1. BK50A2700 Selection Criteria of Structural Materials
Lesson 7
2014

2. Selection of composites
Lesson 7
2014

3. The goal of this lesson

4. Our goal is, that after this lesson, students are able to recognize the key criteria for selecting composites and are able to use this knowledge to support the systematic material selection process.

5. Composites Advantages Disadvantages
Typically the strength of the material is increased
Light weight constructions
80% lighter than steel
60% lighter than aluminium
Also other properties than strength could be tuned according to the requirements:
Rigidity vs. elasticity
Thermal and electrical properties
Corrosion resistance
Recycling is necessary due to ”too high” lifetime
Some raw materials and manufacturing methods are expensive
Some manufacturing methods suffer from poor energy efficiency
Strength analysis are usually challenging due to anisotropic structure of many composites

6. Outline

7. Outline 1 Definitions and composite types 2 Basic composite theory
3 Materials used in composites
4 Tools to support systematic selection of composites
5 Applications of composites

8. Definitions and composite types

9. Composition + =
MATRIX
REINFORCEMENT
COMPOSITE

10. How to define, what is a real composite?
MATERIAL 1
PROPERTIES A +
MATERIAL 2
PROPERTIES B =
NEW MATERIAL
PROPERTIES A+B
1 + 1 = 2
MATERIAL ALLOY
MATERIAL 1
PROPERTIES A +
MATERIAL 2
PROPERTIES B =
NEW MATERIAL
PROPERTIES A+B
+ ADDED VALUE!
1 + 1 > 2
COMPOSITE MATERIAL

11. Composite types DIFFERENT STRUCTURES DIFFERENT SCALES DIFFERENT
Mixed materials
Added fibres
Sandwich-structures
Cell-structures
DIFFERENT
SCALES
Continuous fibres
Particles
Nanoparticles
DIFFERENT
MATERIALS
Matrix
Reinforcement
Alloys/Compounds

12. Basic composite theory

13. Theory of fibre-reinforced composites
Fibres are typically used to improve composite’s strength, rigidity and fatigue resistance.
The matrix conveys the affecting load to be carried by the fibres.
Typically fibre-reinforced composites can withstand better tensile loads than compression.
The direction, length, density and cross-section’s shape and area of the fibres can be tuned to produce the required material properties.

14. TYPES OF FIBRE-REINFORCED MATERIALS
CONTINUOUS FIBRE-REINFORCED MATERIAL
- Direction can be tuned
SHORT FIBRE-REINFORCED MATERIAL
- Length and direction can be tuned B C
WOVEN FIBRE-REINFORCED
- Direction and density can be tuned

15. IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
MATRIX
FIBRE F
LOW MODULUS OF ELASTICITY
HIGH MODULUS OF ELASTICITY

16. IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
HIGH MODULUS OF ELASTICITY
LOW MODULUS OF ELASTICITY

17. IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
Ultimate tensile strength F
0° ° 45° 60° °
The angle between the directions of the affecting load and reinforcing fibres [°]

18. STRESS-STRAIN-CURVE OF A FIBRE COMPOSITEσ
σcr σc σm
STRAIN ε
The matrix yelds and the composite’s modulus of elasticity decreases. The additional load is carried by the fibres with elastic elongation.
Elastic elongation of the composite. The value of the modulus of elasticity is stable.
When fibres break, the strength of the composite decreases to the level of matrix’s yeld strength.
Finally: the composite breaks when also the matrix breaks down.

19. CROSS-SECTION AREAS OF DIFFERENT FIBRES
BORON CARBIDE
SILICON CARBIDE
COATED FIBRES:
130 µm
CARBON FIBRES
5-7 µm
BORON NITRIDE
5 µm
METAL WIRES
25 µm
GLASS FIBRES
10 µm

20. THE ”VISION” OF 3D-WOVEN FIBRE-REINFORCEMENT

21. The modulus of the elasticity can be determined with an analogic way.
“THE RULE OF MIXTURES:”
The strain of the composite is equal to the mean value of strains of each material of the composite, if the strain magnitudes of each material of the composite are weighted by their percentage of composite volume.
The modulus of the elasticity can be determined with an analogic way.

22. By applying the rule of mixtures the modulus of elasticity of the fibre reinforced composite is (two values are needed due to the anisotropic structure):
In which:
Vf fibres’ percentage of the total composite volume
Ef modulus of elasticity of the fibres
Em modulus of elasticity of the matrix
Ec modulus of elasticity of the composite

23. GRAPHIC INTERPRETATION OF THE RULE OF MIXTURES
Stress σ1
Fibre Ef=σ1/ε σ2
Composite Ec=σ2/ε
(e.g.70% portion of fibres) σ3
Matrix Em=σ3/ε ε
Strain

24. DUCTILITY OF FIBRE-REINFORCED COMPOSITES
Usually the ductility of fibre-reinforced composites does NOT refer to elongation to break
BUT
it describes the ability of the composite to absorb the damaging energy, which could cause the crack growth in the composite.
Usually the most important characteristic to describe this ability is the bonding strength between the fibre and matrix.

25. Fallowed=σcontact area×π×D×L
Fixed end of the fibre
Fallowed=σcontact area×π×D×L
FRACTURE IN THE MATRIX
MATRIX ØD
FIBRE L
The empty space due to the loosen end of the fibre

26. Theory of particle reinforced composites
Particle reinforced composites have mostly isotropic material properties.
Based on the size of the alloyed particles two types of composites are available:
Particle reinforced composites
Dispersion reinforced particle composites
Dispersion reinforced particle composites have usually better strength properties due to evenly distributed particle amount inside the whole matrix

27. By applying the rule of mixtures the modulus of elasticity of the fibre reinforced composite is :
In theory the exponent ”n” gets the value of ”1” if the structure is like ”rubber particles in steel matrix”.
In theory the exponent ”n” gets the value of ”-1” if the structure is like ”steel particles in rubber matrix”.
The real values of exponent ”n” are between -1…1.

28. Theory of laminate composites
Three basic variations of layered composites are available:
Construction based on different directions of fibres in laminate’s layers
Construction based on different material layers
Combination of the previous two constructions

29. LAMINATE COMPOSITE 0° 90° +45° -45° 0° 90°
Direction angle of fibre reinforcements
Example of a laminate composite structure

30. LAMINATE COMPOSITE
In one direction reinforced aramid fibre polymer matrix composite
Aluminium plate

31. Theory of sandwich composites
In most of cases the question is more about sandwich constructions than composite materials.
Composite materials can be utilized as parts of sandwich structures.
Usually the rigidity of the construction is tuned by utilizing special core constructions in layered applications.
The final strength and rigidity is achieved by combining the different layers and the core construction.

32. ? Coating Load bearing plate Fixing layer Honeycomb Fixing layer
A COMPOSITE MATERIAL OR
A CONSTRUCTION ?
Fixing layer
Honeycomb
Fixing layer
Load bearing plate
Coating
PRINCIPLE OF THE HONEYCOMB STRUCTURE

33. DIFFERENT SHAPES AND SIZES OF THE HONEYCOMB STRUCTURE

34. Theory of cell structure composites
Typically the properties of cell structure composites depend on:
density ratio between the whole cell structure and the wall material of the cells
the selected cell structure type: open cells or closed cells
the filler material of the cell (in many cases it is air).

35. The modulus of elasticity of cell structure composites can be estimated with the equation:
In which:
Ecs =modulus of the elasticity of the cell structure composite
Ρ = density of the cell structure composite (of the ”foam”)
Esm = modulus of the elasticity of the wall material
ρsm = density of the wall material
The density ratio ρ/ρsm of the most common cell structure constructions can vary between 0,5 – 0,005, which means that with the same wall material the modulus of elasticity of the cell structure composite can have the ratio up to 1/

36. CELL STRUCTURE COMPOSITES
In the beginning there is the area, where the walls of the cell composite bend in an elastic-linear way.
COMPRESSION STRESS
Cell structure starts to behave like the pure wall material of the composite, because the walls have compressed against each other.
Deformation increases while the stress remains almost stable. Cell walls suffer from buckling.
DEFORMATION (COMPRESSION)

37. Viewpoints of strength analysis
Fibre reinforced composites have anisotropic material properties (also fibre reinforced MMC composites!). Anisotropic behaviour is relevant for strength, heat expansion and heat conductivity properties.
Some manufacturing technologies can cause anisotropic properties also to particle reinforced composites (e.g. some extrusion technologies).
Stress-strain behaviour is non-linear.
Particle reinforced composites and MMC composites might suffer from brittle behaviour.
Due to anisotropic properties many composites suffer from internal stresses, which are hard to estimate, but which should be taken into account in strength analysis.
Joining technology of composite components requires special attention.

38. Materials used in composites

39. Composite materials
METALS
METALS
POLYMERS
POLYMERS
CERAMICS
CERAMICS

40. Family of composites FAMILY OF COMPOSITES POLYMERS FIBRES METALS NANO-
MATRIX
COMPOSITES
POLYMERS
FIBRES
FIBRE
REINFORCED
COMPOSITES
METALS
METAL
MATRIX
COMPOSITES
FAMILY OF
COMPOSITES
CERAMICS
CERAMIC
COMPOSITES
NANO-
MATERIALS
COMPOSITES
ADAPTIVE
MATERIALS

41. The most common composites
Metal Matrix Composites (MMC)
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.
Polymer Matrix Composites (PMC)
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.
Ceramic Matrix Composites (CMC)
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.

42. What do we know already? TEMPERATURE RELATED CHARACTERISTICS
ASPECTS OF CHEMISTRY (POLYMER CHAIN)
CREEPING STERNGTH, VISCOELASTICITY
POLYMER
MATRIX
COMPOSITES
POLYMERS
POWDER METALURCICAL PROCESS
IMPORTANCE OF SINTERING AND
COMPRESSION DIRECTION
PURITY LEVEL, POROSITY, GRAIN SIZE
ALLOYING (ZrO2 / BRITTLENESS)
CERAMICS
CERAMIC
COMPOSITES
METALS
METAL
MATRIX
COMPOSITES
PRESSURE CASTING PROCESSES
POWDER METALLURGICAL PROCESS
IMPORTANCE OF ALLOYING

43. Examples of fibre reinforced constructional composites:
Fibre / Polymer matrix
Kevlar / epoksi
C (graphite) / PEEK
C (graphite) / PPS
Fibre / Metal matrix
SiC / Al
SiC / Ti
Fibre / Ceramic matrix
C / SiC
SiC / Si3N4

44. Aramid fibres (Kevlar)
CLASSIFICATION OF FIBRE REINFORCEMENTS
Glass fibres
Inorganic
Carbon fibres
Basalt fibres
SYNTHETIC
Aramid fibres (Kevlar)
Polymers
Organic
Cellulose fibres
REINFORCEMENT FIBRES
Mineral fibres
Asbestos
BIOFIBRES
Animal fibres
Wood fibres
Hemp fibres
Vegetation fibres
Flax fibres
Bamboo fibres

46. Metal matrix composites (MMC)
TYPES
FIBER COMPOSITES
PARTICLE COMPOSITES
LAYER COMPOSITES
Continuous fibers, discontinuous fibers, whiskers, particlers, wires

47. Metal matrix composites (MMC)
MANUFACTURING
Melting metallurgical processes
Powder metallurgical processes
Pressing processes
Pressure casting infiltration of metallic matrix between long or short fiber or particle reinforcement nets.
Pressing and sintering composite powders or extrusion of metal-powder particle composites
Hot isostatic pressing of powder mixtures and fibers

48. Pressure casting infiltration
PROCESS PROGRESS

49. The most important MMC’s
Aluminum matrix
Continuous fibers: boron, silicon carbide, alumina, graphite
Discontinuous fibers: alumina, alumina-silica
Whiskers: silicon carbide
Particles: silicon carbide, boron carbide
Magnesium matrix
Continuous fibers: graphite, alumina
Particulates: silicon carbide, boron carbide
Titanium matrix
Continuous fibers: silicon carbide, coated boron
Particles: titanium carbide
Copper matrix
Continuous fibers: graphite, silicon carbide
Wires: niobium-titanium, niobium-tin
Particles silicon carbide, boron carbide, titanium carbide.
Superalloy matrices
Wires: tungsten

50. MMC’s compared to metals
Higher strength-to-density ratio
Higher stiffness-to-density ratio
Better fatigue resistance
Higher strength in elevated temperatures
Lower coefficients of thermal expansion
Better wear resistance

51. MMC’s compared to PMC’s
Higher temperature capability
(Better) fire resistance
Higher transverse stiffness and strength
No moisture absorption
Higher electrical and thermal conductivities
Better radiation resistance

52. Polymer Matrix Composites (PMC)
Two types of polymers are used as matrix materials:
Thermosets (epoxies, phenolics)
Thermoplastics (Low Density Polyethylene LDPE, High Density Polyethylene HDPE, polypropylene, nylon, acrylics).
According to the reinforcement material the following groups of Polymer Matrix Composites (PMC) are used:
Fibre glasses – Glass Fibre Reinforced Polymer Composites
Carbon Fibre Reinforced Polymer Composites
Kevlar (Aramid) Fibre Reinforced Polymer Composites.
Properties of Polymer Matrix Composites are determined by the earlier presented theory of fibre reinforced composites.

53. Polymer Matrix Composites (PMC)
By fibre reinforced structures the properties of ordinary polymers can be improved remarkably (strength, stiffness, abrasion resistance, toughness etc.)
PMC’s have low material and manufacturing costs compared to other composite materials.
The main disadvantages of Polymer Matrix Composites are:
Low thermal resistance
High coefficient of thermal expansion.

54. Fibre comparison for PMC’s
Property
Fibre material
Kevlar
Carbon
Glass
High tensile strength 2 1
High compression strength 3
High modulus of elasticity
Impact strength
Low density
Good fire resistance
Low thermal expansion
Low cost
Range 1..3, 1=best

55. Ceramic Matrix Composites (CMC)
Examples of ceramic matrices include Al2O3 , Al2Ti5, AlN, TiN, ZrN, TiC, and ZrC.
Most typical CMC systems are:
C / SiC
SiC / Si3N4
Although developed initially to reinforce aluminum and titanium matrices (MMC), SiC filaments have been used as reinforcement in silicon nitride.

56. Development steps of CMC’s
Ways to control the bond between the matrix and the reinforcement : boron nitride (BN) and carbon
Ways to increase the fracture toughness of the composite: thermal treatments or CVD coatings of the fibers before their incorporation into an Al2O3 matrix
Ways to develop fibres, which are stable in oxidizing environments (after the possible matrix failure when the reinforcement fiber has air contact).
Ways to develop damage-tolerant and ductile ceramic-ceramic composites.
Ways to develop high-temperature reinforcements for ceramic-ceramic composites (utilization of silicon carbide SiC reinforcements)

57. Tools to support systematic selection of composites

58. + _ _ + PROPERTY MAPS Polymer matrix composites
Titanium matrix composites
Titanium alloys
Strength
Ni/Co-alloys
Ceramic matrix composites _ _ +
Temperature

59. PROPERTY MAPS CONNECTED WITH COSTS+
Metals and metal alloys
RECYCLABILITY
Polymers
Ceramics
Biocomposites
Traditional composites _ _ +
COSTS

60. + _ _ + PROPERTY MAPS WITH PROPERTY RATIOS METALS AND METAL ALLOYS
CERAMICS
COMPOSITES
POLYMERS
Modulus of elasticity/weight -ratio _ _ +
Strength/weight -ratio

61. PROPERTY CURVES WITH PROPERTY RATIOS
Kevlar-fibres in the epoxy-matrix
Boron-fibres in the aluminium-matrix
Garbon-fibres in the magnesium-matrix
Metals
Glass fibres
Polymers

62. Industrial applications

64. CARBONFIBRE LAMINATE COMPOSITE
STEEL/ TITANIUM
CARBONFIBRE SANDWICH COMPOSITE
CARBONFIBRE SANDWICH COMPOSITE
ALUMINIUM
GLASSFIBRE COMPOSITE

66. ROTOR BLADE CONNECTION
FRP COMPOSITE
ROTOR BLADES

69. High-tech applications

70. F1-car’s ”nose”
- polyamide/carbon
fibre composite
F1-car’s safety body ”the monocoque”
- carbon fibre composite
- carbon fibre/aluminium laminate structure
- Honeycomb-sandwich-structure
Wind wings and vanes and other aero detailed parts
- kevlar- coating
F1-car’s brake disks
- carbon fibre/graphite (c/c)
- composite

71. CASE: F1 Front Nose - Aerodynamic application for F1 wind tunnel, positioned on the front of an F1 car and supporting the front wing (and so called “Nose” of an F1 car).
The required base properties are:
dimensional accuracy and detail definition
the best compromise between stiffness and resistance to vibration.
Class of material
Polyamide (PA) and Carbon based Composite Material
Manufacturing Technology
Selective Laser Sintering

72. CASE: A construction material for Formula 1 cars, “The monocoque”
could be made of epoxy resin reinforced with carbon fibre
Manufacturing: laminated together 
Requirements: great rigidity and strength, but very lightweight
Notice from the table that carbon fibres are 3 times stronger and more than 4 times lighter than steels.
Tensile strength
Density
Carbon fibre
3.50
1.75
Steel
1.30
7.90

73. CASE: The carbon brake discs used in Formula 1 Requirements:
May not be thicker than 28 millimetres and their diameter may not exceed 278 millimetres.
When braking, the discs heat up to as much as 600…1000 degrees Celsius within one second
Full braking will bring a Formula 1 car from 200 to 0 km/h within 55 metres, all within 1.9 seconds. Deceleration forces achieve up to 5 G
Material: carbon-carbon composite (Carbon fibre-reinforced Carbon (carbon-carbon, C/C) is a composite material consisting of carbon fiber reinforcement in a matrix of graphite
Properties: Composite brake discs are used instead of steel or cast iron because of their
superior frictional, thermal, and anti-warping properties,
as well as significant weight savings.

74. CASE: To avoid sharp carbon fibre splinters on the track after accidents, all front wings, barge boards and small aerodynamic body parts must be given an additional outer coating of Kevlar® (or a similar type of material).

75. From high-tech to everyday applications

76. Metal Matrix composites (MMC)
E.g 75% high-strength Al-Cu alloy (AA-2124) + 25% SiC

77. Typical low cost body armor systems utilize Aramid fibers while Kevlar is used in cost-effective high performance systems.