Lightning arc channel effects on surface damage development on a PRSEUS composite panel: An experimental study

Composite aircraft structures are vulnerable to lightning strike damage due to their relatively low electrical and thermal conductivities. A preceding work has investigated the lightning damage resistance of a carbon-epoxy Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) panel. The damage includes intense local damage (i.e., matrix decomposition/sublimation, fiber rupture, delamination) accompanied by widespread surface damage (i.e., distributed fiber rupture and tow splitting) further from the lightning attachment point. This study focuses on investigating the cause of the widespread surface damage. Two possible driving mechanisms are explored: i) magnetically-induced currents and ii) lightning arc-root/channel expansion. Fifteen laboratory-scale lightning strike tests at nominal peak currents of 50-125 kA were performed on modified PRSEUS mid-bay locations. The surface modifications were placed adjacent to or enclosing the intended lightning arc attachment point, including through-slots, a non-conductive silicon-filled slot, insulating tape, and acrylic plates. The objective is to examine the effect of such barriers on lightning-induced surface damage for cases where the anisotropic lightning arc-root/channel expansion and/or the lightning arc primary current are constrained by the barriers, without affecting the magnetically-induced currents. In each of the lightning strike tests, both the intense local damage and widespread surface damage were limited by or enclosed within the insulating boundary. The placement of these boundaries altered the lightning arc-channel expansion or limited the interaction between the expanding-arc and the surface of the PRSEUS panel. These experiments demonstrate that the widespread surface damage outside of the attachment point primarily results from lightning arc-root/channel expansion rather than magnetically induced currents.