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The mystery of tiny teardrop-shaped glass confections that can survive a hammer blow, yet shatter to smithereens with the slightest touch to the stem, has finally been solved.

#NSFfunded researchers have identified why small glass structures called Prince Rupert’s drops can withstand the blows of a hammer and yet burst into dust by simply snipping their threadlike tails.

A set of unique stresses makes this 'glass tadpole' so intriguing.

The extraordinary strength of the head, they reported in Applied Physics Letters, comes not from tensile, or pulling, stress—as researchers have long believed—but from compressive stress. The team measured compressive stress in the drop’s head equivalent to more than 4000 times atmospheric pressure.

“The tensile stress is what usually causes materials to fracture analogous to tearing a sheet of paper in half,” said Koushik Viswanathan of Purdue University, an author of the paper, says in a press release. “But if you could change the tensile stress to a compressive stress, then it becomes difficult for cracks to grow, and this is what happens in the head portion of the Prince Rupert’s drops.”

We’ve long known the drops are strong, and we’ve long known why. But researchers at a team from Purdue University, the University of Cambridge and Tallinn University of Technology have quantified just how strong, recently publishing their results in the journal Applied Physics Letters. - Washington Post

Generally, when glass is struck with a hammer it shatters into bits. That is not the case with the bulbous part of Prince Rupert's drops, and researchers recently determined why.

In a paper published in the journal Applied Physics Letters, scientists at Purdue University’s Center for Materials Processing and Tribology describe how they figured this all out using photography that involves polarizing filters to visually reveal the stress lines in the teardrops.

Shared ScienceAlert.com's article

Along with Purdue professor of industrial engineering Srinivasan Chandrasekar, team leader Hillar Aben of Tallinn University used integrated photoelasticity to investigate the drops. This is a technique where a transparent 3D object is suspended in an immersion bath and polarized light is passed through it. The alterations in the light's polarization inside the object show up as rainbow bands that correspond to stress lines.