Self-healing materials have been in the light of research for the past few years, particularly influenced by the progression of self-healing epoxy resin. Initially, the concept of ‘healing ability’ was inspired by nature, a mimic of living organisms, such as animals and trees that motivated the researchers to implement this fascinating property in fabricating self-healing materials. The mechanism of these smart polymers is categorized into two prime types, namely intrinsic and extrinsic healing. They are additionally classified based on the healing method, which includes autonomic and non-autonomic. The technologies employed in constructing healing composite materials include hollow fibers, microcapsules, or vascular networks equipped with healing agents.
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The global self-healing material market was exploring substantial growth with factors favoring its development, namely, demand for sustainable infrastructure, rise in awareness, multiple benefits and proliferating presence among a number of end-users. Considering the steady growth, these smart materials are able to cover applications in almost all industries, mainly construction, automotive, healthcare, anticorrosive coatings, delivery, optical data storage, textiles, military, hydrogels, etc. Nevertheless, one of the most potential areas in the aerospace sector, where it has found a milestone on the pathway of development. The self-healing material has gained access in the aerospace sector through its ability to heal any damage automatically, without any physical intervention, that reduces the overall cost and improves components life. One of the key advantages of using self-healing polymers is that it provides the composites, chemical stability in any atmospheric conditions, lightweight and excellent processability.
Aerospace Sector: A Potential End-User
The ‘self-healing’ concept can be applied broadly in the field of aerospace technology. Fiber-reinforced plastic composites are used on a large scale in the aircraft industries. These composites are not capable of upholding the structural integrity, particularly of parts that fall below heavy loading. This results in the formation of cracks, which usually go unnoticed, thus, propagating and resulting in fracture. As a result, self-healing polymers are used in the form of composite or coating that helps in solving the problem of micro cracks. Also, polymer composites are lighter as compared to the conventional ones, which will also diminish the probability of cracks due to heavy loads in the first place. One of the prime applications of SHM in the aircraft industry is the construction of helicopter blades.
Since, the global market for self-healing material is fast developing, manufacturers are required to control the cost and increase efficiency at the same time to remain competitive. Thus, smart polymers that are protective and wear-resistant is significantly employed by manufacturers to extend the composites life and minimize the replacement costs. However, in some cases, self-healing materials can restore product quality to higher than the original equipment manufacturer.
In addition, the reduction in repairing costs is projected to offer the required surge to the aeronautical sector. To this, SHM might be a solution, as it requires limited maintenance and possesses the ability to self repair the cracks, thus, providing opportunities to the aerospace industry.
Key Aerospace Applications Achieved with Self-Healing Materials are elaborated below:
For a long time now, conventional ceramic composites enjoyed extensive usage in jet engines, owing to its exceptional thermal resistance. However, the sensitivity issue, resulting in brittle failure and impact of the damage, decreases the reliability and lifespan of the components. Hence, thorough research was conducted to study self-healing CMCs as an alternative for fixed and mobile jet engine components. An attempt proceeded to replace the conventional ceramic composites with self-healing composites in engine combustion chambers. The best-suited solutions investigated were multilayered, matrix composites, containing boron, based on its oxidation behavior under relatively low temperatures. The research for the use of boron was studied further for interfacial pyrocarbon. This composite type is reported to possess corrosion resisting capability under high temperature and mechanical loads. Thus, it seems suitable for jet engine combustion chambers. The study has also been explored for self-healing nanocomposites and multi-composite approaches, which demonstrated its effective self-heal performance under low oxygen partial pressure and high temperature.
Self-healing materials have a higher resistance to fatigue, as they can repair microcracks before any further growth that leads to failure. In addition, sometimes, its mechanical properties are higher than the conventional ones. The assessment determining the effect on the healing capability of the mechanical properties suggest their employment in aerospace structural applications. Hence, self-healing polymer possesses the ability to replace the conventional aerospace structural composites, to improvise their service life, damage tolerance and safety.
FRP (Fiber-reinforced plastic) composites are widely utilized in aircraft fuselage, namely, Boeing 787 and civil aircrafts Airbus A350, which are manufactured with approx. 50% FRP composites by weight. FRP composites experience damage under impacts, which has increased the necessity for more substantial designs to meet safety requirements. Self-healing is considered as the most capable approach to subdue the effect of load vulnerability and to aim at a lightweight, low maintenance composite fuselages. Several kinds of research is carried out on self-healing hollow glass fiber epoxy composites for structural applications in the aerospace sector.
Paints and coatings hold a critical significance in the aerospace industry because they safeguard the structural components and fuselage from environmental and external conditions that can provoke corrosion damage. The application of SHC appears to hold potential, owing to its advantageous quality of automatic healing after any damage. Self-healing epoxy resin composites help in realizing and protecting aerospace structures from minor impacts and corrosion.
Self-healing materials are path-breaking technology due to its unique properties, making them a prime choice in several aerospace applications. From self-repairing aircraft composites to anti-damage coatings and restorable automobile brake pads, the relevant potentials for these intelligent polymers is limitless and solely dependent on the inventive spirits of scientists and engineers. Also, as the market has touched exciting crossroads, international efforts are being made towards one common goal of autonomic reversible healing materials, and fast-track research is set to cover wider avenues towards the affordability of these smart materials.