Nav: Home

Physics of windshield-cracking raindrops could demolish kidney stones

November 05, 2019

DURHAM, N.C. -- A plane has to be going pretty fast for a mere raindrop to crack its windshield, but it can happen. Now, new models of the physics behind the improbable feat may just help doctors crack kidney stones to pieces.

When supersonic jets were first being developed for commercial use in the 1960s, researchers discovered a curious phenomenon that sometimes occurs on test flights through rainforests. Even though raindrops weigh almost nothing, they are capable of creating ring-shaped cracks in the jets' substantial windshields.

Although scientists initially had difficulty explaining this curiosity, Professors Frank Philip Bowden and John Field of the University of Cambridge eventually recognized surface waves as the culprits. Because surface waves spread in only two dimensions, they pack a much more powerful punch than their three-dimensional counterparts. Certain details of the phenomenon, however, have remained poorly understood due to a lack of mathematics to describe it and experimental setups to validate proposed models.

In a new paper published Nov. 1 in Physical Review Research, Pei Zhong, professor of mechanical engineering and materials science at Duke University, and his former graduate student Ying Zhang, now an acoustical engineer for Bose, have closed that gap in scientific knowledge.

The pair created an experimental system to visualize the stress created by such surface waves. They put a lithotripsy device designed to shatter kidney stones with soundwaves in a vat of water covered by a sheet of glass, then set off a point-source explosion that expanded as a spherical shock wave. Depending on the angle at which the shockwave hits the glass, it can produce surface waves that spread on the water-glass boundary.

With a high-speed camera, the team measured the speed of various elements of a shock wave over the mere moments it takes to propagate through the glass. Zhang used those measurements to validate a finite element model constructed using a multiphysics software called COMSOL. The models successfully reproduced the characteristics of a series of bulk and surface waves often observed in such situations, including one that may save people from needing surgery to remove kidney stones.

The researchers discovered that the type of wave primarily responsible for most of the stress and damage -- called a leaky Rayleigh wave -- propagates much faster than a second type of wave called an evanescent wave. While they're created at the same time on the water-glass boundary, the leaky Rayleigh wave eventually pulls away from the evanescent wave, which is the moment and location of the highest tensile stress caused by the phenomenon.

They also discovered that the circular cracks originally observed on the supersonic jet windshields don't necessarily form at this point -- they require an existing imperfection in the glass to get started. But once initiated, the crack propagates along a circular trajectory, following the first principal stress in the solid set off by the advancing leaky Rayleigh wave.

"The challenge for treating kidney stones is to reduce the stones to very fine fragments so the doctors don't have to follow up with any ancillary procedures," said Zhong. "Based on the insight gained through this model, we may be able to optimize the shape of the shock waves and lithotripter design to create more tension on the surface of the kidney stones to open up the defects more efficiently."
-end-
This work was supported by the National Institutes of Health (R37-DK052985-22).

CITATION - "Nanosecond Shock Wave-Induced Surface Acoustic Waves and Dynamic Fracture at Fluid-Solid Boundaries," Ying Zhang, Chen Yang, Hao Qiang, and Pei Zhong. Physical Review Research, Nov. 1, 2019. DOI: 10.1103/PhysRevResearch.1.033068

Duke University

Related Stress Articles:

Why stress doesn't always cause depression
Rats susceptible to anhedonia, a core symptom of depression, possess more serotonin neurons after being exposed to chronic stress, but the effect can be reversed through amygdala activation, according to new research in JNeurosci.
How plants handle stress
Plants get stressed too. Drought or too much salt disrupt their physiology.
Stress in the powerhouse of the cell
University of Freiburg researchers discover a new principle -- how cells protect themselves from mitochondrial defects.
Measuring stress around cells
Tissues and organs in the human body are shaped through forces generated by cells, that push and pull, to ''sculpt'' biological structures.
Cellular stress at the movies
For the first time, biological imaging experts have used a custom fluorescence microscope and a novel antibody tagging tool to watch living cells undergoing stress.
Maternal stress at conception linked to children's stress response at age 11
A new study published in the Journal of Developmental Origins of Health and Disease finds that mothers' stress levels at the moment they conceive their children are linked to the way children respond to life challenges at age 11.
A new way to see stress -- using supercomputers
Supercomputer simulations show that at the atomic level, material stress doesn't behave symmetrically.
Beware of evening stress
Stressful events in the evening release less of the body's stress hormones than those that happen in the morning, suggesting possible vulnerability to stress in the evening.
How plants cope with stress
With climate change comes drought, and with drought comes higher salt concentrations in the soil.
Gene which decreases risk of social network-related stress, increases finance-related stress risk
Researchers have discovered that the same gene which increases your risk of depression following financial stress as you grow older also reduces your chance of depression associated with friendship and relationships stresses when young- your social network.
More Stress News and Stress Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab