Virtual testing for design and certification of structural batteries for aviation

In a global context, in which modern societies must move towards more environmental sustainability, ambitious targets have been set out in various branches of transportation sector to restrict pollutant emissions and to combat climate change and environmental degradation. As a matter of fact, global transport emissions have increased dramatically over the past half-century. However, 74.5% of transport emissions come from road vehicles and the global aviation industry produces around 2% of all human-induced carbon dioxide (CO2) emissions and is responsible for 12% of all CO2 emissions coming from the transport sector. Aviation, therefore, is today one of the most efficient, safe and reliable means of transport in the world. However, the most recent estimates suggest that the demand for air transport will increase by an average of 4.3% annually over the next 20 years. For this reason, technological innovation must meet environmental expectations and growth in demand. Research centers and industries are carrying out new projects aimed at sustainability and reducing emissions, and this ambitious goal cannot be achieved using existing aviation technologies. The main objective of these projects is the development of new aircraft designs with increased use of electrical energy onboard aircraft for both non-propulsive (e.g., secondary systems) and propulsive purposes, leading to the concepts of “More Electric Aircraft” (MEA), “Hybrid Electric Aircraft” (HEA) and “All-Electric Aircraft” (AEA). HEA solutions provide several benefits: low- or even zero-emission flight, new potential air transportation missions, safer flights, and enhanced design flexibility thanks to innovative design solutions like the Distributed Electric Propulsion (DEP). However, there are also some drawbacks hindering the trend to HEA propulsion. Examples are low weight performance of energy storage devices, lack of regulation for future mobility concepts, and uncertainty on future market demand. Whatever the selected aircraft configuration is, hybrid electric solutions based on conventional battery technology to store the required electrical power, will be affected by the addition of an extra weight, represented by the batteries themselves. The battery mass will trigger the detrimental “snowball” effect on the aircraft weight since that the more the demand for electric power the higher the battery mass is and in turn the aircraft maximum take-off weight. To break the detrimental loop of the snowball effect on the aircraft weight, or to mitigate its negative impact, an alternative approach to store electrical energy in a conventional battery system installed in the aircraft is to combine energy storage and load-bearing capabilities in multifunctional structures, or structural batteries. Traditional battery packs are mainly used to provide electrical energy, but the structural battery packs take this role much further creating a solid structure that strengthens the structural body. In the literature, starting from a side-by-side combination of a structural element and a conventional battery (zero degree of integration) in a fully integrated system, in which the structural element also acts as an energy accumulator, structural batteries can be divided into two general categories: multifunctional structures and multifunctional materials. In the first case different materials within the structural battery perform a single function, however the overall composite is multifunctional, whereas in the latter all materials adopt multiple functions. Although higher mass savings are predicted for multifunctional materials, current research efforts show that multifunctional structures exhibit better overall performances. Apart from the classification, the use of this technology raises relevant issues concerning airworthiness requirements that need to be applied when considering such multi-functional materials. The aim of the presented activity is to make a step toward defining aircraft certification requirements in presence of structural batteries, considering them both as structure and as battery, since they play such multiple function.