Post on 03-Dec-2021
Chapter 16 -
A Composite material is a material system composed of
two or more macro constituents that differ in shape and
chemical composition and which are insoluble in each
other.
Introduction
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
The history of composite materials dates back to early 20th
century. In 1940, fiber glass was first used to reinforce
epoxy.
Why composites?
Chapter 16 -
Why Composites? :
getting the best of all worlds
heavy Lower Tm
Chapter 16 -
Concrete Automobile tire
Boats
Cutting tools
Used for shaping of
hard materials
Structural Composites, i.e.
Honeycomb structure
Ceramic + ceramic
polymer + ceramic
Polymer + ceramic (glass)
metal+ ceramic
Ceramic + metal
Composites : Examples
Chapter 16 -
Talking about Bones
From: http://bioweb.uwlax.edu/aplab/Table_of_Contents/Lab_05/Bone_Model_1/bone_model_1.html
Bone is a composite material with various different components
Composition of Bone:
• ~45 wt% mineral salts (calcium phosphate and calcium carbonate)
• ~35 wt% organics (collagen protein)
• ~20 wt% water
Composites : Examples
Chapter 16 -
Composites
Multiphase material that contains matrix and dispersed phase
Purpose of disersed phase:
MMC: increase sy, TS, creep resist.
CMC: increase Kc
PMC: increase E, sy, TS, creep resist.
-- Classification: Particle, fiber, structural
-- Classification: MMC, CMC, PMC
metal ceramic polymer
Terminology/Classification
Matrix: Continuous and surrounds other phase
- transfer stress to other phases
- protect phases from environment
Dispersed phase:
-enhance matrix properties (reinforcement)
Epoxy (matrix)
Polymer matrix composite (PMC)
Glass fiber
(dispersed phase)
Chapter 16 -
Large-
particle
Dispersion-
strengthened
Particle-reinforced
Continuous
(aligned)
Aligned Randomly
oriented
Discontinuous
(short)
Fiber-reinforced
Laminates Sandwich
panels
Structural
Composites
Adapted from Fig.
16.2, Callister 7e.
Classification of Composites
Composite classification according to dispersed phase
Chapter 16 -
- Spheroidite
steel
matrix: ferrite (a)
(ductile)
particles: cementite ( Fe 3 C )
(brittle) 60 mm
- Cermets
WC/Co
cemented
carbide
matrix: cobalt (ductile)
particles: WC (brittle, hard) V m :
10-15 vol%! 600 mm
- Automobile
tires
matrix: rubber (compliant)
particles: C (stiffer)
0.75 mm
Particle-reinforced Fiber-reinforced Structural
Dispersed
Large-particle
nano-composite
Composite Survey: Particle-Reinforced
Chapter 16 -
Concrete – gravel + sand + cement LARGE particle!
- Why sand and gravel? Sand packs into gravel voids
Particle-reinforced Fiber-reinforced Structural
CMC
Dispersed phase Matrix phase
Disadvantage
Like ceramics concrete is weak
in tension (10-15 times smaller
than its compressive st
Composite Survey: Particle-Reinforced
Chapter 16 -
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
threaded
rod
nut
Post tensioning – tighten nuts to put under tension
Steel rods are added to improve
tensile strength of the concrete.
(called reinforced concrete) Concrete
(matrix)
Steel rod
(dispersed phase)
(Fibers of glass, steel, nylon and PE are also used)
Composite Survey: Particle-Reinforced
Chapter 16 -
1-Elastic modulus, Ec, of composites:
Composite Survey: Particle-Reinforced
Mechanical Properties of Large Particle
Reinforced Composites
Ec: elastic modulus of composite
Em: elastic moduluc of matrix
Ep: elastic modulus of particles
Vm: volume fraction of matrix
Vp:volume fraction of particles
Chapter 16 -
Fibers provide significant strength improvement to material
Example: fiber-glass
• Continuous glass filaments in a polymer matrix
Composite Survey: Fiber-Reinforced
Glass fiber
Epoxy matrix
• Strength of the composite increases due to fibers
• Polymer simply holds them in place
Polymer matrix composite (PMC) /
Fiber reinforced composite
Fiber reinforced composites are characterized by high
strength/weight ratio
Usually used for polymers
Chapter 16 -
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 and have small diameters
• generally polymers or ceramics
• Ex: Carbon, Al2O3 , Aramid, E-glass, Boron, UHMWPE
Wires
• Large diameter
• Metal – steel, Mo, W
• i.e. Steel reinforcement in automobile tires
Composite Survey: Fiber-Reinforced
According to diameter and character fibers are groupped
into 3 different classifications: whiskers, fiber, wires
Chapter 16 -
Particle-reinforced Fiber-reinforced Structural
Composite Survey: Fiber-Reinforced
1-Continuous
(aligned)
2-Discontinuous
(aligned) (random)
Chapter 16 -
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.
-- Metal matrix
g'(Ni3Al)-a(Mo) composite by eutectic solidification.
matrix: a (Mo) (ductile)
fibers: g ’ (Ni3Al) (brittle)
2 mm
-- Ceramic matrix
: Glass w/SiC fibers (Eglass = 76 GPa; ESiC = 400 GPa.)
(a)
(b)
fracture surface
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 CRC
Press, Boca Raton, FL.
Composite Survey: Fiber-Reinforced
1-Continuous aligned fibers: Examples
Chapter 16 -
Carbon-Carbon composite (ceramic matrix)
-Used in disk brakes,
gas turbine exhaust flaps, nose cones.
• Other variations: -- Discontinuous, random 3D
-- Discontinuous, 1D
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.
fibers lie in plane
view onto plane
C fibers: very stiff very strong
C matrix: less stiff less strong
2-Discontinuous fibers: Examples
Composite Survey: Fiber-Reinforced
Discontinuous in 2D
Chapter 16 - 17
How much load is being transferred to the fiber ?
depends on the bonding between fiber and matrix !
at the end of the fiber load is solely carried by matrix !
Mechanical Properties of Fiber-Reinforced
Composites
Mechanical properties depend on;
1-propeties of fiber
2-transmission of load to the fibers by the matrix phase
Chapter 16 -
How does fiber reinforcement work ?
Mechanical Properties of Fiber-Reinforced
Composites
Chapter 16 -
Critical fiber length (lc) for effective stiffening & strengthening:
fiber diameter
shear strength of
fiber-matrix interface
fiber strength in tension
c
f d
s
2l
*
c
Mechanical Properties of Fiber-Reinforced
Composites
l >> lc (when l>15lc): Continuous fibers
l< lc : discontinuous or short fibers
• Ex: For fiberglass, fiber length > 15 mm needed
Longer fibers carry stress more efficiently!
1-Shorter, thicker fiber: 2-Longer, thinner fiber:
Poorer fiber efficiency Better fiber efficiency
s (x) s (x)
l>15lc l< lc
Chapter 16 -
Tensile Stress-Strain Behavior:
Continuous-aligned fibers,
Loading in longitudinal direction
Most load is
carried by
fibers
Fibers
start
fracturing
Mechanical Properties of Fiber-Reinforced
Composites
Chapter 16 -
Amount of load
carried by
fibers vs matrix
L>15Lc
ELASTIC BEHAVIOR in Longitudinal direction
Continuous-aligned fibers
Mechanical Properties of Fiber-Reinforced
Composites
Assume fiber/matrix bond is strong and they deform at the same time => isostrain condition ( εc = εm = εf)
Load carried by composite: Fc = Fm + Ff
Composite strength : sc = smVm + sfVf
Composite elastic modulus : Ecl = Em Vm + EfVf
mm
ff
m
f
VE
VE
F
F
f = fiber m = matrix
Chapter 16 -
Mechanical Properties of Fiber-Reinforced
Composites
TENSILE STRENGTH in Longitudinal direction
Continuous-aligned fibers
Tensile strength
Chapter 16 -
Example Problem 16.1
A continuous aligned glass fiber-reinforced composite consists of 40
vol% of glass fibers having a modulus of elasticity of 69 GPa and 60
vol% of a polyester resin that, when hardened, displays a modulus of
3.4 GPa.
(a) Compute the modulus of elasticity of this composite in the
longitudinal direction.
(b) If the cross-sectional area is 250 mm2 and a stress of 50 MPa is
applied in this longitudinal direction, compute the magnitude of the
load carried by each of the fiber and matrix phases.
(c) Determine the strain that is sustained by each phase when the
stress in part(b) is applied
Mechanical Properties of Fiber-Reinforced
Composites
Chapter 16 -
• Exposed stresses are same: isostress state
sc = sm = sf = s
c= mVm + fVf
f
f
m
m
ct E
V
E
V
E
1
transverse modulus of the composite
BUT
ELASTIC BEHAVIOR in Transverse direction
Continuous-aligned fibers
Mechanical Properties of Fiber-Reinforced
Composites
Since ε=s/E
Chapter 16 -
Mechanical Properties of Fiber-Reinforced
Composites
Example Problem 16.2
Compute the elastic modulus of the composite material
described in example problem 16.1, but assume that the
stress is applied perpendicular to the direction of fiber
alignment.
Chapter 16 -
Mechanical Properties of Fiber-Reinforced
Composites
Tensile strength in Longitudinal direction
Discontinuous and aligned fibers
When l>lc
When l<lc
Chapter 16 -
-- Elastic modulus in fiber direction:
-- TS in fiber direction:
efficiency factor, K: -- 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
Ec = EmVm + KEfVf
Mechanical Properties of Fiber-Reinforced
Composites
ELASTIC BEHAVIOR and Tensile strength in
Longitudinal direction
Discontinuous and randomly oriented fibers
Chapter 16 -
• Stacked and bonded fiber-reinforced sheets
-- stacking sequence: e.g., 0º/90º -- benefit: balanced, in-plane stiffness
Structural Composites
Laminar composites and sandwich panels are two most
common structural composites
Example: snow-ski
Laminar Composites
Chapter 16 -
Contains honeycomb core, two outer stiff/strong sheets
(Sheet material: Al-alloy, fiber reinforced plastic, titanium
steel or plywood)
Core : low modulus, Outer: high stiffness
honeycomb
adhesive layer
face sheet
Structural Composites
Sandwich Composites
They are designed to be light-weight beams or panels having
relatively high stiffness and strength
Use in roofs, floors of buildings and aerospace and aircrafts (wings, fuselage)
Chapter 16 -
Composite Production Methods-
Fiber Reinforced Composites
• Pultrusion
– Continuous fibers pulled through resin tank, then
preforming die & oven to cure
Adapted from Fig.
16.13, Callister 7e.
Chapter 16 - 31
• Filament Winding
– Ex: pressure tanks
– Continuous filaments wound onto mandrel
Composite Production Methods-
Fiber Reinforced Composites
Chapter 16 -
• CMCs: Increased toughness
Composite Benefits
fiber-reinf
un-reinf
particle-reinf Force
Bend displacement
• PMCs: Increased E/r
E(GPa)
G=3E/8 K=E
Density, r [mg/m3] .1 .3 1 3 10 30
.01
.1
1
10
10 2
10 3
metal/ metal alloys
polymers
PMCs
ceramics
Adapted from T.G. Nieh, "Creep rupture of a
silicon-carbide reinforced aluminum
composite", Metall. Trans. A Vol. 15(1), pp.
139-146, 1984. Used with permission.
• MMCs: Increased
creep
resistance
20 30 50 100 200 10
-10
10 -8
10 -6
10 -4
6061 Al
6061 Al w/SiC whiskers s (MPa)
ss (s-1)
Chapter 16 -
• 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.
Summary