The Ice Man Cometh: Cryo-ultrasonics Make NDE Cooler

By: Diana Riggs
Date: April 30, 2018

Francesco Simonetti, PhD, is performing research so cutting edge, it did not even have a name yet—a new method of ultrasonic non-destructive testing that he calls “cryo-ultrasonics”.

a cylinder of ice sits on a spindle, and a green plastic and metal machine arm is mounted above it

A metal part is encapsulated in ice before inspection.

In a journal article published in Transactions on Ultrasonics, Ferroelectrics and Frequency Control, published by the Institute of Electrical and Electronics Engineers (IEEE) in January, Simonetti and his colleagues describe a new method of non-destructive evaluation (NDE): using ice as a coupling medium for ultrasonic evaluation of complex machine parts.

Simonetti, an associate professor in the department of aerospace engineering and engineering mechanics, is also the director of the Ultrasonic Imaging Laboratory (USIL) at University of Cincinnati (UC). Researchers at USIL are developing NDE techniques for detecting damage in advanced materials by interpreting the properties of ultrasonic waves as they pass through the materials.

Simonetti explains that major advances in computational techniques, new exotics materials, and more versatile manufacturing methods such as 3-D printing, have given engineers the ability to design highly complex machines in which each subcomponent can be optimized to achieved the highest performance. As a result, the field is witnessing a dramatic increase in the geometrical complexity of these components.

Simonetti stands in the ultrasonics lab

Simonetti in the USIL.

When they are used in safety critical applications, the components need to be inspected for the presence of manufacturing defect or damage that has developed while the component is in service. This requires the availability of NDE methods that can work with highly complex shapes. However, conventional NDE techniques, including traditional ultrasound, cannot effectively inspect these parts. Ultrasound requires a coupling medium or direct contact between the sensor and the material being tested. Many parts have irregular surfaces and internal contours that are inaccessible to even the smallest ultrasound probes.

By using ice encapsulation, a part with a complex design is transformed into a simple solid shape whose volume can be probed with ultrasonic waves. Ultrasonic waves are highly sensitive to both pores and crack-like defects over a wide range of material properties, possibly making the method extremely effective for an array of applications.

The ice provides a medium that is easy to remove, and causes no damage to test samples. Water expands when it freezes, creating a better bond to the part. This is a property unique to water; other materials shrink when they solidify, and debond from the surface of metals, which prevents ultrasonic waves from traveling through the part.

Industries desperately need NDE to progress on pace with manufacturing. NDE is needed to mitigate the risks associated with system failure which often may result in the loss of incalculable sums due to damages, lost revenue, legal costs and environmental harm or even the loss of lives. Due to increasing demands for reliable and timely NDE, Simonetti says, NDE research attracts tremendous interest from top companies in the aerospace, oil, gas, and power generation industries. His lab is often approached by industry partners seeking solutions to unique NDE problems.

Despite this demand, NDE has not historically appealed to many engineers. Simonetti disagrees with the common assumption that NDE is not creative. He feels that NDE is a very exciting research field as it combines an unlimited variety of disciplines—physics, mathematics, materials science, computer science, electronics and more.

Simonetti enjoys NDE research because it encompasses the full product development process. “In many other fields, you end up working on a single aspect of a larger product. If you work on airplanes, you never build an entire plane by yourself. You work on a tiny aspect of these complex machines. In NDE, you can work from essentially zero to the final commercial product. It’s extremely gratifying, but unfortunately most people don’t know it. It’s a niche field,” Simonetti explained.

Simonetti is concerned about the shortage of NDE engineers compared to the growing demand, and hopes this project will attract more engineers to the field. He encourages students with strong interests in science and industrial applications to consider NDE. He employs undergraduate and graduate students at USIL, and enjoys giving co-op students an early introduction to NDE. One of his students is evaluating proprietary ceramic matrix composites for General Electric Aviation.

Simonetti is currently refining the ice-forming technique. The lab team has been working with a uni-directional freezer at -16°C to remove the bubbles that usually form in ice as it freezes (bubbles reduce the efficacy of ultrasonic waves). Simonetti is also investigating the use of nanotechnology to engineer an ice composite whose properties are closer to industry metals. He also hopes to improve the ultrasonic imaging signals by integrating methods from geophysics that are used to examine the layers of the Earth.

Simonetti plans to share the wonder of NDE with the next generation of engineers by blending art and science. He submitted a grant proposal to the National Science Foundation which includes the exploration of artistic applications of cryo-ultrasonics. In Simonetti’s proposed exhibit, viewers would interact with various ice-encapsulated industrial parts using both unassisted vision and the ultrasonic images created by NDE equipment.

For more information on cryo-ultrasonic research at UC, please contact Francesco Simonetti.