The strength of carbon fiber is so high, why do fighter jets use alloy instead of carbon fiber?

As we all know, carbon fiber has many advantages. One of the most prominent advantages is that the weight is lighter while maintaining good hardness. So the question is, why not choose aluminum alloy? The most important thing is related to toughness and temperature requirements.

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1) toughness requirements

The aircraft is subject to the risk of impact during flight. If we use carbon fiber to make parts such as wings with a larger area, a large area of material is prone to decomposition and fracture after a high-speed impact, and the consequences are devastating. At this time, we have to abandon the lighter and more rigid carbon fiber because it is more brittle; and choose a less brittle material, such as aluminum alloy with better toughness. However, the use of carbon fiber materials for parts with smaller areas and lower collision risks, such as the tail and radome, can significantly reduce the weight of the aircraft and bring additional risks.

2) temperature requirements

The speed of fighter jets is generally higher than that of civil aircraft, and the demand for variable speed in a short period of time is also significantly higher than the latter. Large-area parts such as wings and body will generate extremely high temperatures when friction with the air during flight. According to the data of the US military F22, the maximum operating temperature of the wing surface is between 230-250 degrees Celsius. However, the carbon fiber composite materials used in industrial manufacturing do not have such a high melting point, because the resin material used as the base material is not too high temperature resistant. Most carbon fibers on the market have a maximum temperature of 180 degrees Celsius. Because the process and cost of processing high temperature resistant composite materials are extremely high, it is very reasonable to use mature aluminum alloy materials.

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