The development of the aviation industry is inseparable from the development of advanced materials, so there is a saying in the industry: one generation of materials, one generation of aircraft…
1950-1969: Aluminum, titanium, steel structure
After entering the 1950s, mankind has entered the supersonic era. Accompanying supersonic flight is the problem of structural strength degradation caused by high heat generated by air friction. When the temperature reaches 100°C, the static strength of the light alloy will greatly decline. If the aircraft stays at 120°C for 100 hours, the ability of the light alloy to resist creep will be greatly reduced.
To achieve supersonic flight, it is necessary to have high-strength heat-resistant materials. Aluminum alloys have poor high-temperature resistance. At 200°C, the strength has dropped to about half of the normal temperature value, which obviously fails to meet this indicator. As a result, a strong and heat-resistant titanium alloy for aviation has emerged.
Titanium alloy products
Titanium alloy has high strength and low density (only about 57% of steel), and its specific strength (strength/density) is much greater than other metal structural materials. It can produce parts with high unit strength, good rigidity and light weight. Titanium alloys can be used for aircraft engine components, skeletons, skins, fasteners and landing gear.
The Douglas DC-7 aircraft, which first flew in 1953, applied titanium alloy to the design of the engine compartment and heat shield for the first time.
In 1964, the first "all-titanium" high-altitude and high-speed strategic reconnaissance aircraft SR-71 "Blackbird" (flying at 3 times the speed of sound at an altitude of 30,000 meters) made its first flight. SR-71 uses a large amount of titanium alloy, the amount of which reaches 93% of the total weight of the aircraft structure (the structural weight refers to the total weight of the wing, fuselage, tail and landing gear structure), can withstand aerodynamic friction temperature of 230 degrees, and engine tail spray The area around the tube can withstand temperatures up to 510℃, and the special heat-resistant glass of the cockpit cover can withstand high temperatures of 340℃. In addition, there are many slender grooves on the main wing to cope with thermal expansion and contraction.
1970-21st century: Aluminum, titanium, steel, composite structure (mainly aluminum)
With the advancement of materials science, since the 1970s, a new generation of aerospace materials-composite materials-came into being. Composite materials have the characteristics of high specific strength, high rigidity, light weight, and a series of advantages such as fatigue resistance, vibration reduction, high temperature resistance, corrosion resistance, and designability. It can reduce the weight of the aircraft while maintaining the original strength, or make the aircraft stronger under the same weight. In addition, the structural fatigue life of composite materials is several times stronger than that of traditional aluminum alloys. In order to improve the performance of the aircraft and extend the life of the aircraft, it is an inevitable trend to select new materials with better fatigue resistance.
Composite material refers to a new material composed of two or more different materials combined in different ways. It can take advantage of various materials, overcome the defects of a single material, and expand the application range of materials. The base material is divided into two categories: metal and non-metal. Commonly used metal substrates are aluminum, magnesium, copper, titanium and their alloys. Non-metallic substrates mainly include synthetic resin, rubber, ceramics, graphite, carbon and so on. Reinforcing materials mainly include glass fiber, carbon fiber, boron fiber, aramid fiber, silicon carbide fiber, asbestos fiber, whisker, and metal.
At this stage, composite materials still cannot completely replace traditional aluminum-based metal materials, and most of them are only used for non-primary load-bearing parts, such as rudder skins, equipment flaps, fuselage and wing skins of small aircraft Wait.
The representative model at this stage is Airbus A380, although most of the A380 fuselage uses new weldable aluminum alloy (this makes laser welding manufacturing technology widely used, and eliminates rivets, making the structure lighter and stronger. ), aluminum alloy accounts for 61% of the entire aircraft materials, but composite materials are also widely used on the fuselage (22%).
Application of composite materials on A380
The Airbus A380 is the first commercial aircraft to use carbon fiber reinforced plastic to make a central wing box. The central wing box weighs 8.8t and is made of composite material 5.3t, which is 1.5t lighter than the metal wing box. In addition, the vertical tail, horizontal tail, floor beam, rear pressure frame, flaps and ailerons at the rear edge of the wing are also made of carbon fiber composite materials. The leading edge of the fixed wing uses thermoplastic composite material, and the mixed fiber metal laminate material GLARE (glass laminate aluminium reinforced epoxy) is used on the upper part of the fuselage and the leading edge of the tail. This glass fiber composite material is lighter than the aluminum alloy commonly used in aviation, and has better corrosion resistance and impact resistance.
Early 21st century-present: composite materials, aluminum, titanium, steel structures (mainly composite materials)
With the advancement of aviation technology, the composite materials used on aircraft have been gradually expanded to be applied to secondary load-bearing components such as air brakes and tail fins from the original only used for non-load-bearing components such as flaps and hatches, and are used in the forward direction. In the direction of the main bearing components such as the wings and even the front fuselage.
Among them, carbon fiber composite materials have high strength (5 times that of steel), excellent heat resistance (can withstand high temperatures above 2000 ℃), excellent thermal shock resistance, low thermal expansion coefficient, small heat capacity (energy saving), and specific gravity Small (1/5 of steel), excellent corrosion resistance and radiation performance, etc. are widely used.
The Boeing 787 aircraft is the first civil jet airliner with composite materials as the main material. Carbon fiber composite materials have been widely used in Boeing 787 aircraft, which not only reduces the mass of the fuselage, but also improves the fatigue and corrosion resistance of the aircraft. The main structural parts of the B787's fuselage skin, frame, long stringer, floor beam, keel beam, front and rear wing, wing skin and ribs are all made of carbon fiber composite materials, of which the fuselage and tail are made of carbon fiber laminate structure ; The movable surface of elevator and rudder adopts carbon fiber laminated board sandwich structure; the fairing part adopts glass fiber laminated board sandwich structure. In the structural weight of B787, composite materials account for 50%, aluminum alloy 20%, steel 10%, titanium alloy 15%, and others 5%.
The advancement and development of aviation technology has played a positive role in the renewal of aviation materials. At the same time, the emergence of new materials, the advancement of manufacturing processes and physical and chemical testing technologies have provided an important material and technical foundation for the design and manufacture of aviation products, thereby continuously promoting the development of the aviation industry.