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AIRCRAFT MATERIALS

AIRCRAFT MATERIALS. Review of the Course STRENGH of AIRCRAFT I. AIRCRAFT MATERIALS. Basic requirements High strength and stiffness Low density => high specific properties e.g. strength/density, yield strength/density, E/density High corrossion resistance

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AIRCRAFT MATERIALS

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  1. AIRCRAFT MATERIALS Review of the Course STRENGH of AIRCRAFT I

  2. AIRCRAFT MATERIALS • Basic requirements • High strength and stiffness • Low density => high specific properties e.g. strength/density, yield strength/density, E/density • High corrossion resistance • Fatigue resistance and damage tolerance • Good technology properties (formability, machinability, weldability) • Special aerospace standards and specifications • Basic aircraft materials for airframe structures • Aluminium alloys • Magnesium alloys • Titanium alloys • Composite materials

  3. Development ofaircraft materialsfor airframe structures other materials Relative share of structural materials composites Ti alloys Mg alloys other Al alloys pure AlZnMgCu alloys AlCuMg alloys wood pure AlCuMg alloys new Al alloys steel Year

  4. Structural materials on small transport aeroplane

  5. Development of compositeaerospace applications over the last 40 years

  6. Composite share in military aircraft structures in USA and Europe Structural materials on Eurofighter

  7. Structural materials on Eurocopter

  8. Comparison of mechanical performance of composite materials and light metals

  9. Aluminium Alloys

  10. Advantages Low density 2.47- 2.89 g/cm³ Good specific properties – Rm/ρ, E/ ρ Generally very good corrosion resistance (exception alloys with Cu) Mostly good weldability – mainly using pressure methods Good machinability Good formability Great range of semifinished products (sheet, rods, tubes etc.) Long-lasting experience Acceptable price Shortcomings Low hardness, susceptibility to surface damage High strength alloys (containing Cu) need additional anti-corrosion protection: Cladding – surface protection using a thin layer of pure aluminium or alloy with the good corrosion resistance Anodizing – forming of surface oxide layer (Al2O3) It is difficult to weld high strength alloys by fusion welding Danger of electrochemical corrosion due to contact with metals: Al-Cu, Al-Ni alloys, Al-Mg alloys, Al-steel Characteristics of aluminium alloys

  11. Reference aluminium alloys in airframe structure

  12. Typicalmechanical properties of alloy 20144.4Cu-0.8Si-0.8Mn-0.5Mg, E = 72.4 GPa , ρ = 2 .77 g/ccm

  13. Typicalmechanical properties of alloy 20244.4Cu-1.5Mg-0.6Mn, E = 72.4 GPa , ρ = 2 .77 g/ccm

  14. Typicalmechanical properties of alloy 21244.4Cu-1.5Mg-0.6Mn, E = 72.4 GPa , ρ = 2 .77 g/ccm

  15. Typicalmechanical properties of alloy 60611.0Mg-0.6Si-0.3Cu-0.2Cr ; E = 68.9 GPa; ρ = 2 .70 g/ccm

  16. Minimalmechanical properties of alloy 60561.0Si-0.9Mg-0.8Cu-0.7Mn-0.25Cr-0.2Ti+Zr; ρ = 2 .72 g/ccm

  17. Mechanical properties of alloy 70506.22Zn-2.3Mg-2.3Cu-0.12Zr; E = 70.3 GPa; ρ = 2 .83 g/ccm

  18. Typical mechanical properties of alloy 70755.6Zn-2.5Mg-1.6Cu-0.23Cr; E = 71.0 GPa; ρ = 2 .80 g/ccm

  19. Use of aluminum-lithium alloys in commercial aircraft

  20. Typical mechanical properties of aluminium- lithium alloys

  21. Typical castings in aircraft structures Al – front body of engine 32 kg - D=700 mm Al- steeringpart - 1,1 kg 390 x 180 x 100 mm Al – casing - 1,3 kg 470 x 190 x 170 mm Al – pedal - 0,4 kg 180 x 150 x 100 mm

  22. Magnesium Alloys

  23. Basic wrought Mg alloys Mg-Al-Zn (AZ)alloys The most common alloys in aircraft industry, applicable up to 150 °C Composition – 3 to 9 % Al, 0.2 to 1.5 % Zn, 0.15 to 0.5 % Mn Increasing Al content → strength improvement , but growth of susceptibility to stress corrosion Zn → ductilityimprovement (Cd + Ag) as Zn replacement → high strength up to 430 MPa Precipitation hardening → strength improvement + decrease of ductility The most common alloy for sheet and plates – AZ31B (applicable to 100 °C)

  24. Mg-Zn-Zralloys (ZK) Zn→strength improvement Zr→fine grain → improvement of strength, formability and corrosion resistance Better plasticity after heat treatment Alloying with RE a Cd →tensile strength up to 390 MPa Application up to 150 °C Mg-Mnalloys (M) Good corrosion resistance, hot formability, weldability Not hardenable→lower strength

  25. Mg-Th-Zr (HK) High temperature alloys Example: alloy HK31A - service temperature 315 to 345 °C Mg-Th-Mn (HM) Medium strength Creep resistance → service temperature up to 400 °C Mg-Y-RE (WE) Hardenability, formability, good weldability Y → strength after hardening, Nd → heat resistance, Zr → grain refinement Application to 250 °C

  26. Typical properties of several cast magnesium alloys

  27. Titanium Alloys

  28. Characteristics of titanium and titanium alloys • Pure titanium - 2 modifications • αTi – to 882 °C, hexagonal lattice • βTi – 882 to 1668°C, cubic body centered lattice • With alloying elements, titanium forms substitution solid solutionsαandβ • Commercially pure titanium can be used as structural material in many applications, but Ti alloys have better performance. • Basic advantages of Ti • Lower density comparing steel ( ρ = 4.55 g/cm³) • High specific strength at temperatures 250 – 500 °C, when alloys Al, Mg already cannot be used • High strength also at temperatures deep below freezing point • Good fatigue resistance (if the surface is smooth, without grooves or notches) • Excellent corrosion resistance due to stabile layer of Ti oxide • Good cold formability, some alloys show superplasticity • Low thermal expansion =>low thermal stresses

  29. Properties of important wrought titanium alloys

  30. Cast titanium alloys • Comparison with wrought alloys • Similar chemical composition • Higher content of impurities, specific casting structure and defects (e.g. porosity) • Lower ductility and fatigue life • Often better fracture toughness • Manufacture of shape castings • Good casting properties (fluidity, mold filling) • Hydrogen absorption, porosity • Vacuum melting, special molds,hot izostatic pressing of castings (HIP) • HIP – heating close to solidus + pressure of inert gas (elimination and welding of voids due to plastic deformation) – conditions 910 to 965 °C/100 MPa/2 h. Examples of cast alloys

  31. Composite Materials

  32. Most composites consist of a bulk material (the ‘matrix’), and a reinforcement, added primarily to increase the strength and stiffness of the matrix. This reinforcement is usually in fibre form. Today, the most common man-made composites can be divided into three main groups: Polymer Matrix Composites (PMC’s) – These are the most common and will be discussed here. Also known as FRP - Fibre Reinforced Polymers (or Plastics) – these materials use a polymer-based resin as the matrix, and a variety of fibres such as glass, carbon and aramid as the reinforcement. Metal Matrix Composites (MMC’s)- Increasingly found in the automotive industry, these materials use a metal such as aluminium as the matrix, and reinforce it with fibres such as silicon carbide (SiC). Ceramic Matrix Composites (CMC’s)- Used in very high temperature environments, these materials use a ceramic as the matrix and reinforce it with short fibres, or whiskerssuch as those made from silicon carbide and boron nitride (BN).

  33. Polymer fibre reinforced composites Common fiber reinforced composites are composed of fibers and a matrix. Fibers are the reinforcement and the main source of strength while the matrix'glues' all the fibres together in shape and transfers stresses between the reinforcing fibres. Sometimes, fillers or modifiers might be added to smooth manufacturing process, impart special properties, and/or reduce product cost.

  34. Polymer matrix composites • The properties of the composite are determined by: - The properties of the fibre - The properties of the resin - The ratio of fibre to resin in the composite (Fibre Volume Fraction) - The geometry and orientationofthefibres in thecomposite Properties of unidirectional composite material

  35. Main resin systems • Epoxy Resins Thelargefamilyofepoxyresinsrepresentsomeofthehighest performance resinsofthoseavailableatthistime. Epoxiesgenerallyout-perform most otherresintypes in termsofmechanicalproperties and resistance to environmentaldegradation, whichleads to theiralmostexclusive use in aircraftcomponents • Phenolics Primarilyusedwherehighfire-resistanceisrequired, phenolicsalsoretaintheirpropertieswellatelevatedtemperatures. • Bismaleimides (BMI) Primarilyused in aircraftcompositeswhereoperationathighertemperatures (230 °C wet/250 °Cdry) isrequired. e.g. engineinlets, high speed aircraftflightsurfaces. • Polyimides Usedwhereoperationathighertemperaturesthanbismaleimidescanstandisrequired (use up to 250 °C wet/300 °Cdry). Typicalapplicationsincludemissile and aero-enginecomponents. Extremelyexpensiveresin.

  36. UD laminate Properties directionally dependent Quasi-isotropic laminate Properties nearly equalin all directions Properties of composites Tensile strength, MPa Angle between fibers and stress, °

  37. Prepreg Fabrics and fibres are pre-impregnated by the materials manufacturer with a pre-catalysed resin. The catalyst is largely latentat ambient temperatures giving the materials several weeks, or sometimes months, ofuseful life. To prolong storage life the materials are storedfrozen (e.g. -20°C).High fibre contents can be achieved, resulting in high mechanical properties. Properties of epoxy UD prepreg laminatesFibre fracture volume typical for aircraft structures

  38. Fiber metal laminates • Consist of alternating thin metal layers and uniaxial or biaxial glass, aramid or carbon fiber prepregs

  39. Fibre metal laminates • Developed types • ARALL - Aramid Reinforced ALuminium Laminates (TU-DELFT) • GLARE - GLAss REinforced (TU-DELFT) • CARE - CArbon REinforced (TU-DELFT) • Titanium CARE (TU-DELFT) • HTCL - Hybrid Titanium Composite Laminates (NASA) • CAREST – CArbon REinforced Steel (BUT - IAE) • - TiGr – Titanium Graphite Hybrid Laminate (The Boeing Company) • Advantages • Fibre metal laminates produce remarkable improvements in fatigue resistance and damage tolerance characteristics due to bridging influence of fibres. They also offer weight and cost reduction and improved safety, e.g. flame resistance. They can be formed to limited grade.

  40. Standard FML configurations

  41. Mechanical properties of FML

  42. Fatigue resistance of FML comparing to 2024 alloy

  43. Fiber metal laminates - applicationAIRBUS A 380 Panels of fuselage upper part – 470 m² , GLARE 4Maximum panel dimensions 10.5 x 3.5 mWeight saving - 620 kgAdhesive bonded stringers from 7349 alloy

  44. Structure – consists of a lightweight core material covered by face sheets on both sides. Although these structures have a low weight, they have high flexural stiffness and high strength. Skin (face sheet) Metal (aluminium alloy) Composite material Core Honeycomb – metal or composite (Nomex) Foam – polyurethan, phenolic, cyanate resins, PVC Applications – aircraft flooring, interiors, naccelles, winglets etc. Sandwich materials Sidewall panel for Airbus A320

  45. Effectivness of sandwich materials

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