Characterization of damage formation in a composite single stringer hat stiffened panel using passive thermography

Passive thermography is used for real time damage detection during quasi-static load testing of a composite single stringer hat stiffened panel. When significant subsurface damage is detected the composite panel is unloaded to enable a more precise determination of damage extent by X-ray CT or ultrasound inspections. This enables characterization of damage growth through-the-thickness and provides critical information to validate structural designs and damage progression models. A significant advantage of passive thermography is precise, real time location and imaging of damage thus making structural testing more efficient. Passive thermography data were processed to enhance defect contrast for comparison to other NDE techniques. In particular, passive thermography data have shown good correlation between the real time thermal indications and the detected acoustic emission events. A two-dimensional thermal simulation is compared to the thermal data for damage depth estimation. Lastly, passive thermography data are compared to ultrasonic through-the-thickness measurements.