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This paper presents a coupled thermal-electric-mechanical model to predict the delamination damage of a Carbon Fiber Reinforced Polymer (CFRP) material when subjected to a lightning strike. A Finite Element Model (FEM) is used to predict the heat response of the CFRP material by solving the Joule heating governing equations. The results of the heat response are coupled with thermal stresses to predicte interlaminar stresses. A bilinear traction law is used to predict the delamination of the laminate. Solutions to the model are developed using a time dependent simulation with the 10/350µs standard waveform to mimic a typical lightning strike on a wind turbine blade in accordance to IEC61400 section 24 Ed 1.0. The time dependent model implements damage criteria and is able to identify damaged elements. The COMSOL software engine was used to derive the results from the thermal-electrical-mechanical model. The final result is a delamination map of the CFRP panel subjected to a lightning discharge.

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.