An optical technique for detecting fatigue cracks in aerospace structures

The development of a field-deployable non-intrusive optical-based crack-detection and measurement system based on temperature-sensitive-paint (TSP) technology is described. The TSP developed is based on a platinum porphyrin immobilized in a sol-gel-derived thin film. For this test, the TSP is deposited on top of an aluminum plate that is then subjected to dynamic fatigue through the use of an electrodynamic shaker. Detection of cracks in the aluminum is accomplished by monitoring the changes in the surface temperature of the plate as it was excited at its resonant frequency. Visualization and measurement of the cracks is easily accomplished in near real time using this method. Finally, this method is compared with conventional thermography, and the results indicate that for aluminum, the surface-temperature change was below the resolution of conventional instrumentation.