The influence of carbon fiber composite specimen design parameters on artificial lightning strike current dissipation and material thermal damage

Previous artificial lightning strike direct effect research has examined a broad range of specimen design parameters. No works have studied how such specimen design parameters and electrical boundary conditions impact the dissipation of electric current flow through individual plies. This paper assesses the influence of carbon fiber composite specimen design parameters (design parameters = specimen size, shape and stacking sequence) and electrical boundary conditions on the dissipation of current and spread of damage resulting from Joule heating. Thermal-electric Finite Element (FE) modelling is used and laboratory scale (<1 m long) and aircraft scale (>1 m long) models are generated in which laminate ply current dissipation is predicted considering a fixed artificial lightning current waveform. The simulation results establish a positive correlation between current exiting the specimen from a given ply and the amount of thermal damage in that ply. The results also establish that the distance to ground, from the strike location to the zero potential boundary conditions (ground), is the controlling factor which dictates the electric current dissipation in each ply. Significantly, this distance to ground is dependent on each of the specimen shape, dimensions, stacking sequence and the location of ground boundary conditions. Therefore, it is not possible to decouple current dissipation and damage from specimen design and boundary condition setup. However, it is possible to define a specimen size for a given specimen shape, stacking sequence and waveform which limits the influence of specimen dimensions on the resulting current distribution and damage. For a rectangular specimen design which appears in literature multiple times, as 100 x 150 mm and with a stacking sequence of [45/0/-45/90]4s a specimen design of greater than 300 x 200 mm is required to limit the influence of specimen dimensions on current distribution and damage.