MICHIGAN ENGINEERING – Funded with $1 million from the Department of Energy’s Nuclear Energy University Partnerships program, Serife Tol, an assistant professor of mechanical engineering, will be developing a quality assessment method for nuclear reactor parts made by additive manufacturing (AM) using advanced ultrasonic imaging. Currently, a non-destructive method for the qualification of AM parts, which takes less time and money to produce, has not been accepted for nuclear applications.
Parts produced through additive manufacturing can become defected with keyholes—holes created during the printing process due to lack of adhesion between layers, low materials and other types of defects. These can cause major issues if not noticed before the part is put into use. This is where the research team is leveraging ultrasonic waves to produce images of the parts to ensure their quality.
“Ultrasonic imaging provides a rapid and accurate non-destructive assessment of internal microstructures in metallic parts.” said Tol, “No matter the size or complexity of a part, we are able to scale the imaging to see their internal structures. That isn’t possible with other non-destructive techniques.”
Ultrasonic imaging has its own limitations, such as its image resolution. Ultrasonic imaging uses high-frequency sound waves to create images, like bats or dolphins use in the wild, and by increasing the frequency, the team can have better image resolution and see more details in the structure of these parts.
The trade-off in using higher frequency is the decreased penetration of waves and depth seen into a material because of the way these types of sound waves diffract or spread out compared to lower frequency waves. The team will seek to enable high-resolution images and break the diffraction limits of ultrasonic imaging by exploiting the concept of negative refraction. This is the bending of wave in a way that it travels in the opposite direction as expected when it enters a medium with certain properties, resulting in unusual effects. This technique will also enable the viewing of subwavelength features, details on an object smaller than a wavelength.
“Negative refraction is one of the unconventional phenomena observed in metamaterials and phononic crystals. We will develop a super-lens with periodic micro-architectures and integrate it into the ultrasonic sensor for high-resolution imaging and detection of subwavelength features in the structures and components we build through additive manufacturing,” said Tol.
By working with partners in academia, industry, and a national lab, the team will be able to see 20 micrometers per millimeter into a material using these techniques. To test their work, materials will be compared with results from X-ray tomography, thermography, and destructive evaluation using scanning electron microscopy.
Another U-M contributor is Jerard Gordon, an assistant professor of mechanical engineering. The project includes collaborators at the University of Illinois Chicago, Argonne National Laboratory, and Westinghouse Electric Company.
This project is one of sixty-eight that the US Department of Energy is supporting with a total of $56 million, of which the U-M College of Engineering has received $7.5 million for six projects to advance nuclear technology.
