Development of a new modelling tool to better represent the interaction of lightning with aircraft composites

Lightning is a naturally occurring phenomenon caused by water and ice moving past each other in the clouds, transferring charges and building up electrical energy. Lightning typically occurs during extreme weather conditions, or electrical storms, as a result of an electrical discharge. The discharges are very quick, in the region of a tenth to one hundredth of a second. Lightning can be defined as either a flash or a strike. Lightning strikes can be classified in one of three ways, depending on their particular interactions. If the discharge remains within a single cloud it is classified as intra-cloud lightning (IC). If more than one is involved then it is cloud to cloud (CC) lightning and the final type is cloud to ground (CG) lightning.

A cloud to ground strike can interact with the ground or other objects, e.g. tall buildings or even aircraft. On average a lightning strike interacts with an airliner once per year, approximately every 3000 hours, during its operating life and can have a detrimental effect on flight safety. During an aircraft's flight there are two scenarios which can occur with a lightning strike. These are dependent on whether the aircraft is the cause or result of the strike. In most cases the aircraft will be struck by a branch of lightning. However, in some cases, when the aircraft enters a highly charged region of the atmosphere it can be the trigger for the lightning discharge. When a lightning strike interacts with an aircraft there is a large flow of electrical current. This current produces a superheating effect on the conducting channel which forms a highly electrically-conductive plasma channel. This can cause large amounts of damage to the aircraft.

Electromagnetic shielding of the aircraft by metallic airframes was the primary measure to prevent damage from a lightning strike. However, in recent years, due to cost and weight targets the use of carbon composite materials has dramatically increased in the aircraft industry. Composites suffer comparatively large damage from lightning strikes due to high orthotropic electric resistivity. The high orthotropic electric resistivity leads to high thermal loads which can cause delamination of the composite plies.

Research of this topic has centered on modelling of this lightning phenomenon. This has broadly fallen into five categories; Thermal-electric, mechanical pressure loading, thermal expansion, internal pyrolysis pressure loading and electromagnetic pulses.

The aim of this project is to develop the modelling capabilities to replicate the effects occurring during the lightning strike. This will allow for a better understanding of the unique interactions between the lightning strike and the aircraft composite. To date literature had shown the steady development of modelling techniques for this purpose but has also shown gaps still exist. This project will aim to advance the discipline by producing a new modelling approach/tool to develop new knowledge in the field. This modelling approach will likely take the form of finite element and multi-physics simulations to capture both the material changes and physics occurring during a strike.