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Chapter 16: Composite Materials. 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?. Composites. - PowerPoint PPT Presentation
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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 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
Particle-reinforced Fiber-reinforced Structural
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”
Particle-reinforced Fiber-reinforced Structural
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
Particle-reinforced Fiber-reinforced Structural
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
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
Fiber Alignment
alignedcontinuous
aligned randomdiscontinuous
• Aligned Continuous fibers• Examples:
-- Metal: '(Ni3Al)-(Mo) by eutectic solidification.
Composite Survey: Fiber-III
Particle-reinforced Fiber-reinforced Structural
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
Particle-reinforced Fiber-reinforced Structural
(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
Particle-reinforced Fiber-reinforced Structural
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
Particle-reinforced Fiber-reinforced Structural
(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
Particle-reinforced Fiber-reinforced 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.
• Maximize the Performance Index:
-- 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.
• Maximize the Performance Index:
-- 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.
• Maximize the Performance Index:
• 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