2. AIRCRAFT MATERIALS
1. 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
2. Basic aircraft materials for airframe structures
• Aluminium alloys
• Magnesium alloys
• Titanium alloys
• Composite materials
3. Development of aircraft materials for airframe structures
composites
Mg alloys
other Al alloys
pure AlZnMgCu
alloys
pure AlCuMg
alloys
new Al
alloys
steel
Year
AlCuMg alloys
wood
other materials
Relative share
of structural
materials Ti alloys
10. 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
a) alloying atom > aluminium atom
b) pure aluminium
c) alloying atom < aluminium atom
11. Characteristics of aluminium alloys
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
12. 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
25. 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. 201 - A201, 356 - A356, 357 - A357)
Additional digit .0 means shape casting, digit .1 or .2 ingots
26. • 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 – pedal - 0,4 kg
180 x 150 x 100 mm
Al – casing - 1,3 kg
470 x 190 x 170 mm
27. • 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
28. Alloy Al-7Si – the effect
of grain refinement
Solubility of hydrogen in
aluminum
During solidification - dissolved
hydrogen can precipitate and form
voids.
29. 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
30. • 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 424351, 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)
31. • 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
32. Representative aluminum alloys – sand casting
Alloy Temper
Mechanical properties
Rm
MPa
Rp0,2
MPa
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
207
-
75
90
6
6
10
A 357.0
AlSi7Mg0,55ZnBe0,05
T6
T6*
317
359
248
290
85
100
3
5
* permanent mold casting
F as cast
.0 shape casting
34. 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.
35. • 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)
36. • Designation according to EN 2032-1
– 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
Designation of Mg alloys
37. 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 bars, shapes 310 230 16
AZ80A-T5 8.5Al-0.5Zn bars, shapes 380 240 7
AZ82A-T5 8.5Al-0.5Zn bars, shapes 380 275 7
AZ31B-H24 3.0Al-1.0Zn sheet, plates 290 220 15
38. • Mg-Zn-Zr alloys (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-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 bars, shapes 255 180 12
39. • 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
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 sheet, plates 255 160 9
Mg-RE (WE) 8.4Y-0.5Mn-
0.1Ce-0.35Cd
bars, shapes 410 360 4
40. 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
43. 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
44. • 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)
45. 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)
46. • 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 2032-1
• 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)
48. 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.
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
Examples of cast alloys
50. 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).
51. 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.
52. 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
53. 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.
54.
55. 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
56. 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.
57.
58. 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, °
59. Properties of epoxy UD prepreg laminates
Fibre fracture volume typical for aircraft structures
Prepreg
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.
60.
61. Fiber metal laminates
• Consist of
alternating thin
metal layers and
uniaxial or biaxial
glass, aramid or
carbon fiber
prepregs
62. 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)
- - 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.
67. 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 - 620 kg
Adhesive bonded stringers from 7349 alloy
68. 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
70. 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:
- 2024 T4
- 7075 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)
71. 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?
