Review of the Course AIRCRAFT MATERIALS

Review of the Course AIRCRAFT MATERIALS

Basic aircraft materials for airframe structures
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

Development of aircraft materials for 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

Structural materials on small transport aeroplane

Development of composite aerospace applications over the last 40 years

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

Structural materials on Eurocopter

Comparison of mechanical performance of composite materials and light metals

Aluminium Alloys

Aluminium – Al plane centered cubic lattice melting point 660 °C
density 2.7 g/cm³ very good electrical and heat conductivity very good corrosion resistance low mechanical properties solid solutions with alloying elements maximum solubility is temperature dependent Cu: 6 % at 548 °C; 0.1 % at RT Mg: 17 % at 449 °C; 1.9 % at RT Zn: 37 % at 300 °C; 2 % at RT Si: 1.95 % at 577 °C; 0 % at RT Substitution solid solution alloying atom > aluminium atom pure aluminium alloying atom < aluminium atom

Characteristics of aluminium alloys
Advantages Low density 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

Designation of aluminium alloys according to EN
Wrought alloys AL-PXXXX(A) designation basic alloying element 1XXX – pure aluminium 2XXX copper (Cu) 3XXX - manganese (Mn) 4XXX - silicon (Si) 5XXX - magnesium (Mg) 6XXX - Mg + Si 7XXX - zinc (Zn) 8XXX - other (eg. Li) Casting alloys AL-CXXXXX designation basic alloying element 1XXXX - > 99.0 % Al 2XXXX - Cu 3XXXX - Si-Mg - Si-Cu - Si-Cu-Mg 4XXXX - Si 5XXXX - Mg 7XXXX - Zn 8XXXX - Sn

Important wrought aluminium alloys for aircraft structures
2XXX (Al-Cu, Al-Cu-Mg) - high strength, lower corrosion resistance 2014 (0.8Si, 4.4Cu, 0.8Mn, 0.5Mg) 2017 (0.5Si, 4Cu, 0.7Mn, 0.6Mg) 2024 (4.4Cu, 0.6Mn, 1.5Mg) 2024Alclad (with the surface layer of Al) 2027 (4.4Cu, 0.9Mn, 1.3Mg, 0.2Zn, 0.05Cr, 0.25Ti) 2124 (4.4Cu, 0.6Mn, 1.5Mg, 0.1V) 2219 (6.3Cu, 0.3Mn, 0.1V) 6XXX (Al-Mg-Si) -comparing to 2XXX - lower strength, better ductility and corrosion resistance 6013 (0.8Si, 0.8Cu, 0.50Mn, 1.0Mg) 6061 (0.6Si, 0.28Mn, 1.0Mg, 0.2Cr) 6061Alclad 6056 (1.0Si, 0.9Mg, 0.8Cu, 0.7Mn, 0.25Cr, 0.2Ti+Zr) 7XXX (Al-Zn-Mg-Cu) – the highest strength, lower ductility, notch sensitivity 7050 (2.3Cu, 2.2Mg, 0.12Zr, 6.2Zn) 7075 (1.6Cu, 2.5Mg, 0.13Cr, 5.6Zn), 7075Alclad 7175 (1.6Cu, 2.5Mg, 0.23Cr, 5.6Zn) 7475 (1.6Cu, 2.2Mg, 0.22Cr, 5.7Zn)

Most important tempers aluminium alloys
O - anealing W - solution treating + quenching (non stabil state) H - strain-hardening (strength is increased only due to cold working) T3 - solution treating + quenching + cold working + room temperature aging T351 - solution treating + quenching + stress relief due to controlled stretching + room temperature aging T4 - solution treating + quenching + room temperature aging T6 - solution treating + quenching + artificial aging T651- solution treating + quenching + stress relief due to controlled streching + artificial aging T7 - solution treating + quenching + artificial overaging T73 - solution treating + quenching + artificial overaging for the best stress corrosion resistance T8 - solution treating + quenching + cold working + artificial aging

Reference aluminium alloys in airframe structure
Part Control parametr Reference alloys Wing Upper panels Upper stringers Lower panels Lower stringers Beams, ribs compression damage tolerance (DT) tension + DT static properties 7150-T6/T77 7050-T74 2024-T3, 2324-T39 2024-T3 7050-T74, 7010-T76 Fuselage Stiffeners Main frame compression, DT, formability tension/compression complex 2024 clad-T3 7175-T73 T74 Other parts All types 7010/7050/7075

Typical mechanical properties of alloy 2014 4. 4Cu-0. 8Si-0. 8Mn-0
Typical mechanical properties of alloy Cu-0.8Si-0.8Mn-0.5Mg , E = 72.4 GPa , ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil. cycles Bare sheet 2014 186 97 18 90 T4 427 290 20 140 T6 483 414 13 125 Alclad sheet 2014 172 69 21 - T3 434 273

Typical mechanical properties of alloy 2024 4. 4Cu-1. 5Mg-0
Typical mechanical properties of alloy Cu-1.5Mg-0.6Mn, E = 72.4 GPa , ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil. cycles Bare 2024 185 75 20 90 T3 485 345 18 140 T4, T351 470 325 Alclad 2024 180 - 450 310 440 290 19

Typical mechanical properties of alloy 2124 4. 4Cu-1. 5Mg-0
Typical mechanical properties of alloy Cu-1.5Mg-0.6Mn, E = 72.4 GPa , ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil. cycles Plate L T851 490 440 9 - Plate LT 435 Plate ST 470 420 5 Better transvers properties, good strengths and creep resistance at higher temperatures - for application between 120 – 175 °C.

Typical mechanical properties of alloy 6061 1. 0Mg-0. 6Si-0. 3Cu-0
Typical mechanical properties of alloy Mg-0.6Si-0.3Cu-0.2Cr ; E = 68.9 GPa; ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil cycles Bare 6061 124 55 25 62 T4 241 145 22 97 T6 310 276 12 Alclad 6061 117 48 - 228 131

Minimal mechanical properties of alloy 6056 1. 0Si-0. 9Mg-0. 8Cu-0
Minimal mechanical properties of alloy Si-0.9Mg-0.8Cu-0.7Mn-0.25Cr-0.2Ti+Zr; ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil cycles Thin extrusions - L T4511 355 245 16 - T6511 380 360 10 T78511 335 Bare sheet - LT T4 265 135 18 T78 340 315 8

Mechanical properties of alloy 7050 6. 22Zn-2. 3Mg-2. 3Cu-0
Mechanical properties of alloy Zn-2.3Mg-2.3Cu-0.12Zr; E = 70.3 GPa; ρ = g/ccm Direction Tensile strength MPa Yield strength Elongation % Fatigue strength At 10 mil. cycles Minimum properties - Die forgings T-736 (T-74), thickness up to 50 mm L 496 427 7 - L-T 469 386 5 Minimum properties – Hand forgings T73652, thickness up to 50 mm 434 490 421 Typical properties – Plate T73651 510 455 11 Typical properties – Forgings T73652 524 15

Typical mechanical properties of alloy 7075 5. 6Zn-2. 5Mg-1. 6Cu-0
Typical mechanical properties of alloy Zn-2.5Mg-1.6Cu-0.23Cr; E = 71.0 GPa; ρ = g/ccm Temper Tensile strength MPa Yield strength Elongation % Fatigue strength At 500 mil. cycles Bare 7075 228 103 17 - T6, T651 572 503 11 159 T73 434 Alclad 7075 221 97 524 462

Use of aluminum-lithium alloys in commercial aircraft

Typical mechanical properties of aluminium- lithium alloys
Temper Direction Tensile strength MPa Yield strength Elongation % Alloy 2090: 2.7Cu-2.2Li-0.12Zr; E = 76 GPa, ρ = 2.59 g/ccm T 83 (near peak aged) L 530 527 3 LT 505 503 6 45° 440 Alloy 8090: Li-1.3Cu-0.95Mg-0.12Zr; E = 77 GPa; ρ = 2.55 g/ccm T8X 480 400 4.5 465 395 5.5 325 7.5

Casting aluminum alloys
Designation (in addition to EN) Often used system (Aluminum Association - USA): three digit designation - the first digit indicates a main alloying element 1XX  99,0 % Al 2XX Al - Cu 3XX Al - Si - Mg Al - Si - Cu Al - Si - Cu - Mg 4XX Al - Si 5XX Al – Mg 7XX Al - Zn 8XX Al – Sn A letter ahead of designation marks alloys with the same content of main alloying elements but with different content of impurities or micro alloying elements.(e.g A201, A356, A357) Additional digit .0 means shape casting, digit .1 or .2 ingots

Typical castings in aircraft structures
Al – front body of engine 32 kg - D=700 mm Al- steering part - 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

General characteristics
Micro and macro structures of metal are influenced by conditions of metal solidification – quantity of nuclei, temperature interval of solidification, cooling rate … A fine, equiaxed grain structure is normally desired in aluminum casting (Al-Ti or Al-Ti-B alloys are most widely used grain refiners) Mechanical properties are influenced by existence of casting defects – porosity, inclusions (mainly oxides), shrinkage voids …. Alloys – heat treatable , non heat treatable Mechanical properties are mostly lower comparing wrought alloys of the similar chemical composition High quality aircraft casting need careful metallurgical processing of liquid metal Degassing – hydrogen elimination (hydrogen causes porosity) Grain refinement and modification for better mechanical properties Filtration for inclusions removing

Solubility of hydrogen in aluminum
During solidification - dissolved hydrogen can precipitate and form voids. Alloy Al-7Si – the effect of grain refinement

Dendritic microstructure of hypoeutectic alloy AlSi10Mg – sand casting
wall thickness 2 mm wall thickness 10 mm There is direct relation between mechanical properties and dendrite arm spacing (DAS) → different properties in different portions of casting

Alloys of Al–Cu system Composition 4 – 6 % Cu
- Copper substantially improves strength and hardness in the as-cast and heat- treated conditions Copper generally reduces corrosion resistance and, in specific compositions stress corrosion susceptibility Copper also reduces hot tear resistance and decreases castability Main advantage: high strength up to 300 °C Basic alloys ČSN , 201, A 201, AL 7 242, A242 B295 Application: Smaller , simple, high-strength castings for service at higher temperatures (cylinder heads, pistons, pumps, aerospace housings, aircraft fittings)

Alloys of Al–Si + (Mg, Cu, Ni) system
The most important alloys for aircraft castings Silicon improves casting characteristics (fluidity, hot tear resistance, feeding), Si content depends on casting methods Sand and plaster molds, investment casting 5-7% Si Permanent molds 7-9% Si Die casting 8-12% Si Alloys containing Mg are heat treatable, hardening phase is Mg2Si Alloys Al-Si with alloying elements Mg and Cu have after heat treatment high mechanical properties but lower plasticity and corrosion resistance Ni is alloying element in hypereutectic alloys for service at higher temperatures (e.g. engine pistons) Strength and ductility can be improved using modification for refinement of eutectic phases Principal – addition small quantities of Na or Sr into liquid metal before casting Results – increased tensile strength (40 %), impact strength (up to 400 %), ductility (2x) Mechanical properties can be improved also due to grain refinement buy rapid cooling in permanent metal molds

Representative aluminum alloys – sand casting
Temper Mechanical properties Rm MPa Rp0,2 HB A % A 201.0 AlCu4,5Ag0,7Mg0,25Mn0,3 T7 496 448 - 6 A 356.0 AlSi7Mg0,35 F T6 T61* 159 278 283 83 207 75 90 10 A 357.0 AlSi7Mg0,55ZnBe0,05 T6* 317 359 248 290 85 100 3 5 * permanent mold casting F as cast .0 shape casting

Magnesium Alloys

General characteristics of Mg alloys
Pure magnesium Hexagonal crystal lattice ρ=1,74 g/cm³ , Rm=190 MPa, Rp0,2=95 MPa Used in metallurgy (alloying element in Al alloys, titanium metallurgy, ductile iron metallurgy). Not used for structural purposes – magnesium alloys have better utility values Advantages of Mg alloys Low density (ρ = 1,76–1,99 g/cm³ ) → high specific strength (Rm/ ρ) Comparing Al alloys, lower rate of strength decrease in relation with temperature Lower notch sensitivity and higher specific strength at vibrating loads High damping capacity (influence of low modulus of elasticity ~47GPa) High specific bending stiffness (higher to 50 % comparing steel, to 20 % comparing Al) → high resistance against buckling High specific heat → minor temperature increasing at short time heating Very good machinability Applicability – most alloys up to 150 °C, some of them up to 350 °C.

Shortcomings of Mg alloys
High reactivity at increased temperatures Above 450 °C rapid oxidation, above 620 °C ignition (fine chips, powder) Melting and casting – protection against oxidation (chlorides, fluorides, oxides Mg, powder sulfur, gases SO2, CO2). Lower corrosion resistance , generally difficult anti-corrosion protection Corrosion environment (air, sea water), impurities Fe, Cu, Ni forming intermetallic compounds Electrochemical corrosion – in contact with the most of metals (Al alloys, Cu alloys, Ni alloys, steel) Low formability at room temperature - most alloys cannot be formed without heating After forming – high strength anisotropy along and crosswise deformation –→ differences 20 to 30 %. Low shear strength and notch impact strength Low wear resistance Low diffusion rate during heat treatment → longtime processes , artificial aging is necessary at precipitation hardening Relatively difficult joining – possible electrochemical corrosion, limited weldability (hot cracking, weld porosity, possible welding techniques - inert gas welding, spot welding)

Designation of Mg alloys
Designation according to EN Wrought alloys MG-PXXXXX Casting alloys MG-CXXXXX In numerical designation, one or two digits represent one or two main alloying elements according to their weight percentage. The third digit is zero, the last two digits represent serial number. (1- Al, 2 – Si, 3 – Zr, 4 – Ag, 5 – Th, 6 – rare earth, 7 – Y, 8 – Zn, 9 - other) More common designation - according to ASM: Series AZ (alloying elements Al, Zn) Series AM (Al, Mn) Series QE (Ag, RE - rare earth ) Series ZK (Zn, Zr) Series AE (Al, RE) Series WE (Y, RE) Series HM, HZ, HK (Th, Mn, Zn, Zr) – high temperature alloys Two first digits – percentage of alloying elements

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 → ductility improvement (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) Alloy Composition Semi-product Rm, MPa Rp0.2, MPa Ductility,% AZ31B-F 3.0Al-1.0Zn bars, shapes 260 200 15 AZ61A-F 6.5Al-1.0Zn 310 230 16 AZ80A-T5 8.5Al-0.5Zn 380 240 7 AZ82A-T5 275 AZ31B-H24 sheet, plates 290 220

Mg-Zn-Zr alloys (ZK) Mg-Mn alloys (M) 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-Mn alloys (M) Good corrosion resistance, hot formability, weldability Not hardenable → lower strength Alloy Composition Semi-product Rm, MPa Rp0.2, MPa Ductility, % ZK60A-T5 5.5Zn-0.45Zr bars, shapes 365 305 11 M1A-F 1.2Mn 255 180 12

Mg-Th-Zr (HK) Mg-Th-Mn (HM) Mg-Y-RE (WE) 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 alloy composition semi-product Rm, MPa Rp0.2, MPa ductility, % HM21A-T8 2.0Th-0.6Mn sheet, plates 235 130 11 HK31A-H24 3.0Th-0.6Zr 255 160 9 Mg-RE (WE) 8.4Y-0.5Mn-0.1Ce-0.35Cd bars, shapes 410 360 4

Sand and permanent mold castings
Cast magnesium alloys Basic systems Mg-Al-Mn with or without Zn (AM, AZ) Mg-Ag-RE (QE) Mg-Y-RE (WE) Mg-Zn-Zr with or without rare earth (ZK, ZE, EZ) Pressure die castings - alloys AZ → excellent castability, good corrosion resistance in sea water - aloys AM → good castability, corrosion resistance, better ductility and lower strength - castings are not heat treated Sand and permanent mold castings - used mostly in heat treated state

Typical properties of several cast magnesium alloys
composition product Rm MPa Rp0.2 ductility % AM60A-F 6.0Al-0.13Mn pressure die casting 205 115 6 AZ91A-F 9.0Al-0.13Mn-0.7Zn 230 150 3 AZ63A-T6 6.0Al-3.0Zn-0.15Mn sand casting 275 130 5 AZ91C-T6 8.7Al-0.13Mn-07Zn 145 AZ92A-T6 9Al-2Zn-0.1Mn AM100A-T61 10.0Al-0.1Mn 1 QE22A-T6 2.5Ag-2.1RE-0.7Zr 260 195 WE43A-T6 4.0Y-3.4RE-0.7Zr 250 165 2 ZK61A-T6 6.0Zn-0.7Zr 310 10 EZ33A-T5 3.3RE-2.7Zn-0.6Zr 160 110

Titanium Alloys

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 solutions α and β 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

Preferred use of titanium alloys
Shortages of titanium High manufacturing costs => high prices (~8x higher comparing Al) Chemical reactivity above 500 °C – intensive reactions with O2, H2, N2, with refractory materials of furnaces and foundry molds => brittle layers, which are removed with difficulties Lower modulus of elasticity comparing steel ( E = 115 GPa against 210 GPa) Poor friction properties, tendency for seizing Poor machinability (low thermal conductivity → local overheating, adhering on tool, above 1200 °C danger of chips and powder ignition. Welding problems (reactivity with atmospheric gases => welding in inert gas, diffusion welding, laser beam welding, electron beam welding) Special manufacturing methods (vacuum melting and heat treating, manufacture of castings in special molds – graphite molds and/or ceramic molds with a layer of carbon, hot isostatic pressing - HIP) Preferred use of titanium alloys If strength and temperature requirements are too high for Al or Mg alloys At conditions, when high corrosion resistance is required At conditions, when high yield strength and lower density comparing steel are required Compressor discs, vanes and blades, beams, flanges, webs, landing gears, pressure vessels, skin up to 3M, tubing… Increasing usage (Boeing 727 – 295 kg, Boeing 747 – 3400 kg)

Classification of titanium alloys
Alloying elements α – stabilizers (Al, O, N, C) – stabilize solid solution α and enlarge zone of its existence β – stabilizers – stabilize solid solution β, decrease temperature α-β transformation β stabilizers forming eutectoid phase (Si, Cr, Mn, Fe, Co, Ni, Cu) β stabilizers isomorphic (V, Mo, Nb, Ta) Neutral elements (Sn, Zr) – only small influence on the α-β transformation Phase diagrams of Ti with different stabilizers (solid state)

Classification of alloys according to microstructure after annealing
α alloys – microstructure consists of homogeneous solid solution α pseudo α alloys (solid solution α + 5% solid solution β at most) α+β alloys – microstructure consists of mixture solid solutions α and β β alloys – microstructure consists of homogeneous solid solution β pseudo β alloys (solid solution β + small amount solid solution α) Alloys consisting of intermetallic compouds Classification according to usage Wrought alloys Cast alloys Designation of titanium alloys according to EN Wrought material TI-PXXXXX Cast material TI-CXXXXX Product of powder metallurgy TI-RXXXXX First two digits represent main alloying elements (1-Cu, 2-Sn, 3-Mo, 4-V, 5-Zr, 6-Al, 7-Ni, 8-Cr, 9-others), TI-P64005 (Ti-6Al-4V), TI-P99XXX (pure titanium) Designation according to basic chemical composition (e.g. Ti-6Al-4V)

Properties of important wrought titanium alloys
Temper Rm, MPa Rp0.2, MPa Elongation, % E, GPa α and pseudo α Ti-5Al-2,5Sn annealed 16 110 Ti-5,6Al 875 750 8 - Ti-11Sn-1Mo-2,2Al-5Zr-0,2Si 15 114 α + β Ti-3Al-2,5V 20 107 Ti-6Al-4V hardened 1170 1100 10 14 Ti-6Al-2Sn-2Zr-2Cr-2Mo-0,25Si 1275 1140 11 122 pseudo β and β Ti-10V-2Fe-3Al 112 Ti-15V-3Cr-3Al-3Sn 6 - 12

stress relief annealing
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 Alloy Heat Treatment Rm, MPa Rp0.2, MPa A5 , % Ti-6Al-4V stress relief annealing 880 815 5 Ti-6Al-2Sn-4Zr-2Mo 970°C/2h + 590°C/8h 860 760 4 Ti-15V-3Cr-3Al-Sn 955°C/1h + 525°C/12h 1120 1050 6

Composite Materials

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 whiskers such as those made from silicon carbide and boron nitride (BN).

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.

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 orientation of the fibres in the composite Properties of unidirectional composite material

Main resin systems Epoxy Resins
The large family of epoxy resins represent some of the highest performance resins of those available at this time. Epoxies generally out-perform most other resin types in terms of mechanical properties and resistance to environmental degradation, which leads to their almost exclusive use in aircraft components Phenolics Primarily used where high fire-resistance is required, phenolics also retain their properties well at elevated temperatures. Bismaleimides (BMI) Primarily used in aircraft composites where operation at higher temperatures (230 °C wet/250 °C dry) is required. e.g. engine inlets, high speed aircraft flight surfaces. Polyimides Used where operation at higher temperatures than bismaleimides can stand is required (use up to 250 °C wet/300 °C dry). Typical applications include missile and aero-engine components. Extremely expensive resin.

Fabric types and constructions
Unidirectional fabrics The majority of fibres run in one direction only, a small amount of fibre may run in other directions to hold the primary fibres in position Prepreg unidirectional tape- only the resin system holds the fibres in place The best mechanical properties in the direction of fibres Basic woven fabrics Plain -Each warp fibre passes alternately under and over each weft fibre. The fabric is symmetrical, with good stability. However, it is the most difficult of the weaves to drape. Twill - One or more warp fibres alternately weave over and under two or more weft fibres in a regular repeated manner. Superior wet out and drape, smoother surface and slightly higher mechanical properties

Fabric types and constructions – cont.
Basket -Basket weave is fundamentally the same as plain weave except that two or more warp fibres alternately interlace with two or more weft fibres. An arrangement of two warps crossing two wefts is designated 2x2 basket.It is possible to have 8x2, 5x4, etc. Basket weave is flatter, and, through less crimp, stronger than a plain weave, but less stable. Hybrid fabric A hybrid fabric will allow the two fibres to be presented in just one layer of fabric. Carbon / Aramid - The high impact resistance and tensile strength of the aramid fibre combines with high the compressive and tensile strength of carbon. Aramid / Glass - The low density, high impact resistance and tensile strength of aramid fibre combines with the good compressive and tensile strength of glass, coupled with its lower cost. Carbon / Glass - Carbon fibre contributes high tensile compressive strength and stiffness and reduces the density, while glass reduces the cost.

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

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

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

Fibre metal laminates Developed types Advantages
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) - T iGr – 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.

Standard FML configurations
Type Configuration Metal alloy Prepreg constituents Prepreg orientation ARALL 2 2/1 – 6/5 2024-T3 Aramid-epoxy unidirectional ARALL 3 7475-T76 GLARE 1 Glass-epoxy GLARE 2 GLARE 3 Cross-ply GLARE 4 Cross-ply /unidirectional

Mechanical properties of FML
Laminate Metal thickness mm Prepreg thickness mm Tensile strength MPa Yield E GPa Density g/ccm ARALL 1 0.3 0.22 897 535 67.5 2.16 ARALL 2 849 411 68.3 GLARE 1 0.25 1494 530 62.2 2.42 GLARE 2 0.2 1670 416 60.9 2.34 1449 406 63.0 0.4 1295 399 64.5 2.47 GLARE 3 382 51.3

Fatigue resistance of FML comparing to 2024 alloy

GLARE fire resistance comparing to 2024 alloy

Fiber metal laminates - application AIRBUS A 380 Panels of fuselage upper part – 470 m² , GLARE 4 Maximum panel dimensions 10.5 x 3.5 m Weight saving kg Adhesive bonded stringers from 7349 alloy

Sandwich materials 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. Sidewall panel for Airbus A320

Effectivness of sandwich materials

List of problems (light alloys)
What are the main advantages of aluminium alloys for applications in aircraft structures? What numerical designation system is used for identification of wrought aluminium alloy? What is meaning of the first digit? What groups of wrought aluminium alloys are usually used in aircraft structures? Explain the designation of the following alloys: T4 T6 - Alclad 2219 Why is sheet from 2xxx alloys often clad with pure aluminium? What group of wrought aluminium alloys exhibits the best mechanical properties? Compare alloys 6056 and 7050! What are the main advantages and limitations of Al-Li alloys comparing to other Al alloys? What is a common value of aluminium alloys elastic modulus in tension? Recommend the alloys for aircraft skin! Why are Mg alloys valuable for aerospace application? What is damping capacity of magnesium alloys? What are the main reasons for using of titanium alloys in airframe and engine structures? What titanium alloy is the most widely used? Compare the specific tensile strength and specific tensile modulus of 2090 and Ti-6Al-4V alloys! - (Specific value = value/density)

List of problems (composite and sandwich materials)
What is composite material? What are advantages of composites comparing to metals? What is prepreg? What are common types of fibres? What fibres have the highest specific tensile strength and specific tensile modulus? ( the specific property is the ratio value/density ) What is main role of matrix? What are main advantages of epoxy, phenolic and bismaleimide (polyimide) matrices? What are main advantages of using prepregs? How the fibre orientation influences resulting mechanical properties of a composite? What are typical tensile properties of epoxy prepregs UD laminates along and across fibres? What is structure of sandwich material? What are main advantages of sandwich panels compared to solid panels? What materials are usually used for sandwich skins and core?

Review of the Course AIRCRAFT MATERIALS

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Review of the Course AIRCRAFT MATERIALS

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Presentation on theme: "Review of the Course AIRCRAFT MATERIALS"— Presentation transcript:

Similar presentations

About project

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