AEGIS (Advanced EnerGy-Absorption polymer for Impact-resistant Smart composites)

新一代先进纤维复合材料的开发在航空航天领域的未来发展中发挥着关键作用，因为它们具有非常高的重量与强度比，可以提高每收入乘客公里的运营效率。然而，虽然纤维的主要特性保证了出色的面内承载特性，但传统复合材料对面外载荷的抵抗能力较弱，使其在制造或使用过程中可能发生的冲击载荷下容易发生分层损伤。事实上，对于金属介质，它们是均匀的，可以通过屈服耗散能量，表面凹陷只会增加局部应变硬化，对于复合材料，由于其固有的分层结构，它与内部层的分离有关，因此必须避免它，因为它可以不受控制地生长，损害整个结构的完整性，导致严重的局部机械性能退化，在某些情况下，突发关键故障。这种较弱的抗冲击能力，加上复合材料系统典型的失效机制的复杂性，导致在过去十年中，航空结构的当前设计理念被定义为“无损伤增长”方法，导致了基于一开始就假设存在缺陷的高厚度和主要准各向同性布局的过度设计结构。基于这些前提，很明显，航空航天领域需要一个全面的解决方案，以满足轻量化结构和高抗冲击性的要求。AEGIS旨在开发一种具有特殊能量吸收性能的新型混合复合材料，该材料基于一种新型“智能”“伪非牛顿”聚合物的开发，可用于传统的板状组件和复杂夹层板的制造工艺。这些新结构的特殊抗冲击性是由新智能聚合物中存在的大量交联键的瞬态性质所产生的动态硬化效应引起的，这迫使聚合物链在受到外部负载时消散大量能量以解缠。这种新型聚合物层的开发将消除与传统液体介质吸湿相关的问题，使其能够作为“智能层”高效快速地应用于层压结构，可以用作表面涂层，对结构的最终重量影响最小。此外，由于聚合物的高粘度，可以将其嵌入到支架材料中，以开发“智能核心”，保证易于制造并增加频率相关聚合物的刚度，从而导致新型混合三明治结构的发展。AEGIS开发的混合复合材料将能够对特定的外部刺激做出积极响应，只有当请求超过临界阈值时，才能动态地使聚合物链缠结。通过将复合材料卓越的面内特性与智能聚合物卓越的面外电阻相结合，AEGIS将解决当前复合材料组件的局限性，从而提高复合材料结构的可靠性，从而改变当前的设计方法，降低安全参数并优化当前组件的几何形状。

The development of a new generation of advanced fibrous composite materials plays a key role in the future evolution of the aerospace sector due to their very high weight-to-strength ratio that can lead to higher operating efficiencies per revenue passenger kilometre. However, while the fibre dominant properties guarantee excellent in-plane load-bearing characteristics, traditional composite materials exhibit weak resistance to out-of-plane loads, making them susceptible to delamination damage under impact loads that can happen during manufacturing or in service. Indeed, while for metallic media, which are homogeneous and can dissipate energy through yielding, a surface dent will only increase strain hardening locally, for composite materials it is associated with the separation of interior plies due to their intrinsic layered structure, and therefore it must be avoided since it can grow uncontrollably compromising the integrity of the entire structure and leading to severe local degradation of the mechanical properties and, in some cases, sudden critical failures. This weak impact resistance together with the complexity of the failure mechanisms typical of composite systems led in the past decade to the definition of the current design philosophy in aeronautical structures as a "no damage growth" approach, leading to overdesigned structures with high thickness and mainly quasi-isotropic layout based on the assumption of the presence of defects from the outset. Based on these premises, it appears clear the need of a comprehensive solution for the aerospace sector that matches the requirements of lightweight structures with the need for high impact resistance. AEGIS is aimed at the development of a novel hybrid composite material with exceptional energy absorption property which is based on the development of a new "smart" "pseudo non-Newtonian" polymer that can be used in traditional manufacturing processes of plate-like components and complex sandwich panels. The exceptional impact resistance of these new structures is caused by a dynamic stiffening effect given by the transient nature of a large number of crosslink bonds present in the new smart polymer, which forces the polymeric chains to dissipate a large quantity of energy in order to disentangle themselves when subjected to an external load. The development of this new polymeric layer will eliminate the issues associated with moisture absorption of traditional liquid media, allowing its efficient and rapid application on laminated structures as a "smart layer" that can be used as a superficial coating with a minimum effect on the final weight of the structure. Furthermore, due to the higher viscosity of the polymer, it will be possible to intercalate it within a scaffold material in order to develop a "smart core", guarantying ease of manufacturing and increasing the stiffness of the frequency-dependant polymer, leading to the development of novel hybrid sandwich structures. The hybrid composite materials developed in AEGIS will be able to actively respond to specific external stimuli via dynamically enabling the entanglement of the polymeric chains only when the solicitations are above a critical threshold. By combining the exceptional in-plane specific properties of composite materials with the outstanding out-of-plane resistance of the smart polymer, AEGIS will tackle the current limitations of composite components leading to a general increase of the reliability of composite structures that can change the current design approach reducing the safety parameters and optimising the geometries of current components.