[email protected] engr-45_lec-28_composites.ppt 1 bruce mayer, pe engineering-45: materials...

[email protected] • ENGR-45_Lec-28_Composites.ppt1

Bruce Mayer, PE Engineering-45: Materials of Engineering

Bruce Mayer, PERegistered Electrical & Mechanical Engineer

[email protected]

Engineering 45

CompositeMaterials



Learning Goals – Composites

List The CLASSES and TYPES of Composites

When to Use Composites Instead of Metals, Ceramics, or Polymers

How to Estimate Composite Stiffness & Strength

Examine some Typical Applications



Terms & Classifications Composite MultiPhase

Material with Significant Proportions of Each Phase• Phase Components

– MATRIX– DISPERSED Phase

Matrix• The CONTINUOUS Phase• The Matrix Function

– transfer stress to other phase(s)– Protect other phase(s) from

the (corrosive) Environment

woven fibers

cross section view

0.5mm

0.5mmReprinted with permission fromD. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47.



Terms & Classifications cont.1 Composite Classifications

• MMC Metal Matrix Composite• CMC Ceramic Matrix Comp.• PMC Polymer Matrix Comp.

Dispersed Phase (DP)• Function = To Enhance the

Matrix Properities– MMC: increase σy, TS/σu, creep resistance

– CMC: increase Kc (fracture toughness)

– PMC: increase E, σy, TS/σu, creep resistance

• Classes: Particle, fiber, structural



Composite Taxonomy

Composites

PARTICLE Reinforced FIBER Reinforced STRUCTURAL

LARGEParticle

DISPERSIONStrengthened

Continous(Aligned)

DIScontinous(Short)

LaminatesSandwich

Panels

Aligned

Randomly Oriented



Composite Survey – Particle-I

60

Adapted from Fig. 10.10, Callister 7e. (Fig. 10.10 is copyright United States Steel Corporation, 1971.)

-Spheroidite steel

matrix: ferrite ( a) (ductile)

particles: cementite

(Fe3C) (brittle)

mm

Adapted from Fig. 16.4, Callister 7e. (Fig. 16.4 is courtesy Carboloy Systems, Department, General Electric Company.)

-WC/Co cemented carbide

matrix: cobalt (ductile)

particles: WC (brittle, hard)Vm:

10-15vol%! 600mm

Adapted from Fig. 16.5, Callister 7e. (Fig. 16.5 is courtesy Goodyear Tire and Rubber Company.)

-Automobile tires

matrix: rubber (compliant)

particles: C (stiffer)

0.75mm

Particle-reinforced

Fiber-reinforced Structural Examples



ReInforced ConCrete

Concrete is a PARTICLE ReInforced Composite• Matrix = PortLand Cement

– 3CaO-SiO2 + 2CaO-SiO2

• Dispersed Phases – Sand+Gravel Aggregate– 60%-80% by Vol

Steel ReInforcing Bars (Rebar)• A type of FIBER

Reinforcement• Improves Tensile

& Shear Strength



More ReInforced Concrete Concrete ≡ gravel + SAND + cement

• Why sand and gravel? → Sand packs into gravel VOIDS

Reinforced concrete - Reinforce with steel reBAR or reMESH• Increases TENSILE strength - even if Concrete

matrix is cracked PreStressed concrete - reMesh under tension

during setting of concrete. Tension release puts concrete under COMPRESSIVE Stress• Concrete is much stronger under compression.



Composite Survey – Particle-II

Composite Material Elastic Modulus, Ec

• Two “Rule of Mixtures” Approximations

Data: Cu matrix w/tungsten particles

0 20 40 60 80 100

150200250300350

vol% tungsten

E(GPa)

lower limit:1Ec

=VmEm

+Vp

Ep

c m m

upper limit:E =V E +VpEp

(Cu) (W)

“rule of mixtures”

Particle-reinforced

Fiber-reinforced Structural

Rule-of-Mixtures Applies to Other Properties• Electrical conductivity, σelect: Replace E by σelect

• Thermal conductivity, k: Replace E by k.

←Springs in PARALLEL

←Springs in SER

IES



Composite Survey: Fiber-I

Fibers very strong• Provide significant strength improvement

compared to pure matrix-material

Example: fiber-glass• Continuous glass filaments in a

polymer matrix• Strength due to fibers• Polymer simply holds them in place



Fiber Materials

Whiskers - Thin single crystals - large length to diameter ratio• graphite, SiN, SiC• high crystal perfection – extremely strong,

strongest known• very expensive

Traditional Fibers polycrystalline or amorphous Generally polymers or ceramics Ex: Al2O3 , Aramid, E-glass, Boron,

UHMWPE



Composite Survey: Fiber-II

Fiber Materials• Whiskers - Thin single crystals with

large length to diameter ratio– graphite, SiN, SiC– high crystal perfection – extremely strong,

strongest physical form known– very expensive to produce

Particle-reinforced Fiber-reinforced Structural

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

– Wires• Metal – steel, Mo, W



alignedcontinuous

aligned randomdiscontinuous

Adapted from Fig. 16.8, Callister 7e.

Fiber Alignment



ISOstress & ISOstrain

isoSTRAIN → Tensile strength and elastic modulus when fibers are parallel to the direction of stress

isoSTRESS → Tensile strength and elastic modulus when fibers are perpendicular to the direction of stress



Composite Survey – Fiber-I

ALIGNED, CONTINUOUS Fibers• Examples

Fiber-reinforcedParticle-reinforced Structural

Metal: g’ (Ni3Al)-a(Mo) by eutectic solidification.

From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp. 987-998, 1988. Used with permission.

matrix: a(Mo) (ductile)

fibers:g’ (Ni3Al) (brittle)

2mm

Glass w/SiC fibers formed by glass slurry

Eglass = 76GPa; ESiC = 400GPa.

fracture surface

(a)

(b)

From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, 2000. (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig. 11.20, p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRCPress, Boca Raton, FL.



Composite Survey – Fiber-II

DISCONTINUOUS, RANDOM, 2D (Planer) Fibers


Example: Carbon-Carbon• Process: fiber/pitch, then

burn out at up to 2500C.• Uses: disk brakes, gas

turbine exhaust flaps, rocket nose cones.

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

– Fully Aligned

Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, 2000. (a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151. (Courtesy I.J. Davies) Reproduced with permission of CRC Press, Boca Raton, FL.

(b)

view onto plane

C fibers: very stiff very strong

C matrix: less stiff less strong

(a)

fibers lie in plane



Composite Survey – Fiber-III

CRITICAL fiber length for effective stiffening & strengthening:


The Equation Balances (want PullOut Tear)• The Fiber Load capacity → σf•[ACylXsec] = σf•[πd2/4]

• The Fiber Pull-Out Force→ c•[ACylSurf] = c•[πd•l]

Stronger Fibers → need LONGER fiber Stronger Fiber-Matrix Shear-Bond →

need SHORTER Fiber

fiber length 15

fdc

fiber diameter

shear strength offiber-matrix interface

fiber strength in tension



Fiber Lengths cont. Example: FiberGlass

• Need Fiber Lengh > 15mm

Reason for length Criteria → examine Extreme cases• Very Short Fiber has very little hold-in force

and would PULL-OUT (Fiber PULLS OUT before Fracture)• Very Long Fiber would take almost all the axial load

(Fiber FRACTURES before PullOut)

(x) fiber length 15

fdc

Shorter, thicker fiber:

fiber length 15

fdc

(x)

Longer, thinner fiber:

Poorer fiber efficiency Better fiber efficiency

Adapted from Fig. 16.7, Callister 6e.



Composite Survey – Fiber-IV

Estimate Ec and TS• Valid for LONG Fiber

Condition:


The Elastic Modulus in Fiber Direction

fiber length 15

fdc

efficiency factor Ec EmVm KE fVf

Typical Values for K:• Aligned 1D: K = 1 (anisotropic)• Random 2D: K = 3/8

2D isotropy)• Random 3D: K = 1/5

(3D isotropy)

TS in fiber direction (1D, Aligned) by VOLUME Weighted Average

(TS)c (TS)mVm (TS)f Vf



Composite Survey – Structural

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

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

StructuralFiber-reinforcedParticle-reinforced

honeycombadhesive layer

face sheet

Similar to Composite Beam Lab Exercise



Composite Benefits

Ceramic Matrix Composites → Better FRACTURE TOUGHNESS

fiber-reinf

un-reinf

particle-reinfForce

Bend displacement

Metal Matrix Composites → Improved CREEP RESISTANCE

2030 50 100 20010-10

10-8

10-6

10-46061 Al

6061 Al w/SiC whiskers (MPa)

ss (s-1)



Composite Benefits cont.1

Polymer Matrix Composites → Better E:ρ (Stiffness:Weight) ratio

E(GPa)

G=3E8K=E

Density, r [Mg/m3].1 .3 1 3 10 30

.01.1

1

10102103

metal/ metal alloys

polymers

PMCs

ceramics



Specific Strength The PRIMARY

Motivation for the Use of Composites → Hi-Strength, Hi-Stiffness & Lo-Weight

Thus Two Important Metrics• Specific STRENGTH

• Similarly The Specific STIFFNESS

Now Specific Weight

WeightSpecific

StrengthS

WeightSpecific

ModulusElasticSE

3N/min g• Where

– ρ Density in kg/m3

– g Acceleration of Gravity (9.81 m/s2)



Specific Strength cont.1 Now Determine

Units for Sσ and SE by Way of Examples• For 7075 Al in the

Heat treated State– u = 83 ksi

– = 0.101 lb/in3

• For Kevlar-49 (Aramid Fiber)– E = 131 GPa– ρ = 1444 kg/m3

• Find

Now Specific Stiffness

3

2

inlb 101.0

inlb 83000S

3231416681.91444

m

N

s

m

m

kgg

in 10218.8 5S

3

29

mN 41661

mN 10131ES

m 10248.9 6ES



Sσ vs SE Comparison

The High DENSITY of Metal Reduces Sσ and SE

The Low STRENGTH & STIFFNESS of most Polymers Reduces Sσ and SE



Summary – Composite Matls

Composites Classified by:• The Matrix Material

– Ceramic (CMC)– Metal (MMC)– PolyMer (PMC)

• ReInforcement Geometry– Particles– Fibers – Layers



Summary – Composites cont.1

Composites enhance matrix properties:• MMC: enhance sy, TS, creep performance

• CMC: enhance Kc

• PMC: enhance E, sy, TS, creep resistance

Particle ReInforced• Elastic modulus can be estimated by the

Rule of Mixtures• Properties are isotropic



Summary – Composites cont.2

Fiber ReInforced:• Elastic modulus and TS can be estimated

along fiber direction By Rule of Mixtures• Properties can be isotropic or anisotropic

Structural:• Based on build-up of sandwiches in

layered form– Plys– HoneyCombs



WhiteBoard Work

Prob 16.11• Given IsoStrain,

Longitudinal Loading for a Continuous Fiber Composite: fmc FFF

• Then Show

mm

ff

m

f

VE

VE

F

F

• Where– F Force– E Elastic Modulus– V Volume fraction– Sub-f → “fiber”– Sub-m → “matrix”– Sub-c → “composite”



Bruce Mayer, PELicensed Electrical & Mechanical Engineer

[email protected]

Chabot Engineering

Appendix

E-glass



E Glass - BackGround

http://www.azom.com/details.asp?ArticleID=764

Background• E-Glass or electrical grade glass was

originally developed for stand off insulators for electrical wiring. It was later found to have excellent fibre forming capabilities and is now used almost exclusively as the reinforcing phase in the material commonly known as fibreglass.





E Glass - Composition

Composition• E-Glass is a low alkali glass with a typical

nominal composition of SiO2 54wt%, Al2O3 14wt%, CaO+MgO 22wt%, B2O3 10wt% and Na2O+K2O less then 2wt%. Some other materials may also be present at impurity levels.



E Glass – Key Properties Properties that have made E-glass so popular in

fibreglass and other glass fibre reinforced composite include:• Low cost• High production rates• High strength, (see table on next slide)• High stiffness• Relatively low density• Non-flammable• Resistant to heat• Good chemical resistance• Relatively insensitive to moisture• Able to maintain strength properties over a wide range of

conditions• Good electrical insulation



E Glass – Fibre Strength

Table 1. Comparison of typical properties for some common fibres.

Materials Density (g/cm3) Tensile Strength

(MPa) Young modulus

(GPa) E-Glass 2.55 2000 80 S-Glass 2.49 4750 89 Alumina (Saffil) 3.28 1950 297 Carbon 2.00 2900 525 Kevlar 29 1.44 2860 64 Kevlar 49 1.44 3750 136



E Glass – Use in Composites The use of E-Glass as the reinforcement material in

polymer matrix composites is extremely common. Optimal strength properties are gained when straight, continuous fibres are aligned parallel in a single direction. To promote strength in other directions, laminate structures can be constructed, with continuous fibres aligned in other directions. Such structures are used in storage tanks and the like.

Random direction matts and woven fabrics are also commonly used for the production of composite panels, surfboards and other similar devices.

[email protected] engr-45_lec-28_composites.ppt 1 bruce mayer, pe engineering-45: materials...

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