ISSUES TO ADDRESS... What are the classes and types of composites ? Why are composites used instead of metals, ceramics, or polymers? How do we estimate

ISSUES TO ADDRESS...

• What are the classes and types of composites?

• Why are composites used instead of metals, ceramics, or polymers?

• How do we estimate composite stiffness & strength?

• What are some typical applications?

Chapter 16: Composite Materials

Composites

• Combine materials with the objective of getting a more desirable combination of properties– Ex: get flexibility & weight of a polymer plus the

strength of a ceramic

• Principle of combined action– Mixture gives “averaged” properties

• Composites: -- Multiphase material with significant proportions of each phase.

• Dispersed phase: -- Purpose: enhance matrix properties. MMC: increase y, TS, creep resist. CMC: increase Kc

PMC: increase E, y, TS, creep resist. -- Classification: Particle, fiber, structural

• Matrix: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment -- Classification: MMC, CMC, PMC

metal ceramic polymer

Terminology/Classification

woven fibers

cross section view

0.5mm

0.5mm

Matrix and Disperse phase of composites

Composite Survey

Large-

particle

Dispersion-

strengthened

Particle-reinforced

Continuous

(aligned)

Aligned Randomly

oriented

Discontinuous

(short)

Fiber-reinforced

LaminatesSandwich

panels

Structural

Composites

Composite Survey: Particle-I

• Examples:- Spheroidite steel

matrix: ferrite ()(ductile)

particles: cementite (Fe3C)

(brittle)60 m

- WC/Co cemented carbide

matrix: cobalt (ductile)

particles: WC (brittle, hard)Vm:

10-15 vol%! 600 m

- Automobile tires

matrix: rubber (compliant)

particles: C (stiffer)

0.75 m

Particle-reinforced Fiber-reinforced Structural

Composite Survey: Particle-II

Concrete – gravel + sand + cement - Why sand and gravel? Sand packs into gravel voids

Reinforced concrete - Reinforce with steel rerod or remesh - increases strength - even if cement matrix is cracked

Prestressed concrete - remesh under tension during setting of concrete. Tension release puts concrete under compressive force

- Concrete much stronger under compression. - Applied tension must exceed compressive force


threadedrod

nut

Post tensioning – tighten nuts to put under tension

• Elastic modulus, Ec, of composites: -- two approaches.

• Application to other properties: -- Electrical conductivity, e: Replace E in equations with e. -- Thermal conductivity, k: Replace E in equations with k.

Composite Survey: Particle-III

lower limit:1

Ec= Vm

Em+

Vp

Ep

c m m

upper limit:E = V E + VpEp

“rule of mixtures”


Data: Cu matrix w/tungsten particles

0 20 40 60 80 100

150

200

250

300

350

vol% tungsten

E(GPa)

(Cu) (W)

Composite Survey: Fiber-I

• Fibers very strong– Provide significant strength improvement to

material– Ex: fiber-glass

• Continuous glass filaments in a polymer matrix• Strength due to fibers• Polymer simply holds them in place


Composite Survey: Fiber-II

• Fiber Materials– Whiskers - Thin single crystals - large length to diameter ratio

• graphite, SiN, SiC• high crystal perfection – extremely strong, strongest known• very expensive


– Fibers• polycrystalline or amorphous• generally polymers or ceramics• Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE

– Wires• Metal – steel, Mo, W

Fiber Alignment

alignedcontinuous

aligned randomdiscontinuous

• Aligned Continuous fibers• Examples:

-- Metal: '(Ni3Al)-(Mo) by eutectic solidification.

Composite Survey: Fiber-III


matrix: (Mo) (ductile)

fibers: ’ (Ni3Al) (brittle)

2 m

-- Ceramic: Glass w/SiC fibers formed by glass slurry

Eglass = 76 GPa; ESiC = 400 GPa.

(a)

(b)

fracture surface

• Discontinuous, random 2D fibers• Example: Carbon-Carbon -- process: fiber/pitch, then burn out at up to 2500ºC. -- uses: disk brakes, gas turbine exhaust flaps, nose cones.

• Other variations: -- Discontinuous, random 3D -- Discontinuous, 1D

Composite Survey: Fiber-IV


(b)

fibers lie in plane

view onto plane

C fibers: very stiff very strong

C matrix: less stiff less strong

(a)

• Critical fiber length for effective stiffening & strengthening:

• Ex: For fiberglass, fiber length > 15 mm needed

Composite Survey: Fiber-V


c

f d

15length fiber

fiber diameter

shear strength offiber-matrix interface

fiber strength in tension

• Why? Longer fibers carry stress more efficiently!Shorter, thicker fiber:

c

f d

15length fiberLonger, thinner fiber:

Poorer fiber efficiency

c

f d

15length fiber

Better fiber efficiency

(x) (x)

Composite Strength:Longitudinal Loading

Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix

• Longitudinal deformation

c = mVm + fVf but c = m = f

volume fraction isostrain

Ece = Em Vm + EfVf longitudinal (extensional)modulus

f = fiberm = matrix

Composite Strength:Transverse Loading

• In transverse loading the fibers carry less of the load - isostress

c = m = f = c= mVm + fVf

f

f

m

m

ct E

V

E

V

E

1transverse modulus

• Estimate of Ec and TS for discontinuous fibers:

-- valid when

-- Elastic modulus in fiber direction:

-- TS in fiber direction:

efficiency factor:-- aligned 1D: K = 1 (aligned )-- aligned 1D: K = 0 (aligned )-- random 2D: K = 3/8 (2D isotropy)-- random 3D: K = 1/5 (3D isotropy)

(aligned 1D)

Composite Strength

c

f d

15length fiber


(TS)c = (TS)mVm + (TS)fVf

Ec = EmVm + KEfVf

Composite Production Methods-I

• Pultrusion– Continuous fibers pulled through resin tank, then

preforming die & oven to cure

Composite Production Methods-II

• Filament Winding– Ex: pressure tanks– Continuous filaments wound onto mandrel

• Stacked and bonded fiber-reinforced sheets -- stacking sequence: e.g., 0º/90º -- benefit: balanced, in-plane stiffness

Composite Survey: Structural


• Sandwich panels -- low density, honeycomb core -- benefit: small weight, large bending stiffness

honeycombadhesive layer

face sheet

• CMCs: Increased toughness

Composite Benefits

fiber-reinf

un-reinf

particle-reinfForce

Bend displacement

• PMCs: Increased E/

E(GPa)

G=3E/8K=E

Density, [mg/m3].1 .3 1 3 10 30

.01

.1

1

10102

103

metal/ metal alloys

polymers

PMCs

ceramics

• MMCs: Increased creep resistance

20 30 50 100 20010-10

10-8

10-6

10-4

6061 Al

6061 Al w/SiC whiskers (MPa)

ss (s-1)

• Composites are classified according to: -- the matrix material (CMC, MMC, PMC) -- the reinforcement geometry (particles, fibers, layers).• Composites enhance matrix properties: -- MMC: enhance y, TS, creep performance -- CMC: enhance Kc

-- PMC: enhance E, y, TS, creep performance• Particulate-reinforced: -- Elastic modulus can be estimated. -- Properties are isotropic.• Fiber-reinforced: -- Elastic modulus and TS can be estimated along fiber dir. -- Properties can be isotropic or anisotropic.• Structural: -- Based on build-up of sandwiches in layered form.

Summary

Material Selection

Material Classification

Materials

Metallic Nonmetallic

Ferrous Nonferrous Polymer Ceramic Composite

The Materials Selection Process

ApplicationsFunctions

Properties

Materials

Processes

EnvironmentLoad

StructureShape

CompositionMechanical

ElectricalThermal

OpticalEtc.

• Current Prices on the web: e.g., http://www.metalprices.com -- Short term trends: fluctuations due to supply/demand. -- Long term trend: prices will increase as rich deposits are depleted.

• Materials require energy to process them:-- Energy to produce materials (GJ/ton)

AlPETCusteelglasspaper

237 (17)103 (13) 97 (20) 20 13 9

-- Cost of energy used in processing materials ($/MBtu)

elect resistancepropaneoilnatural gas

25171311

Energy using recycledmaterial indicated in green.

PRICE AND AVAILABILITY

RELATIVE COST, c, OF MATERIALS

• Reference material: -- Rolled A36 plain carbon steel.• Relative cost, , fluctuates less over time than actual cost.

Based on data in AppendixC, Callister, 7e.AFRE, GFRE, & CFRE = Aramid,Glass, & Carbon fiber reinforced epoxy composites.

c

material ref)kg/($

kg/$c

Graphite/ Ceramics/ Semicond

Metals/ Alloys

Composites/ fibers

Polymers

Rel

ativ

e C

ost (

c)

pl. carbon

Au

Si wafer

PETEpoxy

Nylon 6,6

0.05

0.1

5

100000

1000020000

50000

5000

20001000

500

200100

50

2010

21

0.5

Steel

high alloy

Al alloysCu alloys

Mg alloys

Ti alloys

Ag alloys

Pt

Tungsten

Al oxide

Concrete

Diamond

Glass-soda

Si carbide

Si nitride

PC

LDPE,HDPEPPPS

PVC

Aramid fibersCarbon fibers

E-glass fibers

AFRE prepreg

CFRE prepreg

GFRE prepreg

Wood

• Bar must not lengthen by more than under force F; must have initial length L.

• Maximize the Performance Index:

-- Stiffness relation: -- Mass of bar:

LE

c

F

2 (= E)2LcM

• Eliminate the "free" design parameter, c:

E

FLM

2

EP

specified by applicationminimize for small M

(stiff, light tension members)

STIFF & LIGHT TENSION MEMBERS

F,

L

cc

• Bar must carry a force F without failing; must have initial length L.


-- Strength relation: -- Mass of bar:

• Eliminate the "free" design parameter, c:

specified by applicationminimize for small M

(strong, light tension members)

STRONG & LIGHT TENSION MEMBERS

F,

L

cc

2c

F

Nf

2LcM

fFLNM

fP

• Bar must carry a moment, Mt ; must have a length L.


-- Strength relation: -- Mass of bar:

• Eliminate the "free" design parameter, R:

specified by application minimize for small M

(strong, light torsion members)

STRONG & LIGHT TORSION MEMBERS

LRM 23

2

R

M

Ntf

3/23/2)2(

ft LNMM

3/2

fP

L

2R

Mt

• Other factors: --require f > 300 MPa.

--Rule out ceramics and glasses: KIc too small.


• Numerical Data:

• Lightest: Carbon fiber reinforced epoxy (CFRE) member.

material

CFRE (vf = 0.65)

GFRE (vf = 0.65)

Al alloy (2024-T6)Ti alloy (Ti-6Al-4V)4340 steel (oil quench & temper)

(Mg/m3)1.52.02.84.47.8

P [(MPa)2/3m3/Mg]7352161511

f (MPa)11401060 300 525 780

DETAILED STUDY I: STRONG, LIGHT TORSION MEMBERS

3/2

fP

• Lowest cost: 4340 steel (oil quench & temper)

• Need to consider machining, joining costs also.

DETAILED STUDY II: STRONG, LOW COST TORSION MEMBERS

• Minimize Cost: Cost Index ~ M ~ /P (since M ~ 1/P)where M = mass of material

c c

c = relative cost =cost/mass of low-carbon steel

cost/mass of material

• Numerical Data:material

CFRE (vf = 0.65)

GFRE (vf = 0.65)

Al alloy (2024-T6)Ti alloy (Ti-6Al-4V)4340 steel (oil quench & temper)

804015

1105

P [(MPa)2/3m3/Mg]7352161511

( /P)x100112769374846

c c

• Material costs fluctuate but rise over the long term as: -- rich deposits are depleted, -- energy costs increase.• Recycled materials reduce energy use significantly.• Materials are selected based on: -- performance or cost indices.• Examples: -- design of minimum mass, maximum strength of: • shafts under torsion, • bars under tension, • plates under bending,

SUMMARY

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ISSUES TO ADDRESS... What are the classes and types of composites ? Why are composites used instead of metals, ceramics, or polymers? How do we estimate