## 1 Introduction  
In recent years, several steps forward in increasing civil aircraft safety levels have been taken in relation to crashworthiness during an emergency landing. In this context, crashworthiness has become of fundamental relevance for the design and certification of an aircraft. The main aim in designing crashworthy aircrafts is to ensure the ability to absorb as much energy, deformations and breakage as possible during an impact event, without compromising the occupants' safety. Hence, the structure, under deformations and/or breakage conditions, must preserve the living space of passengers and crew, allowing escape routes from the aircraft [1]. Indeed, the entire structure should be able to guarantee the transfer to passengers of acceleration which can be tolerated by the human body [2; 3; 4; 5]. In the past, the assessment of the crashworthiness performance of aircrafts was verified exclusively by several costly full scale experimental testing campaigns, as in the case of the Airbus A320 [6; 7], Boing 707 [8; 9; 10], Boing 737 [11; 12] and NAMC YS [13; 14]. According to the literature, the experimental drop tests have allowed to identify the structural components which are generally involved in the absorption of energy during an impact event: circumferential frames close to the vertical supports and fasteners where large structural deformations occurred [15; 16]. Nowadays, the use of advanced numerical tools can contribute to reduce the number of expensive experimental testing campaigns. Numerical developments focused on crash simulations of civil aircraft fuselages. Due to the crash phenomenon and fuselage structure's inherent complexity, numerical models with increasing levels of accuracy were progressively introduced by several authors. Basic models, using concentrated masses positioned at different locations and beams were used to start exploring the mechanical response of a fuselage during a crash phenomenon. Subsequently, models with non-linear springs and concentrated masses were introduced [17; 18]. Today, the use of finite element simulations with explicit methodologies allows to mimic, with good accuracy, the evolution of the crash phenomenon of a fuselage during a fall, allowing to identify both the damages and their development [19; 20; 21; 22; 23]. The high complexity of the phenomenon under examination is amplified by the complexity of the modern aircrafts. In particular, the huge size of the fuselage structure, the number of different sub-components characterised by several sources of non-linearity (geometry, materials, contacts, etc.) make the validation of numerical models very complicated. In addition to all these conditions, new aircraft generations are characterised by a further source of complexity represented by the use of fibre-reinforced composite materials. Composite fibre-reinforced material, by their nature, are subjected to intra-laminar and inter-laminar damages, which are not easily numerically analysed [24]. The use of fibre-reinforced composite materials, even with the intrinsic advantages in terms of weight-performing ratio, is source of further complexities in terms of components crash behaviour. Indeed, the absence of a material plastic phase [25] and the presence of different interacting mechanisms, such as fibre and/or matrix breakage, delamination and fibre matrix de-bonding, for absorbing impact energy [26; 27; 28] makes the crash behaviour even more complex with respect to conventional metallic materials. Furthermore, a crash events response is a highly geometrical and materially nonlinear event [29]. Hence the crash behaviour of a complex composite structure is strongly influenced by the failure characteristics and strength of its material system. Consequently, the use of effective theories for the prediction for the onset and evolution of the damage becomes mandatory to understand and describe the complex mechanism of breakages in composite materials during a crash event.