Is Indirect Electrode a Good Choice for Simulated Lightning Damage Tests? - The Effect of Metal Vapor

The laboratory lightning testing commonly uses an indirect electrode as the current injection configuration to restraint the electrode jet for evaluation of lightning strike damage tolerance of aircraft materials. Such an indirect electrode configuration requires using a conductive ignition wire to initiate the arc. This work discusses the influence of added metal vapor, produced due to evaporation of the ignition wire, on the electric-arc-induced heat flux and current density as well as the material damage through numerical modeling and simulated experiments. Metal vapor originated from the requisite ignition wire considerably alters the net emission coefficient and transport properties of the arc, leading to questionable testing results and unreliable guidance for lightning protection design. The damage depth of an aluminum alloy is affected by 312.5% due to the changes in the net emission coefficient and thermal conductivity. The damage area shows moderate changes due to a Gaussian-shape decrease profile of heat flux and its insensitivity to the changes in the net emission coefficient. The direct electrode configuration is promising to avoid the use of ignition wire and produce material damage representative of actual damage caused by natural lightning. The results and discussions provide insights into the design of improved lightning certification tests.