4Our 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.
5Composites Advantages Disadvantages Typically the strength of the material is increasedLight weight constructions80% lighter than steel60% lighter than aluminiumAlso other properties than strength could be tuned according to the requirements:Rigidity vs. elasticityThermal and electrical propertiesCorrosion resistanceRecycling is necessary due to ”too high” lifetimeSome raw materials and manufacturing methods are expensiveSome manufacturing methods suffer from poor energy efficiencyStrength analysis are usually challenging due to anisotropic structure of many composites
10How to define, what is a real composite? MATERIAL 1PROPERTIES A+MATERIAL 2PROPERTIES B=NEW MATERIALPROPERTIES A+B1 + 1 = 2MATERIAL ALLOYMATERIAL 1PROPERTIES A+MATERIAL 2PROPERTIES B=NEW MATERIALPROPERTIES A+B+ ADDED VALUE!1 + 1 > 2COMPOSITE MATERIAL
11Composite types DIFFERENT STRUCTURES DIFFERENT SCALES DIFFERENT Mixed materialsAdded fibresSandwich-structuresCell-structuresDIFFERENTSCALESContinuous fibresParticlesNanoparticlesDIFFERENTMATERIALSMatrixReinforcementAlloys/Compounds
13Theory 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.
14TYPES OF FIBRE-REINFORCED MATERIALS CONTINUOUS FIBRE-REINFORCED MATERIAL- Direction can be tunedSHORT FIBRE-REINFORCED MATERIAL- Length and direction can be tunedBCWOVEN FIBRE-REINFORCED- Direction and density can be tuned
15IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING MATRIXFIBREFLOW MODULUS OF ELASTICITYHIGH MODULUS OF ELASTICITY
16IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING HIGH MODULUS OF ELASTICITYLOW MODULUS OF ELASTICITY
17IMPORTANCE OF FIBRE DIRECTION COMPARED TO LOADING Ultimate tensile strengthF0° ° 45° 60° °The angle between the directions of the affecting load and reinforcing fibres [°]
18STRESS-STRAIN-CURVE OF A FIBRE COMPOSITE σσcrσcσmSTRAINεThe 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.
19CROSS-SECTION AREAS OF DIFFERENT FIBRES BORON CARBIDESILICON CARBIDECOATED FIBRES:130 µmCARBON FIBRES5-7 µmBORON NITRIDE5 µmMETAL WIRES25 µmGLASS FIBRES10 µm
21The 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.
22By 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 volumeEf modulus of elasticity of the fibresEm modulus of elasticity of the matrixEc modulus of elasticity of the composite
23GRAPHIC INTERPRETATION OF THE RULE OF MIXTURES Stressσ1Fibre Ef=σ1/εσ2Composite Ec=σ2/ε(e.g.70% portion of fibres)σ3Matrix Em=σ3/εεStrain
24DUCTILITY OF FIBRE-REINFORCED COMPOSITES Usually the ductility of fibre-reinforced composites does NOT refer to elongation to breakBUTit 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.
25Fallowed=σcontact area×π×D×L Fixed end of the fibreFallowed=σcontact area×π×D×LFRACTURE IN THE MATRIXMATRIXØDFIBRELThe empty space due to the loosen end of the fibre
26Theory 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 compositesDispersion reinforced particle compositesDispersion reinforced particle composites have usually better strength properties due to evenly distributed particle amount inside the whole matrix
27By 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.
28Theory of laminate composites Three basic variations of layered composites are available:Construction based on different directions of fibres in laminate’s layersConstruction based on different material layersCombination of the previous two constructions
29LAMINATE COMPOSITE 0° 90° +45° -45° 0° 90° Direction angle of fibre reinforcementsExample of a laminate composite structure
30LAMINATE COMPOSITEIn one direction reinforced aramid fibre polymer matrix compositeAluminium plate
31Theory 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 MATERIALORA CONSTRUCTION?Fixing layerHoneycombFixing layerLoad bearing plateCoatingPRINCIPLE OF THE HONEYCOMB STRUCTURE
33DIFFERENT SHAPES AND SIZES OF THE HONEYCOMB STRUCTURE
34Theory 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 cellsthe selected cell structure type: open cells or closed cellsthe filler material of the cell (in many cases it is air).
35The modulus of elasticity of cell structure composites can be estimated with the equation: In which:Ecs =modulus of the elasticity of the cell structure compositeΡ = density of the cell structure composite (of the ”foam”)Esm = modulus of the elasticity of the wall materialρsm = density of the wall materialThe 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/
36CELL STRUCTURE COMPOSITES In the beginning there is the area, where the walls of the cell composite bend in an elastic-linear way.COMPRESSION STRESSCell 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)
37Viewpoints 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.
40Family of composites FAMILY OF COMPOSITES POLYMERS FIBRES METALS NANO- MATRIXCOMPOSITESPOLYMERSFIBRESFIBREREINFORCEDCOMPOSITESMETALSMETALMATRIXCOMPOSITESFAMILY OFCOMPOSITESCERAMICSCERAMICCOMPOSITESNANO-MATERIALSCOMPOSITESADAPTIVEMATERIALS
41The 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.
42What do we know already? TEMPERATURE RELATED CHARACTERISTICS ASPECTS OF CHEMISTRY (POLYMER CHAIN)CREEPING STERNGTH, VISCOELASTICITYPOLYMERMATRIXCOMPOSITESPOLYMERSPOWDER METALURCICAL PROCESSIMPORTANCE OF SINTERING ANDCOMPRESSION DIRECTIONPURITY LEVEL, POROSITY, GRAIN SIZEALLOYING (ZrO2 / BRITTLENESS)CERAMICSCERAMICCOMPOSITESMETALSMETALMATRIXCOMPOSITESPRESSURE CASTING PROCESSESPOWDER METALLURGICAL PROCESSIMPORTANCE OF ALLOYING
47Metal matrix composites (MMC) MANUFACTURINGMelting metallurgical processesPowder metallurgical processesPressing processesPressure 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 compositesHot isostatic pressing of powder mixtures and fibers
50MMC’s compared to metals Higher strength-to-density ratioHigher stiffness-to-density ratioBetter fatigue resistanceHigher strength in elevated temperaturesLower coefficients of thermal expansionBetter wear resistance
51MMC’s compared to PMC’s Higher temperature capability(Better) fire resistanceHigher transverse stiffness and strengthNo moisture absorptionHigher electrical and thermal conductivitiesBetter radiation resistance
52Polymer 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 CompositesCarbon Fibre Reinforced Polymer CompositesKevlar (Aramid) Fibre Reinforced Polymer Composites.Properties of Polymer Matrix Composites are determined by the earlier presented theory of fibre reinforced composites.
53Polymer 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 resistanceHigh coefficient of thermal expansion.
54Fibre comparison for PMC’s PropertyFibre materialKevlarCarbonGlassHigh tensile strength21High compression strength3High modulus of elasticityImpact strengthLow densityGood fire resistanceLow thermal expansionLow costRange 1..3, 1=best
55Ceramic Matrix Composites (CMC) Examples of ceramic matrices include Al2O3 , Al2Ti5, AlN, TiN, ZrN, TiC, and ZrC.Most typical CMC systems are:C / SiCSiC / Si3N4Although developed initially to reinforce aluminum and titanium matrices (MMC), SiC filaments have been used as reinforcement in silicon nitride.
56Development steps of CMC’s Ways to control the bond between the matrix and the reinforcement : boron nitride (BN) and carbonWays to increase the fracture toughness of the composite: thermal treatments or CVD coatings of the fibers before their incorporation into an Al2O3 matrixWays 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)
57Tools to support systematic selection of composites
70F1-car’s ”nose”- polyamide/carbonfibre compositeF1-car’s safety body ”the monocoque”- carbon fibre composite- carbon fibre/aluminium laminate structure- Honeycomb-sandwich-structureWind wings and vanes and other aero detailed parts- kevlar- coatingF1-car’s brake disks- carbon fibre/graphite (c/c)- composite
71CASE: 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 definitionthe best compromise between stiffness and resistance to vibration.Class of materialPolyamide (PA) and Carbon based Composite MaterialManufacturing TechnologySelective Laser Sintering
72CASE: A construction material for Formula 1 cars, “The monocoque” could be made of epoxy resin reinforced with carbon fibreManufacturing: laminated together Requirements: great rigidity and strength, but very lightweightNotice from the table that carbon fibres are 3 times stronger and more than 4 times lighter than steels.Tensile strengthDensityCarbon fibre3.501.75Steel1.307.90
73CASE: 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 secondFull 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 GMaterial: carbon-carbon composite (Carbon fibre-reinforced Carbon (carbon-carbon, C/C) is a composite material consisting of carbon fiber reinforcement in a matrix of graphiteProperties: Composite brake discs are used instead of steel or cast iron because of theirsuperior frictional, thermal, and anti-warping properties,as well as significant weight savings.
74CASE: 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).