop.
In their experiments, the researchers suspended a Prince Rupert's drop in a clear liquid, and then illuminated the drop with a red LED. Using the polariscope, the researchers measured the optical retardation of the light as it traveled through the glass drop, and then used the data to construct the stress distribution throughout the entire drop.
The results showed that the heads of the drops have a much higher surface compressive stress than previously thought—up to 700 megapascals, which is nearly 7,000 times atmospheric pressure. This surface compressive layer is also thin, about 10% of the diameter of the head of a drop.
As the researchers explain, these values give the droplet heads a very high fracture strength. In order to break a droplet, it's necessary to create a crack that enters the interior tension zone in the drop. Since cracks on the surface tend to grow parallel to the surface, they cannot enter the tension zone. Instead, the easiest way to break a drop is to disturb the tail, since a disturbance in this location allows cracks to enter the tension zone.
Overall, the researchers believe that the results finally explain the great strength of Prince Rupert's drops.
"The work has fully explained why the head of a drop is so strong," Chaudhri told Phys.org. "I believe we have now solved most of the main aspects of this area. However, new questions may emerge unexpectedly."
More information: H. Aben et al. "On the extraordinary strength of Prince Rupert's drops." Applied Physics Letters. DOI: 10.1063/1.4971339
Journal reference: Applied Physics Letters
Read more at: https://phys.org/news/2017-05-scientists-year-old-mystery-prince-rupert.html#jCp
Very interesting.
But can you make anything useful out of that ultra-strong glass? Can something similar be made from other materials? Solving mysteries is nice, but without some practical benefit, it is not much more than a mind game (I could call it something else, but I’m trying to be polite).
Go look up YouTube videos showing them shattering. Fascinating. People have gone so far as _shoot_ the drops, recorded with high-speed cameras, showing the bullet fragmenting on the glass and the glass surviving unscathed until the shockwave reaches the drop’s tail.
Nope. The problem is the high-strength portion is coupled to a high-fragility portion; the instant any part of the glass breaks at all, the whole thing practically explodes.
I wonder if there might be a way to avoid the tail and create a very strong glass bearing.
Maybe by releasing the molten glass in zero G and somehow surrounding it with water quickly?
I asked those same questions.
Could a drop made of iron be suddenly so strong that it could defy known materials at high speeds?...............
Imagine something made out of a material that is compressed at 7000 times atmospheric pressure...
There has to be a way to harness this knowledge to create a nearly impenetrable surface. There has to be....
Check out this video at approximately 2:00
Bullet vs Prince Rupert’s Drop at 150,000 fps - Smarter Every Day 165
https://www.youtube.com/watch?v=24q80ReMyq0
The military uses would be enormous.................
A Liberal's brain
Science is the garden of knowledge from which engineers harvest inventions.
Tempered glass windows and doors already makes use of the understanding of compression and tension to create products which shatter into small harmless bits instead of large, pointed knifelike shards.
The understanding described in the article might make it possible to design car windows of tempered glass (which they do now) but with a built in mechanism to shatter the glass without the use of a tool. Some people carry a tool now to use during an accident to free themselves from a car by breaking a window. Instead, one could have a "Push button in order to break glass" mechanism near the door handle, basically building in the tool.
This is an allegory/riddle.
Can be hit on the head with out any effect.
But tweak the tail, and everything shatters.
What/who am I?
Would've come in handy for the Argo City dome.
harness this knowledge to create a nearly impenetrable surface.
= = =
Line up the heads all together, and the tails all together.
Head side is impenetrable, but tail side is vulnerable.
Cirdle them up like a wagon train!
My ex...
Finally, I can sleep tonight.
Someone will. Bank on it.
I'm sure the boys on the banglist will be interested to hear more about that!
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