The stealth performance of the aircraft has been effectively verified in many wars, and the survival ability and penetration ability of the aircraft with stealth performance have been greatly improved. Taking the Yugoslav War as an example, many stealth fighters were frequently dispatched, which not only destroyed 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, and the latter mainly absorbs low-frequency signals, which minimizes the radar scattering area of the aircraft, thereby making the aircraft Avoid the opponent's radar tracking and avoid the risk of being shot down.
Generally, absorbing materials can be divided into two categories, one is coating absorbing, and the other is structural absorbing. The application of carbon fiber in this aspect belongs to structural absorbing. Ordinary carbon fiber reflectors for electromagnetic waves do not have wave absorption properties. Only carbon fiber composite materials with special-shaped cross-section carbon fibers and special-shaped structures have wave-absorbing functions. When using carbon fiber as a wave-absorbing material, you need to pay special attention to these aspects:
1. Surface modified carbon fiber
A layer of porous carbon particles or a layer of porous carbon microspheres are deposited on the surface of the carbon fiber to improve its electromagnetic properties and give certain wave-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 adjust 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 fiber. Comprehensive consideration should be taken to find the optimal carbonization temperature that can balance resistivity, modulus and tensile strength.
3. Honeycomb structure
The carefully designed carbon fiber layer in the 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 radar wave of the carbon fiber; 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, at the same time, it is added to the foam inside the honeycomb. Magnetic and electrical loss absorbers, such as carbon powder and ferrite, cause incident radar waves to be reflected multiple times, converted into heat energy and absorbed. This structure of absorbing materials can be used to manufacture the fuselage, wings and nose.
4. Verification of carbon fiber with special cross-section
Adjust its shape and size to obtain the required resistance and surface resistivity. This research work has been carried out at home and abroad. Taking the special-shaped cross-section carbon fiber developed by Toray of Japan as an example, the tensile strength of the obtained special-shaped cross-section carbon fiber can reach 4.43GPa and the tensile modulus is 245GPa, which can be used to manufacture composite members with wave absorption and load bearing.
5. Hybrid absorbing structure
The resistivity of the reinforcing fibers varies greatly. Carbon fiber is a good conductor, an insulator of glass fiber, and a semiconductor of silicon carbide fiber. 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 to give it a certain Absorbing performance. This type of wave absorption is an electrical loss, and the magnetic loss is much stronger than the electrical loss.
As a national strategic new material, carbon fiber is not only used in the aerospace industry, but also in fields such as tank armor materials, sea ships, missiles, rocket weapons, etc. It is also a key strategic material for national defense and national economic construction. It is the material basis and technological leader for countries in the world to develop high-tech, cutting-edge defense technology and transform traditional industries. It is of great significance to actively develop carbon fiber composite related technologies.