The stealth performance of the aircraft has been effectively verified in many wars, and the survivability and penetration ability of aircraft with stealth performance have been greatly improved. Taking the Yugoslav war as an example, many stealth fighters frequently launched, not only destroying many targets, but also only one stealth fighter was shot down. The main reason is that its surface stealth coating and internal structure stealth can effectively absorb radar waves. The former mainly absorbs high-frequency signals, while the latter mainly absorbs low-frequency signals, which minimizes the aircraft's radar scattering area, thereby enabling aircraft Avoid the radar tracking of the opponent and avoid the risk of being shot down.
Generally, the wave absorbing materials can be divided into two categories, one is coating wave absorbing, and the other is structure wave absorbing. The application of carbon fiber in this respect belongs to structure wave absorbing. Ordinary carbon fibers do not have the ability to absorb electromagnetic waves. Only special-shaped carbon fibers and special-shaped carbon fiber composite materials have the function of absorbing waves. When using carbon fibers as absorbing materials, special attention must be paid to these aspects:
1.Surface modified carbon fiber
A layer of porous carbon particles or a layer of porous carbon microspheres is deposited on the surface of the carbon fiber to improve its electromagnetic properties and impart certain absorbing properties.
2.Low temperature carbonized carbon fiber
Low temperature carbon fiber means that the final carbonization temperature is lower than the normal carbonization temperature, and its purpose is to regulate the resistance value. The higher the carbonization temperature, the smaller the resistance value and the worse the absorbing performance. However, the low carbonization temperature affects the tensile strength and modulus of carbon fibers. Comprehensive consideration should be made to find the best carbonization temperature that can balance resistivity, modulus and tensile strength.
3. Honeycomb structure
The carbon fiber layer in the carefully designed skin forms a certain angle with the incident wave, giving it a certain ability to absorb waves. Because the electric field direction is parallel to the fiber axis, the reflector of the carbon fiber's radar wave; when the electric field direction is perpendicular to the fiber axis direction or oblique to the fiber axis direction, the carbon fiber has a certain thinning function, and it is added to the cellular plastic foam Magnetic loss and electrical loss wave absorbing agents, such as carbon powder, ferrite, etc., make incident radar waves reflected multiple times, converted into thermal energy and absorbed. This structural absorbing material can be used to make fuselage, wings and nose.
4.Verify carbon fiber with special cross section
Adjust its shape and size to obtain the required resistance and surface resistivity. This research has been carried out at home and abroad. Taking the shaped carbon fiber developed by Toray Japan as an example, the shaped carbon fiber has a tensile strength of 4.43 GPa and a tensile modulus of 245 GPa, which can be used to manufacture composite components that absorb and bear waves.
5.Hybrid absorbing structure
The resistivity of reinforcing fibers varies greatly. Carbon fiber is a good conductor, glass fiber insulator, and silicon carbide fiber semiconductor. According to the design parameters of surface resistance, carbon fiber and glass fiber are mixed and reinforced according to a certain ratio, or carbon fiber and silicon carbide fiber are mixed and reinforced. Absorption performance. This type of absorbing wave is an electrical loss, and the magnetic loss is much stronger than the electrical loss.
As a national strategic new material, carbon fiber has a wide range of applications not only in the field of aerospace, but also in other fields such as tank armor materials, maritime ships, and missile rocket weapons. It is also a key strategic material for national defense and national economic construction. It is the material foundation and technology leader for the development of high-tech, national defense cutting-edge technologies and the transformation of traditional industries in various countries around the world. It is of great significance to actively develop related technologies for carbon fiber composite materials.