Composite materials technology overview andrew george

Composite Materials

Technology Overview

Dr. Andrew R. George

Brigham Young University

May 18, 2015

BRIGHAM YOUNG UNIVERSITY

WHAT ARE COMPOSITES?

(BASIC CONCEPTS)


3

What are Composites?

Combine fiber reinforcement with a polymer matrix

4000 years ago Today


4


Applications


5


Applications


U.S. Composites Shipments

BRIGHAM YOUNG UNIVERSITY 6

Source: Lucintel

Structure of the Composites Industry


Compared to traditional materials (metals):

✓Disadvantages

✓(-) Greater materials cost and cycle time

✓(-) Less material characterization

✓(-) Less CAE/simulation tool development

✓(-) Lower service temperature

Composite Properties


• (+) Great engineering freedom

• (-) “Black aluminum”, wetting fibers

• (+) Light-weight

✓Save 10kg on A320

✓= 1974 L / year / plane

✓3404 planes

✓= 6,7M L / year



9

Source: BTG

Composites



10


•Compared to traditional materials (metals):

✓(+) Superior corrosion resistance




✓+Superior crash performance

HP Composites Wichita State University




✓(+) Superior crash performance

BMW Megacity Bumper carrier




✓(+) Better dampening properties

ACPT auto driveshaft study


Steel

Al

Composites

Thermal Expansion

Steel

Al

Composites

Fatigue Resistance




✓Disadvantages

✓(-) Low ductility

✓(-) Damage susceptibility

✓(-) Hidden damage

✓Advantages

✓(+) Easily moldable

✓(+) Easily bondable / part consolidation

✓(+) Low electrical conductivity / high stealth



Composites Categories

Advanced Thermoset Advanced Thermoplastics

Engineering Thermoset Engineering Thermoplastic

High temperature capabilities

High Cost

High strength

High modulus

Good fiber wet-out

Brittle

High cost

Solvent resistance

High toughness

Poor wet-out

High strength

Low cost

Excellent wet-out

Moderate strength

Brittle

Low cost

Standard TP mfg

Short fibers

Moderate strength

Good toughness


RESINS

18 BRIGHAM YOUNG UNIVERSITY

Resins

• Resin = matrix

• Some properties of the composite are dominated by the matrix

Property Cause

Resistance to solvents or water Polarity

Gas permeability Crystallinity

Fire resistance Aromaticity or halogen content

Thermal resistance Molecular weight, internal stiffness

Weather resistance Aliphatic content, additives and fillers

Toughness Aliphatic content, rubber tougheners

Wet-out of fibers Molecular entanglement (viscosity)

Electrical properties Polarity and filler content


Resin Choices

• Unsaturated polyesters (UPE’s)

• Vinyl esters

• Epoxies

• Phenolics


Resins


Polymer Chemistry! (don’t be afraid)

• Increases in molecular weight (length of the polymer chain) result

in increases in most mechanical and thermal properties

✓Entanglement inhibits molecular motion

Resins


Typical Polymer

Heat

Deflection

Glass

Transition (Tg)

Decomposition (Td) { Melting (Tm)

Temperature

Tg Tm

Td

Temperature

Fle

xib

ility

Heat Deflection Test (HDT)

Resins


Increases in molecular weight (length of the polymer chain)

result in decreases in ease of processing

Low viscosity fluid High viscosity fluid

Resins


The Great Dilemma in Polymers

• Polymers must have good

properties

✓Good properties are favored by

high molecular weight

• Polymers must have good

processing

✓Good processing is favored by

low molecular weight

Molecular Weight

Me

ch

an

ica

l P

rop

ert

ies

Molecular WeightE

as

e o

f P

roc

es

sin

g


The Great Dilemma In Polymers

•Thermoplastics meet the dilemma by compromise

✓High enough molecular weight to get adequate properties

✓Low enough molecular weight to process OK

•Thermosets meet the dilemma by crosslinking

✓Low molecular weight initially (for wetout and processing) followed by curing to increase molecular weight

✓No compromise is required


Crosslink bonds

Covalent bond

(shared electrons) Polymeric molecules

Crosslinking


The presence of crosslinks dramatically changes

the viscosity, mechanical and thermal

properties of polymers

Crosslinking


Thermoplastics…

•Are not crosslinked and so they melt

•Are molded as molten liquids

•Are cooled to re-solidify

•Can be re-melted repeatedly

candy


Thermosets…

•Are crosslinked and do not melt ✓Crosslinking is sometimes called curing

•Are molded as room temperature liquids or low-melting solids

•Are heated to solidify (harden)

•1-time only

cake

Coconut-filled cake

= a reinforced composite


Vis

co

sity

Time/Temperature

Liquid-Solid Line

Solids

Liquids Thermoset

thinning due to

temperature

Thermoset

crosslinking

Thermoset

combination

(What is seen)

Gel Point

Thermoplastic

Viscosity

Processing Window


Thermal Properties

Typical Thermoplastic

Heat

Deflection

Glass

Transition Decomposition {

Melting

Typical Thermoset

Heat

Deflection

Glass

Transition Melt Decomposition X

Temperature


Thermoplastics and Thermosets

• Melting vs. decomposition

Melted

Decomposed


Crosslinking =

• Strength (good)

• Flexibility (poor)

• Thermal (good)

• Creep (low)

• Ability to wet-out reinforcements

(good)

• Ability to cure at room temperature

(some)

Thermosets


Thermosets


Thermoset resins depend upon two chemical

reactions for their properties:

1. Polymerization

2. Crosslinking (curing)

Unsaturated Polyesters (UPE)


• Largest group of thermosets

• Least expensive thermoset

• Easiest to cure resin

• Usually reinforced with fiberglass



• Polymerization of unsaturated polyesters occurs

by a “condensation” reaction

✓Polyester = a polymer in which ester groups are the

repeating units formed in polymerization

✓Polyesters are made from two types of monomers:

•Di-acids

•Di-alcohols (“Glycols”)

Polyester Polymerization



Monomers

Glycols G

(Di-alcohols)

Acids A

(Di-acids)

G

G

G

G

A

A

A

A

A

Polyester polymer



One end of the di-acid (the OH group) reacts

with one end of the glycol (the H group) to

form water (H−OH)

The water separates from the polymer and condenses

out as a liquid (hence “condensation reaction”)


HO―G―OH

Glycol

O H C A C O H

O O

Di-acid

Step 1: Monomers react

+

Step 2: New molecule reacts with new monomers

O O

HO―G―O―C―A―C―OH + HO―G―OH

Glycol

O H C A C O H

O O

Di-acid

+

Ester Ester Ester

O O O O

HO―C―A―C―O―G―O―C―A―C―O―G―OH

HO―G―O―C―A―C―OH

O O

Ester

New bond

+ H2O

+ 2 H2O



Building your perfect UPE


“Cooking recipe” - The types of di-acids and

glycols and their percentages determine the

properties of the unsaturated polyester.

Example: the amount of unsaturated monomer

controls the amount of crosslinking (crosslink density)

“Unsaturated” = contains carbon-carbon

double bonds after polymerization (but

before crosslinking)



Structure Name Comments

Fumaric acid

Maleic acid

Maleic anhydride

Trans isomer,

highly reactive,

crosslinkable

Cis isomer,

converts to fumaric acid,

crosslinkable

Readily converts to

maleic acid and

fumaric acid

in presence of water,

crosslinkable

Choice: unsaturated di-acid monomers


Structure Name

Orthophthalic acid (ortho)

Orthophthalic anhydride

Comments

Low cost,

styrene compatible

Converts to ortho

Isophthalic acid (iso) Strength, thermal,

water/chemical resistance

Choice: saturated di-acid monomers


Aromatic

Contains benzene

rings

Aliphatic

Does not contain

benzene rings

Organic molecules are either:

aromatic or aliphatic (Determines several key properties)



CC...C C...

CC

CC

C

C

C...OC

C

C

C

C

CC

C

C

C

C

C

C

OCC C

O

OH OH

OHOHOH

C

C

CC

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

....C C...

C.......C

a) Aromatic group (benzene) b) Polystyrene (pendant

aromatic)

c) Epoxy (aromatic backbone)

d) Phenolic (aromatic network)

CC...C C...

CC

CC

C

C

H

H

H

H

H

H

Aromatic molecules

CC...C C...

CC

CC

C

C


Aliphatic molecules

C C

C C

H

H

H H

H

H

H

H

C

H

H H

C C ― ― │

COOH

│

│ │

HOOC H

H

C

C C

C O

O

C

H

H

H H

H

HH

HH

H

( )n


Aromatic

Increased:

✓Strength and

stiffness

✓Flame resistance

✓Thermal properties

Aliphatic

Increased:

✓Elongation

✓Toughness

✓UV/oxidation

resistance



Halogen atoms (F, Cl, Br, I) add flame

retardancy

Smoke evolution increased halogens, but that

smoke smothers the flames



Halogenated polymers

)(n

)(n

C

Cl

C...C C...

...C C C C...

F F

FF

C

C

C

C

C

C

Br

BrBr

C...

Br

OCCC

O

Polyvinyl chloride (PVC)

Polytetrafluoroethylene (PTFE)

Brominated Epoxy


Structure Name

Terephthalic acid (tere)

Adipic acid

Tetrabromophthalic

anhydride

Comments

Thermal stability

Tough,

weatherable

Flame retardance

Chlorendic acid Flame retardance,

chemical resistance

Choice: saturated di-acid monomers


Structure Name Comments

Ethylene glycol

Propylene glycol

Diethylene glycol

Neopentyl glycol

Bisphenol A

Low cost

Styrene compatibility

Flexibility, toughness

Weathering,

water/chemical

resistance

Strength, toughness,

water/chemical

resistance

Choice: saturated glycol monomers


COCCOCCCCOH

O O O

COCCCCOCCOC

O O O

C OH

Iso (meta)

Isophthalic Polyester

unsaturationunsaturation

CCOCCOOC

O

CCC

OH

O

C

C

C C

C

C

O

O

C

C C C O

O

C O

C

C

C

O C C

OH

C

Bisphenol A Fumaric Acid Polyester

(Crosslinking occurs at the carbon-carbon double bonds)

Acid Acid Acid

Acid Acid BPA BPA

Glycol Glycol

Glycol Glycol Glycol



Fumaric acid Fumaric acid Isopthalic Acid

Isopthalic Polyester

Bisphenol A Fumaric Polyester

-C-O-

UPE Crosslinking

•Unsaturated polyesters cure by “addition” / “free

radical” reaction

✓Started by an initiator molecule reacting with a carbon-

carbon double bond

✓Proceeds as a chain reaction

•Once started, it will keep going until stopped

•Doesn’t need more initiator

•Makes its own reactive sites


Initiators

• Initiators sometimes called catalysts.

•The most common initiators are peroxides.

✓Split into free radicals which react easily with the double bonds.

✓Free radicals have unshared electrons.

I–I I + I

Peroxide Initiator Free radical

Reaction can be heat or chemical induced


C C C C

Unsaturated bonds

Polyesters must have unsaturated portions to crosslink

UPE Crosslinking


C C C C

I Initiator ●

Initiation reaction

UPE Crosslinking


C C C C

I

● ● ●

UPE Crosslinking


C C C C I

●

Bond (2 electrons)

Unshared electron or

free radical (reacts readily)

Formation of a bond and a new free radical

The new free radical needs to encounter (collide with) a double

bond on another polymer chain

Long and entangled (highly viscous), the chances of lining up are

not good

UPE Crosslinking


•Dissolve (dilute) the polymer in a solvent

✓Ideally, the solvent will react during crosslinking

•Called “reactive solvents” or “reactive diluents” or “co-reactants”

•Styrene (most common diluent)

•Added benefit: The solvent will also reduce the

viscosity; resin wets the fibers better

C

C

C

C

C

C

C C

or

UPE Crosslinking (Solution)


C C C C I

●

Bond (2 electrons)

Styrene molecule

is attacked at

non-ring double bond site C

C

C

C

C

C

C C

UPE Crosslinking


C C C C I

Bond (2 electrons)

Formation of a new bond

and a new free radical

C

C

C

C

C

C

C C ●

Can link to another unsaturation site

(usually on another styrene molecule or another polymer)

UPE Crosslinking


C C C

C I

Styrene

C C C C

New free radical

●

New bonds

(crosslink)

The new free radical is available to react with another double bond

UPE Crosslinking


• The addition reaction continues until one of the following conditions is met:

✓Nothing more to bond with

•Reactive diluent (styrene) is not available

•Stops encountering other polymers’ double bonds

–Post-curing can improve crosslinking

✓The free radical site meets another free radical site on another polymer

✓The free radical site meets another initiator free radical

•Danger of adding too much initiator

✓The free radical reacts with a terminator molecule

•Ozone

UPE Crosslinking


Inhibitors

…Added to increase storage time, usually by the resin manufacturer

Inhibitors typically absorb free radicals, protects from sunlight, heat, contaminants, etc.

To cure, must add sufficient initiator to overcome the inhibitors


Promotors (accelerators)

•Added to polymer to make the initiator work more efficiently or at a lower temperature

✓Each peroxide has a temperature at which it will break apart into free radicals, it’s usually above room temperature

✓For room temperature curing, a chemical method for breaking apart peroxides is needed

•Most common = cobalt compounds and analines (DMA)

•Never add a promoter directly into an initiator


Additives

•Components with various functions not

related to curing

✓Fillers (to lower cost and/or give stiffness)

✓Thixotropes (to control viscosity)

✓Pigments

✓Fire retardants

✓Surfactants (to promote surface wetting)

✓UV inhibitors/Anti-oxidants


212

440

Tem

pera

ture

(°F

)

Peak Exotherm Temperature

Gel time

Time to peak

exotherm

UPE Crosslinking


Epoxies


Epoxies

•Second most widely used family of thermosets (after polyesters)

•Large portion of uses are non-reinforced (adhesives, paints, etc.)

•Circuit boards = largest reinforced application (low conductivity, low volatiles)

•Advanced composites use epoxies because of:

✓Thermal stability

✓Adhesion

✓Mechanical properties


H―C―C―R │ │ H H

O

H―C―C―C―R

│ │ H H

O

│ H

│ H

a) Epoxy group

b) Glycidyl group

“R” = Any organic chemical group

Epoxies


C C

Epoxy ring – where crosslinking occurs

O C

C

O

( )n

Polymer portion

Number of repeat units

Epoxies


―CH2―C―CH2― │ CH3

CH3 │

HO― ―OH

Bisphenol A

Cl―CH2―CH―CH2

O

+

Epichlorohydrin

―CH2―C―CH2― │ CH3

CH3 │

―O― ―O― CH2―CH―CH2

O O

CH2―CH―CH2 + n(HCl)

Diglycidyl Ether of Bisphenol A (DGEBPA)

Glycidyl

( )x

n reactions

Epoxy Polymerization (condensation)


Epoxy Properties − chain length (n)

Number of repeat

units (n)

Heat Distortion Temperature

(HDT) (°F/°C)

Physical state

2 105/40 Semi-solid

4 160/70 Solid

9 265/130 Solid

12 300/150 Solid


Epoxies

The number of epoxy groups determines the

amount of crosslinking.

Epoxy groups are at the ends of a chain, but the

molecule can have more than just 2 ends (“higher

functionality”).

This makes higher crosslinking density, gives thermal

stability but requires high curing temperatures


O

CH2―CH―CH2―O―

O―CH2―CH―CH2

O │

―O―CH2―CH―CH2

O

Trifunctional: Multiple epoxy groups increases crosslinking

Epoxies


Tetraglycidylmethylenedianiline (TGMDA)

Tetraglycidyldiaminodiphenylmethane (TGDDM)

Standard of high performance resins for 40 years

Exotherm can be very high (depending on curing agent)

High thermal stability, high degree of crosslinking

Epoxies


CH2―CH―CH2

O CH2―CH―CH2

O

H2C―CH―CH2

O

H2C―CH―CH2

O

―CH2― N― ―N

―C― │

CH3

CH3

│ H2C― CH―O― ―O― CH2―CH―CH2

O O

Br

Br

Br

Br

A flame retardant epoxy

Low flame spread but high smoke and choking fumes.


Flexibilized Epoxy

OO

CCOCCOCCC

OH

C O C C C

OH

O C C O C C C

OH

N

C

C

C

NH2

C C C

OH

O C C O C C CO

Flexibility allows motion and that absorbs energy (bullet-proof vest effect)


Epoxy curing


•Epoxies use hardeners instead of initiators for

curing.

✓Hardeners = react with (open) the epoxy ring

✓Hardeners have active groups at both ends


Epoxy Crosslinking

C C

Epoxy ring

O C

O

( )n

Epoxy ring

N

N

H H

H H

N

N

H H

H H

C

Hardener molecules have two

reactive ends, so they can each

react with two epoxy molecules.

82

H

HN

C

C...

C

O

C C...

N

C

C...

C C C...

O

C C

H H

Hardener

Epoxy

The other ends can also react (usually with other epoxy molecules).

Cured Polymer H

~

~

Epoxy Crosslinking


Building your perfect Epoxy

•Many different hardeners are available to cure

epoxies.

✓Very active ends on the hardener molecule allow

crosslinking at lower temperatures

•Hydrogens attached to highly electronegative atoms are

very active

•Nearby aromatic groups decrease activity, but increase

mechanical and thermal properties

•Nearby large groups of atoms hinder access and

therefore decrease activity (but increase stiffness)



Choice: hardener Hardeners Advantages Disadvantages

Aliphatic amines Convenience, low cost, room

temp cure, low viscosity

Skin irritant, critical mix

ratios, blushes

Aromatic amines Moderate heat resistance,

chemical resistance

Solids at room temp, long

and elevated cures

Polyamides

Room temp cure, flexibility,

toughness, low toxicity

High cost, high viscosity,

low HDT

Amidoamines Toughness Poor HDT

Dicyandiamide Good HDT, good electrical Long, elevated cures

Anhydrides Heat and chem resistance Long, elevated cures

Polysulfide Moisture insensitive, quick set Odor, poor HDT

Catalytic Long pot life, high HDT Long, elevated cures,

poor moisture

Melamine/form. Hardness, flexibility Elevated temp cure

Urea/form. Adhesion, stability, color Elevated temp cure

Phenol/form. HDT, chem resistance, hardness Solid, weatherability


Epoxy and Polyester Comparison

Comparisons Polyester Epoxy Active site C=C

Crosslinking reaction Addition/free radical Ring opening

Crosslinking agent Initiator (peroxide) Hardener

Amount of x-link agent 1-2% of resin 1:1 with resin

Solvent/viscosity Styrene (active)/low Infrequent/high

Volatiles High Low

Inhibitors, accelerators Frequent Infrequent

Reactant toxicity Low Moderate

Cure conditions Room temp or heated Heated (some room)

Shrinkage High Low

Post cure Rare Common

O

C C

Property Polyester Epoxy

Adhesion Good Excellent

Shear strength Good Excellent

Fatigue resistance Moderate Excellent

Strength/stiffness Good Excellent

Creep resistance Moderate Moderate to good

Toughness Poor Poor to good

Thermal stability Moderate Good

Electrical resistance Moderate Excellent

Water absorption resist Poor to moderate Moderate

Solvent resistance Poor to moderate Good

UV resistance Poor to moderate Poor to moderate

Flammability resistance Poor to moderate Poor to moderate

Smoke Moderately dense Moderately dense

Cost Low Moderate

Epoxy and Polyester Comparison


Vinyl Esters


www.corrosionfluid.com

Vinyl Esters

•Epoxy resins that have been modified so that they can

be cured like a polyester

✓The modification is usually a reaction with an acrylic (acrylic

modified epoxy)

✓The modification must substitute a carbon-carbon double

bond for the epoxy ring


C C C

C (

)n

Unsaturated

end group

Unsaturated end group

Often an epoxy backbone

Vinyl Esters


C

C

C

C

O

O

C

C

C

C

O

C

C

C

C

O

O

C

C

C

C

O

C

C

C

O

O

C

C

C

C

O

OHOH OH

Epoxy Novolac Vinyl Ester Resin

CCCOCCCO

OH O

C

CC C C O C C C O

OHO

C

C

C

Bisphenol-A Epichlorohydrin-based vinyl ester

( )n

Vinyl Esters


•Almost all properties of vinyl esters (and cost) are intermediate between polyesters and epoxies

✓Water and chemical resistance

✓Electrical stability

✓Thermal stability

✓Toughness

✓Low volatiles during manufacture

✓Low shrinkage

Vinyl Esters


Phenolics


•Both polymerizing and crosslinking

reactions occur simultaneously

✓The reactions can be stopped before completion to

still allow molding, but easier handling of the polymer

✓The resultant intermediate material is called the B-

stage and the processing is called B-staging.

Phenolics


C......C

C

C...

OH

C

C

...C C

OHOH

C

CC

C

OH OH

...C C...

OH

+

3-D Phenolic

Crosslinked Network

Formaldehyde Phenol

Condensation of

Water

* *

*

(* = Active site)

O H

H H C

O

Phenolics



Problem Solution

Toxic monomer

(formaldehyde)

B-staging to novolac (solid)

or resole (liquid)

Condensation of water Slow cures and venting of

mold

High shrinkage Fillers (minerals, sawdust,

wood flour, ground nut

shells, etc.)

Brittleness Fillers (selected) and

thickness of parts

Inconsistent color Black pigment

Phenolics

96

―CH2― ―CH2― ( )n

│

│ CH2

O │ CH │ CH2

O

│

│ CH2

O │ CH │ CH2

O

│

│ CH2

O │ CH │ CH2

O

Novolac (Epoxydized phenolic resin)

High density of crosslink sites can give high Tg. High temp cure.

The central chain is a repeat unit (n repeats)


Phenolics

• Highly Aromatic

- Very low flammability and low smoke

- Very stiff and hard

- Very low heat transfer

- High thermal stability

- Good electrical properties

- Moderately low price (10-15% above polyesters)


Phenolics

•Applications

✓Interiors of public transportation

✓Glue for laminates (such as plywood)

✓Electrical switches and other equipment

✓Molded parts in moderately hot environments (e.g. near the motor of an automobile)

✓Rocket exit nozzles and carbon-carbon composites (ablation)


10 20 30 40

Vinyl Ester

Epoxy

FR Polyester

Phenolic

(ASTM E-162 for thermoset

composites)

Vinyl Ester

Epoxy

FR Polyester

Phenolic

(ASTM E-662 for thermoset

composites)

100

Specific Optical Density Flame Spread Index

200 300 400 500 600

Phenolics


106-

105-

104-

103-

102-

10-

1-

0 1000 2000 3000 4000

-18 538 1093 1650 2204

Temperature

oF oC

Exposure

Time

(sec)

Epoxy C

om

po

sites

Poly

imid

es

Adva

nced

Meta

lics

Carbon-Carbon

Experimental

Ablative Materials

(such as phenolics)

Mechanical Endurance at high T


Rocket Exit Throat Exit Nozzle

(Ablative

Material)

10 oF

500 oF

4000 oF

Rocket

Motor

Rocket

Propellant

Nose

Cone

Phenolics in Ablation


• Aromaticity comes from cyclical groups

other than benzene

✓These rings give even higher thermal stability.

✓Very difficult to process.

✓Usually also contain many benzene rings, too.

• Example: Bismaleimide (BMI)

CC C

CN

C

O

O

CC

CN

C

O

O

Crosslink sites

Polyimides


www.sldinfo.com

│ CH3

C―O C

C

C N

C

O

O

C― ―O― C―C―C

O

O― C―C―C

O

C C

C N

C

O

O

O―C

Ι ―C

O

O

C―C―C―O―

C―C―C―O

│ │

│

│

│

│

│

Very stiff and very high thermal resistance

An imide-based epoxy


Polyimides


Composites Categories

Advanced Thermoset Advanced Thermoplastics

Engineering Thermoset Engineering Thermoplastic

High temperature capabilities

High Cost

High strength

High modulus

Good fiber wet-out

Brittle

High cost

Solvent resistance

High toughness

Poor wet-out

High strength

Low cost

Excellent wet-out

Moderate strength

Brittle

Low cost

Standard TP mfg

Short fibers

Moderate strength

Good toughness


Engineering thermoplastics

•Traditional resins

✓Nylon

✓Polycarbonate

✓Polypropylene

•Usually fiberglass, in very short fibers (whiskers)

•Processed on conventional thermoplastic molding equipment

✓Injection molding

✓Extrusion

✓Thermoforming


2.2 14 0.22 80 276

1.7 10 0.16 60 207

1.1 6.9 0.11 40 138

0.6 3.4 0.05 20 69

0% 10% 20% 30% 40% 50%

Co

eff

icie

nt

of

Th

erm

al

Ex

pa

ns

ion

(p

pm

/oC

)

Fle

x M

od

ulu

s (

GP

a)

Izo

d Im

pa

ct

(J/m

m )

Elo

ng

ati

on

(%

)

Ten

sile

Str

en

gth

(M

Pa

) CTE

Flex Modulus

Izod Impact

Elongation

Tensile Strength

(Scales for each property)

Fiber content in nylon


Fiber content:

Advanced thermoplastic composites

•Very long or continuous fibers

•High mechanical properties

•Processed by several techniques

•Compression molding

•Conventional layup (manual and automated)

•Thermoforming

•Diaphragm molding

•Co-mingled fibers


Polyether ether ether ketone (PEEK)

Ether link Ether link Ketone link

C O O

O )n (


Polyetherimide (PEI)

( ) n O

N

O

O

O

N

O

O

C

CH3

CH3

Ether groups

Imide group


S O C ( )n O

CH3

CH3

O

O

S S S ( )n

a) Polysulfone (PSU)

b) Polyphenylene sulfide (PES)

Sulphur-containing advanced thermoplastics


www.mprplastics.com

Polybenzimidazole (PBI)


PBI foam

Conventional foam

114

Polybenzimidazole (PBI)


Thermoplastic − Advantages

•Toughness

•Solvent resistance

•Re-molding

•Processing by conventional thermoplastic

method (engineering thermoplastics with very

short fibers)

•Processing times (cool versus cure)

•Shelf life


Thermoplastics − Problems

•Fiber wet-out (long fibers)

•High processing temperatures (especially

advanced thermoplastics)

•More difficult layup (not tacky)

•Higher cost


Non-polymer matrices

• Other types

✓Carbon-carbon (C/C)

•3000°C (5400°F)

✓Metal matrix (MMC)

•Even higher T with ceramic fibers

•Matrix = Mg, Ti, Al

•Fiber = Boron, SiC, carbon

✓Ceramic-matrix (CMC)

•Matrix/fibers = carbon, SiC, alumina


REINFORCEMENTS


•Some properties of the composite are dominated

by the reinforcement

✓Reinforcements are anisotropic materials

✓Reinforcements typically carry over 90% of the load

✓Longer fibers can carry more load

Reinforcements


Reinforcements

Fiberglass Aramid

Carbon/Graphite

UHMWPE Basalt Ceramic whiskers


Composite usage by weight

•Market Share by weight

✓96% Fiberglass

✓4% Advanced Composites

•Market share by $

- 77% Fiberglass

- 23% Advanced Composites


General Fiber Characteristics

•Aspect Ratio (length/diameter)

•D = 7 microns (hair = 100 microns)


Fiber Selection


Fiber Selection (Specific Properties)


•Least expensive fiber

•80-90% of composites (by volume)

•FRP = fiberglass reinforced plastics

Fiberglass


Fiberglass – Production


Property Type of fiberglass

E-Glass S-Glass C-Glass

Coefficient of thermal expansion (10-6 ˚C) 5.2 5.7 7.3

Specific heat (kJ/kg ˚C) .810 .737 .787

Softening point (˚C) 846 970 750

Dielectric strength (kV/cm) 103 130 –

Index of refraction 1.562 1.525 1.532

Weight gain after 24h in water (%) 0.7 0.5 1.1

Weight gain after 24h in 10% HCl (%) 4.2 3.8 4.1

Weight gain after 24h in 10% H2SO4 (%) 3.9 4.1 2.2

Fiberglass – Grades


•Stiffest of the common fibers

•Generally the best specific strength and specific stiffness

Carbon

Car and Driver


Carbon – Production


Stabilization step (PAN):



Carbonization step:



Graphitization step:



Carbon fiber structure:



•Material changes from PAN fibers to carbon

fibers:

✓Diameter cut in half

✓Tensile strength / modulus increase by 20x

✓Elongation-to-failure drop from 4.8 to 1.6%

✓Resistivity drop from 454 to .0008 ohm-in

✓Cost increase from $3.88 to $8.30 per pound

•Carbon vs. graphite



Fiber Type Tensile Strength,

ksi (MPa)

Tensile Modulus,

Msi (GPa)

Elongation to

Break (%)

Pan-based Fibers

Standard modulus 512 (3,530) 33 (228) 1.5

Intermediate modulus 880 (6,067) 42 (290) 2.1

Ultra-high modulus 554 (3,820) 85 (586) 0.7

Pitch-based fibers

Standard modulus 276 (1,903) 55 (379) 0.5

Intermediate modulus 305 (2,103) 75 (517) 0.4

Ultra-high modulus 527 (3,633) 128 (883) 0.4

Rayon-based fibers

Standard modulus 119 (821) 5 (35) –

Carbon – Grades


Carbon Fibers

•Applications

✓Based on strength, stiffness, and low weight

✓Based on thermal properties

✓Based on chemical inertness

✓Based on rigidity and good damping

✓Based on electrical properties

✓Based on biological inertness and x-ray permeability

✓Based on fatigue resistance and self-lubrication


CFRP Forecast – 25% growth/year


0

50

100

150

200

250

300

350

2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Thermoplastic / Electronics

Transportation / Marine

Sporting Goods

Infrastructure / Construction

Oil/Off-shore Drilling

CNG / Industrial

Automotive

Alternate Energy / Wind Energy

Aircraft / Aerospace

BTG Composites Inc. 2014

•Toughest of the common fibers

Aramid


Aramid


Impact toughness of pressure bottles

Aramid fiber reinforced

Carbon fiber reinforced

Impact energy, ft-lb

Pre

ssure

str

ength

rete

ntion,

%

5 10 15 20 25 30 0

25

50

75

100

Aramid


• Ballistic Protection

✓Stop the bullet

✓Spread the energy

Threat Level Number of

Layers

Ammunition

Stopped

2A 22 9mm

2 32 44 magnum,

357 magnum

3A 40 Wad cutter,

240 grain

bullet

Aramid (and UHMWPE)


Fiber-Matrix Interactions

•Wetting / bonding of matrix on fibers

•Sizings / Finishes

✓Protect the brittle fibers from mechanical damage

✓Enhance the bonding of the fibers to the matrix

•Polyester and fiberglass


Fiberglass

Sizing or coupling agent

...O Si O Si O...

OH

OH

OH

OH

....C C O C C C

O

C C...

CH3 Si O C C C

CH3

C C C C...

CH3 Nonpolar regions (weak attraction)

d-

d-

d+

d+

d+ − A highly polar molecule

− Largely non-polar with a polar end Polyester

− Mixed polar/non-polar

Polar

regions

attract

Non-polar



Common failure modes for polymeric matrix

composites



•Measurement of Fiber-Matrix Bond Strength

✓Bias tensile / Short Beam Shear / Inter-Laminar Shear

Force

Composite sample that is

too thick and short to bend

Supports


Northwestern U.


REINFORCEMENT FORMS


Reinforcements: various terms

•Roving / Tow (yarn)

✓Tex = grams in 1 km

•Fabric


Fabrics

•Fabric configurations

✓Mats, weaves, NCF, UD prepreg

Schürmann, Konstruieren mit Faser-Kunststoff-Verbunden, 2007

Saertex Toho-Tenax


Fabrics


Mat Plain Unidirectional Non-crimped

Weave Weave Fabric (carbon)


•Laminate

•Sandwich


Sandwich / Cores

•Stiffness is proportional to thickness

✓Add thickness without adding weight

Jungbluth, “Verbund- und Sandwichtragwerke” Springer-Verlag 1986


Sandwich / Cores

• Honeycomb

• Folded

• Foam

IFB-Stuttgart

Rohacell



•Preform (binders / tackifiers, net-shape)


Braiding

(IFB-Stuttgart)


Embroidery

(IFB-Stuttgart)

Tailored fiber placement (TFP)


CONCLUSIONS


Composites

Succeeding in current products from airplanes to bathtubs


158

THANK YOU


Documents

Composite materials technology overview andrew george