[China Glass Network] The development of composite materials such as glass fiber chopped strand mats is of great significance to the development of aviation equipment. Half of the aircraft's performance depends on the design and the other half depends on the material. The pros and cons of materials have undoubtedly significant impact on speed, altitude, range, maneuverability, stealth, service life, safety and reliability, and maintainability. According to statistics, 70% of aircraft weight loss is contributed by advances in aerospace materials technology. The material structure of the aircraft body has undergone four stages of development, and the widespread use of composite materials is making it into the fifth stage. These five stages are: The front stage (1903-1919), wood and cloth structure; The second stage (1920~1949), aluminum and steel structure; The third stage (1950 ~ 1969), aluminum, titanium, steel structure; The fourth stage (early 1970 to the beginning of the 21st century), aluminum, titanium, steel, composite structure (mainly aluminum); The fifth stage (from the beginning of the 21st century to the present.): composite materials, aluminum, titanium, steel structure (mainly composite materials). Aircraft using carbon fiber reinforced resin-based composites have significant advantages in reducing aircraft weight, reducing fuel consumption, reducing maintenance costs, and extending aircraft life, while conventional aluminum alloy materials are slowly corroded over time, reducing aircraft. safety. The maintenance cost of the Boeing B787 aircraft with 50% composite material is still stable after several years of service, while the maintenance cost of the traditional aluminum alloy structure aircraft B767 aircraft will increase significantly. Boeing pointed out that composite materials will become "the future of aerospace structures." The development of composite materials in the aerospace field has experienced four stages of sub-loading members—the main bearing members of the tail-level—the main bearing members of the airfoil—the main components of the fuselage, gradually moving from small components to large core components, from military to civilian development. In Europe and the United States, the 1960s was the research and development stage of composite materials. In the 1970s, it entered the application stage. Since then, the proportion of composite materials used in aircraft has gradually increased. 1. Military aircraft As an emerging material technology, composite materials are first used in military aircraft. In the 1960s, glass fiber reinforced composites were first applied to the fairings and ailerons of aircraft. At this time, the mechanical properties of the composite material are still relatively low, and the aircraft parts manufactured by the composite material are small in size and small in force level. In the late 1960s, boron fiber/epoxy composites began to be used in aircraft structures. For example, F-14 began using boron fiber reinforced epoxy composites on flat tails in 1971. In the mid-1970s, high-performance composite materials with carbon fiber reinforcement were born, which opened up the large-scale application of composite materials on aircraft. Carbon fiber reinforced composites with excellent high specific strength, high specific modulus, corrosion resistance and fatigue resistance are ideal for aviation equipment. The heavy-duty and flat-sized parts of the military aircraft began to gradually use carbon fiber reinforced composite materials such as F-15, F-16, Mig-29, Mirage 2000, and F/A-18. Material tail, vertical tail. From the 70s to the present, foreign military aircraft tails have all adopted composite materials. The flat tail and vertical tail of the composite material generally account for 5%-7% of the total structural weight of the aircraft. After the empennage entered the era of composite materials, the application of composite materials began to develop into the main components of the military aircraft wing, fuselage and other structures with large force and large size. In 1976, McDonnell Douglas pioneered the development of the F/A-18 composite wing and officially entered service in 1982, increasing the amount of composite material to 13%. Since then, the wings of military aircraft developed by various countries have almost all adopted composite materials. For example, AV-8B, B-2, F/A-22, F/A-18E/F, F-35 in the United States, "Gust" in France, JAS-39 in Sweden, and "Typhoon" jointly developed by the four European countries, Russian S-37 and so on. At present, the amount of composite materials in the world's advanced military aircraft ranges from 20% to 50% of the total structural weight. The main applications of composite materials include fairings, flat tails, vertical tails, flat tail boxes, wings, and mid-front fuselage. If the composite material accounts for about 50% of the total weight of the aircraft, most of the structural components of the whole machine are made of composite materials, such as the B-2 stealth bomber. 2. Civil aircraft Civil aircraft is more concerned with the safety and economy of the aircraft, so it is more cautious in the application of composite materials. However, with the advancement of composite technology and the reduction of manufacturing costs, civil aircraft began to use composite parts gradually in the 1970s. Similar to military aircraft, the components of civil aircraft composite materials also develop from small bearing members to main bearing members. In the United States, for example, the application of composite materials in civil aircraft has probably gone through four processes. In the previous stage, in the mid-1970s, composite materials were mainly used on components such as the leading edge, the flap, the fairing, and the spoiler. In the second stage, in the mid-1980s, composite materials were mainly used in components such as elevators and ailerons that were less stressed. In the third stage, the composite material is applied to components such as vertical tails and flat tails that are subjected to large forces. For example, the Boeing 777 aircraft uses composite materials in the vertical and flat tails, and the composite material accounts for 11% of the total weight of the structure. In the fourth stage, the composite material is applied to the wing and fuselage of the main force component of the aircraft. The Boeing 787 Dreamliner uses 50% composite material, which exceeds the sum of the weight of metal materials such as aluminum, steel and titanium. Mainly used in the wing, fuselage, vertical tail, flat tail, fuselage floor beam, rear pressure frame and other parts, is the first large commercial aircraft with composite wing and fuselage. In Europe, Airbus also began research on the application of carbon fiber reinforced composites on the A300 series aircraft from the mid-1970s. In 1985, the development of the composite tail of the A320 aircraft was completed. Since then, the first-class components of the A300 series aircraft have been composited, and the amount of composite materials has been rapidly advanced to 15%, surpassing Boeing. The Airbus A380 has a composite material usage of about 25%, and is mainly used in the central wing, outer wing, vertical tail, flat tail, fuselage floor beam and rear pressure frame. And the use of a large number of advanced composite materials, such as the world's larger resin film impregnation of the fuselage rear pressure frame, the application of glass fiber reinforced aluminum alloy (Glare) fuselage upper wall and so on. The new generation of Airbus aircraft will also enter the era of composite materials. Airbus' A400M large transport aircraft will use 35%-40% composite materials, the main application areas include wing, vertical tail, flat tail and propeller blades. The A350WB, which first flew in 2013, used 52% of composite materials, more than 50% of the Boeing B787. 3. Helicopter Helicopters are very significant for composite applications. Military, civilian and light helicopters use a large number of carbon fiber composite materials, and the amount of helicopter composite materials has reached 40%-60% of the structural weight. For example, the US helicopter gunship Comanche (RAH-66) uses 50% composite material; the European NH-90 helicopter uses 80% composite material, close to the all-composite structure. The V-22 rotorcraft is a new type of flight structure that can take off and land vertically. After tilting the rotor, it can cruise at high speed. The composite material usage is 51%, including the fuselage, wing, tail, and rotating mechanism. Made of materials, it is also an all-composite aircraft. 4, drone Military drones have an urgent need for weight reduction, so composite materials are widely used in drones. For example, the US X-45 series aircraft uses more than 90% of composite materials; the X-47 series aircraft are basically all-composite aircraft, and the Global Hawk unmanned reconnaissance aircraft uses 65% of composite materials, including wings and tails. The rear fuselage, large radome, etc. are all made of composite materials; the European experimental drone "barracuda" and the US long-range attack drone "skunk" are basically the same. 5, aero engine The amount and proportion of composite materials has also become a measure of the advanced level of aerospace engines. According to the different working temperature of the hot and cold end, the aerospace engine is correspondingly applied with a composite material of a plurality of different substrates. The superior specific strength and specific modulus properties of resin-based composites are important for high-ratio aviation engines to reduce weight, improve propulsion efficiency, reduce noise and emissions, and reduce costs. They are mainly used on cold-end components of aircraft engines. The working temperature is below 150-200 °C, such as turbofan engine compressor blades, guide vanes and their frame components, turbofan nose cone and rectifying device. Metal-based, ceramic-based, and carbon/carbon composites have important applications on hot-end components due to special conditions such as high temperatures. SiC long fiber reinforced titanium matrix composite (Ti-MMC) has the advantages of high specific strength, high specific stiffness, high temperature resistance, good fatigue resistance and good creep performance. Ti-MMC leaf ring can replace parts of compressor disc. Lose weight by 70%. Future aerospace engine compressor blades and mirror blades, integral leaf rings, casings and turbine shafts will all be manufactured from metal matrix composites. Ceramic-based composite materials have always been the focus of high-temperature materials research. The engine parts made of fine ceramics and silicon nitride can work at 1371 °C, and the performance is even better than that of high-temperature alloys, but the brittleness problem is still not solved. The carbon/carbon composite material also has the advantages of low density, high specific strength, high specific modulus, good thermal shock resistance, etc. It is currently an alternative material at an operating temperature of 1650 ° C or higher, and the higher theoretical temperature reaches 2600 ° C, which is considered to be Promising high temperature materials.
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