Understanding and representing heating and heating rate effects on composite material properties for lightning strike direct effect simulations

Lightning strike simulations have used decomposition models, derived from TGA experiments, to model material behaviour at elevated heating rates and temperatures. Such experiments, conducted non-isothermally and at low heating rates, are extrapolated to conditions assumed during a lightning strike event. However, no experiments have been carried out in the literature to verify and understand the impact of the extrapolation assumptions. This work seeks to understand the influence of the approach used to adjust material properties to reflect heating rates present during a lightning strike, which cannot be achieved in the TGA experiments. A combination of experimental and simulations studies was undertaken, including prediction sensitivity analysis through simulation, experiments conducted at a variety of heating rates, thermokinetic modelling to extrapolate data, and finally further thermal-electric models to demonstrate the effect of predicted heating rate on thermal damage. It is demonstrated that the extrapolation approach for heating rate can impact thermal damage predictions. For the studied lightning strike tests and using a maximum heating rate extrapolation (20,000 ^oC/min), herein damage predictions are improved, reducing the error in predicted severe damage area to within 8% of the experimental values.