Composite MaterialsFundamental considerations

• How do composite materials differ from other engineering materials?

• What are the constituent materials, and how do their properties compare?

• How do the properties of the composite depend on the type, amount and arrangement of the constituents?

• How are composite products made, and why does manufacture affect quality?

Fibres have better stiffness and strength compared to bulk materials

• Atomic or molecular alignment(carbon, aramid)

• Removal of flaws and cracks (glass)

• Strain hardening (metals)

J Gordon: The New Science of Strong Materials

D Hull: Introduction to Composite Materials

Carbon fibre – alignment of graphite sheets. Strong, in-plane covalent bonds; weak secondary bonds between sheets (cf polymer structures).

As fibre diameter is reduced, so is maximum possible crack size in glass. Theoretical strength is achieved in defect-free material (zero diameter!).

Carbon fibres seen under the electron microscope. Note the irregular surface. Fibre diameters are around 5 – 7 microns (thousandths of a mm).

Glass fibres being drawn from the furnace. Molten glass emerges through a bushing – the rate of pulling determines the fibre diameter. Because the fibres are so small, they lose heat very quickly.

The surface of a fractured composite, containing both carbon and glass fibres. Note the larger, smoother glass, and regions where fibres have been pulled out of the plastic matrix.

0 100 200 300 400 500 600

E-glass

S-glass

T300 carbon

IM-7 carbon

GY70 graphite

boron

aramid

SiC (Textron)

Saphikon alumina

Fibre Tensile Modulus (GPa)

0 1000 2000 3000 4000 5000 6000

E-glass

S-glass

T300 carbon

IM-7 carbon

GY70 graphite

boron

aramid

SiC (Textron)

Saphikon alumina

Fibre Tensile Strength (MPa)

steelaluminium

heat-treated alloy steelheat-treated aluminium alloy

Compare stiffness and strength per unit weight:

specific strength

0 500 1000 1500 2000

glass fibre

HS carbonfibre

aluminium

steel

specific modulus

0 50 100 150

glass fibre

HS carbonfibre

aluminium

steel

Tensile strength / density

Tensile modulus / density

Nominal properties – ‘high strength’ carbon fibres

tensile modulus (GPa)

ten

sile

str

eng

th (

GP

a)

Nominal properties – ‘intermediate-high modulus’ carbon fibres

Young's Modulus (SWNT) ~ 1 TPa (1000 GPa)

Young's Modulus (MWNT) 1.28 TPa

Maximum Tensile Strength ~ 30 GPa (30,000 MPa)

~ 0.02 m

Most reinforcing fibres (and thermosetting resins) are brittle (elastic to failure)

Hollaway (ed), Handbook of Polymer Composites for Engineers

Types of Natural Fibre

• Bast fibres (flax, hemp, jute, kenaf…)- wood core surrounded by stem containing cellulose filaments

• Leaf fibres (sisal, banana, palm)• Seed fibres (cotton, coconut (coir), kapok)

Tensile modulus

0

10

20

30

40

50

60

70

80

90

E-glass

flax hemp jute ramie coir sisal abaca cotton

GP

a

Specific tensile modulus

0

10

20

30

40

50

60

E-glas

sfla

xhe

mpjut

era

mieco

irsis

al

abac

a

cotto

n

GP

a /

(g/m

3) modulus / density

Structures cannot be made from fibres alone - the high properties of fibres are not realisable in practice

A matrix is required to:

• hold reinforcement in correct orientation

• protect fibres from damage

• transfer loads into and between fibres

http://www.carlosantulli.net/aim2001.pdf

COMPOSITES - A FORMAL DEFINITION(Hull, 1981)

1. Consist of two or more physically distinct and mechanically separable parts.

reinforcement(discontinuous phase)

matrix (continuous phase)

fibres or particles

+

short, ‘long’ or continuous

Examples of particulate composites

• Concrete - hard particles (gravel) + cement (ceramic/ceramic composite). Properties determined by particle size distribution, quantity and matrix formulation

• Additives and fillers in polymers:carbon black (conductivity, wear/heat resistance)aluminium trihydride (fire retardancy)glass or polymer microspheres (density reduction)chalk (cost reduction)

• Cutting tool materials and abrasives (alumina, SiC, BN bonded by glass or polymer matrix; diamond/metal matrix)

• Electrical contacts (silver/tungsten for conductivity and wear resistance)

• Cast aluminium with SiC particles

Alternative matrix materials

Fibre: SiC; alumina; SiN

Matrix: SiC;alumina;glass-ceramic;SiN

Fibres improve toughness

Metal (MMCs)

Polymer(PMCs)

Ceramic(CMCs)

Fibre: boron; Borsic; carbon (graphite); SiC; alumina (Al2O3)

Matrix: aluminium; magnesium; titanium; copper

Fibres improve high temp creep; thermal expansion.

thermoplastic

thermosetTough; high melt viscosity; ‘recyclable’

Brittle; low viscosity before cure; not recyclable

The matrix material largely determines the processing method…

0 20 40 60 80

GPa

CSM glass/polyester (Vf 25%)

biaxial woven glass/epoxy (Vf 50%)

UD glass/epoxy (Vf 60%)

E-glass fibres

Tensile Modulus

Composite property might be only 10% of the fibre property:

Specific strength (strength per unit weight)

0 100 200 300 400

polyethylene

pure aluminium

epoxy resin

alloy steel

aluminium alloy

aramid-epoxy composite

carbon-epoxy composite

titanium alloy

COMPOSITES - A FORMAL DEFINITION(Hull, 1981)

1. Consist of two or more physically distinct and mechanically separable parts.

2. Constituents can be combined in a controlled way to achieve optimum properties.

COMPOSITES - A FORMAL DEFINITION(Hull, 1981)

1. Consist of two or more physically distinct and mechanically separable parts.

2. Constituents can be combined in a controlled way to achieve optimum properties.

3. Properties are superior, and possibly unique, compared those of the individual components

Addition of properties:

GLASS + POLYESTER = GRP

(strength) (chemical resistance) (strength and chemical resistance)

Unique properties:

GLASS + POLYESTER = GRP

(brittle) (brittle) (tough!)

ADVANCED COMPOSITES vs REINFORCED PLASTICS

• Aerospace, defence, F1…• Highly stressed• Glass, carbon, aramid fibres• Honeycomb cores• Epoxy, bismaleimide…• Prepregs• Vacuum bag/oven/autoclave

• Highly tested and qualified materials

• Marine, building…• Lightly stressed• Glass (random and woven)• Foam cores• Polyester, vinylester…• Wet resins• Hand lay up, room

temperature cure

• Limited range of lower performance materials

Why are composites used in engineering?

• Weight saving (high specific properties)• Corrosion resistance• Fatigue properties• Manufacturing advantages:

- reduced parts count- novel geometries- low cost tooling

• Design freedoms- continuous property spectrum- anisotropic properties

Anisotropic properties - fibres can be aligned in load directions to make the

most efficient use of the material

Why aren’t composites used more in engineering?

• High cost of raw materials• Lack of design standards• Few ‘mass production’ processes available• Properties of laminated composites:

- low through-thickness strength- low interlaminar shear strength

• No ‘off the shelf’ properties - performance depends on quality of manufacture

There are no ‘off the shelf’ properties with composites. Both the structure and the material are

made at the same time.

Material quality depends on quality of manufacture.

Metal (steel, aluminium, titanium, magnesium…)

Composite (carbon fibre / epoxy)?

2005: Airbus engineers are claiming Boeing has rushed the development of the 7E7 Dreamliner. In particular, they say composite technology is not mature enough to build an all-composite fuselage. But the claims may be no more than a marketing ploy, in response to Boeing's criticism of weight overruns on the Airbus A380.

Aluminium or composite?

"This is a piece of aviation history," said Walt Gillette, Boeing vice president of Engineering, Manufacturing and Partner Alignment. "Nothing like this is already in production. Hundreds of aerospace experts from Boeing and our partners developed everything, including the design, tools that served as the mold, programming for the composite lay-down, and tools that moved the structure into the autoclave."

He added that using composites "allowed us to create optimized structural designs and develop an efficient production process. We now see how all advanced airplanes will be built from this time forward."

SEATTLE, Jan. 11, 2005 –

Boeing recently completed the first full-scale composite one-piece fuselage section for its new 7E7 Dreamliner program, demonstrating concepts for 7E7 production that begins next year. The structure, 7 m long and nearly 6 m wide, is the 7E7's first major development piece.

Boeing's Revolutionary Lightweight Jetliner Faces Serious Problems

For Boeing, the 787 Dreamliner, with its radical new lightweight design, represents far more than a potentially juicy profit stream. The carbon-fiber-reinforced plastic aircraft is supposed to be the symbol of a new Boeing — a visionary company that has transcended its recent ethical scandals, designed the most innovative commercial plane ever, and devised the most sophisticated manufacturing process in history to produce the aircraft.

But as crucial deadlines loom, Boeing’s engineers are wrestling with several significant technical and production problems that could threaten the scheduled 2008 delivery of the jetliner.

At a time when Boeing has left itself with little margin for error, the wide-ranging series of glitches could create a domino effect if not resolved quickly. The most important piece of bad news — the fuselage section, the big multi-part cylindrical barrel that encompasses the passenger seating area, has failed in company testing. That’s forcing Boeing to make more sections than planned, and to reexamine quality and safety concerns.

Elsewhere in the aircraft, suppliers are struggling to meet Boeing’s exacting technological standards and ambitious production deadlines. The first two nose sections, for instance, were deemed unacceptable by Boeing. Software programs designed by a variety of manufacturers are having trouble talking to one another. And the overall weight of the airplane is still too high — especially the single biggest part of the 787, the carbon-fiber wing.

The first big sign of struggle with the 787 surfaced three weeks ago at Boeing’s Developmental Center in south Seattle. That’s when engineers discovered that worrisome bubbles were developing in the skin of the fuselage during the process of baking the plastic composite tape in big oven-like machines.

But the main challenge is the sheer size of the fuselage sections. These require multiple layers of carbon-fiber tape to assure structural integrity. However, each added layer increases the likelihood of variations or flaws, say composite experts, such as bubbles on the skin. Bubbles could weaken the material and eventually cause cracks by allowing water to seep under the surface, then freeze up and expand at high altitudes, raising the possibility that the fuselage could crack under extreme conditions. Bair says Boeing has located the source of the problem.

http://www.businessweek.com/technology/content/jun2006/tc20060607_864925.htm

Seattle, Washington, USA, June 8, 2006

Composite – wood, glass, carbon?

Manufacture - prepreg, infusion…?

ADVANTAGES OF COMPOSITES(for construction applications)

Aesthetic appeal

Ability to mould complex shapes

Various surface finishes available

Lightweight

Durability / Corrosion resistance

Parts integration

Cost effectiveness

Electrical properties

Roofs / canopies

Complete buildings

Cladding panels

Masts & towers

Domes

POSSIBLE APPLICATIONS(in construction)

Unusual architectural features / structures

Radomes

Permanent or temporary formwork

Tanks, covers, pipes, ducts etc

Strengthening / repair of conventional structures

BRIDGE APPLICATIONS OF COMPOSITE MATERIALS

GRP LOUVRES AT LANCASTER UNIVERSITY

HARARE INTERNATIONAL AIRPORTARCHITECTURAL GRP STRUCTURE ON THE

TOP OF THE AIR TRAFFIC CONTROL TOWER

FRPMOSQUEDOMES

PHOTOS COURTESY OF NORTHSHORE COMPOSITES

MILLENNIUM DOMEHOME PLANET ZONE

FRPSPHERICAL RADOMES

FRP CYLINDRICAL RADOMES

FRP OBSERVATION CABIN

& CARBON FIBRE

MAST

Photo - Carrillion

GLASGOW SCIENCE CENTRE

GLASGOW SCIENCE CENTREOBSERVATION CABIN

CABIN MANUFACTURE

CABIN INSTALLATION

CONCRETE COLUMN REINFORCEMENT

FRP LIGHTSTATIONS

FRP BRIDGE ENCLOSURES

FRP PULTRUDED STRUCTURAL FRAME

PORTSMOUTH SPINNAKERTOWER

SPIRE SECTION MAYSPIRE SECTION MAYBE MANUFACTUREDBE MANUFACTUREDIN COMPOSITESIN COMPOSITES

Composite Materialsfor the construction industry

Summary

1. Huge potential for polymer composites in civil engineering/construction applications.

2. Large structures need particular types of manufacturing process.

3. Raw materials are expensive – need low-cost manufacture and justification for composites.

4. Building industry is conservative – resistance to ‘new’ materials.

5. Design codes for composite structures – available but not widely adopted.

David Kendall, CETEC (2001)