Identification of lightning strike damage using Pulse Thermography through integration of thermal data

Pulse Thermography (PT) is based on the use of infrared imaging systems to detect thermal decay from a pulsed energy source as it passes through a component or sample. Carbon Fiber Reinforced Polymer (CFRP) composite materials damaged by simulated lightning strike are inspected using PT. A new damage detection approach is proposed which exploits the integral of the difference in temperature data over time between each pixel and a reference non-damaged pixel. The resulting integration provides a value for the thermal decay pixel-by-pixel relative to a non-damaged region, which provides a quantitative damage severity parameter. The proposed data processing method is evaluated using calibrated plate sample made from Glass Fiber Reinforced Polymer (GFRP) composite with known defects, and also to investigate CFRP samples damaged by lightning strikes. The calibrated GFRP plates are 4-ply stitched bi-axial E-glass fibers with a total laminate thickness of 2.4 mm. The known defects are 20 mm square PTFE inserts placed between plies to simulate a delamination. The resulting colormap correctly identifies the known defects and displays constant severity over the PTFE insert region. The same method is applied to the lightning damaged CFRP sample made of 5-ply stitched dry fabric. The resulting integration reveals the full extent of the damage, which cannot be identified by visual inspection.