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Department of Mechanical

Engineering

Mohammad Ali Jinnah U

Islamabad Campus

ME 6093Mechanics of Compos

Offered By: Dr Rizwan Saeed C

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Dr Rizwan Saeed Choudhry

BE NUST, Pakistan - 2002)

MS NUST, Pakistan - 2003)

MS The Uni. ofManchester UK - 2004),

PhD The Uni. of Manchester UK - 2009)

Post Doc Manchester 2009)

Post Doc Cambridge UK 2013)

Assistant Professor NUSTDec 2009 to 2015)

Current role: Assoc iate Professor

Web: www.ceme

Email: rizwan.cho

rizwan.sae

Profile: LinkedInProfGradIMMMIO

Professional EngineeDepartment of Mechanical

Engineering

Mohammad Ali Jinnah University

Islamabad Campus
http://www.cemecomposites.com/mailto:[email protected]:[email protected]://pk.linkedin.com/pub/rizwan-saeed-choudhry/7/502/546http://pk.linkedin.com/pub/rizwan-saeed-choudhry/7/502/546mailto:[email protected]:[email protected]://www.cemecomposites.com/

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Engineering


Islamabad Campus

About the Course

Course Learning OutcomesTo understand the different types of composite materials and their current and futuapplications in engineering.

To understand the effect of choice of processing route / manufacturing strategy on properties of composites

To design and analyze structures made of composites (mechanics of composites).

To familiarize students with advanced concepts of computer aided modeling and simfailure and damage in composites (FRC).

To develop an understanding of differences of testing standards for mechanical tescomposites as opposed to those of traditional materials.

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Books and ReferencesMain Text books:

1. Introduction to Composite Materials Design, 2nd Edition (2011) Ever J Barbero

2. An introduction to Composite Materials, 2nd edition By D. Hull & T. W. Clyne

Special Topics

1. Engineering Mechanics of Composites Materials 2nd edition Isaac M Daniel, Ori I

2. Material selection in mechanical design, 4th

edition, by M. F. Ashby

3. Principles of Composite Material Mechanics, 2nd Edition by Ronald F. Gibson

All other sources consulted will be referred to in slides

A note about slides: The slides for lectures have been prepared using various sources. For the lectweeks most of the slides are modified versions of Lecture slides used by Professor Paul J Hogg at

Manchester for the course Composites Science and Engineering

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Lesson Plan1. Introduction to Composites (constituent materials, forms and properties)

Week 1,2Related reading: Chapter 2 Barbero, Chapter 1,2,3 Clyne + Lecture Slides

2. Manufacturing techniques for composites and process selection methodologyWeek 3,4Related reading: Chapter 3 Barbero, Chapter 11 Clyne, + relevant portions of ch14 Ashby + Lecture Slides

3. Design for composites key considerations

Week 5Related reading: Chapter 1 Barbero, Chapter 1,2,3 Clyne + Lecture Slides

4. Structure property relationship and micromechanics of compositesWeek 6,7,8Related reading: Chapter 4 Barbero, Chapter 4,5 Clyne + Lecture Slides

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Lesson Plan5. Linear elastic stress analysis of composite structures (Macro-mechanics, ply-mec

Week 9,10,11Related reading: Chapter 5,6 Barbero, Chapter 5 Clyne + Lecture Slides

6. Mechanics of Short/discontinuous fiber reinforced composites (optional topic if Week 12Related reading: Chapter 6 Gibson + Chapter 6 Clyne + Lecture Slides

7. Mechanical testing of composites and testing standards

Week 13,14Related reading: Chapter 10 Daniel and Ishai + Lecture Slides

8. Failure theories for composites laminates and progressive damage modellingWeek 15,16Related reading: Chapter 7,8 Barbero, Chapter 8,9 Clyne + Lecture Slides

9. Introduction to FE analysis of composites using ABAQUS (Optional topic if time

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Structure

Credit Hours: 3-0 Contact Hours: 3-0

Final Exam: 40 - 50 %

Midterm: 20 - 30%

Quizzes: 10%

Assignments/Project: 20%

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Composite Materials - Basics

Composites are a heterogeneous combination of two or more materials

usudistinct properties which remain distinct even after forming the composite.

The performance and properties of the combination are designed to be supeof constituents acting independently.

Adhesive or Mechanical bonding between the constituents

Filler material reinforces a weak matrix

Matrix low density ; Filler strong, stiff Traditional examples : Wood, Bricks, Concrete

Advanced composite examples: Fibre reinforced plastics (FRP)CarboKevlar,

Natural fibre reinforced composites

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Introduction What are composites?

Dictionary definition:

A composite refers to something made upof various parts and elements

The different constituents must have twoprime characteristics

Chemically different

Insoluble in each other.

In almost all cases, there is a Strong and stiff component forming the

reinforcement

Soft constituent that binds thereinforcement Structural composites typically re

to the Macrostructural level:

e.g. matrix, particles, fibres

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Types of composites

Classification on basis of matrix Polymeric matrix composites

Metal Matrix composites

Ceramics matrix composites

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Classification of compositesThe first level of classification of composites is by matrix type

The major composite classes are

Polymer Matrix Composites (PMCs) Use a polymer-based material as the matrix, and a variety of fibres such as glass, car

the reinforcement

PMCs are used in the greatest diversity of composite applications, as well as quantities

They can be further classified into small groups according to the Fibre e.g. glass, carbon or aramid composites

Matrix e.g. thermosetting, thermoplastic or rubber composites

They can also be categorised into short-fibre reinforced composites, or contreinforced composites

Also known as FRP - Fibre Reinforced Polymers(or Plastics)

As these are the most common they will be the main focus of the course

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Classification of composites (cont)Metal Matrix Composites (MMCs)

Use a ductile metal such as aluminium for the matrix

Reinforced with fibres or particles of alumina, boron, silicon carbide

Increasingly found in the automotive industry

Ceramic Matrix Composites (CMCs) Use a ceramic as the matrix and reinforce it with short fibres or whiskers such as those

silicon carbide and boron nitride

Used in very high temperature environments

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Types of composites

Classification on basis of reinforcements Continuous fibre strands or roving Chopped strands in short length

Chopped strand mat

Chopped strand aligned mat

Fibre Roving

Woven Fabrics 2D and 3Dmade from roving or strands

Metal filament or wires Solid or hollow microspheres

Metal, glass or mica flakes

Single crystal whiskers of graphite, silicon carbide, copper etc.

Nano-particle and nano-fiber reinforcements

Robotic fibre placeme

f h i l h d li i h

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Classification of composites (cont)The second level of classification is by reinforcement form

Fibre reinforcement Fibre is characterised by a high aspect ratio, i.e. the length of the fibre is much greater

diameter

Fibres can be

Short i.e. where properties of composite vary with fibre length

Long or continuous, i.e. further increase in fibre length has no effect on the comp

properties. Long fibres typically have lengths comparable to that of the final part.are manufactured into preforms for ease of manufacturing

These are the most common and will be discussed in detail later on

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Classification of composites (cont)Whisker reinforcement

Characterised by aspect ratios of approximately 20-100

Particulate reinforcement Dimensions of particles are roughly equal. This category includes

Spheres, rods, flakes etc.

Mostly tend to be included for cost reduction purposes and are non-structural

To provide a useful increase in properties, the reinforcement has to beincluded at a sufficient volume fraction (typically >10%)

Particulate and whisker reinforcemen

are classified as discontinuous

reinforcements. This is especially so

MMCs where the volume fractions of

particles is quite low

Hi t f C it

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History of Composites1940s

PMCs used to produce materials with stiffnesses andstrengths that were higher than for the existingmaterials

Filament wound GRP rocket motors Prototypes for aircraft applications

Structural alloys susceptible to corrosion and creepdamage

Gordon Aerolite Spi

Fuselage from flax

No property advan

same as aluminium

Al shortage never

concept dropped

Department of Mechanical Mohammad Ali Jinnah U

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Improved structural response and corrosion resistance of PMCs

Initial development of MMCs

Idea was to dramatically extend the structural efficiency of metallic materials while retaadvantages

1960s

Commercial applications for PMCs in sporting equipment

Improved design and production capabilities, and PMCs lower in costs

Development of Boron and SiC monofilaments


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Cold war budgets allowed for significant research in high-performance materials

Military aircraft built with composite sections (tailskins &noncritical flight structures)

Energy crisis provided incentive for introduction of PMCs intothe manufacture of commercial aircraft

Development of carbon fibres High cost of SiC whiskers led to development of particulate

reinforcements for MMCs

Nearly equivalent strengths & stiffness as whiskers

Reduced costs, eased processing

MM

he


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Development of monofilament reinforced Ti MMCs

Designed for high temperature aeronautical systems: blades for gas turbine engines

Increased use of composites in military and commercial aircraft

Commercial aircraft use composites for critical load-bearing applications

Development of fibreglass structures for boats and marine applications

M j li ti f PMC i th 80

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Starship Bizjet ->75% of structuralweight wascomposite.

Global Market had grown from about 1000 tonnes in 1980 to 5000 tonnes of fibin 1985 and almost 10,000 tonnes by 1989

AV8B Harrierall composite wing for improvedpayload /range27% of structural weight is composite

Airbus A320all composite tail, up to15% of structural weightis composite

Major applications of PMCs in the 80

SAAB Grippen Wingall composite

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Specialist aircraft such as the B-2 stealth bomber mainly compo

radar absorbance and ability to manufacture suitable shapes. 4

(60% by volume) composite

Stealth

bomber

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New tough composites used for bigger composite wings

range up to 22% composite.

Re-vampingearlier

aircraft


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Development of MMCs for ground transportation, thermal management & electrpackaging

This market is significantly larger thanthe aerospace market

However market volumes are still very small

World market in 1999 was 2500tons

62% for groundtransportation(automotive and rail)


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p

Engineering Islamabad Campus

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Modern aircraft designed to use large quantities of carbon fibre

A380 (eta. 2006)

Combines Al & GRP as a multilayer material (GLARE)

25% weight saving & less susceptible to fatigue than Al

40% CFRP for wingbox = 1.5t weight saving

16% by weight total composites

787 Dreamliner (eta. 2007)

50% structural weight composites = 25t of CFRP per aircraft

Key driving factors are reductions in the cost to manufacture quality parts

17% fuel reduction over current generation

Demand outstripping supply

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A380

C i l

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Commercial aerospace use

Military aerospace use

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Military aerospace use

Development of composite military aerospace applications

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Where do we findcomposites now?

Glass Fibre

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Carbon Fibre

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MMCs & CMCs

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omposites driving forces

Criteria on which composites are selected depend on the industry in which they will

used

Aerospace: mainly weight reduction with increased stiffness/strength High scrap levels are (were?) tolerated

There is a preference for high performance materials in order to reach the weight sav Fibres need to be continuous and volume fractions need to be high

Transportation: Emphasis isdecreasing cost

Return on investment, comple

shapes, recycling, etc.

Need to reduce weight as incr

safety requirements = heavier

vehicles = worse fuel econom

Manufacturing routes need to

low-cost and high speed: fibre

volume fractions not so much

issue

Aerospace:Strength, stiffness,

weight, quality control

Mechanical Industry:Design, strength, quality

Automotive:Automated fabrication

Performance

1/Cost

Why composites?

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Why composites?Monolithic materials contain numerous flaws and cracks

This causes them to fail below their theoretical breaking point as the propagation of the flaw cauthe material

Fibre form still contains the same number of random flaws

However they are restricted to a small number of fibres with the remainder exhibiting the materiastrength

If a flaw causes failure within a fibre, it will not propagate to fail the entire assemblage of fibres

The fibres therefore more accurately reflect the optimum performance of the material

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Why composites?Fibres alone can only exhibit tensile properties along the fibres lengthsimilar to fibres in a rope

Need resin to bind them together

Composites can be engineered for high strengths and stiffnesses

ease of moulding complex shapes

high environmental resistance

low densities, etc.

The resultant material is superior to metals for many applications!

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The benefits of composite materials are traditionally based on

the following:

Corrosion resistance

Lightweight

High strength

High stiffness

Multifunctional materials: Structure of wood

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MSc Composites Science & Engineer ing

Wood is a natural composite

Requirements:

It has to be tall and straight

It must be strong and light and resist

bending forces

Controlled heat dissipation

Controlled moisture retention ... Etc.

It is composed of multiple fibre bundles

(lamellae) each of which contains multiple

layers of cellulose fibres in a lignin matrix

Lamellae are aligned on the long axis of

the wood

Superior bending and longitudinal stiffness

Alignment of cellulose fibres within

lamellae indicates stiffness & strength of

the wood

Anisotropy of wood

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py

Effects of Anisotropy:

Material has high stiffness and strength along fibres, but cracks can als

easily propagate along it

Cracks very difficult to propagate across the fibres

Wood composites

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p

Plywood:

Thin sheets of veneer that are cross-

laminated and glued together with a hot-press

Grain of each layer is positioned in a

perpendicular direction to the adjacent layer

Odd number of layers so that the panel is

balanced around its central axis

Bamboo:

Layered natural wood

composite

Structure of bone

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Bone:

Compact/cortical bone is the

structural part of bones Consists

of multiple osteons within a

matrix of old osteons

Osteons are aligned in the

direction of applied load

Structurally, each osteon is

composed of multiple lamellae

in a plywood type arrangement

(compact bone is known aslamellar bone in adults)

Within each osteons are

hydroxyapatite whiskers in a

collagen matrix

Outer lamell

I

Engineered materials

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Fibresprovide strength and

stiffness

Resin acts as a

binder and spreads the loadapplied to the composite betweeneach of the individual fibres and

protects the fibres from damage controls the transverse properties

Tensile Strain

Ten

sileStress

Fibre

Composite

Resin

The combination of resin and reinforcing fibres produces a composite who

properties are a combination of the properties of each of the constituents

Overall, the properties of the composite are determined by the:

Properties of the fibre (provide stiffness & strength)

Properties of the resin

Ratio of fibre to resin (Fibre Volume Fraction)

The geometry and orientation of the fibres

Reinforcements

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E-glass: Most common glass fibre

Useful balance of mechanical,

chemical & electrical properties

Glass fibres

Original structural reinforcement

& most common

Competitively priced & widely

available Ease of processing & good

handleability.

Carbon fibres

Best known & most widely us

high performance fibre

Wide range of mechanical

properties Linear stress-strain behaviour

Strength 3.45 GPa

Stiffness 75.8 GPa

Density 2.56 g/cm3

Diameter 8-15 mm

Cost ~70-150 /kg

Typical properties of carbon fibres

Strength 3.5-6.4 GPa

Stiffness 240-310 GPa

Density ~1.85 g/cm3

Diameter 5-10 mm

Cost ~1000-3000 /kg

Reinforcements

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Kevlar-49: Most common aramidreinforcement fibre

Aramid fibres Organic fibre

High tensile stiffness & strength

Low stiffness = ballistic grade

High stiffness = reinforcementgrade

Very poor compressive properties(similar to that of glass fibres)

Most commonly known as Kevlar

SiC & Alumina

Used in MMCs and CMCs

Good thermal stability

Boron fibres Monofilament wires

Excellent strength and stiffnes

More expensive than carbon f

Used in PMCs and MMCs

High performance

thermoplastics Highly drawn UHMWPE

Natural fibres

Derived from plants, i.e. eco-

friendly

Strength 3.45 GPa

Stiffness 180 GPa

Density ~1.4 g/cm3

Diameter ~12 mm

Cost ~1000-2000 /kg

Comparison of (UD) composite properties

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Unidirectional (UD) Carbonproperties are the highest of all common compos

Aramid fibres have excellent tensile properties but weak compressive propertie

S-Glass (high strength glass fibres) approach the tensile stiffness of aramids,

strengths of HS Carbon in addition to very high failure strains

E-Glass is a general all-rounder that possesses high failure strains

Comparative fibre costs

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Woven fabric - yarn UD fabric - roving

Matrices thermosetting resins

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Typical properties of unsaturated polyesters

Polyester resins

Most commonly used resins &

wide range of formulations,

curing agents, etc.

Acceptable mechanical properties& acceptable environmental

durability

Very good adhesion to glass fibre

High styrene emissions & high

shrinkage on cure

Vinyl ester resins

Similar processing to polyeste

Very high chemical and

environmental resistance

Better overall properties topolyesters

Higher cost

Strength 55-90 MPa

Stiffness 3.4-4.4 GPa

Strain to failure 1.6-4.5 %

Density 1.1-1.5 g/cm3

Cost ~70-150 /kg

Typical properties of vinyl esters

Strength 60-93 MPa

Stiffness 2.9-3.9 GPaStrain to failure 3.0-16 %


Cost ~150-300 /kg

Matrices thermosetting resins

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Typical properties of epoxies

Epoxy resins

Most used resin for advanced

composites

Very good mechanical and

thermal properties Good water resistance

Low shrinkage on cure

Needs proper mixing formulation

Expensive

Phenolics

High fire resistance & excellent

thermal properties

Cure by condensation reaction

resulting in voidy laminate

Cyanate esters

Superb electrical properties & low

moisture absorbance

Used in radomes, antennas, etc

Very expensive (~3000 /kg)

Bismalemides (BMI)

Superior to epoxies for hot/wet us

suitable for high operational temp >3500 /kg

Polyimides

Higher operational temps. than BM

Cures similar to phenolics

Extremely expensive (>5500 /kg

Strength 55-130 MPa

Stiffness 2.5-6.0 GPa

Strain to failure 3.1-15 %


Cost ~200-1000 /kg

Matrices thermoplastic resins

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Thermoplastic resins

Offer

Increased toughness

Higher strain to failure than

thermosets Improved impact resistance

Improved hot/wet resistance:

They do not absorb any

significant amount of water but

are subject to chemical attack

Indefinite shelf life

Can be molten and moulded as

needed

Problem

Operational temperature must be

below the Tg

Subject to creep at high

temperatures

Engineering thermoplastics

PA (Polyamide) Self-lubricating & exhibit goo

abrasion resistance

Good chemical resistance buthigh water absorption

PP (Polypropylene) Low density & low cost

High impact properties

PET (Polyester terephtalate) Comparable processing to PP

Higher service temperature &

Stiffer than PP

PEEK (Polyether ether ketone Highest performing engineeri

thermoplastic

High cost & cost of processin

Matrices other

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Metal matrices

Aluminium

Most common reinforced metal

Typically used as a pre-mixed

casting alloy but wrought alloycan be used for infiltration

casting

Titanium

Typically used with continuous

reinforcement due to difficulty

with processing titanium

Others Other metals, e.g. Cu, Be, Ag,

used to retain their excellent

thermal and electrical properties

and improve their thermal

expansion/ wear resistance

Ceramic matrices

Use of ceramic matrix is to

improve poor toughness

characteristics of these matric

Very few applications exist, mcommon being Carbon/Carbo

brakes.


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Consider the properties ofthe individual constituents

The mechanical properties of th

fibres are superior to monolith

materials especially as they are

light weight.


resins are worse than most

engineering materials


composite depends on theplacement of the reinforcement

Composites possess superior specific stiffness and strength than steel.

However this mostly occurs when properties are measured in the direction of th

fibres.

Specific property = property / density


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Metals: Properties are largely determined by

material supplier;

End-processors can do little to change

those 'in-built' properties

Composite material: Often formed at the same time as the

end-product is being fabricated ;

This means that the person who makes

the end-product creates the properties

of the material in use

Because of the large variation in material parameters including fibre stren

stiffness, volume fraction, length and orientation it is possible toengineer

designthe required properties and the direction in which they are required

Strain

Stress

Composite

Composite

Metals

Alloys

Controlling Anisotropy

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There are three levels of orientation

Random (quasi-isotropic properties)

Cross-ply (transversely isotropic)

Unidirectional (orthotropic)

Effects of anisotropy

Aligning fibres in direction of load

(i.e. producing unidirectional

composite) produces the highest

properties Perpendicular load carrying capac

becomes rather poor

Can be relieved by placing fibres

transverse direction, but lowers

effective properties

Benefits from anisotropy

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Orienting the reinforcements in the direction of the applied loads has asignificant effect on the properties of the final composite

Properties are roughly equal to the stiffness volume fraction of the

fibres

In unidirectional orientation, there are more fibres in the loading direction

than in the random orientation

Effect of aligning fibres

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For random orientatio

improvement of prope

over metallic material

not that significant.

Need to use CFRP

equates to higher c

Strengths

Weight reduction

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Weight reduction

High specific stiffness & strength

Low maintenance cost

Corrosion resistance

Design flexibility & integrated parts Large, complex structures can be created in one piece

Pigmentation and textures can be incorporated directly into thecomposite at the manufacturing stage

Environmentally friendly

Low energy consumption in manufacture.

Safety Crush structures

Durability

Carbon fibre reinforced plastics possess excellent fatigue properties

Glass fibre reinforced plastics are excellent electrical insulators

Comparison with other materials:Stiffness & Strength

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Stiffness Strength

Properties will vary with fibre

contents and orientations.

Lowest property for short &

random fibre composites, andhighest for UD fibre prepregs.traditionalmaterials

compositematerials

Stiffness & Strength

Comparison with other materials:Density

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Density: Composite materialshave a very low density

compared to metals and aretherefore of interest for light-

weight design

y

Comparison with other materials:Specific Properties

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Specific strengthSpecific stiffness

Why composites?Integrated parts

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Integrated parts

Safety

C it b b

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Displacement (mm)

Load(kN)

Initial Peak Load Average Crush Load

Region of

sustained crush

Load Fluctuation

Amplitude

Composites absorb more energyper kilo than metals in a crash Crushing pattern is stable unlike

that of metals that fail by buckling

Composites exploited in Formula 1

(since 1982) and trains

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Composite weaknesses

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Costs of processing still high

Most processing methods require a huge investment in manual labour and/or mach

Absence of mass production technology for high-performance composi

Typical routes are pre-preg which is performed either by manual layup or by tape

Recycling of thermosets impractical

Only real route apart from regrinding as filler is pyrolysis

Recycling of thermoplastics with glass fibres difficult

Option is to regrind long-fibre composites as lower grades for injection moulding

Lack of knowledge in designing with anisotropic materials

Composite weaknesses (cont)

i di l i

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Uncertainty regarding long-term properties

Factors such as moisture degradation, damage tolerance after impact requires larg

in design

Uncertainties in predicting failure modes

Crack propagation mechanisms, damage tolerance after impact delamination etc

Aircraft industry works on a zero crack tolerance approach (structures are therefor

Inadequate industrial capacity (world annual production of carbon only

tonnes/annum)

The use of just 20% structural weight of carbon in the Airbus A380 is consuming

production

Performance versus Production

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?

Ideal situation for composite takeup

would be to have high modulus

parts capable of being produced at

over 1000 parts per day

Factors favourable for metal substitution

C it ld d f j t b fit

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The gain achieved in using composites to

achieve these objectives is greater than the

costs associated with using composites

Composites are seldom used for just one benefit It is usual that a combination of properties is required before they are

used to substitute for alternative materials.

Most successful composite designs are NOT direct shape

replacements for an existing metal component.

Design should incorporate aspects of the composite Features such as anisotropy and mouldability should be used to achi

a cost effective product.

Inefficient manufacturing processes

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Prepreg (autoclave) prepregs were expensive

Capital equipment (Autoclaves, tape layers) are expensive, material

deposition rates and processing are slow

More than 70% of part cost from fabrication!

Costs

$ saved (Fuel) / kg weight reduction per lifetime

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Car

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Off-shore applications

Alternative energy

Infrastructure repair

Sustainable development

Passenger cars

Threats to composite industry

Recycling legislation

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Recycling legislation

Composite recycling is relatively difficult compared to metals and techniques for r

in their infancy

Rise in cost of oil

This has significantly impacted the cost of the resins over the past year

Drop in cost of oil/fuel

Less drive for weight saving in aircraft structures

Public misconceptions/ high profile failures

Failures such as that of Team Phillips (high-speed catamaran) due to delamination

carbon skins and the core

Metals fight back!

Aluminium industry keeps evolving: new alloys improve strength etc.

Natural fibre composites

Eco-composites

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Natural fibre composites

Can be considered as a carbon sink

Properties of natural fibre composites

can be almost as good as glass fibre

All-PP composites

100% recyclable (no

need to separate fibr

from resin)

Barriers for progress

Materials

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Materials

Poor understanding of structure-property relationships

Selection driven or limited by raw material costs, recycling and manufacturing tec

Design Lack of knowledge of designing with anisotropic materials

Lack of knowledge of designing for durability

Design limited bymanufacturing technology

Manufacturing

Absence of mass production technology (Cycle time < 1 min)

Requirement for same or lower cos ts than metals!

Systems approach to designing withcomposites

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Materials Design

Manufacturing

Department of MechanicalEngineering

Mohammad Ali Jinnah UIslamabad Campus

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Thank you!

w 01-02 me6093 intro (1)

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