Introduction to Composite Materials

ME 423 Polymers & Polymer Composites 08/09 

Introduction to Composite 

Materials 

ME 423 

Polymers & Polymer Composites 

Dr. Conchúr Ó Brádaigh 

Dept. of Mechanical Engineering, 

NUI Galway


Introduction to Composites 

• Advanced composites 

• what do they consist of ? 

– fibres and resins 

• where are they used ? 

- many areas of industry 

e.g. Aerospace, Marine, Automotive, Infrastructure, 

Wind Energy, Biomedical 

• Manufacturing processes (Lecture 2) 

- Thermosets, Thermoplastics


Composite Materials 

• Combination of two or more distinct material 

phases into one engineering material 

• Two components: 

- Matrix & Reinforcement 

• Matrix - Protects Reinforcement 

- Environmental Tolerance 

• Reinforcement - Supports Structural Load



MATRIX + REINFORCEMENT 

Polymer Carbon fibre 

Metal Glass fibre 

Ceramic Aramid fibre (e.g. Kevlar) 

Metal fibre (e.g. Ti, Al)

Short Fibres 



Aligned Fibres 

“Advanced Composites”


Carbon Fibres 

Courtesy of Tenax Fibers


Carbon Fibres 

• May be manufactured from PAN or Pitch 

• Lightweight 

• High performance 

• High strength - intermediate modulus – high modulus 

• Lower modulus – intermediate strength – lower strength 

• High electrical and thermal conductivity 

• Dimensional stability (negative CTE in fibre direction) 

• Relatively expensive (aerospace grade $30-50/Kg) 

• Transversely isotropic 

• Relatively brittle 

• Not very damage resistant


Aramid Fibres (e.g. Kevlar®) 

• High Tensile Strength at Low Weight 

• High Toughness & High Modulus 

• Low Electrical Conductivity 

• High Chemical Resistance 

• Low Thermal Shrinkage 

• Excellent Dimensional Stability 

• High Cut Resistance 

• Flame Resistant, Self-Extinguishing 

• Tends to absorb water (hygroscopic) 

• Problems in compression strength 

• Poor interfacial strength with matrix 

• Also expensive Courtesy of EI DuPont De Nemours


Glass Fibres 

• Cheap – most widely used reinforcement 

• Properties vary from low to medium 

• Good impact properties 

• Low electrical conductivity 

• Higher failure strains than carbon 

• E-Glass – strength, stiffness, weathering, 

electrical props. 

• S-Glass – higher modulus and strength, 

aircraft applics. 

• C-Glass – chemical resistance 

• Relatively heavy 

• Prone to moisture absorption 

• Can suffer surface damage 

Courtesy Owens Corning

ME 423 Polymers & Polymer Composites 08/09


Material Properties 

Material Modulus Strength Relative 

(GPa) (MPa) Density 

Steels 203 600-2000 7.8 

Aluminium 75 70-80 2.6 

Carbon fibre (HM) 340 2500 1.9 

Carbon fibre (HS) 230 3200 1.8 

Aramid fibre 124 2800 1.45 

Glass fibre 76-86 1700 2.5


Composite Matrices 

Thermoset Resins 

• Polyester (GRP) – cheap and widest use 

• Epoxy – more expensive, better mech props 

• Phenolics – fire resistance 

• High temp. polyimides – v. expensive 

Thermoplastic Polymers 

• Polypropylene – cheapest, mainly with glass fibres 

• Nylons – industrial uses – some with carbon fibres 

• Polycarbonate, PET – more exotic 

• PEI, PES, PPS, PEEK – v. high props, v. high cost


Production of Composite – 

PreImpregnated Tape (Prepreg) 

Fibres are introduced into resin in continuous 

resin impregnation process – rolled up on paper 

backing – ready for component manufacturing

Unidirectional 

Pre-impregnated 

Tape (Prepreg) 


+ Pressure + Heat 

Fabrics 

Aircraft 

Trailing 

Edge SUPreM


Micromechanics Combining Rules 

e.g. Rule of Mixtures 

E (long) = Ef . Vf + Em . Vm 

E (transverse) = EmEf 

Vf . Em + Vm. Ef 

Em = Matrix modulus, Vm = matrix volume fraction, 

Ef = Fibre Modulus, Vf = fibre volume fraction 

Vm + Vf = 1


Composite Material Properties 

Material Fibre Modulus Strength 

Volume (GPa) (MPa) 

Steels ---- 203 600-2000 

Aluminium ---- 75 70-80 

UD CF/Epoxy 0.6 180 1500 

UD Kevlar/Epoxy 0.6 76 1400 

UD CF/PEEK 0.66 134 2130 

UD GF/Epoxy 0.6 50 1200 

All composite properties measured in fibre direction


…...the Composite Advantage is Weight 

Material Specific Specific 

Modulus Strength 

UD CF/Epoxy 113 937 

UD CF/PEEK 84 1330 

UD Kevlar/Epoxy 52 965 

Aluminium 30 30 

UD GF/Epoxy 21 590 

Steels 26 76-255 

Specific properties are normalised by relative density


Improving Fibre Properties 

Carbon fibres: Modulus Strength 

(GPa) (MPa) 

T700 (HS) 235 5300 

HTS (HS) 238 4300 

IM6 / IM7 (IM) 303 5200 

HR40 (HM) 381 4800 

HS40 (UHM) 441 4400


Applications of Composites 

Where the increased performance/reduced weight will 

pay for the increased cost of manufacture 

Ordered according to value per Kg weight saved: 

– Space (antennae, structures,satellite dishes etc) 

– Military Aircraft (wings, fuselage etc.) 

– Formula One (practically everything) 

– Civil aircraft (control surfaces, floor beams, empennage) 

– New civil aircraft (wings, fuselage) 

– Personalised protection (sports, ballistic armour) 

– Specialised automotive (e.g. Lotus, Ferraris) 

– Wind turbine blades 

– Marine (yachts, offshore structures)


Composites in Aerospace 

Composites in use in space/military aircraft since 

late 1960s. 

B2 Bomber RAH 66 Comanche Helicopter


Eurofighter 

Typhoon 

Source: 

EADS 

Deutschland


Application - Aerospace 

Composites being increasingly used 

in commercial aircraft

Traditional - Interiors 

Floor beams, seats, 

overhead bins, galleys 


Traditional - Structure 

Empennage, bulkheads, 

control surfaces, engine 

cowlings, fairings etc.

CF/Epoxy 

spoilers 


Quartz fibre radome 

GF/Phenolic 

Smoke - 

detector 

housing


A – 380 “Super-Jumbo” 

• Many innovative composite applications 

• 25% structural weight in composites


Source: EADS Deutschland


Source: EADS Deutschland

Source: EADS Deutschland 


Boeing 787 

– Dreamliner 

Entry into Service 2011 


• Longer range, more fuel-efficient aircraft 

• Over 50% structural weight in composites


Boeing 787 (EIS 2011) 

First 7m composite 

fuselage section 

shown 

Enables bigger 

windows, higher 

cabin pressure and 

higher humidity, 

12 year D-Check 

Maintenance interval


Airbus A350 XWB (planned 2013) 

• Competitor to 787 

• Longer range, more fuel-efficient aircraft 

• Over 50% composite structure


New Aerospace Materials 

Fibre-Metal Laminates (e.g. GLARE) 

Laminates of Al and CF/Epoxy 

Improved impact and fire 

resistance over Al & composites 

Better fatigue resistance than 

aluminium 

Used for upper fuselage of A-380


Issues in Aerospace 

• Composites manufacturing processes still not automated 

sufficiently 

• How will single-aisle replacements (Boeing 737 & Airbus A- 

320 family) be made in composites (60 A/C per month each) ? 

• Composites don’t fatigue or corrode like aluminium (great!) 

• Damage tolerance seen to be a problem (CF / epoxy) 

- developments in thermoplastics 

- fibre / metal laminates 

• Cost….Cost……Cost


Application - Marine


Composites in Marine/Offshore 

Lightweight composite sandwiches are material 

of choice for yacht hulls, minesweepers etc. 

Offshore oil rigs, risers, platforms with special 

resin grades for maritime environment 

New closed-mould, in-bag infusion technologies 

larger mouldings, less environmental impact 

Smart fibre optics embedded in yacht masts


Application - Automotive 

Bus interiors and exterior panels


Bus panels moulded in GF/PP (Twintex)


Application - Automotive 

Daimler-Chrysler 

Dodge ESX-3 

EJ 11


Composites in Automotive 

Mainly short-fibre reinforced thermosets (SMC) and 

thermoplastics (GMT & filled inj. Mouldings) 

Pickup-bed covers, bonnets, front-end carriers, 

seats, spoilers, rocker and valve covers etc. 

Advanced composites structural elements/body 

panels being developed - electric car 

Recyclability & sustainability very important 

thermoplastic matrices 

natural fibres - flax, jute, sisal, hemp


Application - Infrastructure 

Shear reinforcement in 

construction 

Reinforcement of support props 

or anchor bolts in tunnel 

construction

150 


Strengthening with CFRP laminates 

load [kN] 

strengthened with 

CFRP laminates 

steel reinforced 

concrete beam 

midspan 

deflection 

[mm] 

0 100 

after failure 

i b 

k


Composites in Infrastructure 

Carbon fibre prices now dropping rapidly, as low as 

$12/kg for large tows 

Rehabilitation of bridges/buildings with CF 

plates/strips at minimum cost and inconvenience 

Seismic retrofitting of columns with CF wraps 

All-composite foot bridges from pultruded sections 

All-composite vehicular bridges coming into service


Innovative Tubular Grid Structures 

Grid structures can be 

designed for optimum 

properties - combinations of 

torsion & flexure, include 

redundant members for 

impact & durability 

ig.6: Structural grid structure 

(Photo: ABB)


Wind Energy 

• Wind market growing worldwide at 15%/annum 

• Blades up to 50m long made of glass-fibre/epoxy 

• Next generation 50-60m for offshore sites – 

size means use of carbon fibre for stiffness 

• Denmark aims to supply 20% of its own 

energy by wind power by 2010 

• Irish Government target of 30% generation 

of electricity from renewables by 2020

Wind Energy 


Wind Energy 


Wind Energy 



40m Wind Turbine Blade

Skins/Shells 


Box-Spar 

Hub 

Connection


Application - Biomedical Implants 

• Polymeric composites are transparent to radio waves & 

non-magnetic 

metals produce artifacts under CAT scans & MRI 

• Polymer matrices can be bio-inert or biodegradable 

• Composites are anisotropic, so properties can be tailored 

by varying fibre volume fraction 

by varying the angle of reinforcement 

by changing the local density/form of reinforcement

ETH Zurich 


Bone Fixation Screws (CF/PEEK) 

CF/PEEK screws 

Metal screws

ETH Zurich 


Bone Fixation Plate (CF/PEEK) 

Holes moulded- 

In using CF/PEEK 

fabric rather 

than by 

machining

Introduction to Composite Materials

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