Selection Of Aviation Materials

Introduction to Aeronautical Materials

Aeronautical materials are a general term for various materials used in the manufacture of aircraft, aircraft engines and airborne equipment. Usually includes metal materials (aluminum alloys, titanium alloys, nickel alloys), organic polymer materials and composite materials. 

Aviation materials are the material guarantee for the development and production of aviation products, as well as the technical basis for aviation products to achieve the desired performance, service life and reliability. Due to the basic status of aviation materials and the continuous improvement of their contribution to aviation products, aviation materials, aero-engines and information technology have become one of the three key aviation technologies, and one of the six technologies that have an important impact on the development of aviation products. one.

The service environment of aerospace materials 

The service environment of aerospace materials is quite harsh, and they have to withstand high stress and inertial forces. It is also usually in a high temperature or extremely cold environment, and parts are prone to embrittlement. And because of frequent contact with gasoline, kerosene and other fuels and various lubricants, hydraulic oil, etc., it is also prone to corrosion and swelling. Aviation aircraft also have to withstand shock loads and alternating loads caused by factors such as take-off and landing, engine vibration, high-speed rotation of rotating parts, maneuvering flight, and gusts.

Selection and Application of Aerospace Materials

Aerospace vehicles operate in the atmosphere or outer space for a long time, and serve in extreme environments with extremely high reliability and safety, excellent flight performance and maneuverability. In addition to optimizing the structure to meet aerodynamic requirements, technological requirements and maintenance requirements , and more depends on the excellent properties and functions of the material.

01Material selection principle

Structural parts have to withstand various forms of external forces during service, requiring materials not to exceed the allowable deformation and breakage within a specified period, and aerospace structures should try to reduce the structural size and weight as much as possible. Strength design, with little or no consideration for plasticity and toughness, has led to catastrophic accidents.

In order to ensure structural safety and make full use of the performance of materials, the design of aerospace structural components has been transformed from "strength design principles" to "damage tolerance design principles", and gradually transitioned to "full life cycle design principles", which are considered in the design stage. All relevant factors are comprehensively planned and optimized at the product design stage, up to all stages of the product life cycle. The material is required not only to have high specific strength and specific stiffness, but also to have certain fracture toughness and impact toughness, fatigue resistance, high temperature resistance, low temperature resistance, corrosion resistance, aging resistance and mildew resistance. Enhance some performance indicators. In addition, different grades of load zones use different material selection criteria, and the matching materials are selected according to the specific requirements of the components. The large load zone adopts the strength criterion and high-strength materials; the medium load zone adopts the stiffness criterion and selects high elastic modulus. Dimensional stability is mainly considered in the light load area to ensure that the component size is larger than the minimum critical dimension. When selecting and evaluating structural materials, it is necessary to select appropriate mechanical properties (tensile, compression, impact, fatigue, low temperature series impact) test methods according to service conditions and stress states, and for different fracture modes (tough fracture, brittle fracture, stress fatigue, strain fatigue, stress corrosion, hydrogen embrittlement, neutron irradiation embrittlement, etc.), and comprehensively consider the reasonable coordination of material strength, plasticity and toughness. For components under tensile load, the stress distribution on the surface and core is uniform, the selected material should have uniform structure and properties, and large components should have good hardenability. For components subjected to bending and torsional loads, the surface layer and core stress are quite different, and materials with low hardenability can be used. For components bearing alternating loads, fatigue limit and notch sensitivity are important assessment indicators for material selection. For components serving in corrosive media, corrosion resistance, hydrogen embrittlement sensitivity, stress corrosion cracking tendency, corrosion fatigue strength, etc. are important assessment indicators for material selection. High-temperature service materials also need to consider the organizational stability, and low-temperature service materials also need to consider low-temperature performance.

Weight reduction has practical significance for improving the safety of aircraft, increasing payload and endurance, improving maneuverability and range, reducing fuel or propellant consumption and flight costs. The faster the aircraft is, the greater the significance of weight reduction. A 15% reduction in the weight of a fighter can shorten the aircraft's run distance by 15%, increase its range by 20%, and increase its payload by 30%. For short-term one-time use aircraft such as missiles or launch vehicles, it is necessary to exert equivalent functions with the smallest volume and mass, and strive to maximize the material performance to the limit, and select the smallest possible safety margin to achieve an absolutely reliable safety life.

02Main aerospace materials

In the 21st century, the aircraft fuselage structural materials are still dominated by aluminum alloys, including 2XXX series, 7XXXX and aluminum-lithium alloys. Adding lithium into the aluminum alloy can reduce the density while increasing the strength, and achieve the goal of improving the specific strength and specific stiffness of the component. Aluminum-lithium alloys have been used in large transport aircraft, fighter jets, strategic missiles, space shuttles, and launch vehicles, mainly for head shells, load-bearing components, liquid hydrogen and liquid oxygen storage tanks, pipelines, payload adapters, etc. It is a promising aerospace material. The third-generation and the fourth-generation Al-Li alloys under development no longer pursue low density unilaterally, but have better comprehensive properties. They are comparable to the third-generation Al-Li alloys in terms of crack growth rate, fatigue performance, corrosion performance, and elastic modulus. Under certain conditions, the fourth-generation aluminum-lithium alloy has higher static strength (especially yield strength) and higher fracture toughness.

The specific strength of titanium alloy is higher than that of aluminum alloy, and it has been used in aircraft frames, flap guides and brackets, engine bases and landing gear components, etc., and can also be used in heated parts such as exhaust hoods and fire baffles. The surface temperature of supersonic aircraft with Ma>2.5 can reach 200~350℃, and titanium alloy can be used as the skin. The high-purity and high-density titanium alloy prepared by rapid solidification/powder metallurgy method has good thermal stability, and the strength at 700 ℃ is the same as room temperature. The developed high-strength and high-toughness β-type titanium alloy has been approved by NASA. It is the matrix material of SiC/Ti composite material, which is used to manufacture aircraft fuselage and wing panels. The application ratio of titanium alloys in aircrafts is gradually increasing, the usage in civil aviation fuselage will reach 20%, and the usage in military aircraft fuselage will be as high as 50%.

In addition, nickel-based superalloys are more and more widely used in aviation. Nickel alloys play a role in the design and improvement of aerospace engineering due to their excellent adhesion, corrosion resistance, high hardness, wear resistance and corrosion resistance. playing an increasingly important role. It became an excellent material for the manufacture of aerospace parts, equipment and hardware. For example, Monel K500 can be used as an oxygen booster pump, Inconel 625 can be used in turbine grommets, Inconel 718 can be used in rocket engines, etc…

03Analysis of aerospace materials

The amount of composite materials and titanium alloys has gradually increased, and the amount of aluminum alloys has decreased.

A large number of applications of composite materials will become the development trend in the aerospace field. Composite materials have good weight reduction effect, good damage resistance, corrosion resistance and durability, and are suitable for sensitive structures. However, composite materials have high cost, poor impact resistance, no plasticity, increased technical difficulty, poor maintainability, and poor recycling.

The structural materials of each section of the manned spacecraft are mostly aluminum alloys, titanium alloys, and composite materials. For example, most of the orbiters of the space shuttle are made of aluminum alloys, and the thrust structure supporting the main engine is made of titanium alloys. The frame adopts the metal matrix composite material of boron fiber reinforced aluminum alloy, the cargo compartment door adopts the special paper honeycomb sandwich structure, and the graphite fiber reinforced epoxy resin composite material is used as the panel. The missile head, the outer surface of the spacecraft manned cabin and the inner surface of the rocket engine should use ablative materials. Under the action of heat flow, the ablative materials can undergo physical and chemical changes such as decomposition, melting, evaporation, sublimation, and erosion. The mass consumption of the rocket takes away a large amount of heat, so as to prevent the heat flow of the manned atmosphere from entering the interior of the aircraft, and to cool the combustion chamber and nozzle of the rocket engine. In order to maintain a suitable working temperature in the cabin, radiation heat protection measures should be taken for the manned cabin. The outer skin is made of high temperature resistant nickel-based alloy or beryllium plate, and the internal structure is heat-resistant titanium alloy. It is filled with materials with good thermal insulation properties such as quartz fiber and glass fiber composite ceramics.

With the implementation and continuous development of aerospace projects such as manned spaceflight, lunar exploration and deep space exploration, high-resolution satellites, high-speed vehicles, reusable vehicles, and space maneuvering vehicles, new and more stringent requirements are put forward for materials. , which provides new opportunities and motivation for the development of new aerospace materials. The material field must make major breakthroughs in material system innovation, independent guarantee of key raw materials, and engineering applications as soon as possible.

Supplier of Quality Nickel Alloy 

Wudenalloy has focused on the production and manufacture of nickel alloys for more than ten years. We are a principal worldwide supplier of corrosion-resistant alloys and other superalloy metals. We have a professional technical team and after-sales service, so we can offer high -quality Hastelloy, Incoloy, Inconel, Monel, Duplex Stainless Steel, and other alloy material. These materials are available in wire, bar, sheet&plate, pipe&tube, flange, forging, and other forms to meet the needs of our customers.

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