Presentation on theme: "Lesson 7 2014. Lesson 7 2014 Our goal is, that after this lesson, students are able to recognize the key criteria for selecting composites and are."— Presentation transcript:
Lesson 7 2014
Lesson 7 2014
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.
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
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
Composition MATRIXREINFORCEMENTCOMPOSITE + =
How to define, what is a real composite? MATERIAL 1 PROPERTIES A MATERIAL 2 PROPERTIES B NEW MATERIAL PROPERTIES A+B MATERIAL 1 PROPERTIES A MATERIAL 2 PROPERTIES B NEW MATERIAL PROPERTIES A+B + ADDED VALUE! 1 + 1 = 2 MATERIAL ALLOY 1 + 1 > 2 COMPOSITE MATERIAL + + = =
Composite types DIFFERENT STRUCTURES DIFFERENT STRUCTURES DIFFERENT SCALES DIFFERENT SCALES DIFFERENT MATERIALS DIFFERENT MATERIALS Mixed materials Added fibres Sandwich-structures Cell-structures Mixed materials Added fibres Sandwich-structures Cell-structures Continuous fibres Particles Nanoparticles Continuous fibres Particles Nanoparticles Matrix Reinforcement Alloys/Compounds Matrix Reinforcement Alloys/Compounds
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.
A B C CONTINUOUS FIBRE- REINFORCED MATERIAL - Direction can be tuned SHORT FIBRE-REINFORCED MATERIAL - Length and direction can be tuned WOVEN FIBRE-REINFORCED - Direction and density can be tuned TYPES OF FIBRE-REINFORCED MATERIALS
F F MATRIX FIBRE HIGH MODULUS OF ELASTICITY IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
F F HIGH MODULUS OF ELASTICITY LOW MODULUS OF ELASTICITY FF FF FF IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
The angle between the directions of the affecting load and reinforcing fibres [°] Ultimate tensile strength 0° 30° 45° 60° 90° F F F F IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING
STRESS σ STRAIN ε Elastic elongation of the composite. The value of the modulus of elasticity is stable. The matrix yelds and the composite’s modulus of elasticity decreases. The additional load is carried by the fibres with elastic elongation. 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. σcσc σ cr σmσm STRESS-STRAIN-CURVE OF A FIBRE COMPOSITE
BORON NITRIDE 5 µm CARBON FIBRES 5-7 µm GLASS FIBRES 10 µm METAL WIRES 25 µm COATED FIBRES: BORON CARBIDE SILICON CARBIDE 130 µm CROSS-SECTION AREAS OF DIFFERENT FIBRES
THE ”VISION” OF 3D-WOVEN FIBRE-REINFORCEMENT
“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.
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: –V f fibres’ percentage of the total composite volume –E f modulus of elasticity of the fibres –E m modulus of elasticity of the matrix –E c modulus of elasticity of the composite
Strain Stress Fibre E f =σ 1 /ε Composite E c =σ 2 /ε (e.g.70% portion of fibres) Matrix E m =σ 3 /ε σ1σ1 σ2σ2 σ3σ3 ε GRAPHIC INTERPRETATION OF THE RULE OF MIXTURES
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. DUCTILITY OF FIBRE-REINFORCED COMPOSITES
MATRIX FIBRE FRACTURE IN THE MATRIX The empty space due to the loosen end of the fibre Fixed end of the fibre F allowed =σ contact area ×π×D×L L ØD
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 Theory of particle reinforced composites
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.
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 Theory of laminate composites
90° 0° -45° +45° 90° 0° Direction angle of fibre reinforcements Example of a laminate composite structure LAMINATE COMPOSITE
In one direction reinforced aramid fibre polymer matrix composite Aluminium plate LAMINATE COMPOSITE
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. Theory of sandwich composites
Coating Load bearing plate Fixing layer Honeycomb Fixing layer Load bearing plate Coating A COMPOSITE MATERIAL OR A CONSTRUCTION ? PRINCIPLE OF THE HONEYCOMB STRUCTURE
DIFFERENT SHAPES AND SIZES OF THE HONEYCOMB STRUCTURE
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). Theory of cell structure composites
The modulus of elasticity of cell structure composites can be estimated with the equation: In which: E cs =modulus of the elasticity of the cell structure composite Ρ = density of the cell structure composite (of the ”foam”) E sm = modulus of the elasticity of the wall material ρ sm = density of the wall material The density ratio ρ/ρ sm 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 1/10 000.
DEFORMATION (COMPRESSION) COMPRESSION STRESS Cell structure starts to behave like the pure wall material of the composite, because the walls have compressed against each other. In the beginning there is the area, where the walls of the cell composite bend in an elastic- linear way. Deformation increases while the stress remains almost stable. Cell walls suffer from buckling. CELL STRUCTURE COMPOSITES
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.
Family of composites POLYMER MATRIX COMPOSITES POLYMERSCERAMICS CERAMIC COMPOSITES METALS METAL MATRIX COMPOSITES NANO- MATERIALS NANO- COMPOSITES FIBRES FIBRE REINFORCED COMPOSITES FAMILY OF COMPOSITES ADAPTIVE MATERIALS
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.
What do we know already? POLYMER MATRIX COMPOSITES POLYMERS CERAMICS CERAMIC COMPOSITES METALS METAL MATRIX COMPOSITES -TEMPERATURE RELATED CHARACTERISTICS -ASPECTS OF CHEMISTRY (POLYMER CHAIN) -CREEPING STERNGTH, VISCOELASTICITY -TEMPERATURE RELATED CHARACTERISTICS -ASPECTS OF CHEMISTRY (POLYMER CHAIN) -CREEPING STERNGTH, VISCOELASTICITY -POWDER METALURCICAL PROCESS -IMPORTANCE OF SINTERING AND COMPRESSION DIRECTION -PURITY LEVEL, POROSITY, GRAIN SIZE -ALLOYING (ZrO2 / BRITTLENESS) -POWDER METALURCICAL PROCESS -IMPORTANCE OF SINTERING AND COMPRESSION DIRECTION -PURITY LEVEL, POROSITY, GRAIN SIZE -ALLOYING (ZrO2 / BRITTLENESS) -PRESSURE CASTING PROCESSES -POWDER METALLURGICAL PROCESS -IMPORTANCE OF ALLOYING -PRESSURE CASTING PROCESSES -POWDER METALLURGICAL PROCESS -IMPORTANCE OF ALLOYING
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 / Si 3 N 4
Metal matrix composites (MMC) Melting metallurgical processes MMC MANUFACTURING MMC MANUFACTURING 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
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
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
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. 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.
Fibre comparison for PMC’s Property Fibre material KevlarCarbonGlass High tensile strength 212 High compression strength 312 High modulus of elasticity 213 Impact strength 132 Low density 123 Good fire resistance 131 Low thermal expansion 111 Low cost 331 Range 1..3, 1=best
Ceramic Matrix Composites (CMC) Examples of ceramic matrices include Al 2 O 3, Al 2 Ti 5, AlN, TiN, ZrN, TiC, and ZrC. Most typical CMC systems are: C / SiC SiC / Si 3 N 4 Although developed initially to reinforce aluminum and titanium matrices (MMC), SiC filaments have been used as reinforcement in silicon nitride.
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 Al 2 O 3 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)
F1-car’s safety body ”the monocoque” - carbon fibre composite - carbon fibre/aluminium laminate structure - Honeycomb-sandwich-structure F1-car’s brake disks - carbon fibre/graphite (c/c) - composite F1-car’s ”nose” - polyamide/carbon fibre composite Wind wings and vanes and other aero detailed parts - kevlar- coating
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
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 3.501.75 Steel1.307.90
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.
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).
Metal Matrix composites (MMC) E.g 75% high-strength Al-Cu alloy (AA-2124) + 25% SiC
Typical low cost body armor systems utilize Aramid fibers while Kevlar is used in cost-effective high performance systems.