Transcript EBB 220/3 POLYMER COMPOSITE

EBB 220/3
POLYMER COMPOSITE
What is Composites?
Combination of 2 or more materials
 Each of the materials must exist more than
5%
 Presence of interphase
 The properties shown by the composite
materials are differed from the initial
materials
 Can be produced by various processing
techniques

Constituents of composite
materials
1. Matrix phase
Continuous phase, the primary phase.
It holds the dispersed phase and shares a load with it.
2. Dispersed (reinforcing) phase
The second phase (or phases) is imbedded in the matrix in a
continuous/discontinuous form.
Dispersed phase is usually stronger than the matrix, therefore it is sometimes
called reinforcing phase.
3. Interface
Zone across which matrix and reinforcing phases interact (chemical, physical,
mechanical)
Matrix: Function
however the distribution of loads depends on the interfacial bondings
Reinforcement: Function
Reinforcement can be in the form
of:





Continuous fiber
 Organic fiber- i.e. Kevlar, polyethylene
 Inorganic fiber- i.e. glass, alumina, carbon
 Natural fiber- i.e. asbestos, jute, silk
Short fiber
whiskers
Particle
Wire
Interface: Function

To transfer the stress from matrix to
reinforcement
Sometimes surface treatment is carried out
to achieve the required bonding to the
matrix
Characteristics of dispersed phase that might
influence the properties of composites
a) Concentration (b) size (c) shape (d) distribution (e)
orientation
Classification of composites
Examples of composites
a)
b)
c)
d)
Particulate & random
Discontinuous fibers & unidirectional
Discontinuous fibers & random
Continuous fibers & unidirectional
Classification based on Matrices
Composite
materials
Matrices
Polymer Matrix
Composites (PMC)
Thermoset
Metal Matrix
Composites MMC)
Thermoplastic
Rubber
Ceramic Matrix
Composites (CMC)
What is Hybrid composites?
What are the advantages of
hybrid composites?

Widely used- ease of processing & lightweight
Properties of composites depend
on
Amount of phase
- Amount/proportion (can be expressed in
weight fraction (Wf) or volume fraction
(Vf))of phases strongly influence the
properties of composite materials.
Xc = Xf Vf + Xm (1 - Vf ) - Rule of Mixture
Xc = Properties of composites
Xf = Properties of fiber
Xm= Properties of matrix

Voids
 Free
volume
 Gas emission leads to voids in the
final product
 In composites- Voids exist in the
matrix, interface and in between fiber
& fiber
 Voids create stress concentration
points- influence the properties of the
composites
Geometry of dispersed phase
(particle size, distribution,
orientation)




Shape of dispersed phase (particle- spherical or
irregular, flaky, whiskers, etc)
Particle/fiber size ( fiber- short, long,
continuous); particle (nano or micron size)
Orientation of fiber/particle (unidirection, bidirections, many directions)- influence isotropic
dan an-isotropic properties
Dictribution of dispersed phase
(homogenus/uniform, inhomogenus)
Processing technique and
parameters

Influence final product, selection of correct
raw materials, void content, etc
Glass
Fiber
The types of glass used are as follows:



E-Glass – the most popular and inexpensive glass fibers. The
designation letter “E” means “electrical” (E-Glass is excellent
insulator). The composition of E-glass ranges from 52-56%
SiO2, 12-16% A1203, 16-25% CaO, and 8-13% B203
S-Glass – stronger than E-Glass fibers (the letter “S” means
strength). High-strength glass is generally known as S-type
glass in the United States, R-glass in Europe and T-glass in
Japan. S-Glass is used in military applications and in
aerospace. S-Glass consists of silica (SiO2), magnesia (MgO),
alumina (Al2O3).
C-Glass – corrosion and chemical resistant glass fibers. To
protect against water erosion, a moisture-resistant coating such
as a silane compound is coated onto the fibers during
manufacturing. Adding resin during composite formation
provides additional protection. C-Glass fibers are used for
manufacturing storage tanks, pipes and other chemical
resistant equipment.
Glass Fiber







Fiberglasses (Glass fibers reinforced polymer matrix
composites) are characterized by the following
properties:
High strength-to-weight ratio;
High modulus of elasticity-to-weight ratio;
Good corrosion resistance;
Good insulating properties;
Low thermal resistance (as compared to metals and
ceramics).
Fiberglass materials are used for manufacturing:
boat hulls and marine structures, automobile and
truck body panels, pressure vessels, aircraft wings
and fuselage sections, housings for radar systems,
swimming pools, welding helmets, roofs, pipes.
Carbon
Fiber
 The types of carbon fibers are as





follows:
UHM (ultra high modulus). Modulus of
elasticity > 65400 ksi (450GPa).
HM (high modulus). Modulus of
elasticity is in the range 51000-65400
ksi (350-450GPa).
IM (intermediate modulus). Modulus of
elasticity is in the range 29000-51000
ksi (200-350GPa).
HT (high tensile, low modulus). Tensile
strength > 436 ksi (3 GPa), modulus of
elasticity < 14500 ksi (100 GPa).
SHT (super high tensile). Tensile
strength > 650 ksi (4.5GPa).
Carbon Fiber











Carbon Fiber Reinforced Polymers (CFRP) are characterized
by the following properties:
Light weight;
High strength-to-weight ratio;
Very High modulus elasticity-to-weight ratio;
High Fatigue strength;
Good corrosion resistance;
Very low coefficient of thermal expansion;
Low impact resistance;
High electric conductivity;
High cost.
Carbon Fiber Reinforced Polymers (CFRP) are used for
manufacturing: automotive marine and aerospace parts, sport
goods (golf clubs, skis, tennis racquets, fishing rods), bicycle
frames.
Kevlar Fiber




Kevlar is the trade name (registered by DuPont Co.)
of aramid (poly-para-phenylene terephthalamide)
fibers.
Kevlar fibers were originally developed as a
replacement of steel in automotive tires.
Kevlar filaments are produced by extrusion of the
precursor through a spinnert. Extrusion imparts
anisotropy (increased strength in the lengthwise
direction) to the filaments.
Kevlar may protect carbon fibers and improve their
properties: hybrid fabric (Kevlar + Carbon fibers)
combines very high tensile strength with high impact
and abrasion resistance.
Kevlar Fiber












Kevlar fibers possess the following properties:
High tensile strength (five times stronger per
weight unite than steel);
High modulus of elasticity;
Very low elongation up to breaking point;
Low weight;
High chemical inertness;
Very low coefficient of thermal expansion;
High Fracture Toughness (impact resistance);
High cut resistance;
Textile processibility;
Flame resistance.
The disadvantages of Kevlar are: ability to absorb
moisture, difficulties in cutting, low compressive
strength.
Kevlar Fiber




There are several modifications of Kevlar,
developed for various applications:
Kevlar 29 – high strength (520000 psi/3600 MPa),
low density (90 lb/ft³/1440 kg/m³) fibers used for
manufacturing bullet-proof vests, composite armor
reinforcement, helmets, ropes, cables, asbestos
replacing parts.
Kevlar 49 – high modulus (19000 ksi/131 GPa),
high strength (550000 psi/3800 MPa), low density
(90 lb/ft³/1440 kg/m³) fibers used in aerospace,
automotive and marine applications.
Kevlar 149 – ultra high modulus (27000 ksi/186
GPa), high strength (490000 psi/3400 MPa), low
density (92 lb/ft³/1470 kg/m³) highly crystalline
fibers used as reinforcing dispersed phase for
composite aircraft components.
Reasons for the use of polymeric
materials as matrices in composites
i. The mechanical properties of polymers
are inadequate for structural purposes,
hence benefits are gained by reinforcing the
polymers
 Processing of PMCs need not involve high
pressure and high temperature
 The equipment required for PMCs are much
simpler

Disadvantages of PMC

Low maximum working
temperature
 High coefficient of thermal
expansion- dimensional
instability
 Sensitivity to radiation and
moisture
Classification of Polymer
Matrices
 1.
Thermoset
 2. Thermoplastic- crystalline &
amorphous
 3. Rubber
Thermoset





Thermoset materials are usually liquid or malleable prior to curing,
and designed to be molded into their final form
has the property of undergoing a chemical reaction by the action
of heat, catalyst, ultraviolet light, etc., to become a relatively
insoluble and infusible substance.
They develop a well-bonded three-dimensional structure upon
curing. Once hardened or cross-linked, they will decompose rather
than melt.
A thermoset material cannot be melted and re-shaped after it is
cured.
Thermoset materials are generally stronger than thermoplastic
materials due to this 3-D network of bonds, and are also better
suited to high-temperature applications up to the decomposition
temperature of the material.




Thermoplastic
is a plastic that melts to a liquid when heated and
freezes to a brittle, very glassy state when cooled
sufficiently.
Most thermoplastics are high molecular weight
polymers whose chains associate through weak van
der Waals forces (polyethylene); stronger dipoledipole interactions and hydrogen bonding (nylon); or
even stacking of aromatic rings (polystyrene).
The bondings are easily broken by the cobined action
of thermal activation and applied stress, that’s why
thermoplastics flow at elevated temperature
unlike thermosetting polymers, thermoplastic can be
remelted and remolded.
Thermoplastics can go through
melting/freezing cycles repeatedly and the
fact that they can be reshaped upon
reheating gives them their name
 Some thermoplastics normally do not
crystallize: they are termed "amorphous"
plastics and are useful at temperatures
below the Tg. They are frequently used in
applications where clarity is important.
Some typical examples of amorphous
thermoplastics are PMMA, PS and PC.
 Generally, amorphous thermoplastics are
less chemically resistant





Depends on the structure of the
thermoplastics, some of the polymeric structure
can be folded to form crystalline regions, will
crystallize to a certain extent and are called
"semi-crystalline" for this reason.
Typical semi-crystalline thermoplastics are PE,
PP, PBT and PET.
Semi-crystalline thermoplastics are more
resistant to solvents and other chemicals. If the
crystallites are larger than the wavelength of
light, the thermoplastic is hazy or opaque.
Why HDPE exhibits higher cystallinity than
LDPE?
Comparison of typical ranges of
property values for thermoset and
thermoplastics
Properties
t/set
 Young’s Modulus (GPa)1.3-6.0
 Tensile strength(MPa) 20-180
 Max service temp.(ºC) 50-450
 Fracture toughness,KIc 0.5-1.0
(MPa1/2)

t/plastic
1.0-4.8
40-190
25-230
1.5-6.0
Thermoplastics are expected to
receive attention compared to
thermoset due to:
 Ease
of processing
 Can be recycled
 No specific storage
 Good fracture modulus
Rubber





Common characteristics;
 Large elastic elongation (i.e. 200%)
 Can be stretched and then immediately return to
their original length when the load was released
Elastomers are sometimes called rubber or rubbery
materials
The term elastomer is often used interchangeably with
the term rubber
Natural rubber is obtained from latex from Hevea
Brasiliensis tree which consists of 98% poliisoprena
Synthetic rubber is commonly produced from
butadiene, spt styrene-butadiene (SBR) dan nitrilebutadiene (NBR)
 To
achieve properties suitable for
structural purposed, most rubbers
have to be vulcanized; the long
chain rubber have to be crosslinked
 The crosslinking agent in
vulcanization is commonly sulphur,
and the stiffness and strength
increases with the number of
crosslinks