Differential Thermography for Extreme Environment Structural Integrity Measurement

Advanced aircraft designs require technology improvements that incorporate the use of advanced materials and material systems for high specific stiffness and temperature capabilities. Improved crack detection and material property measurement techniques are required to support the development and verification of material systems. A development program is proposed that will improve for high-temperature application two thermography techniques to enable the quantification of flaws both in terms of geometry and stress intensity factors. Forced Diffusion Thermography(FDT)is an NDE method that uses projected, dynamic patterns of light to thermally excite a specimen structure with an oscillating thermal pattern that is synchronously imaged and processed for the detection of flaws. Thermoelastic Stress Analysis(TSA)is a differential thermography technique capable of nearly real-time measurement of mixed-mode stress intensity factors. Both FDT and TSA use the same dynamic thermography equipment to measure the small temperature fluctuations upon which these techniques are based. FDT and TSA have serveral attributes that will make them superior to other methods for assessing structural integrity in extreme environments. FDT and TSA are noncontacting full-field techniques, not significantly impaired by convection currents or other anomalies ina high-temperature environment, able to work on a wide range of materials and composities, and able to produce standard(DC)thermal images as well as differential(AC)thermal images