Finite Element Analysis of Electro-Thermal Coupling of Sandstone Under Lightning Currents

In order to examine the thermal effect of lightning currents on sandstone, an electro-thermal coupling model based on electromagnetic field and heat transfer theory was constructed. This model considers the spatial Gaussian distribution of lightning current. The model is validated by comparing field observations and theoretical analyses from the previously published studies. The transient calculation is performed to investigate the dynamic change process within the sandstone during lightning strikes, and the effects of related factors such as the peak current of the lightning current, waveform parameters, and electrothermal parameters of the sandstone on the model results are analysed. The results indicate that a lightning strike generates a large amount of electromagnetic heat in the sandstone, causing it to heat up and melt or even vaporize. The entire dynamic process exhibits a logarithmic growth tendency, with rapid development of temperature and phase change areas during the early stages of lightning current, followed by gradual increases until constant. The temperature varies most dramatically around the lightning strike point, and the area affected by lightning strikes decreases as the horizontal plane deepens. Within the sandstone, both the temperature isosurface and phase transition area show a hemispherical distribution. When the peak current is greater, the wave front time is shorter, the half-value time is longer, the resistivity is greater, or the specific heat is more, the overall temperature in the sandstone is greater, and the phase change region is larger under the same conditions.