Chapter 16: Composite Materials

1
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?
2
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

3
Terminology/Classification
Composites -- Multiphase material with
significant proportions of each phase.
Dispersed phase -- Purpose enhance
matrix properties. MMC increase sy,
TS, creep resist. CMC increase Kc
PMC increase E, sy, TS, creep resist.
-- Classification Particle, fiber, structural
4
Matrix and Disperse phase of composites
5
Composite Survey
Composites
Fiber-reinforced
Particle- reinforced
Structural
Large-
Dispersion-
Continuous
Discontinuous
Sandwich
Laminates
particle
strengthened
(aligned)
(short)
panels
Randomly
Aligned
oriented
6
Composite Survey Particle-I
7
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
8
Composite Survey Particle-III
Elastic modulus, Ec, of composites -- two
approaches.
Application to other properties --
Electrical conductivity, se Replace E in
equations with se. -- Thermal conductivity,
k Replace E in equations with k.
9
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

10
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

11
Fiber Alignment
aligned continuous
aligned random discontinuous
12
Composite Survey Fiber-III
Aligned Continuous fibers
Examples
-- Metal g'(Ni3Al)-a(Mo) by eutectic
solidification.
-- Ceramic Glass w/SiC fibers formed by
glass slurry Eglass 76 GPa ESiC 400 GPa.
13
Composite Survey Fiber-IV
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
14
Composite Survey Fiber-V
Critical fiber length for effective stiffening
strengthening
fiber strength in tension
fiber diameter
shear strength of fiber-matrix interface
Ex For fiberglass, fiber length gt 15 mm needed
15
Composite StrengthLongitudinal 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 fiber m matrix
16
Composite StrengthTransverse Loading

• In transverse loading the fibers carry less of
  the load - isostress
• ?c ?m ?f ? ?c ?mVm ?fVf

?
transverse modulus
17
Composite Strength
Estimate of Ec and TS for discontinuous
fibers -- valid when -- Elastic
modulus in fiber direction -- TS in
fiber direction
Ec EmVm KEfVf
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)
(TS)c (TS)mVm (TS)fVf
18
Composite Production Methods-I

• Pultrusion
• Continuous fibers pulled through resin tank, then
  preforming die oven to cure

19
Composite Production Methods-II

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

20
Composite Survey Structural
Stacked and bonded fiber-reinforced sheets
-- stacking sequence e.g., 0º/90º --
benefit balanced, in-plane stiffness
21
Composite Benefits
CMCs Increased toughness
22
Summary
Composites are classified according to --
the matrix material (CMC, MMC, PMC) -- the
reinforcement geometry (particles, fibers,
layers). Composites enhance matrix
properties -- MMC enhance sy, TS, creep
performance -- CMC enhance Kc -- PMC
enhance E, sy, 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.
23
Material Selection
24
Material Classification
25
(No Transcript)
26
The Materials Selection Process
Processes
Structure Shape
Composition Mechanical Electrical Thermal Optical
Etc.
Materials
Properties
Environment Load
Applications Functions
27
PRICE AND AVAILABILITY
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
-- Cost of energy used in processing
materials (/MBtu)
-- Energy to produce materials (GJ/ton)
237 (17) 103 (13) 97 (20) 20 13 9
Al PET Cu steel glass paper
elect resistance propane oil natural gas
25 17 13 11
Energy using recycled material indicated in green.
28
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 Appendix C, Callister, 7e. AFRE,
GFRE, CFRE Aramid, Glass, Carbon fiber
reinforced epoxy composites.
29
STIFF LIGHT TENSION MEMBERS
Bar must not lengthen by more than d under
force F must have initial length L.
-- Stiffness relation
-- Mass of bar
(s Ee)
Eliminate the "free" design parameter, c
minimize for small M
specified by application
Maximize the Performance Index
(stiff, light tension members)
30
STRONG LIGHT TENSION MEMBERS
Bar must carry a force F without failing
must have initial length L.
-- Strength relation
-- Mass of bar
Eliminate the "free" design parameter, c
minimize for small M
specified by application
Maximize the Performance Index
(strong, light tension members)
31
STRONG LIGHT TORSION MEMBERS
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
Maximize the Performance Index
(strong, light torsion members)
32
DETAILED STUDY I STRONG, LIGHT TORSION MEMBERS
Maximize the Performance Index
Other factors --require sf gt 300 MPa.
--Rule out ceramics and glasses KIc too small.
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)
r (Mg/m3) 1.5 2.0 2.8 4.4 7.8
P (MPa)2/3m3/Mg 73 52 16 15 11
tf (MPa) 1140 1060 300 525 780
Lightest Carbon fiber reinforced epoxy
(CFRE) member.
33
DETAILED STUDY II STRONG, LOW COST TORSION
MEMBERS
Minimize Cost Cost Index M /P
(since M 1/P)
where M mass of material
relative cost
Lowest cost 4340 steel (oil quench temper)
Need to consider machining, joining costs also.
34
SUMMARY
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,