Development of self-healing mechanisms in aeronautical vehicles

The idea to apply self-healing composites in aeronautics is one of the biggest challenge facing materials scientists. Composite materials are subject to weakening due to impact damage on the structural integrity of the material. Most damaging mechanical stresses in the aircraft are the impacts of the hail on the fuselage crown during a storm, the strong impact of the stones on the keel during the grounding, the accidental fall of the heavy object on the structure during the assembling phases and, in the worst case, the bird impact during the landing and the taking off. Impact damage may lead to substantial matrix microcraking, delamination and fibre-matrix de-bonding of the composite, reducing the structural capability and leading to premature failure, if the damage is not detected and repaired. A self-healing composite has the amazing capability to protect against material failure due to fatigue, to greatly improve structure safety and reliability and to extend product lifetime. A lot of self-repair strategies were proposed in literature, and the solutions to the problem are undergoing rapid changes, which they are approaching to the goal ever more. One of the most promising self-healing systems for aircraft polymer composites is based on microencapsulated systems. This development of an aeronautical material based on such a design has highlighted several restrictions: a) the impossibility to use hardeners as aromatic primary amines (e.g. DDS) in combination with pre-catalysts active in the ROMP; b) the impossibility to use curing cycles at high temperatures as those scheduled for aeronautic materials designed for primary structures; c) the impossibility to use the pre-catalyst dispersed in the form of molecular complex in chemically very reactive environments, such as fluid epoxy mixtures containing reactive epoxy rings at high temperatures and d) the high cost of ruthenium based pre-catalysts which have proven to give high yield in ROMP reactions of polyolefins. The present paper focus on the development of a new pre-catalyst able to overcome the above mentioned critical points.