Evaluating components for discontinuities without damaging the part or system remains a priority for diverse industries and research fields. Low-cost techniques such as fluorescent penetrant inspection (FPI) are used widely by major industries, such as aviation and aerospace, despite limited defect detection and the need for complex, multi-step operations in highly controlled conditions. Nondestructive methods such as sonic infrared (SIR) testing apply ultrasound waves to identify surface defects and cracks. These techniques hold promise for widespread use but stand to improve in the detection of false positives.
Sandia researchers developed a nondestructive coating to enhance observations of dynamic thermal strain and reduce false positives in SIR inspections. This coating may be helpful in making SIR a viable alternative to widely used dye-based methods such as FPI.
Applying a simple coating containing black paint and glass particles to a component or substrate increases emissivity of its surface. By introducing dynamic mechanical strain such as SIR to the coated substrate, the adhered particles generate frictional heating. The resulting localized temperature increases can then be measured with an infrared camera to verify that the entire part was vibrated and thoroughly inspected.
In addition to enhancing SIR-based nondestructive testing, this coating has potential applications in structural monitoring of bridges and buildings, modal testing of parts, and as a replacement for accelerometers to detect where vibrations are occurring.