IIT-M researchers use artificial materials and ultrasound to detect defects in large structures

Conventional bulk ultrasonic inspection is tedious and time-consuming

A view of IIT-Madras

Engineering structures including buildings, pipelines and rails require periodic testing to prevent catastrophic failures occurring due to corrosion, impact, and strain. High-frequency sound waves that travel in the bulk are widely used for non-invasive and non-destructive testing of structural materials. Conventional bulk ultrasonic inspection is tedious and time-consuming as it involves point-by-point assessment of structures.

Researchers in the Indian Institute of Technology Madras and the University of Nairobi have used metamaterials to improve detection of defects in large structures by guided wave ultrasound. The result of this collaborative work was published in AIP Advances , an international peer-reviewed journal.

The paper was co-authored by Prabhu Rajagopal, a professor from the mechanical engineering department at IIT-Madras and Michael Gatari, Director, Institute of Nuclear Science and Technology, University of Nairobi, and John Birir, a Ph.D. student at the university.

Non-destructive evaluation

Mr. Gatari said the collaboration with IIT-Madras was the result of an agreement signed on July 26, 2017. Two Kenyan Ph.D. students and faculty members of the INST benefited from the agreement with a study of courses relevant to non-destructive evaluation research for six months in 2018.

Mr. Rajagopal said: “The use of ultrasound scans in medical diagnostics is well-known and the principle remains the same for structural monitoring. Sound waves travel at a uniform speed if the object is defect-free, but defects impede or deflect sound waves, which results in delays in reception.”

In guided wave testing (GWT), the sound waves are sent along the length of the structure rather than into the structure, allowing the waves to travel longer distances. But GWT has poorer resolution than the conventional ultrasound-based testing due to diffraction limitations. The research team used metamaterials to improve the resolution of guided ultrasound waves.

Not found in nature

“Metamaterials are artificially crafted materials with unique internal microstructures that give them properties not found in nature. The constituent artificial units of the metamaterial can be tailored in shape, size, and interatomic interaction, to exhibit unusual properties,” he said.