An Introduction to Composites

List of materials we know

What is a Composite?

• A combination of two or more different materials – Properties are superior to that of individual

materials

Metals

CeramicsPlastics

CFRP, GFRP

Concrete

What is a Composite

ReinforcementMatrix Composite

EpoxyPolyamidesPolyesterSilicone

SteelAluminium

GlassCarbonThermoplastic fibresMetalsCeramicsTungsten carbide

boron nitrideCarbon fibre

• Why a bunch of ceramic fibres are stronger than the Bulk material?

Reinforcements• Glass fibre• Carbon fibre• Boron fibre• Thermoplastic fibres• Metal

– Wire, powder• Ceramics

– SiC, Al2O3

Reinforcement Schemes• Continuous fibre (or yarn)

– UD laminates– Fibre Woven

• Chopped fibre/ whiskers• Flakes• Skeletal

– Honeycomb

• Glass fibre– Most commonly used– Produced by extrusion– E-Glass – electrical applications– S-Glass – High strength applications

• Boron fibre– Produced by Chemical Vapour Deposition– Higher tensile modulus– High cost– Aerospace/ military applications

Prepregs

• reinforcement material pre-impregnated with a resin matrix in controlled quantities

• The resin is partially cured (called B-state)• fabricator lays up the finished part and completes the

cure with heat and pressure

– Low void content– Control of fibre volume fraction– Control of laminate thickness– Labour cost lower– Better quality and conformity

Fabrication methods

• Vacuum Bag Moulding• Autoclave Moulding • Press Moulding• Pressure Bag Moulding• Filament Winding• Thermal Expansion Moulding• Pultrusion

A widely Used Example

CFRP

Carbon Fibre Reinforced Plastics(Carbon-epoxy composites)

CFRP

– CFRP piece consists:• 50-70% of woven Carbon fibre• 10-25% of Epoxy Resin• 8-28% of Polyamines

Carbon Fibre-How its made• Carbon Fibre production by Pyrolyzing

– 4-10µm in diameter – Coated with epoxy (easy to handle & better bonding)– many fibres are used in a yarn and yarn is woven into fabric

PAN (55%) RayonPitch(85%)

200-300 ℃

Oxidising

1500-2000 ℃

Carbonising

High Strength Carbon

2500-3000 ℃

Graphitising

High Modulus Carbon

Epoxy-matrix material• Used as a Coating, adhesive, insulator

• Dulux® Epoxy floor paint (heavy duty)

• Epoxide/polyamine (Resin/Hardener) Ex.:• Ethylene Oxide• Propylene Oxide

• The matrices most widely used for composites in commercial and high-performance aerospace applications are thermoset resins, consisting of polymer chains that are permanently cured into a crosslinked network when mixed with a catalyst,

Epoxies

• Highest strength/ stiffness• Low viscosity for wetting• Low shrinkage

• What is Stiffness?

CFRP-Properties

•High tensile strength/ weight•Very stiff•low thermal expansion•environmental resistance

Specific Density

Tensile Strength

Carbon Fibre 1.8 1.10 (for CFRP)Epoxy 1.2

Aluminium 2.7 0.23

• Can be Engineered to Suite the application

– add directional strength– high service temperature– impact resistance– improved hot/wet mechanical

performance– fire retardancy– Complex shapes– Can be automated

CFRP-Advantages• Due to the high specific modulus and strength of the materials, very strong

and stiff structures can be designed, with substantial weight savings.• The ability to align the fibre orientation with the direction of principle

stresses and, therefore, achieve high structural efficiency.• Exceptional environmental degradation and corrosion resistance properties. • Very low coefficient of thermal expansion, with the added possibility of

designing the material to give desired thermal expansion in a particular direction.

• Improved vibration damping properties.• Easy repairability of damaged structures.• Ability to manufacture complex shapes at lower costs compared with

fabricated or machined metallic alloys. • Time and cost reductions on tooling and manufacturing of one-offs,

prototypes and short length production runs. • Excellent fatigue life, i.e. carbon fibre composites can be designed to be

essentially fatigue free.• Improved energy absorbing safety structures.

Industry Applications• Aerospace

– Structural components, aircraft flooring, aircraft prototypes, unmanned air vehicles (UAVs), space structures, missile components

• Motorsport – Bodywork & structural components, engine covers, – underbodies, heat shields, impact structures, prototypes

• Marine – Hulls, decks, covers

• Sports – Bicycles, skis/snowboards, helmets, tennis racquets, kayaks, fishing rods, golf

clubs• Automotive

– Prototype panels, combination/checking fixtures, sports/niche car components, interior trims, springs, drive shafts, exhausts

• Others– Medical equipment, measuring equipment, piping, pressure vessels, robot arms,

radar reflectors, bridges

Boeing 787 - Dreamliner

Boeing 787 Dreamliner Largest & most critical application to rely on CFRP

• Close to100% of skin• 50% of all material of the plane• 80% lesser number of drill-holes/rivets• 20% saving on fuel consumption• corrosion and fatigue benefits - remain in

service for 12 years before its first structural test• assemble each 787 in just three days, down

from 11 days for the 737

Some Drawbacks

• Expensive• Non-homogeniety/ discontinuity• Difficult to machine

– Delamination– Potentially toxic dust formation– Fibre pull-outs– Tool wear

• Disposal can be expensive and environmentally hazardous

• Recycling is costly and may not give the same strength

Important websites

• www.toray.com• www.compositesworld.com• www.mmsonline.com• www.wikipedia.org• www.boeing.com• www.riversimple.com

Refferences

• Kenneth G. Budinski, Michael K. Budinski; Engineering Materials – Properties and Selection; Sixth Edition; Prentice Hall, 1999, pp125

Thank You

Any Questions?