A new patent from North Carolina Agricultural and Technical State University will improve nondestructive evaluation methods for subsurface aircraft defects. The patent, “Normalized Defect Characterization of Pulse Thermographic Nondestructive Evaluation,” was awarded to mechanical engineering professor Mannur J. Sundaresan, Ph.D., and his former advisee, Letchuman Sripragash, Ph.D.

Portrait of mechanical engineering professor Mannur J. Sundaresan, Ph.D.

Thermographic nondestructive evaluation is one of the fastest, most inexpensive methods for detecting defects in the newest generation of aircraft wings and fuselage made of carbon fiber composites. The technology uses the physics of the passage of heat from the surface to the interior. A thermographic evaluation can determine where this passage of heat is disrupted and detect the defective area where the layers of the subsurface material have separated.

While commonly used, thermographic detection for defects does have challenges. The images curve near the edges and produce variations in data. Additionally, a discrepancy of 1/20th of a degree Celsius can determine the ability to detect a defect under the aircraft surface.

The patented technology addresses these errors in several ways.

“By introducing a unique normalization procedure, we have eliminated the need for thermomechanical properties,” said Sripragash. “This evaluation method can make correct data evaluations regardless of the type of material under the surface.”

With this barrier gone, it is no longer required to know the age of material used in the surface being tested prior to the evaluation. Additionally, aviation standards require defects to be quantified.

“Just saying a defect exists is not sufficient. It is critical to quantify what the defect is,” said Sundaresan. “This newly-patented technology uses physics-based data augmentation to fill in any gaps in data the thermographic evaluation may have missed. Additionally, we have a library of defects that exactly match real defects.” 

With this new patent, the thermographic subsurface evaluation becomes more powerful, more versatile and better equipped to scan large areas more quickly.

Sundaresan joined the Department of Mechanical Engineering in 1996 as a postdoctoral researcher. This is his sixth patent awarded while at A&T. Sripragash now works at Siemens in Charlotte, North Carolina.

Read more about N.C. A&T research here.