Nav: Home

New inspection process freezes parts in ice

May 01, 2019

"How on Earth did they make that?" asks Francesco Simonetti, commenting on an ice sculpture of a swan.

Simonetti isn't admiring the artistry of shaping a block of ice into a bird. He's admiring the swan's crystal-clear transparency.

Simonetti, an aerospace engineering professor at the University of Cincinnati, is an expert in sound waves, but lately he's been an apprentice in ice. And when it comes to sound waves, the clearer the ice, the better.

Simonetti recently published a novel approach that uses ultrasound to inspect additive-manufactured parts: He dips the part in water and freezes it inside a cylinder of ice. The ice acts as a coupling medium, letting ultrasonic waves enter and reflect against the part's potential defects.

To describe this grouping of ultrasound and ice, Simonetti coined the term cryoultrasonics. Cryoultrasonics can have a dramatic influence on industry, ensuring additive manufacturers build reliable parts.

The work appeared this month in NDT& E International, one of the leading journals in nondestructive testing and evaluation.

Simonetti uses cryoultrasonics to inspect safety-critical parts, like metal parts in jet engines or power plants. Because people's lives are at stake, engineers need to be able to detect any potential defects in these parts before they're used in practice.

In traditional subtractive manufacturing, ultrasound testing works just fine. A manufacturer starts with a solid block of material, which engineers can test for defects by sending ultrasonic waves through it.

But new technologies, like additive manufacturing, challenge this approach. Additive manufacturers build a desired part not by subtracting from a block but by adding layer on layer. Ultrasonic waves bounce off the angles and curves of these new parts, instead of the potential cracks or defects.

"Sound needs a coupling medium to propagate from a source transducer into the volume of a part," says Simonetti. "When the contrast in mechanical properties between the coupling medium and the part is large, very little energy enters, and it doesn't work."

Many people have tested water as a coupling medium. They immersed the part in water and sent ultrasound waves through it. Water's mechanical properties, however, are very different from metals. Very little ultrasonic energy can even make it to the part.

So Simonetti turned to ice.

"Living in Cincinnati, you're always removing ice from the drive way. I got curious to see what the ice properties were," says Simonetti.

"We tried all the conventional techniques and nothing would work. At that point, we looked for desperate measures, and I just thought, 'Why don't we try?'"

Simonetti freezes the metal part in a cylinder of ice and then sends ultrasonic waves through it. Since the physical properties of ice are very similar to those of the metal part, the waves easily pass through the ice and encased metal and pick up any defects in the part. When he's done, the ice simply melts.

At least that's the idea.

"The first attempts were disastrous," says Simonetti.

For ice to act as an effective coupling medium, it has to be crystal clear -- If any cracks or bubbles exist, ultrasound waves will reflect off of the defects in the ice rather than the defects in the part.

But ice isn't crystal clear. It's cloudy and fractured. Send an ultrasound wave through it and the wave bounces in 15 directions. It's even worse for bigger blocks of ice, like those needed to encase some of these metal parts.

Simonetti needed to find a way to freeze ice around the part while keeping the ice transparent. That meant getting a special machine that froze ice without causing bubbles or cracks.

"Of course, we had to build this thing," he says.

Simonetti made this custom ice machine by hand, combining things bought on Amazon like baking pans, griddles and spindles. It's like a science kitchen set, but it does the job. That job is to tackle the two obstacles that prevent the formation crystal-clear ice: cracks and bubbles.

Cracks form because water expands as it solidifies. Water freezes from the outside, forming a solid ice shell with liquid core. As the core solidifies, it tends to expand against the shell, which causes a buildup of internal forces that leads to cracking.

To prevent this cracking, Simonetti has made a cylinder with a metal base and plastic sides. Simonetti puts the metal part he's inspecting inside of the cylinder and fills it with water. He then chills the metal base, which causes the water to freeze from bottom to top. The water eventually solidifies around the metal part and expands to the open top of a cylinder, rather than the sides.

Bubbles are little trickier. Dissolved air exists in water. As water freezes, it expels the excess air. This excess air accumulates on the freeze front, or where the water is turning to ice, to form bubbles.

"In order to prevent this phenomenon, you need to simply reduce the concentration of air on top of the freeze front. To do that, we stir the water to have constant flow," says Simonetti.

To create this constant flow, Simonetti uses a spindle. By keeping the water in motion, the excess air never accumulates and the bubbles never form.

The result is a metal part encased by a block of crystal-clear ice, rivaling even the clearest ice sculpture. Simonetti can send ultrasonic waves unimpeded through this block to measure the safety of a metal part. When he's done, he simply puts the part under water and the ice melts right off.

Simonetti admits that ice is only one step forward in inspecting these critical-safety parts. Ice is a good coupling medium because it has similar properties to that of metal, but it's still not exact.

"Ideally, if the coupling medium were made of the same material as the part, it would be perfect," says Simonetti. "But that is not practical with something like liquid titanium. Experimentally, you couldn't remove it."

Simonetti is now experimenting with nanoparticles to create ice that more closely resembles the properties of a metal part. The idea is to freeze suspensions of nanoparticles into the water to make the ice denser, heavier and mechanically stronger.

Simonetti's taking calls from many industries, including engineering firms, car manufacturers and the military. He thinks the publication has helped establish legitimacy in his cryoultrasonic approach, as well as limit skepticism. He, too, doubted the approach at first.

"It's entirely new. Whenever you have something that is so novel, there are a lot of skeptics from the academic community," he says. "When you freeze water, it looks terrible. You think, 'This is not going to work.'"

Simonetti pulls the finished block of ice out of the freezer to inspect. The ice completely encases the metal part. As Simonetti holds up the ice, he can see right through it. It's as clear as an ice sculpture of a swan and, somehow, just as impressive.

University of Cincinnati

Related Ultrasound Articles:

World's first ultrasound biosensor created in Australia
Most implantable monitors for drug levels and biomarkers invented so far rely on high tech and expensive detectors such as CT scans or MRI.
Ultrasound can make stronger 3D-printed alloys
A study just published in Nature Communications shows high frequency sound waves can have a significant impact on the inner micro-structure of 3D printed alloys, making them more consistent and stronger than those printed conventionally.
Full noncontact laser ultrasound: First human data
Conventional ultrasonography requires contact with the patient's skin with the ultrasound probe for imaging, which causes image variability due to inconsistent probe contact pressure and orientation.
Ultrasound aligns living cells in bioprinted tissues
Researchers have developed a technique to improve the characteristics of engineered tissues by using ultrasound to align living cells during the biofabrication process.
Ultrasound for thrombosis prevention
Researchers established real-time ultrasonic monitoring of the blood's aggregate state using the in vitro blood flow model.
Ultra ultrasound to transform new tech
A new, more sensitive method to measure ultrasound may revolutionize everything from medical devices to unmanned vehicles.
Shoulder 'brightness' on ultrasound may be a sign of diabetes
A shoulder muscle that appears unusually bright on ultrasound may be a warning sign of diabetes, according to a new study.
Ultrasound-firewall for mobile phones
Mobile phones and tablets through so-called audio tracking, can be used by means of ultrasound to unnoticeably track the behaviour of their users: for example, viewing certain videos or staying in specific rooms and places.
Designing a new material for improved ultrasound
Development of a theoretical basis for ultrahigh piezoelectricity in ferroelectric materials led to a new material with twice the piezo response of any existing commercial ferroelectric ceramics, according to an international team of researchers from Penn State, China and Australia.
Atomic structure of ultrasound material not what anyone expected
Lead magnesium niobate (PMN) is a prototypical
More Ultrasound News and Ultrasound Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at