Assessing laboratory scale and aircraft scale specimen design on artificial lightning strike damage

This paper assesses the influence of specimen design (specimen size, shape and stacking sequence) on artificial lightning strike direct effect modelling by considering both laboratory scale specimens ( < 1 m in length) and aircraft scale structural components.

The work explores the influence and sensitivity of specimen design and boundary conditions on ply current and the relationship with thermal damage resulting from Joule heating using thermal-electric Finite Element (FE) modelling. The current distribution in the specimens, under the influence of a fixed magnitude current, Waveform A (40 kA, 4/20 µs), is studied. An established modelling methodology is used with a baseline specimen measuring 150 mm x 100 mm x 4.704 mm and a stacking sequence [45/0/-45/90]4s.

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. Results have shown that when the shape of the specimen was fixed, i.e. rectangular, and the length of the sides were increased, the current dissipated in the first ply reduced by 23% (moving from a 150 mm x 100 mm rectangle to a larger 300 mm x 200 mm rectangle). Circular specimens can normalise the distance to ground in each layer producing a linear reduction in current dissipation in each ply. The specimen stacking sequence also effects the damage predictions and current dissipation.