Simulating Thermal Expansion in Composites with Expanded Metal Foil for Lightning Protection

Modern aircraft such as the Boeing 787 Dreamliner are comprised of more than fifty percent carbon fiber composite, requiring the addition of expanded metal foil for lightning strike protection.

The Boeing 787 Dreamliner is comprised of more than fifty percent carbon fiber reinforced plastic (CFRP) due to the material's light weight and exceptional strength. Figure 1 shows the extensive use of composite materials throughout the aircraft. Although CFRP composites inherently have many advantages, they cannot mitigate the potentially damaging electromagnetic effects from a lightning strike. To solve this problem, electrically conductive expanded metal foil (EMF) can be added to the composite structure layup to rapidly dissipate excessive current and heat for lightning protection of CFRP in aircraft.

Engineers at Boeing Research and Technology (BR&T) are using multi-physics simulation and physical measurements to investigate the effect of the EMF design parameters on thermal stress and displacement in each layer of the composite structure layup shown at left in Figure 2. Stress accumulates in the protective coating of the composite structure as a result of thermal cycling due to the typical ground-to-air flight cycle. Over time, the protective coating may crack providing an entrance for moisture and environmental species that can cause corrosion of the EMF, thereby reducing its electrical conductivity and ability to perform its protective function. Through their research, they aim to improve overall thermal stability in the composite structure and therefore reduce the risks and maintenance costs associated with damage to the protective coating.