A new patent for N.C. A&T will improve nondestructive evaluation methods for subsurface defects. The patent, “Normalized Defect Characterization of Pulse Thermographic Nondestructive Evaluation,” was awarded to Mechanical Engineering professor Dr. Mannur J. Sundaresan and Mechanical Engineering doctoral alumna, Dr. Letchuman Sripragash.
The newly patented technology improves the evaluation of defects on aircrafts. Currently, thermographic nondestructive evaluation is one of the most inexpensive and fastest 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 into the interior. Knowing this, a thermographic evaluation can determine where this passage of heat is disrupted and thus detect the defective area where the subsurface material is delaminated (where the layers have become separated).
While commonly used, thermographic detection for defects does have its problems. Namely, the images vignette, or curve, near the edges and produce variations in data. Even a minute discrepancy of 1/20th of a degree Celsius can be the difference between detecting and not detecting 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,” says Dr. Sripragash. In other words, this evaluation method can make correct data evaluations regardless of what material is under the surface. With this barrier gone, it is no longer required to know prior to the evaluation the age or material used in the surface being tested.
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,” says Dr. 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.
Dr. Sundaresan joined the Mechanical Engineering department in 1996 as a postdoctoral researcher. This is his sixth patent at N.C. A&T. Dr. Sripragash earned his Ph.D. in Mechanical Engineering from N.C. A&T. with Dr. Sundaresan as his advisor, in 2015. Dr. Sripragash now works at Siemens in Charlotte, North Carolina.