The takeoff weight of modern large aircraft is basically more than 100 tons. In order to ensure that it can withstand the weight of hundreds of tons of aircraft and the huge impact force of takeoff and landing, the materials of landing gear must have high strength, high toughness, fatigue resistance, corrosion resistance and other conditions. Such harsh requirements cannot be met by ordinary materials, and can only rely on special steel. It can be said that steel for landing gear represents the highest level of ultra-high strength steel in a country.
(In October 2015, the right landing gear of a Boeing 737 passenger plane was broken during landing)
In view of the special importance of the landing gear, in order to ensure its normal retraction and retraction during the takeoff and landing phase, the aircraft usually has three sets of control systems for each landing gear, one for common use, one for standby and one for emergency, to ensure that it is safe.
What material is used to make landing gear? 300M ultra-high strength steel is the mainstream
The aircraft is supported by three landing gears during takeoff and landing.
As a single-channel trunk aircraft, C919 is a small one among the large aircraft, but its maximum takeoff weight has reached 80 tons, and the total weight of three landing gears is about 1.8 tons. To support an aircraft that reaches more than 40 times its own weight at high speed, its performance must be quite stable.
(Landing gear of C919 large aircraft)
The landing gear materials widely used in the world are low-alloy ultra-high strength steel, such as 300M in the United States, 35NCDl6 in France, and 30xrCH2A in Russia, which is characterized by its extraordinary high strength. How high is the high intensity? At present, the tensile strength of various anti-seismic building steel bars is generally 400-500Mpa, while the tensile strength of 300M is as high as 1960-2100 Mpa, the tensile strength of 35NCDl6 is more than 1850Mpa, and the tensile strength of 30xrCH2A is 1800-2000Mpa.
Taking 300M steel as an example, it is the most widely used landing gear steel with the highest strength level, the best comprehensive performance in the world. It was developed in the early 1950s by adding about 1.5% silicon on the basis of 4340 steel. Its biggest advantages are high strength, good toughness, high inherent fatigue strength, and high transverse plasticity, high fracture toughness, good fatigue resistance, and good stress corrosion resistance.
The landing gear made of it is not only small in structure and size, but also has the same service life as the aircraft body, even for civil aircraft with service life of tens of thousands of hours. In the United States, which has the highest level of aircraft manufacturing, more than 90% of the landing gears of military and civilian aircraft are made of this steel.
(Mechanical properties of 300M steel)
The chemical composition of 300M steel is strictly limited. Different chemical compositions play different roles in the steel: C (carbon) content will improve the strength and hardness of 300M steel, but the plasticity and toughness will be significantly reduced, which will reduce the processability of steel; The main function of Cr (chromium) is to improve the hardenability and strength and toughness of 300M steel; Ni (nickel) can improve the hardness and strength of steel, significantly reduce the notch sensitivity of material, and avoid brittle cleavage fracture; Si (silicon) mainly improves the yield strength and tensile strength of 300M steel.
(Chemical composition of 300M steel)
From the chemical composition of 300M steel, it can be seen that the content of sulfur, phosphorus and other harmful components is not higher than 0.01%, which is extremely demanding.
In contrast, the sulfur and phosphorus content requirements of the top high-strength dual-phase steel DP1180 for automobiles are not higher than 0.04% and 0.015%, which are several times different from the requirements of 300M.
