Hail Impact on Composite Aircraft: Investigation of low-velocity impacts in multiple impact locations and the effect on its fatigue life

The aerospace industry has made the transition from aluminium to carbon fibre composites on the newest, most advanced aircraft. One of the main disadvantages of composites is its high susceptibility to impacts, such as tool drops which occurs on a single point of impact. As such, these types of impact have been thoroughly studied. Nevertheless, a much less studied phenomenon but with possible catastrophic consequences is the effect of impacts covering a large area, such as hail. This research, therefore, investigates the differences between a single point of impact and multiple points of impact through a purely experimental analysis. Upon investigating the difference, the research focused on three crucial hail event parameters which are impact separation, impact energy and the number of repeated impacts per impact location. The main results revealed that even though the damage response is worse for multiple location impacts, the overall damage response for hail events can be approximated with the available research on single point impacts. This observation remains unacceptable because the complete top surface of the aircraft is damaged and can have serious implications for the structural strength and can cause unexpected and unknown reductions in aircraft fatigue life. There are two essential topics for future research which prevail. The first is due to the crushing effect of hail upon impact and is the investigation of the difference in damage response of steel and hail impactors. The second is the investigation of 4-point bending fatigue on a plate impacted in multiple locations to investigate the damage growth and flexural stiffness. By understanding these additional matters it will become possible to determine if the new state of the art composite aircraft is susceptible to hail and if it will have a vulnerable fatigue life. Regardless of the outcome, it remains of utmost importance to possess this knowledge for the safety of air travel.Aerospace Engineerin